Olivier Seynnes

• Ritsche, Paul; Sarto, Fabio; Santini, Francesco; Leitner, Christoph; Franchi, Martino V. & Faude, Oliver [Show all 9 contributors for this article] (2026). UMUD: a web application for easy access to musculoskeletal ultrasonography datasets. BMC Medical Imaging. 26(1). doi: 10.1186/s12880-026-02170-0. Full text in Research Archive
• Viken, Julian Seiler; Nettum, Vebjørn; Paulsen, Gøran & Seynnes, Olivier R. (2025). Influence of passive, diet-based, hydration on muscle quantity assessment. Frontiers in Physiology. 16. doi: 10.3389/fphys.2025.1724047. Full text in Research Archive Show summary

  Background This study investigated the impact of passive changes in hydration level on measurements of lean tissue mass (LTM) and muscle morphology. Methods Sixteen healthy participants (13 males, 3 females) completed two testing sessions 24 h apart, including dual-energy X-ray absorptiometry (DXA), 3D ultrasound imaging of the vastus lateralis (VL), and bioelectrical impedance analysis (BIA). Participants fasted for 12 h before each session. Hydration was manipulated by assigning participants randomly to either a non-hydrated state, abstaining from fluids until testing, or a hydrated state, consuming water equal to 1.5% of body mass 2 hours prior. Results Total body water, measured using bioelectrical impedance analysis (BIA), was lower in the non-hydrated condition (48.6 ± 9.7 kg) than in the hydrated condition (49.0 ± 9.8 kg, p = 0.015). In the hydrated condition, total LTM, measured using DXA, was higher for the full body (60.8 ± 11.8 kg vs. 60.0 ± 11.9 kg, p < 0.001) and the trunk (29.2 ± 5.3 kg vs. 28.6 ± 5.4 kg, p < 0.001). Hydration did not significantly affect LTM in the upper (p = 0.251) or lower limbs (p = 0.298), or the thigh (p = 0.051). Volume (p = 0.105) and cross-sectional area (CSA; p = 0.114) of the VL were also unaffected. Conclusion Small changes in hydration levels induced passively under temperate conditions may not significantly affect measurements of muscle morphology or limb measurements of LTM. However, monitoring changes in muscle quantity with total LTM may be biased by water intake and trunk hydration if these factors are not controlled. Caution is warranted (e.g., standardisation) when using total LTM to monitor changes in muscle quantity.

• Holm, Mia Røkke; Holtvedt, Hågen; Hansen, Mette; Paulsen, Gøran & Seynnes, Olivier (2025). Second‐Generation Oral Contraceptive Use Is Associated With Greater Muscle Hypertrophy Following Resistance Training. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 35(12). doi: 10.1111/sms.70189. Full text in Research Archive Show summary

  ABSTRACT This study aimed to examine whether second‐generation oral contraceptive (OC) users exhibit greater muscle hypertrophy following resistance training compared to non‐users across various targeted muscle groups. Fourteen young, untrained women using OCs (aged 28 ± 4 years) and 12 eumenorrheic non‐users (NOC, aged 30 ± 4 years) underwent a 12‐week resistance training programme. The thickness of seven muscles in the upper‐ and lower‐limbs was measured using ultrasound, while body composition was assessed with dual‐energy X‐ray absorptiometry, and the maximal torque of all relevant joints was tested before and after the intervention. Our results demonstrated a greater increase in arm lean tissue mass (LTM) in OC users (10.5%) compared to non‐users (6.6%, time × group interaction p  < 0.002). Additionally, greater hypertrophic gains were observed in three specific muscle groups in OC users (4.5%–7.9%) compared to non‐users (1.5%–3.1%, time × group interaction, p  ≤ 0.036). Despite these group differences in muscle growth, no group differences in strength gains were observed. This study indicates that second‐generation OC users exhibit greater hypertrophic gains in specific muscle groups and a greater accretion of arm LTM compared to eumenorrheic non‐users of OC. Further research is warranted to explore the physiological mechanisms behind the differences in muscle growth during resistance training between users and non‐users of OC.

• Nettum, Vebjørn; Mathisen, Therese Fostervold; Slater, Gary; Seynnes, Olivier R. & Paulsen, Gøran (2025). Lean Body Mass and Maximal Strength Changes during Physique Contest Preparation and Recovery: A Case Series. Performance Enhancement & Health. 14. doi: 10.1016/j.peh.2025.100404. Full text in Research Archive Show summary

  This study aimed to investigate changes in lean body mass (LBM) and maximal strength during preparation for a physique contest season and one month post-season. Three drug-free male physique athletes were observed. Laboratory tests were conducted at various intervals: immediately before starting weight loss, 2 months, 1 month, and 1 week before their first contest, 1 week before their last contest, and 1 month post-season. Body composition was assessed using Dual-energy X-ray absorptiometry (DXA), bioimpedance (BIA), and skinfold (SK) measurements. Muscle thickness (MT) of the elbow flexors and muscle cross-sectional area (CSA) of the vastus lateralis were evaluated via ultrasound. Strength assessments (isometric and isokinetic peak torque) were measured using a dynamometer. Blood biomarkers and dietary intake were also tracked. During the preparation phase, LBM decreased in all athletes: 1.7-5.3 kg (DXA), 4.3-8.5 kg (BIA), and 7.0-9.5 kg (SK). One month into recovery, LBM rapidly increased: 2.5-3.4 kg (DXA), 4.1-4.6 kg (BIA), and 3.4-5.5 kg (SK). Both MT and CSA decreased during preparation but increased during recovery. Maximal strength performance remained within expected day-to-day variation for isometric peak torque and isokinetic peak torque at 60°/s, but isokinetic peak torque at 240°/s exceeded expected variation, only partially restored post-contest. Testosterone levels decreased and sex-hormone binding globulin increased during preparation, with varying recovery. Reductions in LBM, MT, and CSA during caloric restriction were followed by rapid increases post-contest, resulting in negligible net changes from baseline. This provides evidence that highly trained individuals are able to retain contractile tissue during substantial weight loss following a daily caloric deficit of 500 kcal

• Frankston, Naomi; Ellison, Matthew; Riise, Jonatan Narvestad; Seynnes, Olivier R.; Farris, Dominic & Rice, Hannah (2025). Second Metatarsal Bone Stress During Running Is Independently Influenced by Running Speed and Load Carriage. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 35(10). doi: 10.1111/sms.70152. Full text in Research Archive Show summary

  Bone stress injuries occur in populations who engage in repetitive loading, such as distance runners and military recruits. The second metatarsal is a common bone stress injury site. Running speed and load carriage are modifiable factors which may influence metatarsal loading. The aim of this study was to determine how running at preferred, 90% of preferred, and 110% of preferred speed, with and without a weight vest carrying 10% body mass, influences second metatarsal bone stress. Data were collected from 28 runners (14 female, 14 male) during barefoot running using motion capture cameras, a pressure plate, and a force plate. Bone stress was calculated at the dorsal and plantar surfaces of the midshaft of the second metatarsal using a two‐dimensional beam theory model. No interaction effect was found between running speed and load carriage. Running at 90% of preferred speed decreased peak dorsal and plantar stress by 2.1% and 2.3%, respectively, compared to preferred speed, while running at 110% of preferred speed increased peak dorsal and plantar stress by 4.2%. Running with 110% of body mass increased peak dorsal and plantar metatarsal stress by 3.1% and 2.9%, respectively, compared to running with no additional mass. The mean coefficient of variation across all conditions was 25%, indicating variation in peak stress between participants. Running at faster speeds and with additional loads may increase the risk of second metatarsal bone stress injury. The high variation in peak bone stress between participants demonstrates the importance of considering the individual when assessing injury risk.

• Handegard, Vilde; Lunde, Per Kristian; Frisk, Michael; Seynnes, Olivier R.; Ørtenblad, N. & Louch, William Edward [Show all 8 contributors for this article] (2025). Myofiber structure, sarcoplasmic reticulum Ca2+ handling, and contractile function after muscle-damaging exercise in humans. Physiological Reports. 13(3). doi: 10.14814/phy2.70204. Full text in Research Archive Show summary

  Exercise-induced muscle damage (EIMD) is characterized by a severe and prolonged decline in force-generating capacity. However, the precise cellular mechanisms underlying the observed long-lasting decline in force-generating capacity associated with EIMD are still unclear. We investigated in vivo force generation and ex vivo Ca2+-activated force generation, Ca2+ sensitivity, and myofiber Ca2+ handling systems (SR and t-tubules) in human biceps brachii before and 2, 48, and 96 h after eccentrically muscle-damaging contractions and in non-exercised control arm. The force-generating capacity declined by 50 ± 13% 3 h after exercise and was still not recovered after 96 h. The force-Ca relationship of skinned myofibers revealed an impaired maximal Ca2+-activated force in MHC I-fibers, but not MHC II-fibers 48 h after exercise. Further, Ca2+ sensitivity was increased in MHC II-fibers, which was reversed after incubation with a strong reductant. There was a biphasic increase in SERCA sulfonylation, and a parallel reduction in the SR Ca2+ uptake rate, with no effects on SR vesicle leak or SR vesicle Ca2+ release rate. T-tubules showed a progressive increase in the density of longitudinal tubules by 96 h after exercise. In conclusion, MHC II-fiber Ca2+ sensitivity was increased 48 h after exercise, attributed to changes in the REDOX status. 96 h after exercise SR vesicle Ca2+ uptake was impaired, and an increased number of longitudinal tubules were observed. These alterations may contribute to the impaired force generation evident at the late stage of recovery.

• Engstad, Martin Kvalvik; Seynnes, Olivier R.; Vesterhus, Ingvild; Hesseberg, Eirik; Fjeldberg, Ken & Carlsen, Monica Hauger [Show all 12 contributors for this article] (2025). Effect of Oral Contraceptive Use on Muscle Hypertrophy Following Strength Training. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 35(4). doi: 10.1111/sms.70052. Full text in Research Archive Show summary

  Oral contraceptives (OC) are widely used by women, while their interactions with strength training are yet to be resolved. This study investigated the effects of OC use on muscle hypertrophy and strength adaptation to heavy strength training in young adult women. Fifteen habitual OC users and 17 non-OC users (NOC) with regular menstrual cycles completed ~12 weeks of strength training, which spanned three menstrual cycles for the NOC group. All participants were young, healthy, and strength-untrained. Isometric knee-extensor strength, muscle cross-sectional area of the vastus lateralis (ultrasound imaging), and body composition (DXA) were used to evaluate training adaptations. Blood samples for estradiol and progesterone analyses, dietary registrations, and questionnaires assessing appetite, vitality, motivation, recovery status, and sleep duration were collected during the intervention period. Both groups experienced gains in lean mass and muscle strength. However, the OC group demonstrated a significantly larger increase in arm lean mass (5.5% ± 3.9% [mean ± standard deviation] vs. 2.9% ± 2.8%, p < 0.05) and vastus lateralis cross-sectional area (10.0% ± 4.1% vs. 5.3% ± 4.4%, p < 0.05) compared to the NOC group. Despite these differences, there was no significant group difference in lower body strength gains. Both groups reported similar levels of appetite, dietary intake, vitality, motivation to exercise, and perceived recovery throughout the study, although the OC group slept an average of 42 min longer per day. Our findings suggest that OC use potentiates muscle growth during strength training, although further research is needed to elucidate the underlying mechanisms and long-term effects.

• Paulsen, Gøran; Lindberg, Kolbjørn Andreas; Eriksrud, Ola; Solberg, Paul Andre; Bjørnsen, Thomas & Seynnes, Olivier R. [Show all 9 contributors for this article] (2025). Is the Classification of Athletes Based on Force-Velocity Profiling from Countermovement Jumps Influenced by the Choice of Method? Medicine & Science in Sports & Exercise. ISSN 0195-9131. 57(9), p. 1968–1978. doi: 10.1249/MSS.0000000000003732. Full text in Research Archive Show summary

  Purpose Force–velocity (FV) profiling is a tool for classifying athletes as force- or velocity-deficient, allowing for tailored training prescriptions. However, profiling classification may vary depending on the measurement method used. This study compared FV profile variables derived from countermovement jumps (CMJs) using four approaches: the Flight-time method, a Kinetic method, and two kinematic methods. Methods Sixteen National-level female handball players completed CMJs with 0, 20, 40, 50, and 70 kg of additional mass. All jumps were recorded by a force plate and 3D motion capture system. For each jump, jump height, height of push-off (HPO), average force, and average velocity were estimated, and FV profiles were derived using each of the four methods. The two kinematic methods represented displacement of the center of mass of 1) the body and 2) the whole system (i.e., body + additional mass). A pre-measured HPO (Flight-time method) overestimated the HPO derived from kinetic and kinematic methods at low values and underestimated it at high values. Results The Flight-time method underestimated average force by 7% compared to the Kinetic method and overestimated it by 1–3% compared to the kinematic methods. Average velocity during push-off was lower when derived from the Flight-time method than all other methods, particularly at the highest velocities (~20%). The resultant FV profiles (slopes) differed systematically by 30–39% between methods, such that >80% of participants were classified differently (i.e., force-deficient, velocity-deficient, or balanced) depending on the method applied. Conclusions We question the practical use of the FV profiles based on the Flight-time method, as it could result in the misclassification of athletes.

• Bojsen-Møller, Jens; Seynnes, Olivier R.; Magnusson, S.P.; Hernæs, Herman; Refsdal, Andreas Skiri & Sironga, J. [Show all 10 contributors for this article] (2025). Jumping performance and muscle–tendon characteristics of Maasai men of East Africa. Scientific Reports. 15. doi: 10.1038/s41598-025-01694-9. Full text in Research Archive
• Bizet, Baptiste; Nordez, Antoine; Tallio, Tristan; Lacourpaille, Lilian; Cattagni, Thomas & Colard, Julian [Show all 11 contributors for this article] (2025). Eight weeks of eccentric training at long-muscle length increases fascicle length independently of adaptations in passive mechanical properties. Journal of applied physiology. ISSN 8750-7587. 138(4), p. 939–949. doi: 10.1152/japplphysiol.00859.2024. Full text in Research Archive
• Vesterhus, Ingvild; Hesseberg, Eirik R.; Fjeldberg, Ken; Engstad, Martin Kvalvik; Paulsen, Gøran & Hansen, Mette [Show all 9 contributors for this article] (2025). Patellar tendon adaptations to resistance training in young women using combined oral contraceptives. PeerJ. 13. doi: 10.7717/peerj.19581. Full text in Research Archive Show summary

  Background. The study aimed to examine the impact of combined oral contraceptive pill (OC)use on patellar tendon (PT) adaptation to resistance trainingin young women. Methods. Fifteen users of OC (28 ± 3 years) (OC group) and 17 eumenorrheic non users (32 ± 5 years) (NOC group) performed heavy resistance training of the knee extensors over a period equivalent to three menstrual or pill cycles. Maximal isometric strength of the knee extensor muscles, PT cross-sectional area (CSA), tensile stiffness, and shear wave velocity (SWV) were measured before and after the intervention using combined ultrasonography and dynamometry. Results. The training period increased maximal isometric strength in both groups (≈11%, P <0.001) with no significant interaction with OC use (p=0.965). Likewise, a small yet significant increase in proximal tendon CSA was observed (1.5 ± 1.6% for both groups, main training effect P <0.001) without any significant interaction with OCuse(p=0.267). Tendon tensile stiffness also increased significantly (18.9 ± 26.3% in the OC group and 28.2 ± 35.1% in the NOC group, main effect: P <0.001) but was not significantly affected by OC use (interaction effect: p=0.428). Tendon SWV measurements yielded similar results, indicating a main effect of training (+12% on average, p=0.024) but no significant interaction with OC use. Conclusion. These findings suggest that OC use does not affect the increase in PT CSA and mechanical properties following short-term resistance training in young untrained females.

• Seynnes, Olivier R.; Nordez, Antoine; Lacourpaille, Lilian; Hesseberg, Eirik; Vesterhus, Ingvild & Fjeldberg, Ken [Show all 9 contributors for this article] (2025). Eccentric training effects on hamstring muscles in oral contraceptive users and naturally menstruating women. European Journal of Applied Physiology. ISSN 1439-6319. 125, p. 2133–2144. doi: 10.1007/s00421-025-05753-x. Full text in Research Archive Show summary

  Purpose This study evaluated the effects of eccentric resistance training on hamstring muscles properties in women using oral contraceptives (OC) and naturally menstruating women. Methods Before and after the training intervention, we measured maximal isometric and eccentric moment of the knee flexor muscles, thickness and shear wave velocity (SWV) of the biceps femoris long head (BFlh), semitendinosus (ST) and semimembranosus (SM) muscles, and BFlh fascicle length using ultrasonography and dynamometry. Results The 12-week training intervention resulted in a modest but statistically significant increase in resting BFlh fascicle length (~2% on average, p = 0.005) across both groups, with no observed effect of OC use on any variable. The muscle strength and thickness increased comparably in both groups, with an average increase of ~20% in isometric knee flexor moment and 14% in eccentric knee flexor moment (p < 0.001 for both tests). ST muscle thickness increased by ~4% on aver age (p = 0.016), while no main effect of training was observed for SM and BFlh thickness. The shear modulus of the SM muscle decreased by 9% (p = 0.021) for the combined groups. However, it remained unchanged in the BFlh and ST muscles, and OC use did not influence these measurements either. Conclusion These findings suggest that eccentric training induces similar adaptations in women regardless of OC use. Furthermore, fascicle lengthening was not attributable to changes in muscle shear modulus under the present conditions.

• Ritsche, Paul; Franchi, Martino V.; Faude, Oliver; Finni, Taija; Seynnes, Olivier R. & Cronin, Neil J. (2024). Fully Automated Analysis of Muscle Architecture from B-Mode Ultrasound Images with DL_Track_US. Ultrasound in Medicine and Biology. ISSN 0301-5629. 50(2), p. 258–267. doi: 10.1016/j.ultrasmedbio.2023.10.011. Full text in Research Archive Show summary

  Objective: B-mode ultrasound can be used to image musculoskeletal tissues, but one major bottleneck is analyses of muscle architectural parameters (i.e., muscle thickness, pennation angle and fascicle length), which are most often performed manually. Methods: In this study we trained two different neural networks (classic U-Net and U-Net with VGG16 pre-trained encoder) to detect muscle fascicles and aponeuroses using a set of labeled musculoskeletal ultrasound images. We determined the best-performing model based on intersection over union and loss metrics. We then compared neural network predictions on an unseen test set with those obtained via manual analysis and two existing semi/automated analysis approaches (simple muscle architecture analysis [SMA] and UltraTrack). DL_Track_US detects the locations of the superficial and deep aponeuroses, as well as multiple fascicle fragments per image. Results: For single images, DL_Track_US yielded results similar to those produced by a non-trainable automated method (SMA; mean difference in fascicle length: 5.1 mm) and human manual analysis (mean difference: –2.4 mm). Between-method differences in pennation angle were within 1.5°, and mean differences in muscle thickness were less than 1 mm. Similarly, for videos, there was overlap between the results produced with UltraTrack and DL_Track_US, with intraclass correlations ranging between 0.19 and 0.88. Conclusion: DL_Track_US is fully automated and open source and can estimate fascicle length, pennation angle and muscle thickness from single images or videos, as well as from multiple superficial muscles. We also provide a user interface and all necessary code and training data for custom model development.

• Cumming, Kristoffer Toldnes; Reitzner, Stefan Markus; Hanslien, Marit; Skilnand, Kenneth; Seynnes, Olivier R. & Horwath, Oscar [Show all 9 contributors for this article] (2024). Muscle memory in humans: evidence for myonuclear permanence and long-term transcriptional regulation after strength training. Journal of Physiology. ISSN 0022-3751. 602(17), p. 4171–4193. doi: 10.1113/JP285675. Full text in Research Archive Show summary

  The objective of this work was to investigate myonuclear permanence and transcriptional regulation as mechanisms for cellular muscle memory after strength training in humans. Twelve untrained men and women performed 10 weeks of unilateral elbow-flexor strength training followed by 16 weeks of de-training. Thereafter, 10 weeks’ re-training was conducted with both arms: the previously trained arm and the contralateral untrained control arm. Muscle biopsies were taken from the trained arm before and after both training periods and from the control arm before and after re-training. Muscle biopsies were analysed for fibre cross-sectional area (fCSA), myonuclei and global transcriptomics (RNA sequencing). During the first training period, myonuclei increased in type 1 (13 ± 17%) and type 2 (33 ± 23%) fibres together with a 30 ± 43% non-significant increase in mixed fibre fCSA (P = 0.069). Following de-training, fCSA decreased in both fibre types, whereas myonuclei were maintained, resulting in 33% higher myonuclear number in previously trained vs. control muscle in type 2 fibres. Furthermore, in the previously trained muscle, three differentially expressed genes (DEGs; EGR1, MYL5 and COL1A1) were observed. Following re-training, the previously trained muscle showed larger type 2 fCSA compared to the control (P = 0.035). However, delta change in type 2 fCSA was not different between muscles. Gene expression was more dramatically changed in the control arm (1338 DEGs) than in the previously trained arm (822 DEGs). The sustained higher number of myonuclei in the previously trained muscle confirms myonuclear accretion and permanence in humans. Nevertheless, because of the unclear effect on the subsequent hypertrophy with re-training, the physiological benefit remains to be determined.

• Ritsche, Paul; Seynnes, Olivier R. & Cronin, Neil J. (2023). DL_Track_US: a python package to analyse muscle ultrasonography images. Journal of Open Source Software (JOSS). 8(85). doi: 10.21105/joss.05206. Full text in Research Archive Show summary

  Ultrasonography can be used to assess muscle architectural parameters during static and dynamic conditions. Nevertheless, the analysis of the acquired ultrasonography images presents a major difficulty. Muscle architectural parameters such as muscle thickness, fascicle length and pennation angle are mainly segmented manually. Manual analysis is time expensive, subjective and requires thorough expertise. Within recent years, several algorithms were developed to solve these issues. Yet, these are only partly automated, are not openly available, or lack in user friendliness. The DL_Track_US python package is designed to allow fully automated and rapid analysis of muscle architectural parameters in lower limb ultrasonography images.

• Myrholt, Roger Behrman; Solberg, Paul Andre; Pettersen, Henrik; Seynnes, Olivier R. & Paulsen, Gøran (2023). Effects of Low- Versus High-Velocity-Loss Thresholds With Similar Training Volume on Maximal Strength and Hypertrophy in Highly Trained Individuals. International Journal of Sports Physiology and Performance (IJSPP). ISSN 1555-0265. 18(4), p. 368–377. doi: 10.1123/ijspp.2022-0161. Full text in Research Archive Show summary

  Aims: In the present intervention study, low-velocity-loss (LVL) versus high-velocity-loss (HVL) thresholds in the squat and bench press were compared for changes in muscle strength, power, and hypertrophy. Methods: Strength-trained volunteers (7♀ and 9♂; age: 27.2 [3.4] y; height: 174.6 [8.0] cm; body mass: 75.3 [10.1] kg) were randomized into an LVL or HVL threshold group (LVL n = 3♀ + 5♂, and HVL n = 4♀ + 4♂). Training took place 3 times per week over 6 weeks (loads: ∼75%–90% of 1-repetition maximum [1RM]). The thresholds of LVLs and HVLs were set at 20% and 40% of maximal velocity, respectively, for the squat, and at 30% and 60%, respectively, for the bench press. Before and after the intervention, 1RM, leg press power, and squat jump were tested. The load (∼45% of 1RM) corresponding to 1-m/s velocity was assessed in all sessions for both exercises. In addition, the thickness of the vastus lateralis and triceps brachii and body composition (dual-energy X-ray absorptiometry [DEXA]) were measured. Results: Squat and bench-press 1RM increased similarly in both groups by 7% to 11% (SD: 4%–6%, P < .05). No group differences were observed for changes in jump height, leg press power, or DEXA lean mass. However, HVL showed a small increase in muscle thickness of the vastus lateralis compared with LVL (6 ± 6% [95% CI] group difference, P < .05). Conclusion: For strength-trained individuals, high-volume lower-velocity-loss thresholds were as effective as higher thresholds for improvements in 1RM strength; but local hypertrophy was seemingly elicited faster with higher velocity-loss thresholds.

• Werkhausen, Amelie; Gløersen, Øyvind; Nordez, Antoine; Paulsen, Gøran; Bojsen-Møller, Jens & Seynnes, Olivier R. (2023). Linking muscle architecture and function in vivo: conceptual or methodological limitations? PeerJ. 11. doi: 10.7717/peerj.15194. Full text in Research Archive Show summary

  Background Despite the clear theoretical link between sarcomere arrangement and force production, the relationship between muscle architecture and function remain ambiguous in vivo. Methods: We used two frequently used ultrasound-based approaches to assess the relationships between vastus lateralis architecture parameters obtained in three common conditions of muscle lengths and contractile states, and the mechanical output of the muscle in twenty-one healthy subjects. The relationship between outcomes obtained in different conditions were also examined. Muscle architecture was analysed in panoramic ultrasound scans at rest with the knee fully extended and in regular scans at an angle close to maximum force (60°), at rest and under maximum contraction. Isokinetic and isometric strength tests were used to estimate muscle force production at various fascicle velocities. Results: Measurements of fascicle length, pennation angle and thickness obtained under different experimental conditions correlated moderately with each other (r = 0.40−.74). Fascicle length measured at 60° at rest correlated with force during high-velocity knee extension (r = 0.46 at 400° s−1) and joint work during isokinetic knee extension (r = 0.44 at 200° s−1 and r = 0.57 at 100° s−1). Muscle thickness was related to maximum force for all measurement methods (r = 0.44–0.73). However, we found no significant correlations between fascicle length or pennation angle and any measures of muscle force or work. Most correlations between architecture and force were stronger when architecture was measured at rest close to optimal length. Conclusion: These findings reflect methodological limitations of current approaches to measure fascicle length and pennation angle in vivo. They also highlight the limited value of static architecture measurements when reported in isolation or without direct experimental context.

• Jerger, Simon; Centner, Christoph; Lauber, Benedikt; Seynnes, Olivier R.; Friedrich, Till & Lolli, David [Show all 8 contributors for this article] (2023). Specific collagen peptides increase adaptions of patellar tendon morphology following 14-weeks of high-load resistance training: A randomized-controlled trial. European Journal of Sport Science (EJSS). ISSN 1746-1391. 23(12). doi: 10.1080/17461391.2023.2232758. Full text in Research Archive Show summary

  The purpose of this study was to investigate the effect of a supplementation with specific collagen peptides (SCP) combined with resistance training (RT) on changes in structural properties of the patellar tendon. Furthermore, tendon stiffness as well as maximal voluntary knee extension strength and cross-sectional area (CSA) of the rectus femoris muscle were assessed. In a randomized, placebo-controlled study, 50 healthy, moderately active male participants completed a 14-week resistance training program with three weekly sessions (70–85% of 1 repetition maximum [1RM]) for the knee extensors. While the SCP group received 5g of specific collagen peptides daily, the other group received the same amount of a placebo (PLA) supplement. The SCP supplementation led to a significant greater (p < 0.05) increase in patellar tendon CSA compared with the PLA group at 60% and 70% of the patellar tendon length starting from the proximal insertion. Both groups increased tendon stiffness (p < 0.01), muscle CSA (p < 0.05) and muscular strength (p < 0.001) throughout the intervention without significant differences between the groups. The current study shows that in healthy, moderately active men, supplementation of SCP in combination with RT leads to greater increase in patellar tendon CSA than RT alone. Since underlying mechanisms of tendon hypertrophy are currently unknown, further studies should investigate potential mechanisms causing the increased morphology adaptions following SCP supplementation.

• Rice, Hannah; Seynnes, Olivier R. & Werkhausen, Amelie (2023). Effect of increased running speed and weight carriage on peak and cumulative tibial loading. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. doi: 10.1111/sms.14476. Full text in Research Archive Show summary

  Introduction: Tibial stress injuries are a burdensome injury among military recruits. Military activities include running and the carriage of additional weight, and this may be related to the high risk of bone stress injuries. The aim of this study was to quantify tibial loading when running at two different speeds, with and without additional weight, and to quantify their combined influence. Methods: Fourteen male distance runners who ran at least 40 km per week ran barefoot on a force-instrumented treadmill in four conditions representing preferred running speed (mean (SD) 3.1 (0.3) m/s) and 20% increased running speed (3.8 (0.4) m/s), with and without 20% of body weight carried in a weight vest. Kinematics and kinetics were synchronously collected. Bending moments were estimated about the medial-lateral axis of the tibial centroid located 1/3rd of the length from distal to proximal. Static equilibrium was ensured at each 1% of stance. Peak bending moments were obtained in addition to cumulative-weighted loading, where weighted loading accounted for the relative importance of the magnitude of the bending moment and the quantity of loading using a bone-dependent weighting factor. Results: There were no interaction effects for running speed and weight carriage on peak or cumulative tibial loading. Running at a 20% faster speed increased peak and cumulative loading per kilometer by 8.0% (p < 0.001) and 4.8% (p < 0.001), respectively. Carriage of an additional 20% of body weight increased peak and cumulative loading per kilometer by 6.6% (p < 0.001) and 8.5% (p < 0.001), respectively. Interpretation: Increasing the physical demand of running by increasing speed or weight carriage increased peak tibial loading and cumulative tibial loading per kilometer, and this may increase the risk of tibial stress injury. Running speed and weight carriage independently influenced tibial loading.

• Centner, Christoph; Jerger, Simon; Lauber, Benedikt; Seynnes, Olivier R.; Friedrich, Till & Lolli, David [Show all 8 contributors for this article] (2023). Similar patterns of tendon regional hypertrophy after low-load blood flow restriction and high-load resistance training. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. doi: 10.1111/sms.14321. Full text in Research Archive Show summary

  Purpose: Recent evidence indicates that low-load blood flow restriction (LL-BFR) training elicits an anabolic response in tendinous tissue. The purpose of the present study was to investigate the hypertrophic pattern induced in the Achilles tendon by LL-BFR, in comparison with the regional hypertrophy typically observed with conventional high-load (HL) resistance training. Methods: N = 40 male participants were randomly and concealed allocated to one of two groups: LL-BFR training (20–35% one-repetition maximum/1RM) or HL training (70–85% 1RM). The training was completed three times per week for a total of 14 weeks. Before and after the training period, Achilles tendon morphology was assessed using magnetic resonance imaging along the entire tendon length. Additionally, dynamic strength measures of the plantar flexors were evaluated. Results: In line with previous findings, dynamic plantar flexion strength was improved to a comparable extent in both groups (LL-BFR: 43.6%; HL: 43.5%). The results also confirmed significant increases in Achilles tendon cross-sectional area with LL-BFR (+5.2%). Moreover, they revealed that the hypertrophic pattern obtained with LL-BFR was similar to regional changes seen with conventional HL training. Conclusion: The present findings point towards the notion that despite the low loads being applied, LL-BFR training induces Achilles tendon hypertrophy by potentiating anabolic responses in the same regions as with conventional high-load training. Future studies are needed to (i) focus on the potential mechanisms underlying these tendon morphology changes and (ii) apply and evaluate LL-BFR training in clinical populations to validate these results in rehabilitative settings.

• Lindberg, Kolbjørn Andreas; Lohne-Seiler, Hilde; Fosstveit, Sindre Herskedal; Sibayan, Erlend E.; Fjeller, Joachim S. & Løvold, Sondre [Show all 12 contributors for this article] (2022). Effectiveness of individualized training based on force–velocity profiling on physical function in older men. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 32(6), p. 1013–1025. doi: 10.1111/sms.14157. Full text in Research Archive Show summary

  The study aimed to investigate the effectiveness of an individualized power training program based on force–velocity (FV) profiling on physical function, muscle morphology, and neuromuscular adaptations in older men. Forty-nine healthy men (68 ± 5 years) completed a 10-week training period to enhance muscular power. They were randomized to either a generic power training group (GPT) or an individualized power training group (IPT). Unlike generic training, individualized training was based on low- or high-resistance exercises, from an initial force–velocity profile. Lower-limb FV profile was measured in a pneumatic leg-press, and physical function was assessed as timed up-and-go time (TUG), sit-to-stand power, grip strength, and stair-climbing time (loaded [20kg] and unloaded). Vastus lateralis morphology was measured with ultrasonography. Rate of force development (RFD) and rate of myoelectric activity (RMA) were measured during an isometric knee extension. The GPT group improved loaded stair-climbing time (6.3 ± 3.8 vs. 2.3% ± 7.3%, p = 0.04) more than IPT. Both groups improved stair-climbing time, sit to stand, and leg press power, grip strength, muscle thickness, pennation angle, fascicle length, and RMA from baseline (p < 0.05). Only GPT increased loaded stair-climbing time and RFD (p < 0.05). An individualized power training program based on FV profiling did not improve physical function to a greater degree than generic power training. A generic power training approach combining both heavy and low loads might be advantageous through eliciting both force- and velocity-related neuromuscular adaptions with a concomitant increase in muscular power and physical function in older men.

• Stäudle, Benjamin; Seynnes, Olivier R.; Laps, Guido; Brüggemann, Gert-Peter & Albracht, Kirsten (2022). Altered Gastrocnemius Contractile Behavior in Former Achilles Tendon Rupture Patients During Walking. Frontiers in Physiology. 13. doi: 10.3389/fphys.2022.792576. Full text in Research Archive Show summary

  Achilles tendon rupture (ATR) remains associated with functional limitations years after injury. Architectural remodeling of the gastrocnemius medialis (GM) muscle is typically observed in the affected leg and may compensate force deficits caused by a longer tendon. Yet patients seem to retain functional limitations during—low-force—walking gait. To explore the potential limits imposed by the remodeled GM muscle-tendon unit (MTU) on walking gait, we examined the contractile behavior of muscle fascicles during the stance phase. In a cross-sectional design, we studied nine former patients (males; age: 45 ± 9 years; height: 180 ± 7 cm; weight: 83 ± 6 kg) with a history of complete unilateral ATR, approximately 4 years post-surgery. Using ultrasonography, GM tendon morphology, muscle architecture at rest, and fascicular behavior were assessed during walking at 1.5 m⋅s–1 on a treadmill. Walking patterns were recorded with a motion capture system. The unaffected leg served as control. Lower limbs kinematics were largely similar between legs during walking. Typical features of ATR-related MTU remodeling were observed during the stance sub-phases corresponding to series elastic element (SEE) lengthening (energy storage) and SEE shortening (energy release), with shorter GM fascicles (36 and 36%, respectively) and greater pennation angles (8° and 12°, respectively). However, relative to the optimal fascicle length for force production, fascicles operated at comparable length in both legs. Similarly, when expressed relative to optimal fascicle length, fascicle contraction velocity was not different between sides, except at the time-point of peak series elastic element (SEE) length, where it was 39 ± 49% lower in the affected leg. Concomitantly, fascicles rotation during contraction was greater in the affected leg during the whole stance-phase, and architectural gear ratios (AGR) was larger during SEE lengthening. Under the present testing conditions, former ATR patients had recovered a relatively symmetrical walking gait pattern. Differences in seen AGR seem to accommodate the profound changes in MTU architecture, limiting the required fascicle shortening velocity. Overall, the contractile behavior of the GM fascicles does not restrict length- or velocity-dependent force potentials during this locomotor task.

• Werkhausen, Amelie; Gløersen, Øyvind Nøstdahl; Nordez, Antoine; Paulsen, Gøran; Bojsen-Møller, Jens & Seynnes, Olivier R. (2022). Rate of force development relationships to muscle architecture and contractile behavior in the human vastus lateralis. Scientific Reports. 12(1). doi: 10.1038/s41598-022-26379-5. Full text in Research Archive Show summary

  In this study, we tested the hypotheses that (i) rate of force development (RFD) is correlated to muscle architecture and dynamics and that (ii) force–length–velocity properties limit knee extensor RFD. Twenty-one healthy participants were tested using ultrasonography and dynamometry. Vastus lateralis optimal fascicle length, fascicle velocity, change in pennation angle, change in muscle length, architectural gear ratio, and force were measured during rapid fixed-end contractions at 60° knee angle to determine RFD. Isokinetic and isometric tests were used to estimate individual force–length–velocity properties, to evaluate force production relative to maximal potential. Correlation analyses were performed between force and muscle parameters for the first three 50 ms intervals. RFD was not related to optimal fascicle length for any measured time interval, but RFD was positively correlated to fascicle shortening velocity during all intervals (r = 0.49–0.69). Except for the first interval, RFD was also related to trigonometry-based changes in muscle length and pennation angle (r = 0.45–0.63) but not to architectural gear ratio. Participants reached their individual vastus lateralis force–length–velocity potential (i.e. their theoretical maximal force at a given length and shortening velocity) after 62 ± 24 ms. Our results confirm the theoretical importance of fascicle shortening velocity and force–length–velocity properties for rapid force production and suggest a role of fascicle rotation.

• Jerger, Simon; Centner, Christoph; Lauber, Benedikt; Seynnes, Olivier R.; Sohnius, Tim & Jendricke, Patrick [Show all 9 contributors for this article] (2022). Effects of specific collagen peptide supplementation combined with resistance training on Achilles tendon properties. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 32(7), p. 1131–1141. doi: 10.1111/sms.14164. Full text in Research Archive Show summary

  The purpose of this study was to investigate the effect of specific collagen peptides (SCP) combined with resistance training (RT) on changes in tendinous and muscular properties. In a randomized, placebo-controlled study, 40 healthy male volunteers (age: 26.3 ± 4.0 years) completed a 14 weeks high-load resistance training program. One group received a daily dosage of 5g SCP while the other group received 5g of a placebo (PLA) supplement. Changes in Achilles tendon cross-sectional area (CSA), tendon stiffness, muscular strength, and thickness of the plantar flexors were measured. The SCP supplementation led to a significantly (p = 0.002) greater increase in tendon CSA (+11.0%) compared with the PLA group (+4.7%). Moreover, the statistical analysis revealed a significantly (p = 0.014) greater increase in muscle thickness in the SCP group (+7.3%) compared with the PLA group (+2.7%). Finally, tendon stiffness and muscle strength increased in both groups, with no statistical difference between the groups. In conclusion, the current study shows that the supplementation of specific collagen peptides combined with RT is associated with a greater hypertrophy in tendinous and muscular structures than RT alone in young physically active men. These effects might play a role in reducing tendon stress (i.e., deposition of collagen in load-bearing structures) during daily activities.

• Rieder, Florian; Wiesinger, Hans-Peter; Herfert, Jürgen; Lampl, Katrin; Hecht, Stefan & Niebauer, Josef [Show all 10 contributors for this article] (2022). Whole body vibration for chronic patellar tendinopathy: A randomized equivalence trial. Frontiers in Physiology. 13. doi: 10.3389/fphys.2022.1017931. Full text in Research Archive Show summary

  Purpose: Whole body vibration (WBV) triggers anabolic responses in various tissues, including tendons, without requiring high force production. In this waitlist-controlled equivalence trial, we tested its clinical effectiveness as an alternative treatment for patellar tendinopathy against conventional heavy slow resistance training (HSR). Methods: Thirty-nine patients were randomized to either 3 months of WBV training (n = 13), HSR training (n = 11), or a waitlist control (WLC) group (n = 15). In a partly cross-over design, 14 patients of the WLC group were redistributed to one of the two intervention groups (5 in WBV, 9 in HSR). Pre- and post-intervention testing included pain assessments (VAS), functional limitations (VISA-P), knee extension strength and tendon morphological, mechanical and material properties. Follow-up measurements (VAS, VISA-P) were performed in the WBV and HSR groups 6 months after the intervention. Results: Comparisons with the WLC group revealed significant improvements in VISA-P and VAS scores after HSR (41%, p = 003; 54%, p = 0.005) and WBV (22%, p = 0.022; 56%, p = 0.031) training. These improvements continued until follow-up (HSR: 43%, 56%; WBV: 24%, 37%). Pre-post improvements in VAS scores were equivalent between WBV and HSR groups but inconclusive for the VISA-P score and all pre-test to follow up comparisons. The mid-tendon cross-sectional area was significantly reduced after WBV (−5.7%, p = 0.004) and HSR (−3.0%, p = 0.004) training compared to WLC although the equivalence test between interventions was inconclusive. Conclusion: Whole body vibration improved symptoms typically associated with patellar tendinopathy. This type of intervention is as effective as HSR against maximum pain, although equivalence could not be confirmed for other variables. The beneficial responses to WBV and HSR treatments persisted for 6 months after the end of the intervention.

• Centner, Christoph; Jerger, Simon; Lauber, Benedikt; Seynnes, Olivier R.; Friedrich, Till & Lolli, David [Show all 8 contributors for this article] (2022). Low-Load Blood Flow Restriction and High-Load Resistance Training Induce Comparable Changes in Patellar Tendon Properties. Medicine & Science in Sports & Exercise. ISSN 0195-9131. 54(4), p. 582–589. doi: 10.1249/MSS.0000000000002824. Full text in Research Archive Show summary

  Introduction: Low-load resistance training with blood flow restriction (LL-BFR) has emerged as a viable alternative to conventional high-load (HL) resistance training regimens. Despite increasing evidence confirming comparable muscle adaptations between LL-BFR and HL resistance exercise, only very little is known about tendinous mechanical and morphological adaptations after LL-BFR. Therefore, the aim of the present study was to examine the effects of 14 wk of LL-BFR and HL training on patellar tendon adaptations. Methods: Twenty-nine recreationally active male participants were randomly allocated into the following two groups: LL-BFR resistance training (20%–35% one-repetition maximum (1RM)) or HL resistance training (70%–85% 1RM). Both groups trained three times per week for 14 wk. One week before and after the intervention, patellar tendon mechanical and morphological properties were assessed via ultrasound and magnetic resonance imaging. In addition, changes in muscle cross-sectional area were quantified by magnetic resonance imaging and muscle strength via dynamic 1RM measurements. Results: The findings demonstrated that both LL-BFR and HL training resulted in comparable changes in patellar tendon stiffness (LL-BFR: +25.2%, P = 0.003; HL: +22.5%, P = 0.024) without significant differences between groups. Similar increases in tendon cross-sectional area were observed in HL and LL-BFR. Muscle mass and strength also significantly increased in both groups but were not statistically different between HL (+38%) and LL-BFR (+34%), except for knee extension 1RM where higher changes were seen in LL-BFR. Conclusions: The present results support the notion that both HL and LL-BFR cause substantial changes in patellar tendon properties, and the magnitude of changes is not significantly different between conditions. Further studies that examine the physiological mechanisms underlying the altered tendon properties after LL-BFR training are needed.

• Moltubakk, Marie M.; Villars, Fabienne Olivia; Magulas, Melina Meyer; Magnusson, Stig P.; Seynnes, Olivier R. & Bojsen-Møller, Jens (2021). Altered Triceps Surae Muscle-Tendon Unit Properties after 6 Months of Static Stretching. Medicine & Science in Sports & Exercise. ISSN 0195-9131. 53(9), p. 1975–1986. doi: 10.1249/MSS.0000000000002671. Full text in Research Archive Show summary

  Introduction: This study examined the effects of 24 wk of daily static stretching of the plantarflexors (unilateral 4 × 60-s stretching, whereas the contralateral leg served as a control; n = 26) on joint range of motion (ROM), muscle–tendon unit morphological and mechanical properties, neural activation, and contractile function. Methods: Torque–angle/velocity was obtained in passive and active conditions using isokinetic dynamometry, whereas muscle–tendon morphology and mechanical properties were examined using ultrasonography. Results: After the intervention, ROM increased (stretching, +11° ± 7°; control, 4° ± 8°), and passive torque (stretching, −10 ± 11 N·m; control, −7 ± 10 N·m) and normalized EMG amplitude (stretching, −3% ± 6%; control, −3% ± 4%) at a standardized dorsiflexion angle decreased. Increases were seen in passive tendon elongation at a standardized force (stretching, +1.3 ± 1.6 mm; control, +1.4 ± 2.1 mm) and in maximal passive muscle and tendon elongation. Angle of peak torque shifted toward dorsiflexion. No changes were seen in tendon stiffness, resting tendon length, or gastrocnemius medialis fascicle length. Conformable changes in ROM, passive dorsiflexion variables, tendon elongation, and angle of peak torque were observed in the nonstretched leg. Conclusions: The present findings indicate that habitual stretching increases ROM and decreases passive torque, altering muscle–tendon behavior with the potential to modify contractile function.

• Lindberg, Kolbjørn Andreas; Eythorsdottir, Ingrid Eir Thorp; Solberg, Paul Andre; Gløersen, Øyvind Nøstdahl; Seynnes, Olivier R. & Bjørnsen, Thomas [Show all 7 contributors for this article] (2021). Validity of Force–Velocity Profiling Assessed With a Pneumatic Leg Press Device. International Journal of Sports Physiology and Performance (IJSPP). ISSN 1555-0265. 16(12), p. 1777–1785. doi: 10.1123/ijspp.2020-0954. Full text in Research Archive Show summary

  Purpose: The aim of this study was to examine the concurrent validity of force–velocity (FV) variables assessed across 5 Keiser leg press devices. Methods: A linear encoder and 2 independent force plates (MuscleLab devices) were mounted on each of the 5 leg press devices. A total of 997 leg press executions, covering a wide range of forces and velocities, were performed by 14 participants (29 [7] y, 181 [5] cm, 82 [8] kg) across the 5 devices. Average and peak force, velocity, and power values were collected simultaneously from the Keiser and MuscleLab devices for each repetition. Individual FV profiles were fitted to each participant from peak and average force and velocity measurements. Theoretical maximal force, velocity, and power were deduced from the FV relationship. Results: Average and peak force and velocity had a coefficient of variation of 1.5% to 8.6%, near-perfect correlations (.994–.999), and a systematic bias of 0.7% to 7.1% when compared with reference measurements. Average and peak power showed larger coefficient of variations (11.6% and 17.2%), despite excellent correlations (.977 and .952), and trivial to small biases (3.9% and 8.4%). Extrapolated FV variables showed near-perfect correlations (.983–.997) with trivial to small biases (1.4%–11.2%) and a coefficient of variation of 1.4% to 5.9%. Conclusions: The Keiser leg press device can obtain valid measurements over a wide range of forces and velocities across different devices. To accurately measure power, theoretical maximal power calculated from the FV profile is recommended over average and peak power values from single repetitions, due to the lower random error observed for theoretical maximal power.

• Lindberg, Kolbjørn; Solberg, Paul; Rønnestad, Bent; Frank, Martin; Larsen, Tommy Mella & Abusdal, Gøran [Show all 11 contributors for this article] (2021). Should we individualize training based on force-velocity profiling to improve physical performance in athletes? Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 31(12), p. 2198–2210. doi: 10.1111/sms.14044. Full text in Research Archive Show summary

  The present study aimed to examine the effectiveness of an individualized training program based on force-velocity (FV) profiling on jumping, sprinting, strength, and power in athletes. Forty national level team sport athletes (20 ± 4years, 83 ± 13 kg) from ice-hockey, handball, and soccer completed a 10-week training intervention. A theoretical optimal squat jump (SJ)-FV-profile was calculated from SJ with five different loads (0, 20, 40, 60, and 80 kg). Based on their initial FV-profile, athletes were randomized to train toward, away, or irrespective (balanced training) of their initial theoretical optimal FV-profile. The training content was matched between groups in terms of set x repetitions but varied in relative loading to target the different aspects of the FV-profile. The athletes performed 10 and 30 m sprints, SJ and countermovement jump (CMJ), 1 repetition maximum (1RM) squat, and a leg-press power test before and after the intervention. There were no significant group differences for any of the performance measures. Trivial to small changes in 1RM squat (2.9%, 4.6%, and 6.5%), 10 m sprint time (1.0%, −0.9%, and −1.7%), 30 m sprint time (0.9%, −0.6%, and −0.4%), CMJ height (4.3%, 3.1%, and 5.7%), SJ height (4.8%, 3.7%, and 5.7%), and leg-press power (6.7%, 4.2%, and 2.9%) were observed in the groups training toward, away, or irrespective of their initial theoretical optimal FV-profile, respectively. Changes toward the optimal SJ-FV-profile were negatively correlated with changes in SJ height (r = −0.49, p < 0.001). Changes in SJ-power were positively related to changes in SJ-height (r = 0.88, p < 0.001) and CMJ-height (r = 0.32, p = 0.044), but unrelated to changes in 10 m (r = −0.02, p = 0.921) and 30 m sprint time (r = −0.01, p = 0.974). The results from this study do not support the efficacy of individualized training based on SJ-FV profiling.

• Andersen, Vidar; Paulsen, Gøran; Stien, Nicolay; Baarholm, Martin; Seynnes, Olivier R. & Sæterbakken, Atle Hole (2021). Resistance Training With Different Velocity Loss Thresholds Induce Similar Changes in Strengh and Hypertrophy. Journal of Strength and Conditioning Research. ISSN 1064-8011. doi: 10.1519/JSC.0000000000004067. Full text in Research Archive Show summary

  The aim of this study was to compare the effects of 2 velocity-based resistance training programs when performing resistance training with matched training volume. Ten resistance-trained adults volunteered (age, 23 ± 4.3 years; body mass, 68 ± 8.9 kg; and height, 171 ± 8 cm) with a mean resistance training experience of 4.5 years. A within person, between leg design was used. For each subject, the legs were randomly assigned to either low velocity loss (LVL) threshold at 15% or high velocity loss (HVL) threshold at 30% velocity loss. Leg press and leg extension were trained unilaterally twice per week over a period of 9 weeks. Before and after the intervention, both legs were tested in 1 repetition maximum (RM) (kg), maximal voluntary contraction (MVC) (N), rate of force development (N·s−1), average velocity (m·s−1), and power output (W) at 30, 45, 60, and 75% of 1 RM (all in unilateral leg press). Furthermore, muscle thickness (mm) of the vastus lateralis and rectus femoris, pennation angle (°) of the vastus lateralis, and the fascicle length (mm) of the vastus lateralis were measured using ultrasound imaging. The data were analyzed using mixed-design analysis of variance. No differences between the legs in any of the variables were found; however, both low and HVL were effective for increasing 1 RM (ES = 1.25–1.82), MVC (effect size [ES] = 0.42–0.64), power output (ES = 0.31–0.86), and muscle thickness (ES = 0.24–0.51). In conclusion, performing velocity-based resistance training with low and HVL with equal training volume resulted in similar effects in maximal and explosive strength in addition to muscular adaptations.

• Werkhausen, Amelie; Solberg, Christian E.; Paulsen, Gøran; Bojsen-Møller, Jens & Seynnes, Olivier R. (2021). Adaptations to explosive resistance training with partial range of motion are not inferior to full range of motion. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 31(5), p. 1026–1035. doi: 10.1111/sms.13921. Full text in Research Archive Show summary

  We tested whether explosive resistance training with partial range of motion (ROM) would be as effective as full ROM training using a noninferiority trial design. Fifteen subjects with strength training experience took part in an explosive—concentric only—leg press training program, three times per week for 10 weeks. One leg was randomly assigned to exercise with partial ROM (ie, 9º) and the other leg to full ROM. Before and after training, we assessed leg press performance, isokinetic concentric and isometric knee extension torque, and vastus lateralis muscle architecture. Overall, both training modalities increased maximal strength and rate of force development. Training with partial ROM yielded noninferior results compared to full ROM for leg press peak power (+69 ± 47% vs. +61 ± 64%), isokinetic strength (4-6 ± 6%-12% vs. 1-6 ± 6%-10% at 30, 60, and 180˚s-1), and explosive torque after 100 (47 ± 24 vs. 35 ± 22) and 150 ms (57 ± 22% vs. 42 ± 25%). The comparison was inconclusive for other functional parameters (ie, isokinetic peak torque (300˚s−1), joint angle at isokinetic peak torque, explosive torque after 50 ms, and electrically evoked torque) and for muscle fascicle length and thickness, although noninferiority was established for pennation angle. However, partial ROM was not found statistically inferior to full ROM for any measured variable. Under the present conditions, the effects of explosive heavy resistance training were independent of joint ROM. Instead, these data suggest that the distinct timing of muscle work in explosive contractions confers more influence to the starting joint angle than ROM on adaptations to this type of training.

• Stäudle, Benjamin; Seynnes, Olivier R.; Laps, Guido; Göll, Fabian; Brüggemann, Gert-Peter & Albracht, Kirsten (2021). Recovery from Achilles Tendon Repair: A Combination of Postsurgery Outcomes and Insufficient Remodeling of Muscle and Tendon. Medicine & Science in Sports & Exercise. ISSN 0195-9131. 53(7), p. 1356–1366. doi: 10.1249/MSS.0000000000002592. Full text in Research Archive Show summary

  Introduction: Achilles tendon rupture (ATR) patients have persistent functional deficits in the triceps surae muscle–tendon unit (MTU). The complex remodeling of the MTU accompanying these deficits remains poorly understood. The purpose of the present study was to associate in vivo and in silico data to investigate the relations between changes in MTU properties and strength deficits in ATR patients. Methods: Eleven male subjects who had undergone surgical repair of complete unilateral ATR were examined 4.6 ± 2.0 (mean ± SD) yr after rupture. Gastrocnemius medialis (GM) tendon stiffness, morphology, and muscle architecture were determined using ultrasonography. The force–length relation of the plantar flexor muscles was assessed at five ankle joint angles. In addition, simulations (OpenSim) of the GM MTU force–length properties were performed with various iterations of MTU properties found between the unaffected and the affected side. Results: The affected side of the patients displayed a longer, larger, and stiffer GM tendon (13% ± 10%, 105% ± 28%, and 54% ± 24%, respectively) compared with the unaffected side. The GM muscle fascicles of the affected side were shorter (32% ± 12%) and with greater pennation angles (31% ± 26%). A mean deficit in plantarflexion moment of 31% ± 10% was measured. Simulations indicate that pairing an intact muscle with a longer tendon shifts the optimal angular range of peak force outside physiological angular ranges, whereas the shorter muscle fascicles and tendon stiffening seen in the affected side decrease this shift, albeit incompletely. Conclusions: These results suggest that the substantial changes in MTU properties found in ATR patients may partly result from compensatory remodeling, although this process appears insufficient to fully restore muscle function.

• Carbonaro, Marco; Seynnes, Olivier R.; Maffiuletti, Nicola A.; Busso, Chiara; Minetto, Marco Alessandro & Botter, Alberto (2020). Architectural changes in superficial and deep compartments of the tibialis anterior during electrical stimulation over different sites. IEEE transactions on neural systems and rehabilitation engineering. ISSN 1534-4320. 28(11), p. 2557–2565. doi: 10.1109/TNSRE.2020.3027037. Full text in Research Archive Show summary

  Electrical stimulation is widely used in rehabilitation to prevent muscle weakness and to assist the functional recovery of neural deficits. Its application is however limited by the rapid development of muscle fatigue due to the non-physiological motor unit (MU) recruitment. This issue can be mitigated by interleaving muscle belly (mStim) and nerve stimulation (nStim) to distribute the temporal recruitment among different MU groups. To be effective, this approach requires the two stimulation modalities to activate minimally-overlapped groups of MUs. In this manuscript, we investigated spatial differences between mStim and nStim MU recruitment through the study of architectural changes of superficial and deep compartments of tibialis anterior (TA). We used ultrasound imaging to measure variations in muscle thickness, pennation angle, and fiber length during mStim, nStim, and voluntary (Vol) contractions at 15% and 25% of the maximal force. For both contraction levels, architectural changes induced by nStim in the deep and superficial compartments were similar to those observed during Vol. Instead, during mStim superficial fascicles underwent a greater change compared to those observed during nStim and Vol, both in absolute magnitude and in their relative differences between compartments. These observations suggest that nStim results in a distributed MU recruitment over the entire muscle volume, similarly to Vol, whereas mStim preferentially activates the superficial muscle layer. The diversity between spatial recruitment of nStim and mStim suggests the involvement of different MU populations, which justifies strategies based on interleaved nerve/muscle stimulation to reduce muscle fatigue during electrically-induced contractions of TA.

• Kirkebø, Jan Egil; Werkhausen, Amelie; Seynnes, Olivier R. & Austeng, Andreas (2020). Automated Characterization of Muscle Architectural Variation in Ultrasound Images. Proceedings - IEEE Ultrasonics Symposium. ISSN 1948-5719. doi: 10.1109/IUS46767.2020.9251536. Full text in Research Archive Show summary

  Fascicle (fiber bundle) orientation and length are useful parameters to infer the force potential of skeletal muscles. Ultrasound imaging is commonly used to determine fascicle characteristics. In most of the literature, automated methods simplify analysis by assimilating fascicles and aponeuroses (connective tissue on which fascicles are anchored) to straight lines that are homogeneously arranged along the muscle length. In practice, manual adjustments are often needed to the realizations of the proposed automated methods due to the low signal-to-noise ratio of the images. We propose a fully automated and robust method that determines non-linear aponeuroses and fascicles over entire panoramic images, reflecting the real structure of the muscle and its fibers.

• Wiesinger, Hans-Peter; Seynnes, Olivier R.; Kösters, Alexander; Müller, Erich & Rieder, Florian (2020). Mechanical and Material Tendon Properties in Patients With Proximal Patellar Tendinopathy. Frontiers in Physiology. 11. doi: 10.3389/fphys.2020.00704. Full text in Research Archive Show summary

  Introduction: The effect of chronic patellar tendinopathy on tissue function and integrity is currently unclear and underinvestigated. The aim of this cohort comparison was to examine morphological, material, and mechanical properties of the patellar tendon and to extend earlier findings by measuring the ability to store and return elastic energy in symptomatic tendons. Methods: Seventeen patients with chronic (>3 months, VISA-P < 80), inferior pole patellar tendinopathy (24 ± 4 years; male = 12, female = 5) were carefully matched to controls (25 ± 3 years) for training status, pattern, and history of loading of the patellar tendon. Individual knee extension force, patellar tendon stiffness, stress, strain, Young’s modulus, hysteresis, and energy storage capacity, were obtained with combined dynamometry, ultrasonography, magnetic resonance imaging, and electromyography. Results: Anthropometric parameters did not differ between groups. VISA-P scores ranged from 28 to 78 points, and symptoms had lasted from 10 to 120 months before testing. Tendon proximal cross-sectional area was 61% larger in the patellar tendinopathy group than in the control group. There were no differences between groups in maximal voluntary isometric knee extension torque (p = 0.216; d < −0.31) nor in tensile tendon force produced during isometric ramp contractions (p = 0.185; d < −0.34). Similarly, tendon strain (p = 0.634; d < 0.12), hysteresis (p = 0.461; d < 0.18), and strain energy storage (p = 0.656; d < 0.36) did not differ between groups. However, patellar tendon stiffness (−19%; p = 0.007; d < −0.74), stress (−27%; p< 0.002; d < −0.90) and Young’s modulus (−32%; p = 0.001; d < −0.94) were significantly lower in tendinopathic patients compared to healthy controls. Discussion: In this study, we observed lower stiffness in affected tendons. However, despite the substantial structural and histological changes occurring with tendinopathy, the tendon capacity to store and dissipate energy did not differ significantly.

• Cronin, Neil J.; Finni, Taija & Seynnes, Olivier R. (2020). Using deep learning to generate synthetic B-mode musculoskeletal ultrasound images. Computer Methods and Programs in Biomedicine. ISSN 0169-2607. 196. doi: 10.1016/j.cmpb.2020.105583. Full text in Research Archive Show summary

  Background and objective: Deep learning approaches are common in image processing, but often rely on supervised learning, which requires a large volume of training images, usually accompanied by hand-crafted labels. As labelled data are often not available, it would be desirable to develop methods that allow such data to be compiled automatically. In this study, we used a Generative Adversarial Network (GAN) to generate realistic B-mode musculoskeletal ultrasound images, and tested the suitability of two automated labelling approaches. Methods: We used a model including two GANs each trained to transfer an image from one domain to another. The two inputs were a set of 100 longitudinal images of the gastrocnemius medialis muscle, and a set of 100 synthetic segmented masks that featured two aponeuroses and a random number of ‘fascicles’. The model output a set of synthetic ultrasound images and an automated segmentation of each real input image. This automated segmentation process was one of the two approaches we assessed. The second approach involved synthesising ultrasound images and then feeding these images into an ImageJ/Fiji-based automated algorithm, to determine whether it could detect the aponeuroses and muscle fascicles. Results: Histogram distributions were similar between real and synthetic images, but synthetic images displayed less variation between samples and a narrower range. Mean entropy values were statistically similar (real: 6.97, synthetic: 7.03; p = 0.218), but the range was much narrower for synthetic images (6.91 – 7.11 versus 6.30 – 7.62). When comparing GAN-derived and manually labelled segmentations, intersection-over-union values- denoting the degree of overlap between aponeurosis labels- varied between 0.0280 – 0.612 (mean ± SD: 0.312 ± 0.159), and pennation angles were higher for the GAN-derived segmentations (25.1° vs. 19.3°; p < 0.001). For the second segmentation approach, the algorithm generally performed equally well on synthetic and real images, yielding pennation angles within the physiological range (13.8–20°). Conclusions: We used a GAN to generate realistic B-mode ultrasound images, and extracted muscle architectural parameters from these images automatically. This approach could enable generation of large labelled datasets for image segmentation tasks, and may also be useful for data sharing. Automatic generation and labelling of ultrasound images minimises user input and overcomes several limitations associated with manual analysis.

• Aas, Sigve Nyvik; Breit, Markus; Karsrud, Stian; Aase, Ole Jølle; Rognlien, Simen Helset & Cumming, Kristoffer Toldnes [Show all 11 contributors for this article] (2020). Musculoskeletal adaptations to strength training in frail elderly: a matter of quantity or quality? Journal of Cachexia, Sarcopenia and Muscle. ISSN 2190-5991. 11(3), p. 663–677. doi: 10.1002/jcsm.12543. Full text in Research Archive Show summary

  Background: The improvement in muscle strength generally exceeds the increase in muscle size following strength training in frail elderly, highlighting the complex aetiology of strength deficit in aging. The aim of this study was to investigate the effect of heavy‐load strength training on a broad number of factors related to specific strength in frail elderly. Methods: Thirty‐four frail elderly men (n = 18) and women (n = 16) aged 67 to 98 (86 ± 7 years) were randomized to either a group performing strength training twice a week for 10 weeks (ST) or a non‐exercising control group (CON). Knee extensor muscle strength was tested as one‐repetition maximum (1RM) and isometric maximal voluntary contraction (MVC) torque. Muscle activation was assessed by the interpolated twitch technique, and muscle density [mean Hounsfield units (HU)] and intermuscular adipose tissue (IMAT) by computed tomography scans of the quadriceps femoris. Muscle biopsies from the vastus lateralis were obtained to investigate changes in intramyocellular lipids and single‐fibre specific tension. Results: In ST, knee extension 1RM and MVC improved by 17 and 7%, respectively. Muscle cross‐sectional area of the quadriceps femoris increased by 7%, accompanied by a 4% increase of muscle density. No changes in IMAT, voluntary activation level, single‐fibre specific tension, or lipid content were observed. Conclusions: In contrast to several previous reports, the improvements in isometric muscle strength and muscle area were in good agreement in the present study. The training‐induced increase in muscle density was not due to changes in skeletal muscle lipid content. Instead, the increase in muscle density may reflect increased packing of contractile material or simply an increased ratio of muscle tissue relative to IMAT.

• Seynnes, Olivier R. & Cronin, Neil J. (2020). Simple muscle architecture analysis (SMA): An ImageJ macro tool to automate measurements in B-mode ultrasound scans. PLOS ONE. 15(2). doi: 10.1371/journal.pone.0229034. Full text in Research Archive Show summary

  In vivo measurements of muscle architecture (i.e. the spatial arrangement of muscle fascicles) are routinely included in research and clinical settings to monitor muscle structure, function and plasticity. However, in most cases such measurements are performed manually, and more reliable and time-efficient automated methods are either lacking completely, or are inaccessible to those without expertise in image analysis. In this work, we propose an ImageJ script to automate the entire analysis process of muscle architecture in ultrasound images: Simple Muscle Architecture Analysis (SMA). Images are filtered in the spatial and frequency domains with built-in commands and external plugins to highlight aponeuroses and fascicles. Fascicle dominant orientation is then computed in regions of interest using the OrientationJ plugin. Bland-Altman plots of analyses performed manually or with SMA indicate that the automated analysis does not induce any systematic bias and that both methods agree equally through the range of measurements. Our test results illustrate the suitability of SMA to analyse images from superficial muscles acquired with a broad range of ultrasound settings.

• Aas, Sigve Nyvik; Seynnes, Olivier R.; Benestad, Haakon Breien & Raastad, Truls (2019). Strength training and protein supplementation improve muscle mass, strength, and function in mobility-limited older adults: a randomized controlled trial. Aging Clinical and Experimental Research. ISSN 1594-0667. doi: 10.1007/s40520-019-01234-2. Full text in Research Archive Show summary

  Background Adaptation to strength training in very old mobility-limited individuals is not fully characterized. Therefore, the aim of this study was to perform a thorough investigation of the adaptation to a lower body strength training regime in this population, with particular emphasis on the relationship between changes in selected variables.MethodsTwenty-two mobility-limited older men and women (85 ± 6 years) were randomized to either a group performing 30 min of heavy-load strength training three times a week, with daily protein supplementation, for 10 weeks (ST), or a control group. End points were leg lean mass assessed by DXA, muscle thickness assessed by ultrasound, isometric and dynamic strength, rate of torque development, and functional capacity.ResultsLeg lean mass increased from baseline in ST (0.7 ± 0.3 kg), along with increased thickness of vastus lateralis (4.4 ± 3.2%), rectus femoris (6.7 ± 5.1%), and vastus intermedius (5.8 ± 5.9%). The hypertrophy was accompanied by improved knee extensor strength (20–23%) and functional performance (7–11%). In ST, neither the change in leg lean mass nor muscle thickness correlated with changes in muscle strength. However, a strong correlation was observed between the change in isometric strength and gait velocity (r = 0.70).ConclusionsThe mismatch between gains in muscle size and strength suggests that muscle quality-related adaptations con-tributed to the increases in strength. The correlations observed between improvements in strength and function suggests that interventions eliciting large improvements in strength may also be superior in terms of functional gains in this population.

• Horwath, Oscar; Paulsen, Gøran; Esping, Tobias; Seynnes, Olivier R. & Olsson, Monica Charlotte (2019). Isokinetic resistance training combined with eccentric overload improves athletic performance and induces muscle hypertrophy in young ice hockey players. Journal of Science and Medicine in Sport. ISSN 1440-2440. 22(7). doi: 10.1016/j.jsams.2018.12.017. Full text in Research Archive Show summary

  Objectives: To determine the combined effects of slow isokinetic resistance training and eccentric overload and compare it to traditional resistance training on strength, power, body composition and muscle hypertrophy in young ice hockey players. Design: Experimental, randomized trial. Methods: Twenty-two resistance-trained ice hockey players (18 ± 1 year) were assigned to either isokinetic resistance training and eccentric overload (ISO/ECC; n = 11) or traditional resistance training (TRAD; n = 11). Participants underwent supervised progressive resistance training for 8 weeks (2–3 sessions/week) involving lower body multiple-joint exercises (heavy squats and explosive jump squats). The ISO/ECC group performed their training using a computerized robotic engine system (1080 Quantum synchro, Sweden), whereas the TRAD group performed the same resistance exercises with isotonic loading. Before and after the intervention, participants were evaluated in 1RM back squat, loaded jump squats, sprint- and jump performance, body composition and muscle thickness using ultrasound measurement. Results: Similar moderate increases in 1RM back squat and power output in the jump squats were found in both the ISO/ECC and TRAD groups (11–17%, P < 0.01), whereas only the ISO/ECC group showed improvements in drop jump performance (9.8%, P = 0.01). Moreover, similar trivial changes in body composition were observed in both groups, while only the ISO/ECC training group increased muscle thickness in the vastus intermedius (P = 0.01) and rectus femoris muscles (P = 0.03). Conclusions: Both modalities effectively increased maximal strength and power output, whereas isokinetic resistance training, combined with eccentric overload, improved drop jump performance and induced greater muscle hypertrophy than traditional training in young ice hockey players.

• Paulsen, Gøran; Eidsheim, Hedda; Helland, Christian; Seynnes, Olivier R.; Solberg, Paul Andre & Rønnestad, Bent (2019). Eccentric cycling does not improve cycling performance in amateur cyclists. PLOS ONE. 14:e0208452(1), p. 1–15. doi: 10.1371/journal.pone.0208452. Full text in Research Archive Show summary

  Eccentric cycling training induces muscle hypertrophy and increases joint power output in non-athletes. Moreover, eccentric cycling can be considered a movement-specific type of strength training for cyclists, but it is hitherto unknown if eccentric cycling training can improve cycling performance in trained cyclists. Twenty-three male amateur cyclists were randomized to an eccentric or a concentric cycling training group. The eccentric cycling was performed at a low cadence (~40 revolution per minute) and the intensity was controlled by perceived effort (12–17 on the Borgs scale) during 2 min intervals (repeated 5–8 times). The cadence and perceived effort of the concentric group matched those of the eccentric group. Additionally, after the eccentric or concentric cycling, both groups performed traditionally aerobic intervals with freely chosen cadence in the same session (4–5 x 4–15 min). The participants trained twice a week for 10 weeks. Maximal oxygen uptake (VO2max), maximal aerobic power output (Wmax), lactate threshold, isokinetic strength, muscle thickness, pedaling characteristics and cycling performance (6- and 30-sec sprints and a 20-min time trial test) were assessed before and after the intervention period. Inferences about the true value of the effects were evaluated using probabilistic magnitude-based inferences. Eccentric cycling induced muscle hypertrophy (2.3 ± 2.5% more than concentric) and augmented eccentric strength (8.8 ± 5.9% more than concentric), but these small magnitude effects seemed not to transfer into improvements in the physiological assessments or cycling performance. On the contrary, the eccentric training appeared to have limiting or detrimental effects on cycling performance, measured as Wmax and a 20-min time trial. In conclusion, eccentric cycling training did not improve cycling performance in amateur cyclists. Further research is required to ascertain whether the present findings reflect an actual lack of efficacy, negative effects or a delayed response to eccentric cycling training.

• Helland, Christian; Haugen, Thomas André; Rakovic, Elvir; Eriksrud, Ola; Seynnes, Olivier R. & Mero, Antti A. [Show all 7 contributors for this article] (2019). Force–velocity profiling of sprinting athletes: single-run vs. multiple-run methods. European Journal of Applied Physiology. ISSN 1439-6319. 119(2), p. 465–473. doi: 10.1007/s00421-018-4045-2. Full text in Research Archive Show summary

  Purpose: This study explored the agreement between a single-run and a multiple-run method for force–velocity (Fv) profiling of sprinting athletes; we evaluated both absolute values and changes over time caused by sprint training. Methods: Seventeen female handball players (23 ± 3 years, 177 ± 7 cm, 73 ± 6 kg) performed 30 m un-resisted and resisted sprints (50, 80 and 110 N resistance) before and after an 8-week sprint training intervention. Two approaches were used to calculate theoretical maximal velocity (v0), horizontal force (F0), power (Pmax), and the force–velocity slope (SFv): (1) the single-run method, based on inverse dynamics applied to the centre-of-mass movement, was calculated from anthropometric and sprint split time data; and (2) the multiple-run method, where peak velocity from un-resisted and resisted sprints were plotted against the horizontal resistances. Results: Trivial differences in v0 (0.7%) were observed between the two calculation methods. Corresponding differences for F0, Pmax and SFv were 16.4, 15.6 and 17.6%, respectively (most likely; very large effect size). F0 showed poor agreement between the methods (r = 0.26 and 0.16 before and after the intervention). No substantial correlation between the changes (from pre- to post-training tests) in SFV calculated with the single-run and the multiple-run methods were observed (r = 0.02). Conclusions: This study revealed poor agreement between the Fv relationships of the investigated calculation methods. In practice, both methods may have a purpose, but the single-run and the multiple-run methods appear to measure somewhat different sprint properties and cannot be used interchangeably.

• Centner, Christoph; Lauber, Benedikt; Seynnes, Olivier R.; Jerger, Simon; Sohnius, Tim & Gollhofer, Albert [Show all 7 contributors for this article] (2019). Low-load blood flow restriction training induces similar morphological and mechanical Achilles tendon adaptations compared to high-load resistance training. Journal of applied physiology. ISSN 8750-7587. 127(6), p. 1660–1667. doi: 10.1152/japplphysiol.00602.2019. Full text in Research Archive Show summary

  Low-load blood flow restriction (LL-BFR) training has gained increasing interest in the scientific community by demonstrating that increases in muscle mass and strength are comparable to conventional high-load (HL) resistance training. Although adaptations on the muscular level are well documented, there is little evidence on how LL-BFR training affects human myotendinous properties. Therefore, the aim of the present study was to investigate morphological and mechanical Achilles tendon adaptations after 14 weeks of strength training. Fifty-five male volunteers (27.9 ± 5.1 years) were randomly allocated into the following three groups: LL-BFR (20-35% of one-repetition maximum, 1RM), HL (70-85% 1RM) or a non-exercising control group (CON). The LL-BFR and the HL completed a resistance training program for 14 weeks and tendon morphology, mechanical as well as material properties along with muscle cross-sectional area (CSA) and isometric strength were assessed before and after the intervention. Both, HL (+40.7%) and LL-BFR (+36.1%) training induced significant increases in tendon stiffness (p < 0.05) as well as tendon CSA (HL: +4.6%, LL-BFR: +7.8%, p < 0.001). These changes were comparable between groups without significant changes in Young's modulus. Furthermore, gastrocnemius medialis muscle CSA and plantar flexor strength significantly increased in both training groups (p < 0.05), while the CON group did not show significant changes in any of the evaluated parameters. In conclusion, the adaptive change in Achilles tendon properties following low-load resistance training with partial vascular occlusion appears comparable to that evoked by high-load resistance training.

• Werkhausen, Amelie Corinna; Cronin, Neil J; Albracht, Kirsten; Bojsen-Møller, Jens & Seynnes, Olivier R. (2019). Distinct muscle-tendon interaction during running at different speeds and in different loading conditions. Journal of applied physiology. ISSN 8750-7587. 127(1), p. 246–253. doi: 10.1152/japplphysiol.00710.2018. Full text in Research Archive Show summary

  The interaction between the Achilles tendon and the triceps surae muscles seems to be modulated differently with various task configurations. Here we tested the hypothesis that the increased forces and ankle joint work during running under contrasting conditions (altered speed or load) would be met by different, time-dependent adjustments at the muscle-tendon level. Ultrasonography, electromyography, kinematics, and ground reaction force measurements were used to examine Achilles tendon, gastrocnemius, and soleus muscle mechanics in 16 runners in four different running conditions, consisting of a combination of two different speeds (preferred and 20% of preferred speed) and two loading conditions (unloaded and 20% of body mass). Positive ankle joint work increased similarly (13%) with speed and load. Gastrocnemius and soleus muscle fascicle length and peak velocity were not altered by either condition, suggesting that contractile conditions are mostly preserved despite the constraints imposed in this experimental design. However, at higher running speed, tendon length changes were unaltered but mean muscle electromyographic activity increased in gastrocnemius (10%, P 0.01) and soleus (14%, P 0.01). Conversely, when loading was increased, mean muscle activity remained similar to unloaded conditions but the mean velocity of gastrocnemius fascicles was reduced and tendon recoil increased (29%, P 0.01). Collectively, these results suggest that the neuromuscular system meets increased mechanical demands by favoring economical force production when enough time is available.

• Werkhausen, Amelie Corinna; Cronin, Neil J; Albracht, Kirsten; Paulsen, Gøran; Larsen, Askild V. & Bojsen-Møller, Jens [Show all 7 contributors for this article] (2019). Training-induced increase in Achilles tendon stiffness affects tendon strain pattern during running. PeerJ. 2019(4). doi: 10.7717/peerj.6764. Full text in Research Archive Show summary

  Background: During the stance phase of running, the elasticity of the Achilles tendon enables the utilisation of elastic energy and allows beneficial contractile conditions for the triceps surae muscles. However, the effect of changes in tendon mechanical properties induced by chronic loading is still poorly understood. We tested the hypothesis that a training-induced increase in Achilles tendon stiffness would result in reduced tendon strain during the stance phase of running, which would reduce fascicle strains in the triceps surae muscles, particularly in the mono-articular soleus. Methods: Eleven subjects were assigned to a training group performing isometric single-leg plantarflexion contractions three times per week for ten weeks, and another ten subjects formed a control group. Before and after the training period, Achilles tendon stiffness was estimated, and muscle-tendon mechanics were assessed during running at preferred speed using ultrasonography, kinematics and kinetics. Results: Achilles tendon stiffness increased by 18% (P < 0.01) in the training group, but the associated reduction in strain seen during isometric contractions was not statistically significant. Tendon elongation during the stance phase of running was similar after training, but tendon recoil was reduced by 30% (P < 0.01), while estimated tendon force remained unchanged. Neither gastrocnemius medialis nor soleus fascicle shortening during stance was affected by training. Discussion: These results show that a training-induced increase in Achilles tendon stiffness altered tendon behaviour during running. Despite training-induced changes in tendon mechanical properties and recoil behaviour, the data suggest that fascicle shortening patterns were preserved for the running speed that we examined. The asymmetrical changes in tendon strain patterns supports the notion that simple in-series models do not fully explain the mechanical output of the muscle-tendon unit during a complex task like running.

• Rittweger, Jörn; Albracht, Kirsten; Flück, Martin; Ruoss, Severin; Brocca, Lorenza & Longa, Emanuela [Show all 18 contributors for this article] (2018). Sarcolab pilot study into skeletal muscle’s adaptation to long-term spaceflight. npj Microgravity. 4. doi: 10.1038/s41526-018-0052-1. Full text in Research Archive Show summary

  Spaceflight causes muscle wasting. The Sarcolab pilot study investigated two astronauts with regards to plantar flexor muscle size, architecture, and function, and to the underlying molecular adaptations in order to further the understanding of muscular responses to spaceflight and exercise countermeasures. Two crew members (A and B) spent 6 months in space. Crew member A trained less vigorously than B. Postflight, A showed substantial decrements in plantar flexor volume, muscle architecture, in strength and in fiber contractility, which was strongly mitigated in B. The difference between these crew members closely reflected FAK-Y397 abundance, a molecular marker of muscle’s loading history. Moreover, crew member A showed downregulation of contractile proteins and enzymes of anaerobic metabolism, as well as of systemic markers of energy and protein metabolism. However, both crew members exhibited decrements in muscular aerobic metabolism and phosphate high energy transfer. We conclude that countermeasures can be effective, particularly when resistive forces are of sufficient magnitude. However, to fully prevent space-related muscular deterioration, intersubject variability must be understood, and intensive exercise countermeasures programs seem mandatory. Finally, proteomic and metabolomic analyses suggest that exercise benefits in space may go beyond mere maintenance of muscle mass, but rather extend to the level of organismic metabolism.

• Moltubakk, Marie M.; Magulas, Melina Meyer; Villars, Fabienne Olivia; Seynnes, Olivier R. & Bojsen-Møller, Jens (2018). Specialized properties of the triceps surae muscle-tendon unit in professional ballet dancers. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 28(9), p. 2023–2034. doi: 10.1111/sms.13207. Full text in Research Archive Show summary

  This study compared professional ballet dancers (n = 10) to nonstretching controls (n = 10) with the purpose of comparing muscle and tendon morphology, mechanical, neural, and functional properties of the triceps surae and their role for ankle joint flexibility. Torque‐angle and torque‐velocity data were obtained during passive and active conditions by use of isokinetic dynamometry, while tissue morphology and mechanical properties were evaluated by ultrasonography. Dancers displayed longer gastrocnemius medialis fascicles (55 ± 5 vs 47 ± 6 mm) and a longer (207 ± 33 vs 167 ± 10 mm) and more compliant (230 ± 87 vs 364 ± 106 N/mm) Achilles tendon compared to controls. Greater passive ankle dorsiflexion range of motion (40 ± 7 vs 17 ± 9°) was seen in dancers, resulting from greater fascicle strain and greater elongation of the muscle. Peak electromyographic (EMG) activity recorded during passive stretching was lower in dancers, and at common joint angles, dancers displayed lower EMG amplitude and lower passive joint stiffness. No differences between groups were seen in maximal isometric plantar flexor torque, isokinetic peak torque, angle of peak torque, or work. In conclusion, the greater ankle joint flexibility of professional dancers seems attributed to multiple differences in morphological and mechanical properties of muscle and tendinous tissues, and to factors related to neural activation.

• Werkhausen, Amelie Corinna; Albracht, Kirsten; Cronin, Neil J; Paulsen, Gøran; Bojsen-Møller, Jens & Seynnes, Olivier R. (2018). Effect of training-induced changes in Achilles tendon stiffness on muscle-tendon behavior during landing. Frontiers in Physiology. 9. doi: 10.3389/fphys.2018.00794. Full text in Research Archive Show summary

  During rapid deceleration of the body, tendons buffer part of the elongation of the muscle–tendon unit (MTU), enabling safe energy dissipation via eccentric muscle contraction. Yet, the influence of changes in tendon stiffness within the physiological range upon these lengthening contractions is unknown. This study aimed to examine the effect of training-induced stiffening of the Achilles tendon on triceps surae muscle–tendon behavior during a landing task. Twenty-one male subjects were assigned to either a 10-week resistance-training program consisting of single-leg isometric plantarflexion (n = 11) or to a non-training control group (n = 10). Before and after the training period, plantarflexion force, peak Achilles tendon strain and stiffness were measured during isometric contractions, using a combination of dynamometry, ultrasound and kinematics data. Additionally, testing included a step-landing task, during which joint mechanics and lengths of gastrocnemius and soleus fascicles, Achilles tendon, and MTU were determined using synchronized ultrasound, kinematics and kinetics data collection. After training, plantarflexion strength and Achilles tendon stiffness increased (15 and 18%, respectively), and tendon strain during landing remained similar. Likewise, lengthening and negative work produced by the gastrocnemius MTU did not change detectably. However, in the training group, gastrocnemius fascicle length was offset (8%) to a longer length at touch down and, surprisingly, fascicle lengthening and velocity were reduced by 27 and 21%, respectively. These changes were not observed for soleus fascicles when accounting for variation in task execution between tests. These results indicate that a training-induced increase in tendon stiffness does not noticeably affect the buffering action of the tendon when the MTU is rapidly stretched. Reductions in gastrocnemius fascicle lengthening and lengthening velocity during landing occurred independently from tendon strain. Future studies are required to provide insight into the mechanisms underpinning these observations and their influence on energy dissipation.

• Mersmann, Falk; Seynnes, Olivier R.; Legerlotz, Kirsten & Arampatzis, Adamantios (2018). Effects of tracking landmarks and tibial point of resistive force application on the assessment of patellar tendon mechanical properties in vivo. Journal of Biomechanics. ISSN 0021-9290. 71, p. 176–182. doi: 10.1016/j.jbiomech.2018.02.005. Full text in Research Archive Show summary

  The different methods used to assess patellar tendon elongation in vivo may partly explain the large variation of mechanical properties reported in the literature. The present study investigated the effects of tracking landmark position and tibial point of resistive force application during leg extensions in a dynamometer. Nineteen adults performed isometric contractions with a proximal and distal dynamometer shank pad position. Knee joint moments were calculated employing an inverse dynamics approach. Tendon elongation was measured using the patellar apex and either the tibial tuberosity (T) or plateau (P) as tracking landmark. Using P for tracking introduced a bias towards greater values of tendon elongation at all force levels from 100 N to maximum tendon force (TFmax; p < 0.05). The differences between landmarks considering maximum tendon strain were greater at the proximal shank pad position (p < 0.05). Tendon stiffness was lower for P compared with T, but only in intervals up to 50% of TFmax (p < 0.05). The agreement between T and P for stiffness calculated between 50% and TFmax was acceptable with the distal, but poor with the proximal pad position. We demonstrated that using the tibia plateau and not the insertion as tracking landmark clearly affects the assessment of the force–elongation curve of the patellar tendon. However, using a distal point of resistive force application and calculating tendon stiffness between 50% and TFmax seems to yield an acceptable agreement between landmarks. These findings have important implications for the assessment of tendon properties in vivo and cross-study comparisons.

• Wiesinger, Hans-Peter; Rieder, Florian; Kösters, Alexander; Müller, Erich & Seynnes, Olivier R. (2017). Sport-specific capacity to use elastic energy in the patellar and Achilles tendons of elite athletes. Frontiers in Physiology. 8:132, p. 1–10. doi: 10.3389/fphys.2017.00132. Full text in Research Archive Show summary

  Introduction: During running and jumping activities, elastic energy is utilized to enhance muscle mechanical output and efficiency. However, training-induced variations in tendon spring-like properties remain under-investigated. The present work extends earlier findings on sport-specific profiles of tendon stiffness and cross-sectional area to examine whether years of distinct loading patterns are reflected by tendons' ability to store and return energy. Methods:Ultrasound scans were performed to examine the morphological features of knee extensor and plantar flexor muscle-tendon units in elite ski jumpers, distance runners, water polo players, and sedentary controls. Tendon strain energy and hysteresis were measured with combined motion capture, ultrasonography, and dynamometry. Results: Apart from the fractional muscle-to-tendon cross-sectional area ratio being lower in the knee extensors of ski jumpers (−31%) and runners (−33%) than in water polo players, no difference in the considered muscle-tendon unit morphological features was observed between groups. Similarly, no significant difference in tendon energy storage or energy return was detected between groups. In contrast, hysteresis was lower in the patellar tendon of ski jumpers (−33%) and runners (−30%) compared to controls, with a similar trend for the Achilles tendon (significant interaction effect and large effect sizes η2 = 0.2). Normalized to body mass, the recovered strain energy of the patellar tendon was ~50% higher in ski jumpers than in water polo players and controls. For the Achilles tendon, recovered strain energy was ~40% higher in ski jumpers and runners than in controls. Discussion: Advantageous mechanical properties related to tendon spring-like function are observed in elite athletes whose sport require effective utilization of elastic energy. However, the mechanisms underpinning the better tendon capacity of some athletes to retain elastic energy could not be ascribed to intrinsic or morphological features of the lower limb muscle-tendon unit.

• Brocca, Lorenza; McPhee, Jamie; Longa, Emanuela; Canepari, Monica; Seynnes, Olivier R. & Vito, Giuseppe de [Show all 9 contributors for this article] (2017). Structure and function of human muscle fibres and muscle proteome in physically active older men. Journal of Physiology. ISSN 0022-3751. 595(14), p. 4823–4844. doi: 10.1113/JP274148. Full text in Research Archive Show summary

  Contradictory results have been reported on the impact of ageing on structure and functions of skeletal muscle fibres, likely to be due to a complex interplay between ageing and other phenomena such as disuse and diseases. Here we recruited healthy, physically and socially active young (YO) and elderly (EL) men in order to study ageing per se without the confounding effects of impaired physical function. In vivo analyses of quadriceps and in vitro analyses of vastus lateralis muscle biopsies were performed. In EL subjects, our results show that (i) quadriceps volume, maximum voluntary contraction isometric torque and patellar tendon force were significantly lower; (ii) muscle fibres went through significant atrophy and impairment of specific force (isometric force/cross-sectional area) and unloaded shortening velocity; (iii) myosin/actin ratio and myosin content in individual muscle fibres were not altered; (iv) the muscle proteome went through quantitative adaptations, namely an up-regulation of the content of several groups of proteins among which were myofibrillar proteins and antioxidant defence systems; (v) the muscle proteome went through qualitative adaptations, namely phosphorylation of several proteins, including myosin light chain-2 slow and troponin T and carbonylation of myosin heavy chains. The present results indicate that impairment of individual muscle fibre structure and function is a major feature of ageing per se and that qualitative adaptations of muscle proteome are likely to be more involved than quantitative adaptations in determining such a phenomenon.

• Werkhausen, Amelie Corinna; Albracht, Kirsten; Cronin, N.J.; Meier, Rahel; Bojsen-Møller, Jens & Seynnes, Olivier R. (2017). Modulation of muscle-tendon interaction in the human triceps surae during an energy dissipation task. Journal of Experimental Biology. ISSN 0022-0949. 220(22), p. 4141–4149. doi: 10.1242/jeb.164111. Full text in Research Archive Show summary

  The compliance of elastic elements allows muscles to dissipate energy safely during eccentric contractions. This buffering function is well documented in animal models but our understanding of its mechanism in humans is confined to non-specific tasks, requiring a subsequent acceleration of the body. The present study aimed to examine the behaviour of the human triceps surae muscle-tendon unit (MTU) during a pure energy dissipation task, under two loading conditions. Thirty-nine subjects performed a single-leg landing task, with- and without added mass. Ultrasound measurements were combined with 3D kinematics and kinetics to determine instantaneous length changes of MTUs, muscle fascicles, Achilles tendon and combined elastic elements. Gastrocnemius and soleus MTUs lengthened during landing. After a small concentric action, fascicles contracted eccentrically during most of the task, while plantarflexor muscles were activated. Combined elastic elements lengthened until peak ankle moment and recoiled thereafter, whilst no recoil was observed for the Achilles tendon. Adding mass resulted in greater negative work and MTU lengthening, which were accompanied by a greater stretch of tendon and elastic elements and a greater recruitment of the soleus muscle, without any further fascicle strain. Hence, the buffering action of elastic elements delimits the maximal strain and lengthening velocity of active muscle fascicles and is commensurate with loading constraints. In the present task, energy dissipation was modulated via greater MTU excursion and more forceful eccentric contractions. The distinct strain pattern of the Achilles tendon supports the notion that different elastic elements may not systematically fulfil the same function.

• Moltubakk, Marie M.; Eriksrud, Ola; Paulsen, Gøran; Seynnes, Olivier R. & Bojsen-Møller, Jens (2016). Hamstrings functional properties in athletes with high musculo-skeletal flexibility. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 26(6), p. 659–665. doi: 10.1111/sms.12488. Full text in Research Archive Show summary

  The purpose of this study was to examine whether athletes with highly flexible hamstring muscle-tendon units display different passive and contractile mechanical properties compared with controls. Flexibility, passive, and active torque–angle properties were assessed in 21 female elite rhythmic gymnasts and 16 female age-matched athletes. Passive resistance to stretch was measured during knee extension with the hip fixed at 100° of flexion. Concentric isokinetic maximal voluntary knee flexion and extension torques were measured at 60°/s in the same position. Tests of flexibility and passive resistance to stretch indicated a greater flexibility in the gymnasts. Despite no differences between groups in knee flexion and extension peak torque, gymnasts reached knee flexion peak torque at more extended positions (longer muscle lengths) and displayed significantly different torque–angle relations. When active torque was corrected for passive resistance to stretch, differences increased, gymnasts producing more work, and maintaining ≥ 70% of peak torque over a larger range of joint excursion. In conclusion, individuals with a higher flexibility of the hamstrings MTU present a different torque–angle profile, favoring the production of flexion torque toward extended knee positions, displaying larger functional range of motion and a higher mechanical work output during knee flexion.

• Rieder, Florian; Wiesinger, H.P.; Kösters, Alexander; Müller, E & Seynnes, Olivier R. (2016). Whole-body vibration training induces hypertrophy of the human patellar tendon. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 26(8), p. 902–910. doi: 10.1111/sms.12522. Full text in Research Archive Show summary

  Animal studies suggest that regular exposure to whole-body vibration (WBV) induces an anabolic response in bone and tendon. However, the effects of this type of intervention on human tendon properties and its influence on the muscle-tendon unit function have never been investigated. The aim of this study was to investigate the effect of WBV training on the patellar tendon mechanical, material and morphological properties, the quadriceps muscle architecture and the knee extension torque–angle relationship. Fifty-five subjects were randomized into either a vibration, an active control, or an inactive control group. The active control subjects performed isometric squats on a vibration platform without vibration. Muscle and tendon properties were measured using ultrasonography and dynamometry. Vibration training induced an increase in proximal (6.3%) and mean (3.8%) tendon cross-sectional area, without any appreciable change in tendon stiffness and modulus or in muscle architectural parameters. Isometric torque at a knee angle of 90° increased in active controls (6.7%) only and the torque–angle relation remained globally unchanged in all groups. The present protocol did not appreciably alter knee extension torque production or the musculo-tendinous parameters underpinning this function. Nonetheless, this study shows for the first time that WBV elicits tendon hypertrophy in humans.

• Helland, Christian; Hole, Eirik; Olsson, Monica Charlotte; Seynnes, Olivier R.; Solberg, Paul Andre & Paulsen, Gøran (2016). Training Strategies to Improve Muscle Power: Is Olympic-style Weightlifting Relevant? Medicine & Science in Sports & Exercise. ISSN 0195-9131. 49(4), p. 736–745. doi: 10.1249/MSS.0000000000001145. Full text in Research Archive Show summary

  Introduction: This efficacy study investigated the effects of (1) Olympic-style weightlifting (OWL), (2) motorized strength and power training (MSPT), and (3) free weight strength and power training (FSPT) on muscle power. Methods: Thirty-nine young athletes (20±3 yr.; ice hockey, volleyball and badminton) were randomized into the three training groups. All groups participated in 2-3 sessions/week for 8 weeks. The MSPT and FSPT groups trained using squats (two legs and single leg) with high force and high power, while the OWL group trained using clean and snatch exercises. MSPT was conducted as slow-speed isokinetic strength training and isotonic power training with augmented eccentric load, controlled by a computerized robotic engine system. FSPT used free weights. The training volume (sum of repetitions x kg) was similar between all three groups. Vertical jumping capabilities were assessed by countermovement jump (CMJ), squat jump (SJ), drop jump (DJ), and loaded CMJs (10-80 kg). Sprinting capacity was assessed in a 30 m sprint. Secondary variables were squat 1-repetitionmaximum, body composition and quadriceps thickness and architecture. Results: OWL resulted in trivial improvements, and inferior gains compared to FSPT and MSPT for CMJ, SJ, and DJ. MSPT demonstrated small, but robust effects on SJ, DJ and loaded CMJs (3-12%). MSPT was superior to FSPT in improving 30 m sprint performance. FSPT and MSPT, but not OWL, demonstrated increased thickness in the vastus lateralis and rectus femoris (4-7%). Conclusion: MSPT was time-efficient and equally or more effective than FSPT training in improving vertical jumping and sprinting performance. OWL was generally ineffective and inferior to the two other interventions.

• Wiesinger, Hans-Peter; Rieder, Florian; Kösters, Alexander; Müller, Erich & Seynnes, Olivier R. (2016). Are Sport-Specific Profiles of Tendon Stiffness and Cross-Sectional Area Determined by Structural or Functional Integrity? PLOS ONE. 11(6). doi: 10.1371/journal.pone.0158441. Full text in Research Archive Show summary

  The present study aimed to determine whether distinct sets of tendon properties are seen in athletes engaged in sports with contrasting requirements for tendon function and structural integrity. Patellar and Achilles tendon morphology and force-deformation relation were measured by combining ultrasonography, electromyography and dynamometry in elite ski jumpers, distance runners, water polo players and sedentary individuals. Tendon cross-sectional area normalized to body mass2/3 was smaller in water polo players than in other athletes (patellar and Achilles tendon; -28 to -24%) or controls (patellar tendon only; -9%). In contrast, the normalized cross-sectional area was larger in runners (patellar tendon only; +26%) and ski jumpers (patellar and Achilles tendon; +21% and +13%, respectively) than in controls. Tendon stiffness normalized to body mass2/3 only differed in ski jumpers, compared to controls (patellar and Achilles tendon; +11% and +27%, respectively) and to water polo players (Achilles tendon only; +23%). Tendon size appears as an adjusting variable to changes in loading volume and/or intensity, possibly to preserve ultimate strength or fatigue resistance. However, uncoupled morphological and mechanical properties indicate that functional requirements may also influence tendon adaptations.

• Rieder, Florian; Wiesinger, Hans-Peter; Kösters, Alexander; Müller, Erich & Seynnes, Olivier R. (2016). Immediate effects of whole body vibration on patellar tendon properties and knee extension torque. European Journal of Applied Physiology. ISSN 1439-6319. 116(3), p. 553–561. doi: 10.1007/s00421-015-3316-4. Full text in Research Archive Show summary

  Purpose: Reports about the immediate effects of whole body vibration (WBV) exposure upon torque production capacity are inconsistent. However, the changes in the torque–angle relationship observed by some authors after WBV may hinder the measurement of torque changes at a given angle. Acute changes in tendon mechanical properties do occur after certain types of exercise but this hypothesis has never been tested after a bout of WBV. The purpose of the present study was to investigate whether tendon compliance is altered immediately after WBV, effectively shifting the optimal angle of peak torque towards longer muscle length. Methods: Twenty-eight subjects were randomly assigned to either a WBV (n = 14) or a squatting control group (n = 14). Patellar tendon CSA, stiffness and Young’s modulus and knee extension torque–angle relationship were measured using ultrasonography and dynamometry 1 day before and directly after the intervention. Tendon CSA was additionally measured 24 h after the intervention to check for possible delayed onset of swelling. Results: The vibration intervention had no effects on patellar tendon CSA, stiffness and Young’s modulus or the torque–angle relationship. Peak torque was produced at ~70° knee angle in both groups at pre- and post-test. Additionally, the knee extension torque globally remained unaffected with the exception of a small (−6 %) reduction in isometric torque at a joint angle of 60°. Conclusion: The present results indicate that a single bout of vibration exposure does not substantially alter patellar tendon properties or the torque–angle relationship of knee extensors.

• Heinemeier, Katja Maria; Lorentzen, Marc P.; Jensen, Jacob K.; Schjerling, Peter; Seynnes, Olivier R. & Narici, Maco V. [Show all 7 contributors for this article] (2016). Local trauma in human patellar tendon leads to widespread changes in the tendon gene expression. Journal of applied physiology. ISSN 8750-7587. 120(9), p. 1000–1010. doi: 10.1152/japplphysiol.00870.2015. Full text in Research Archive Show summary

  Low cellular activity and slow tissue turnover in human tendon may prolong resolution of tendinopathy. This may be stimulated by moderate localized traumas such as needle penetrations, but whether this results in a widespread cellular response in tendons is unknown. In an initial hypothesis-generating study, a trauma-induced tendon cell activity (increased total RNA and collagen I mRNA) was observed after repeated patellar tendon biopsies in young men. In a subsequent controlled study, 25 young men were treated with two 0.8-mm-diameter needle penetrations [n = 13, needle-group (NG)] or one 2.1-mm-diameter needle biopsy [n = 12, biopsy-group (BG)] in one patellar tendon. Four weeks later biopsies were taken from treated (5 mm lateral from trauma site) and contralateral tendons for analyses of RNA content (ribogreen assay), DNA content (PCR based), and gene expression for relevant target genes (Real-time RT-PCR) (NG, n = 11 and BG, n = 8). Intervention increased RNA content, and mRNA expression of collagen I and III and TGF-β1 (P < 0.05), with biopsy treatment having greatest effect (tendency for RNA and collagen I). Results for DNA content were inconclusive, and no changes were detected in expression of insulin-like growth factor-I, connective tissue growth factor, scleraxis, decorin, fibromodulin, tenascin-C, tenomodulin, VEGFa, CD68, IL-6, MMP12, and MMP13. In conclusion, a moderate trauma to a healthy human tendon (e.g., biopsy sampling) results in a widespread upregulation of tendon cell activity and their matrix protein expression. The findings have implications for design of studies on human tendon and may provide perspectives in future treatment strategies in tendinopathy.

• Vikmoen, Olav; Raastad, Truls; Seynnes, Olivier R.; Bergstrøm, Kristoffer; Ellefsen, Stian & Rønnestad, Bent (2016). Effects of Heavy Strength Training on Running Performance and Determinants of Running Performance in Female Endurance Athletes. PLOS ONE. 11(3). doi: 10.1371/journal.pone.0150799. Full text in Research Archive Show summary

  Purpose The purpose of the current study was to investigate the effects of adding strength training to normal endurance training on running performance and running economy in well-trained female athletes. We hypothesized that the added strength training would improve performance and running economy through altered stiffness of the muscle-tendon complex of leg extensors. Methods Nineteen female endurance athletes [maximal oxygen consumption (VO2max): 53±3 ml∙kg-1∙min-1, 5.8 h weekly endurance training] were randomly assigned to either normal endurance training (E, n = 8) or normal endurance training combined with strength training (E+S, n = 11). The strength training consisted of four leg exercises [3 x 4–10 repetition maximum (RM)], twice a week for 11 weeks. Muscle strength, 40 min all-out running distance, running performance determinants and patellar tendon stiffness were measured before and after the intervention. Results E+S increased 1RM in leg exercises (40 ± 15%) and maximal jumping height in counter movement jump (6 ± 6%) and squat jump (9 ± 7%, p < 0.05). This was accompanied by increased muscle fiber cross sectional area of both fiber type I (13 ± 7%) and fiber type II (31 ± 20%) in m. vastus lateralis (p < 0.05), with no change in capillary density in m. vastus lateralis or the stiffness of the patellar tendon. Neither E+S nor E changed running economy, fractional utilization of VO2max or VO2max. There were also no change in running distance during a 40 min all-out running test in neither of the groups. Conclusion Adding heavy strength training to endurance training did not affect 40 min all-out running performance or running economy compared to endurance training only.

• Rieder, Florian; Kösters, Alexander; Wiesinger, Hans-Peter; Dorn, Ulrich; Hofstaedter, Thomas & Fink, Christian [Show all 8 contributors for this article] (2015). Alpine Skiing With total knee ArthroPlasty (ASWAP): Muscular adaptations. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 25(S2), p. 26–32. doi: 10.1111/sms.12451. Full text in Research Archive Show summary

  This study investigated the effectiveness of recreational skiing as an intervention to improve quadriceps muscle architecture, strength, and antagonistic co-activation in patients with unilateral total knee arthroplasty (TKA). Hence, patients with TKA were assigned to either an intervention group (IG) or control group (CG). The IG completed a 12-week guided skiing program whereas the CG was instructed not to change their daily routines for the same period and was not allowed to ski. Before, after the intervention/after an 8-week retention period m. rectus femoris (RF) cross-sectional area (CSA), m. vastus lateralis muscle thickness, fascicle length, and pennation angle were measured with ultrasonography, while isometric (90° knee angle) knee extension, flexion torque and m. biceps femoris co-activation were assessed on an isokinetic dynamometer in 26 patients. There were significant and stable increases in RF CSA for the operated (10%; P < 0.05) and non-operated leg (12%; P < 0.01) after the training period in the IG whereas no changes were observed for the CG (all P > 0.05). There were no significant effects for other parameters (all P > 0.05). Overall, the skiing intervention was successful in increasing muscle mass in TKA older patients.

• Brocca, Lorenza; Longa, Emanuela; Cannavino, Jessica; Seynnes, Olivier R.; Vito, Giuseppe de & McPhee, Jamie [Show all 9 contributors for this article] (2015). Human skeletal muscle fibre contractile properties and proteomic profile: Adaptations to 3-week unilateral lower limb suspension and active recovery. Journal of Physiology. ISSN 0022-3751. 593(24), p. 5361–5385. doi: 10.1113/JP271188. Full text in Research Archive Show summary

  Following disuse muscle fibres function goes through adaptations such as loss of specific force (Po/CSA) and increase in unloaded shortening velocity (Vo), which could be due to both quantitative changes, i.e. atrophy, and qualitative changes in protein pattern. The underlying mechanisms have not been settled yet. In addition, little is known about the recovery of muscle mass and strength following disuse. Here we report an extensive data set describing in detail functional and protein content adaptations of skeletal muscle in response to both disuse and retraining. Eight young healthy subjects were subjected to 3 weeks unilateral lower limb suspension (ULLS), a widely used human model of disuse skeletal muscle atrophy. Needle biopsies samples were taken from the vastus lateralis muscle pre-ULLS, post-ULLS and after 3 weeks recovery during which heavy resistance training was performed (post-RT). After disuse, cross sectional area (CSA), specific force (Po/CSA) and myosin concentration (MC) decreased both in type 1 and 2A skinned muscle fibres. After recovery, CSA and MC returned to levels comparable to those observed before disuse, whereas Po/CSA and unloading shortening velocity reached a higher level. Myosin heavy chain (MHC) isoform composition of muscle samples did not differ among experimental groups. To study the mechanisms underlying such adaptations, a 2Dproteomic analysis was performed. ULLS induced reduction of myofibrillar, metabolic (glycolytic and oxidative) and antioxidant defense system proteins content. Resistance training was very effective in counteracting ULLS induced alterations indicating that long term ULLS did not prevent the positive effect of exercise on human muscle.

• Meijer, J.P.; Jaspers, R.T.; Rittweger, Jörn; Seynnes, Olivier R.; Kamandulis, Sigitas & Brazaitis, M. [Show all 11 contributors for this article] (2015). Single muscle fibre contractile properties differ between bodybuilders, power athletes and controls. Experimental Physiology. ISSN 0958-0670. 100(11), p. 1331–1341. doi: 10.1113/EP085267. Full text in Research Archive Show summary

  We compared muscle fibre contractile properties of biopsies taken from m. vastus lateralis of 12 bodybuilders (BB; low- to moderate-intensity high-volume resistance training), 6 power athletes (PA; high-intensity low-volume combined with aerobic training) and 14 controls (C). Maximal isotonic contractions were performed in single muscle fibres, typed with SDS-PAGE. Fibre cross-sectional area (FCSA) was 67% and 88% (P<0.01) larger in BB than in PA and C, respectively, with no significant difference in FCSA between PA and C. Fibres of BB and PA developed a higher maximal isometric tension (32%, 50%, P < 0.01) than those of C. Specific tension (F0) of BB fibres was 62% and 41% lower than that of PA and C fibres (P < 0.05), respectively. Irrespective of fibre type, peak power (P) of PA fibres was 58% higher than that of BB fibres (P < 0.05), while BB fibres –despite considerable hypertrophy- had similar PP as C fibres. This work suggests that high-intensity low-volume resistance training with aerobic exercise improves PP, while low- to moderate-intensity high-volume resistance training does not affect PP and results in a reduction in F0. We postulate that the decrease in specific tension is caused by differences in myofibrillar density and/or post-translational modifications of contractile proteins.

• Bjørnsen, Thomas; Salvesen, Svein; Berntsen, Sveinung; Hetlelid, Ken Joar; Stea, Tonje Holte & Seiler, Hilde Lohne [Show all 17 contributors for this article] (2015). Vitamin C and E supplementation blunts increases in total lean body mass in elderly men after strength training. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 26(7), p. 755–755. doi: 10.1111/sms.12506. Full text in Research Archive Show summary

  The aim of this study was to investigate the effects of vitamin C and E supplementation on changes in muscle mass (lean mass and muscle thickness) and strength during 12 weeks of strength training in elderly men. Thirty-four elderly males (60–81 years) were randomized to either an antioxidant group (500 mg of vitamin C and 117.5 mg vitamin E before and after training) or a placebo group following the same strength training program (three sessions per week). Body composition was assessed with dual-energy X-ray absorptiometry and muscle thickness by ultrasound imaging. Muscle strength was measured as one-repetition maximum (1RM). Total lean mass increased by 3.9% (95% confidence intervals: 3.0, 5.2) and 1.4% (0, 5.4) in the placebo and antioxidant groups, respectively, revealing larger gains in the placebo group (P = 0.04). Similarly, the thickness of m. rectus femoris increased more in the placebo group [16.2% (12.8, 24.1)] than in the antioxidant group [10.9% (9.8, 13.5); P = 0.01]. Increases of lean mass in trunk and arms, and muscle thickness of elbow flexors, did not differ significantly between groups. With no group differences, 1RM improved in the range of 15–21% (P < 0.001). In conclusion, high-dosage vitamin C and E supplementation blunted certain muscular adaptations to strength training in elderly men.

• Kösters, Alexander; Rieder, Florian; Wiesinger, Hans-Peter; Dorn, Ulrich; Hofstaedter, Thomas & Fink, Christian [Show all 8 contributors for this article] (2015). Alpine Skiing With total knee ArthroPlasty (ASWAP): effect on tendon properties. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 25(S2), p. 67–73. doi: 10.1111/sms.12457. Full text in Research Archive Show summary

  The aim of this study was to investigate the effect of alpine skiing on patellar tendon properties in patients with total knee arthroplasty (TKA). Thirty-one adults (70.4 ± 4.7 years) with unilateral TKA were recruited 2.7 ± 0.9 years after surgery and assigned to an intervention (IG) or a control group (CG). The IG underwent a 12-week guided skiing program. Tendon stiffness, Young's modulus, and cross-sectional area (CSA) were measured before and after the intervention. In both groups, mean tendon CSA was 28% (P < 0.001) larger in the operated (OP) than in the non-operated (NOP) leg at baseline, without any difference in other tendon properties. After training, stiffness increased in the IG by 5.8% and 15.8%, respectively, in the OP and NOP legs. Likewise, mean CSA increased in the IG by 2.9% in the OP and 3.8% in the NOP leg, whereas no significant changes were found for the Young's modulus. None of the tendon parameters changed in the CG. Results indicate that patellar tendon structure and/or loading pattern are altered following TKA, but this tissue seems to retain its adaptation capacity. Further, alpine skiing appears to offer a suitable rehabilitation strategy for TKA patients.

• Seynnes, Olivier R.; Bojsen-Møller, Jens; Albracht, Kirsten; Arndt, Anton; Cronin, N.J. & Finni, Taija [Show all 7 contributors for this article] (2015). Ultrasound-based testing of tendon mechanical properties: A critical evaluation. Journal of applied physiology. ISSN 8750-7587. 118(2), p. 133–141. doi: 10.1152/japplphysiol.00849.2014. Full text in Research Archive Show summary

  In the past twenty years, the use of ultrasound-based methods has become a standard approach to measure tendon mechanical properties in vivo. Yet, the multitude of methodological approaches adopted by various research groups probably contributes to the large variability of reported values. The technique of obtaining and relating tendon deformation to tensile force in vivo has been applied differently, depending on practical constraints or scientific points of view. Divergence can be seen in i) methodological considerations such as the choice of anatomical features to scan and to track, force measurements or signal synchronisation and ii), in physiological considerations related to the viscoelastic behaviour or length measurements of tendons. Hence, the purpose of the present review is to assess and discuss the physiological and technical aspects connected to in vivo testing of tendon mechanical properties. In doing so, our aim is to provide the reader with a systematic, qualitative analysis of ultrasound-based techniques. Finally, a list of recommendations is proposed for a number of selected issues.

• Luteberget, Live; Raastad, Truls; Seynnes, Olivier R. & Spencer, Matthew (2015). Effect of Traditional and Resisted Sprint Training in Highly-Trained, Female Team Handball Players. International Journal of Sports Physiology and Performance (IJSPP). ISSN 1555-0265. 10(5), p. 642–647. doi: 10.1123/ijspp.2014-0276. Full text in Research Archive Show summary

  Fast acceleration is an important performance factor in handball. In addition to traditional sprint training (TST), resisted sprint training (RST) is a method often used to improve acceleration. However, studies on RST show conflicting results, and underlying mechanisms are not studied. Purpose: To compare the effects of RST, by sled towing, against traditional sprint training on sprint performance and muscle architecture. Methods: Participants (n=18) were assigned to either RST or TST and completed two training sessions of RST or TST per week (10 weeks), in addition to their normal team training. Sprint-tests (10-m and 30-m) and measurements of muscle architecture were performed pre- and post-training. Results: Beneficial effects were found in the 30-m sprint test (mean; ±90% CL) for both groups (TST=-0.31; ±0.19 s, RST=-0.16; ±0.13 s), with unclear differences between the groups. Only TST had a beneficial effect on 10-m time (-0.04; ±0.04 s), with a likely difference between the two groups (85 %, ES= 0.60). Both groups had a decrease in pennation angle (-6.0; ±3.3% for TST and -2.8; ±2.0% for RST), which had a nearly perfect correlation with percentage change in 10-m sprint performance (r=0.92). A small increase in fascicle length (5.3; ±3.9% and 4.0; ±2.1% for TST and RST, respectively) was found, with unclear differences between groups. Discussion: TST appears to be more effective than RST in enhancing 10-m sprint time. Both groups showed similar effects in 30-m sprint time. A similar, yet small, effect of sprint training on muscle architecture was observed in both groups.

• Wiesinger, Hans-Peter; Kösters, Alexander; Müller, Erich & Seynnes, Olivier R. (2015). Effects of Increased Loading on In Vivo Tendon Properties: A Systematic Review. Medicine & Science in Sports & Exercise. ISSN 0195-9131. 47(9), p. 1885–1895. doi: 10.1249/MSS.0000000000000603. Full text in Research Archive Show summary

  Introduction: In vivo measurements have been used in the past two decades to investigate the effects of increased loading on tendon properties. Yet, the current understanding of tendon macroscopic changes to training is rather fragmented, limited to reports of tendon stiffening, supported by changes in material properties and/or tendon hypertrophy. The main aim of this review was to analyze the existing literature to gain further insights into tendon adaptations by extracting patterns of dose-response and time-course. Methods: PubMed/Medline, SPORTDiscus and Google Scholar databases were searched for studies examining the effect of training on material, mechanical and morphological properties via longitudinal or cross-sectional designs. Results: Thirty-five out of 6440 peer-reviewed articles met the inclusion criteria. Key findings were i) the confirmation of a nearly systematic adaptation of tendon tissue to training, ii) the important variability in the observed changes in tendon properties between and within studies, and iii) the absence of a consistent incremental pattern regarding the dose-response or the time-course relation of tendon adaptation within the first months of training. However, long-term (years) training was associated with a larger tendon cross-sectional area (CSA), without any evidence of differences in material properties. Our analysis also highlighted several gaps in the existing literature, which may be addressed in future research. Conclusions: In line with some cross-species observations about tendon design, tendon CSA allegedly constitutes the ultimate adjusting parameter to increased loading. We propose here a theoretical model placing tendon hypertrophy and adjustments in material properties as parts of a same adaptive continuum.

• Kösters, Alexander; Wiesinger, H.P.; Bojsen-Møller, Jens; Müller, E & Seynnes, Olivier R. (2014). Influence of loading rate on patellar tendon mechanical properties in vivo. Clinical Biomechanics. ISSN 0268-0033. 29(3), p. 323–329. doi: 10.1016/j.clinbiomech.2013.12.010. Full text in Research Archive Show summary

  Background: Rate-dependent properties of tendons have consistently been observed in vitro but in vivo studies comparing the effects of loading duration on this feature remain conflicting. The main purpose of the present study was to evaluate whether tendon loading rate per se would affect in vivo tendon mechanical properties. Methods: Twenty-two physically active male subjects were recruited. Patellar tendon deformation was recorded with ultrasonography under voluntary isometric contractions at rates of 50, 80 and 110 Nm/s, controlled via visual feedback. Findings: Subjects were able to accurately generate all three loading rates (Accuracy = 2% to 15%), with a greater steadiness at 50 (CV = 12.4%) and 110 Nm/s (CV = 13.1%) than at 80 Nm/s (CV = 22.9%). Loading rate did not appreciably affect strain or stress. However, stiffness ( p2 = 0.555) and Youngs's Modulus ( p2 = 0.670)were significantly higher at 80 Nm/s (21.4% and 21.6%, respectively) and at 110 Nm/s (32.5% and 32.0%, respectively) than at 50 Nm/s. Similarly, stiffness and Young's modulus were 9.9% and 8.8% higher, respectively, at 110 Nm/s than at 80 Nm/s. Interpretation: These results indicate that in vivo measurements of patellar tendon mechanics are influenced by loading rate. Moreover, they bear important methodological implications for in vivo assessment of mechanical properties of this tendon and possibly other human tendons.

• Li, Ruowei; Narici, Marco V.; Erskine, Robert M.; Seynnes, Olivier R.; Rittweger, Jörn & Pisot, Rado [Show all 8 contributors for this article] (2013). Costamere remodeling with muscle loading and unloading in healthy young men. Journal of Anatomy. ISSN 0021-8782. 223(5), p. 525–536. doi: 10.1111/joa.12101. Full text in Research Archive Show summary

  Costameres are mechano-sensory sites of focal adhesion in the sarcolemma that provide a structural anchor for myofibrils. Their turnover is regulated by integrin-associated focal adhesion kinase (FAK). We hypothesized that changes in content of costamere components (beta 1 integrin, FAK, meta-vinculin, gamma-vinculin) with increased and reduced loading of human anti-gravity muscle would: (i) relate to changes in muscle size and molecular parameters of muscle size regulation [p70S6K, myosin heavy chain (MHC)1 and MHCIIA]; (ii) correspond to adjustments in activity and expression of FAK, and its negative regulator, FRNK; and (iii) reflect the temporal response to reduced and increased loading. Unloading induced a progressive decline in thickness of human vastus lateralis muscle after 8 and 34 days of bedrest (−4% and −14%, respectively; n = 9), contrasting the increase in muscle thickness after 10 and 27 days of resistance training (+5% and +13%; n = 6). Changes in muscle thickness were correlated with changes in cross-sectional area of type I muscle fibers (r = 0.66) and beta 1 integrin content (r = 0.76) at the mid-point of altered loading. Changes in meta-vinculin and FAK-pY397 content were correlated (r = 0.85) and differed, together with the changes of beta 1 integrin, MHCI, MHCII and p70S6K, between the mid- and end-point of resistance training. By contrast, costamere protein level changes did not differ between time points of bedrest. The findings emphasize the role of FAK-regulated costamere turnover in the load-dependent addition and removal of myofibrils, and argue for two phases of muscle remodeling with resistance training, which do not manifest at the macroscopic level.

• McPhee, Jamie S.; Hogrel, Jean-Yves; Maier, Andrea B.; Seppet, Enn; Seynnes, Olivier R. & Sipilä, Sarianna [Show all 18 contributors for this article] (2013). Physiological and functional evaluation of healthy young and older men and women: design of the European MyoAge study. Biogerontology (Dordrecht). ISSN 1389-5729. 14(3), p. 325–337. doi: 10.1007/s10522-013-9434-7. Full text in Research Archive Show summary

  Within the European multi-centre MyoAge project, one workpackage was designed to investigate the contribution of age-related changes to muscle mass, contractile characteristics and neural control in relation to reductions in mobility in older age. The methodology has been described here. Test centres were located in Manchester, UK; Paris, France; Leiden, The Netherlands; Tartu, Estonia and Jyväskylä, Finland. In total, 182 young (18–30 years old, 52.2 % female) and 322 older adults (69–81 years old, 50 % female) have been examined. The participants were independent living, socially active and free from disease that impaired mobility levels. The older participants were selected based on physical activity levels, such that half exceeded current recommended physical activity levels and the other half had lower physical activity levels than is recommended to maintain health. Measurements consisted of blood pressure; anthropometry and body composition (dual-energy X-ray absorptiometry and magnetic resonance imaging); lung function; standing balance and cognitive function (CANTAB). Mobility was assessed using the Timed Up and Go, a 6 min walk, activity questionnaires and accelerometers to monitor habitual daily activities. Muscle strength, power, fatigue and neural activation were assessed using a combination of voluntary and electrically stimulated contractions. Fasting blood samples and skeletal muscle biopsies were collected for detailed examination of cell and molecular differences between young and older individuals. The results from this study will provide a detailed insight into “normal, healthy” ageing, linking whole-body function to the structure and function of the neuromuscular system and the molecular characteristics of skeletal muscle.

• Conte, Maria; Vasuri, Francesco; Trisolino, Giovanni; Bellavista, Elena; Santoro, Aurelia & Degiovanni, Alessio [Show all 17 contributors for this article] (2013). Increased Plin2 Expression in Human Skeletal Muscle Is Associated with Sarcopenia and Muscle Weakness. PLOS ONE. 8(8:e73709). doi: 10.1371/journal.pone.0073709. Full text in Research Archive Show summary

  Human aging is associated with a progressive loss of muscle mass and strength and a concomitant fat accumulation in form of inter-muscular adipose tissue, causing skeletal muscle function decline and immobilization. Fat accumulation can also occur as intra-muscular triglycerides (IMTG) deposition in lipid droplets, which are associated with perilipin proteins, such as Perilipin2 (Plin2). It is not known whether Plin2 expression changes with age and if this has consequences on muscle mass and strength. We studied the expression of Plin2 in the vastus lateralis (VL) muscle of both healthy subjects and patients affected by lower limb mobility limitation of different age. We found that Plin2 expression increases with age, this phenomenon being particularly evident in patients. Moreover, Plin2 expression is inversely correlated with quadriceps strength and VL thickness. To investigate the molecular mechanisms underpinning this phenomenon, we focused on IGF-1/p53 network/signalling pathway, involved in muscle physiology. We found that Plin2 expression strongly correlates with increased p53 activation and reduced IGF-1 expression. To confirm these observations made on humans, we studied mice overexpressing muscle-specific IGF-1, which are protected from sarcopenia. These mice resulted almost negative for the expression of Plin2 and p53 at two years of age. We conclude that fat deposition within skeletal muscle in form of Plin2-coated lipid droplets increases with age and is associated with decreased muscle strength and thickness, likely through an IGF-1- and p53-dependent mechanism. The data also suggest that excessive intramuscular fat accumulation could be the initial trigger for p53 activation and consequent loss of muscle mass and strength.

• Helland, Christian; Bojsen-Møller, Jens; Raastad, Truls; Seynnes, Olivier R.; Moltubakk, Marie M. & Jakobsen, Vidar Eivind [Show all 8 contributors for this article] (2013). Mechanical properties of the patellar tendon in elite volleyball players with and without patellar tendinopathy. British Journal of Sports Medicine. ISSN 0306-3674. 47(13), p. 862–868. doi: 10.1136/bjsports-2013-092275. Full text in Research Archive Show summary

  Background: Although differences in mechanical properties between symptomatic and healthy tendons have been observed for the Achilles tendon, the impact of tendinopathy on patellar tendon mechanics is not fully documented. The aim of the present case–control study was to assess the mechanical properties of the tendon and jump performance in elite athletes with and without patellar tendinopathy. Methods: We identified 17 male volleyball players with patellar tendinopathy and 18 healthy matched controls from a 5-year prospective cohort study on junior elite volleyball players. Outcome variables included three measures of maximal vertical jump performance and ultrasound-based assessments of patellar tendon cross-sectional area, stiffness and Young's modulus. Results: The proximal cross-sectional area of the patellar tendon was significantly larger in the tendinopathic group (133±11 vs 112±9 mm2, respectively; p<0.001). Pathological tendons presented lower stiffness (2254±280 vs 2826±603 N/mm, respectively; p=0.006) and Young's modulus (0.99±0.16 vs 1.17±0.25 GPa, respectively; p=0.04) than healthy tendons. However, the difference between the countermovement jump height and the squat jump height (3.4±2.2 vs 1.2±1.5 cm, p=0.005) was significantly higher in the tendinopathic group compared with the control group. Conclusions: Patellar tendinopathy is associated with a decrease in the mechanical and material properties of the tendon in elite athletes subjected to a high volume of jumping activity. However, compared with their healthy counterparts, tendinopathic volleyball players have a better ability to utilise the stretch-shortening cycle when jumping.

• Campbell, Emma-Louise; Seynnes, Olivier R.; Bottinelli, R.; McPhee, J.S.; Atherton, P.J. & Jones, D.A. [Show all 8 contributors for this article] (2013). Skeletal muscle adaptations to physical inactivity and subsequent retraining in young men. Biogerontology (Dordrecht). ISSN 1389-5729. 14(3), p. 247–259. doi: 10.1007/s10522-013-9427-6. Full text in Research Archive Show summary

  Skeletal muscle structure and function are markedly affected by chronic disuse. With unloading, muscle mass is lost at rate of about 0.4 %/day but little is known about the recovery of muscle mass and strength following disuse. Here we report an extensive data set describing in detail skeletal muscle adaptations in structure and function in response to both disuse and retraining. Eight young men (23 ± 2.2 years) underwent 3 weeks of unilateral lower limb suspension (ULLS) followed by a 3-week resistance training recovery program. Knee extensor isometric torque, voluntary activation, quadriceps femoris (QF) muscle volume (QFvol), fascicle length (Lf) and pennation angle (θ), physiological cross-sectional area (PCSA) of all four heads of the QF muscle, were measured before, after ULLS, and post-ULLS-resistance training. Needle biopsies were taken from the vastus lateralis muscle of a subgroup (n = 6) of the same subjects and cross sectional area of individual muscle s and myosin content of muscle samples were determined. Following 3 weeks of ULLS, isometric torque decreased by 26 %, PCSA by 3 %, QFvol by 10 %. Lf and θ of all four heads of QF significantly decreased (p ≤ 0.05). Following the 3-week retraining period, isometric torque, PCSA, QFvol, Lf and θ of all four heads of QF were all fully restored to pre ULLS values. CSA of individual muscle fibres and myosin content of muscle samples decreased by 26 and 35 % respectively (post-ULLS) and recovered to almost pre-ULLS values following retraining. There were no significant changes in voluntary activation of the quadriceps muscles in response to either ULLS or subsequent retraining. These results indicate that: (1) the loss of muscle force with 3-week unloading in humans is mostly explained by muscle atrophy and by a decrease in myosin content and, (2) all the neuromuscular changes induced by this model of disuse can be fully restored after a resistance training intervention of equal duration.

• Seynnes, Olivier R.; Kamandulis, Sigitas; Kairaitis, Ramutis; Helland, Christian; Campbell, Emma-Louise & Brazaitis, Marius [Show all 8 contributors for this article] (2013). Effect of Androgenic-Anabolic Steroids and Heavy Strength Training on Patellar Tendon Morphological and Mechanical Properties. Journal of applied physiology. ISSN 8750-7587. 115(1), p. 84–89. doi: 10.1152/japplphysiol.01417.2012. Full text in Research Archive Show summary

  Combined androgenic-anabolic steroids (AAS) and overloading affects tendon collagen metabolism and ultrastructure, and is often associated with a higher risk of injury. The aim of this prospective study was to investigate whether such effects would be reflected in the patellar tendon properties of individuals with a history of long-term resistance training and AAS abuse (RTS group), when compared to trained (RT) and untrained (CTRL) non-steroids users. Tendon cross-sectional area (CSA), stiffness, Young's modulus and toe-limit strain were measured in vivo, from synchronized ultrasonography and dynamometry data. The patellar tendon of RT and RTS subjects was much stiffer and larger than in the CTRL group. However, stiffness and modulus were higher in the RTS group (26%, P < 0.05 and 30%, P < 0.01, respectively) than in the RT group. Conversely, tendon CSA was 15% (P < 0.05) larger in the RT group than in RTS, although differences disappeared when this variable was normalized to quadriceps maximal isometric torque. Yet maximal tendon stress was higher in RTS than in RT (15%, P < 0.05), without any statistical difference in maximal strain and toe limit strain between groups. The present lack of difference in toe-limit strain does not substantiate the hypothesis of changes in collagen crimp pattern associated with AAS abuse. However, these findings indicate that tendon adaptations from years of heavy resistance training are different in AAS users, suggesting differences in collagen remodelling. Some of these adaptations (e.g. higher stress) could be linked to a higher risk of tendon injury.

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• Ritsche, Paul; Faude, Oliver; Franchi, Martino V.; Finni, Taija; Seynnes, Olivier R. & Cronin, Neil J. (2023). DL_Track - Automated analysis of muscle architecture from B-mode ultrasonography images using deep learning. Current Issues in Sport Science. 8(2), p. 88–88. doi: 10.36950/2023.2ciss088. Full text in Research Archive
• Mersmann, Falk; Bohm, Sebastian; Arampatzis, Adamantios; Karamanidis, Kiros & Seynnes, Olivier R. (2021). Editorial: Muscle and Tendon Plasticity and Interaction in Physiological and Pathological Conditions. Frontiers in Physiology. 12. doi: 10.3389/fphys.2021.678801. Full text in Research Archive
• Wernbom, Mathias; Seynnes, Olivier R. & Paulsen, Gøran (2019). Commentaries on Viewpoint: Distinct modalities of eccentric exercise: different recipes, not the same dish. Journal of applied physiology. ISSN 8750-7587. 127(3), p. 884–891. doi: 10.1152/japplphysiol.00496.2019. Full text in Research Archive
• Helland, Christian; Haugen, Tommy; Rakovic, Elvir; Eriksrud, Ola; Seynnes, Olivier R. & Mero, Antti A. [Show all 7 contributors for this article] (2019). Correction to: Force–velocity profiling of sprinting athletes: single-run vs. multiple-run methods (European Journal of Applied Physiology, (2019), 119, 2, (465-473), 10.1007/s00421-018-4045-2). European Journal of Applied Physiology. ISSN 1439-6319. 119(2), p. 475–475. doi: 10.1007/s00421-018-04057-7. Full text in Research Archive
• Prieur, Fabrice Jean Gabriel & Seynnes, Olivier R. (2018). Ultrasound elastography in muscle. Full text in Research Archive
• Rittweger, Jörn; Albracht, Kirsten; Flück, Martin; Ruoss, Severin; Brocca, Lorenza & Longa, Emanuela [Show all 18 contributors for this article] (2018). Author Correction: Sarcolab pilot study into skeletal muscle’s adaptation to longterm spaceflight (npj Microgravity, (2018), 4, 1, (18), 10.1038/s41526-018-0052-1). npj Microgravity. 4(1). doi: 10.1038/s41526-018-0058-8. Full text in Research Archive
• Prieur, Fabrice Jean Gabriel & Seynnes, Olivier R. (2018). Ultrasound elastography in muscle. Full text in Research Archive
• Moltubakk, Marie M.; Eriksrud, Ola; Paulsen, Gøran; Seynnes, Olivier R. & Bojsen-Møller, Jens (2012). Tendon stiffness following years of systematic stretching. Full text in Research Archive

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