Olivier Seynnes

• Ritsche, Paul; Sarto, Fabio; Santini, Francesco; Leitner, Christoph; Franchi, Martino V. & Faude, Oliver [Vis alle 9 forfattere av denne artikkelen] (2026). UMUD: a web application for easy access to musculoskeletal ultrasonography datasets. BMC Medical Imaging. 26(1). doi: 10.1186/s12880-026-02170-0. Fulltekst i vitenarkiv
• 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. Fulltekst i vitenarkiv Vis sammendrag

  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. Fulltekst i vitenarkiv Vis sammendrag

  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. Fulltekst i vitenarkiv Vis sammendrag

  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. Fulltekst i vitenarkiv Vis sammendrag

  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 [Vis alle 8 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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 [Vis alle 12 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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. [Vis alle 9 forfattere av denne artikkelen] (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), s. 1968–1978. doi: 10.1249/MSS.0000000000003732. Fulltekst i vitenarkiv Vis sammendrag

  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. [Vis alle 10 forfattere av denne artikkelen] (2025). Jumping performance and muscle–tendon characteristics of Maasai men of East Africa. Scientific Reports. 15. doi: 10.1038/s41598-025-01694-9. Fulltekst i vitenarkiv
• Bizet, Baptiste; Nordez, Antoine; Tallio, Tristan; Lacourpaille, Lilian; Cattagni, Thomas & Colard, Julian [Vis alle 11 forfattere av denne artikkelen] (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), s. 939–949. doi: 10.1152/japplphysiol.00859.2024. Fulltekst i vitenarkiv

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