Julie Sørbø Stang

• Kennedy, M.D.; Parent, E.C.; Stang, Julie; Comeau, A.K. & Stensrud, Trine (2025). Influence of multiple cross-country ski races on respiratory function and symptoms in cross-country skiers. Science & sports. ISSN 0765-1597. 40, p. 147–158. doi: 10.1016/j.scispo.2024.08.002. Full text in Research Archive Show summary

  Objectives This study studied how multiple cross-country ski races affect respiratory function and symptoms in different age groups. Methods Eighteen ≥ 19 and 18 ≤ 18 years of age skiers performed morning spirometry, post-race/training spirometry and recorded respiratory symptoms daily over a National Championship (baseline day, 3 races and 2 training days). Results Races decreased resting spirometry and a rest day increased spirometry in both groups. Overall resting maximal mean decline was 4.6 ± 8.8%; 2.5 ± 8.2% for forced expiratory flow in 1 second (FEV1) and 6.3 ± 2.7%; 4.5 ± 2.7% forced vital capacity (FVC) in ≥ 19 and ≤ 18 aged skiers respectively. FEV1 decreased in 50% of skiers post-race, mean symptoms were 3.3 ± 0.5 (≤ 18 yrs); and 2.5 ± 0.5 (≥ 19 yrs). Post-race cough (86%) was most common symptom. Conclusions Multiple races reduced resting function, especially FVC in both age groups. Greater cough and decreased function in FEV1 pre-post-race in older skiers indicate potential age-related change. This study is the first to show how multiple ski races affect respiratory function and symptoms cumulatively.

• Ameri, Sammy; Stang, Julie; Walsted, Emil & Price, Oliver J. (2024). Mechanisms and Biomarkers of Exercise-induced Bronchoconstriction: Current Insights and Future Directions. Immunology and allergy clinics of North America. ISSN 0889-8561. 45(1), p. 63–75. doi: 10.1016/j.iac.2024.08.009. Full text in Research Archive
• Reier-Nilsen, Tonje; Stang, Julie; Flatsetøy, Hanne; Isachsen, Martine; Ljungberg, Henrik & Bahr, Roald [Show all 7 contributors for this article] (2023). Unsupervised field-based exercise challenge tests to support the detection of exercise-induced lower airway dysfunction in athletes. BMJ Open sport & exercise medicine. 9(3). doi: 10.1136/bmjsem-2023-001680. Full text in Research Archive Show summary

  Background: Athletes are at risk for developing exercise-induced lower airway narrowing. The diagnostic assessment of such lower airway dysfunction (LAD) requires an objective bronchial provocation test (BPT). Objectives: Our primary aim was to assess if unsupervised field-based exercise challenge tests (ECTs) could confirm LAD by using app-based spirometry. We also aimed to evaluate the diagnostic test performance of field-based and sport-specific ECTs, compared with established eucapnic voluntary hyperpnoea (EVH) and methacholine BPT. Methods: In athletes with LAD symptoms, sensitivity and specificity analyses were performed to compare outcomes of (1) standardised field-based 8 min ECT at 85% maximal heart rate with forced expiratory volume in 1 s (FEV1) measured prechallenge and 1 min, 3 min, 5 min, 10 min, 15 min and 30 min postchallenge, (2) unstandardised field-based sport-specific ECT with FEV1 measured prechallenge and within 10 min postchallenge, (3) EVH and (4) methacholine BPT. Results: Of 60 athletes (median age 17.5; range 16–28 years.; 40% females), 67% performed winter-sports, 43% reported asthma diagnosis. At least one positive BPT was observed in 68% (n=41/60), with rates of 51% (n=21/41) for standardised ECT, 49% (n=20/41) for unstandardised ECT, 32% (n=13/41) for EVH and methacholine BPT, while both standardised and unstandardised ECTs were simultaneously positive in only 20% (n=7/35). Standardised and unstandardised ECTs confirmed LAD with 54% sensitivity and 70% specificity, and 46% sensitivity and 68% specificity, respectively, using EVH as a reference, while EVH and methacholine BPT were both 33% sensitive and 85% specific, using standardised ECTs as reference. Conclusion: App-based spirometry for unsupervised field-based ECTs may support the diagnostic process in athletes with LAD symptoms.

• Molina-Garcia, Pablo; Notbohm, Hannah L.; Schumann, Moritz; Argent, Rob; Hetherington-Rauth, Megan & Stang, Julie [Show all 14 contributors for this article] (2022). Validity of Estimating the Maximal Oxygen Consumption by Consumer Wearables: A Systematic Review with Meta-analysis and Expert Statement of the INTERLIVE Network. Sports Medicine. ISSN 0112-1642. doi: 10.1007/s40279-021-01639-y. Full text in Research Archive Show summary

  Background: Technological advances have recently made possible the estimation of maximal oxygen consumption (VO2max) by consumer wearables. However, the validity of such estimations has not been systematically summarized using meta-analytic methods and there are no standards guiding the validation protocols. Objective: The aim was to (1) quantitatively summarize previous studies investigating the validity of the VO2max estimated by consumer wearables and (2) provide best-practice recommendations for future validation studies. Methods: First, we conducted a systematic review and meta-analysis of studies validating the estimation of VO2max by wearables. Second, based on the state of knowledge (derived from the systematic review) combined with the expert discussion between the members of the Towards Intelligent Health and Well-Being Network of Physical Activity Assessment (INTERLIVE) consortium, we provided a set of best-practice recommendations for validation protocols. Results: Fourteen validation studies were included in the systematic review and meta-analysis. Meta-analysis results revealed that wearables using resting condition information in their algorithms significantly overestimated VO2max (bias 2.17 ml·kg−1·min−1; limits of agreement − 13.07 to 17.41 ml·kg−1·min−1), while devices using exercise-based information in their algorithms showed a lower systematic and random error (bias − 0.09 ml·kg−1·min−1; limits of agreement − 9.92 to 9.74 ml·kg−1·min−1). The INTERLIVE consortium proposed six key domains to be considered for validating wearable devices estimating VO2max, concerning the following: the target population, reference standard, index measure, testing conditions, data processing, and statistical analysis. Conclusions: Our meta-analysis suggests that the estimations of VO2max by wearables that use exercise-based algorithms provide higher accuracy than those based on resting conditions. The exercise-based estimation seems to be optimal for measuring VO2max at the population level, yet the estimation error at the individual level is large, and, therefore, for sport/clinical purposes these methods still need improvement. The INTERLIVE network hereby provides best-practice recommendations to be used in future protocols to move towards a more accurate, transparent and comparable validation of VO2max derived from wearables.

• Bernhardsen, Guro Pauck; Stang, Julie; Halvorsen, Thomas & Stensrud, Trine (2022). Differences in lung function, bronchial hyperresponsiveness and respiratory health between elite athletes competing in different sports. European Journal of Sport Science (EJSS). ISSN 1746-1391. doi: 10.1080/17461391.2022.2113144. Full text in Research Archive Show summary

  The aim of this study was to examine lung function, bronchial hyperresponsiveness (BHR) and exercise-induced respiratory symptoms in elite athletes performing different sports. Norwegian national-team athletes (30 swimmers, 32 cross-country skiers, 16 speed-skaters, 11 rowers/paddlers, 17 handball players and 23 soccer players) completed a validated questionnaire, measured exhaled nitric oxide (FENO), spirometry, methacholine provocation (PD20met) and skin prick test. Three cut-off levels defined BHR; i.e. PD20met ≤2 µmol, ≤4 µmol and ≤8 µmol. Mean forced vital capacity (FVC) was highest in swimmers (Mean z-score[95%CI]  = 1.16 [0.80, 1.51]), and close to or higher than reference values according to the Global Lung Initiative equation, across all sports. Mean forced expiratory volume in 1 s (FEV1) was higher than reference values in swimmers (0.48 [0.13, 0.84]), and ball game athletes (0.69 [0.41, 0.97]). Mean forced expiratory flow between 25 and 75% of FVC (FEF25-75), and/or FEV1/FVC were lower than reference values in all endurance groups. BHR defined by ≤2 and ≤8 µmol methacholine was observed in respectively 50%–87% of swimmers, 25%–47% of cross-country skiers, 20%–53% of speed-skaters, 18%–36% of rowers/paddlers, and 0%–17% of the ball game athletes. Exercise-induced symptoms were common in all groups, most frequent in cross-country skiers (88%), swimmers (83%) and speed-skaters (81%).

• Argent, Rob; Hetherington-Rauth, Megan; Stang, Julie; Tarp, Jakob; Ortega, Francisco B. & Molina-Garcia, Pablo [Show all 14 contributors for this article] (2022). Recommendations for Determining the Validity of Consumer Wearables and Smartphones for the Estimation of Energy Expenditure: Expert Statement and Checklist of the INTERLIVE Network. Sports Medicine. ISSN 0112-1642. 52(8), p. 1817–1832. doi: 10.1007/s40279-022-01665-4. Full text in Research Archive Show summary

  Background: Consumer wearables and smartphone devices commonly offer an estimate of energy expenditure (EE) to assist in the objective monitoring of physical activity to the general population. Alongside consumers, healthcare professionals and researchers are seeking to utilise these devices for the monitoring of training and improving human health. However, the methods of validation and reporting of EE estimation in these devices lacks rigour, negatively impacting on the ability to make comparisons between devices and provide transparent accuracy. Objectives: The Towards Intelligent Health and Well-Being Network of Physical Activity Assessment (INTERLIVE) is a joint European initiative of six universities and one industrial partner. The network was founded in 2019 and strives towards developing best-practice recommendations for evaluating the validity of consumer wearables and smartphones. This expert statement presents a best-practice validation protocol for consumer wearables and smartphones in the estimation of EE. Methods: The recommendations were developed through (1) a systematic literature review; (2) an unstructured review of the wider literature discussing the potential factors that may introduce bias during validation studies; and (3) evidence-informed expert opinions from members of the INTERLIVE network. Results: The systematic literature review process identified 1645 potential articles, of which 62 were deemed eligible for the final dataset. Based on these studies and the wider literature search, a validation framework is proposed encompassing six key domains for validation: the target population, criterion measure, index measure, testing conditions, data processing and the statistical analysis. Conclusions: The INTERLIVE network recommends that the proposed protocol, and checklists provided, are used to standardise the testing and reporting of the validation of any consumer wearable or smartphone device to estimate EE. This in turn will maximise the potential utility of these technologies for clinicians, researchers, consumers, and manufacturers/developers, while ensuring transparency, comparability, and replicability in validation.

• Melsom, Helene Støle; Randa, Anders; Hisdal, Jonny; Stang, Julie & Stensrud, Trine (2022). Prevalence of asthma among Norwegian elite athletes. Translational Sports Medicine (TSM). 2022, p. 1–10. doi: 10.1155/2022/3887471. Full text in Research Archive Show summary

  Objective. Asthma is a common problem among elite athletes and represents a health risk interfering with the athlete’s performance status. This study aimed to evaluate the asthma prevalence among Norwegian summer and winter elite athletes and asthma prevalence across sport categories. We also aimed to examine whether bronchial hyperresponsiveness (BHR), lung function, fraction of exhaled nitric oxide (FENO), and allergy status differed between asthmatic and non-asthmatic elite athletes. Methods. Norwegian athletes qualifying for the Beijing Olympic Summer Games 2008 (n = 80) and the Vancouver Olympic Winter Games 2010 (n = 55) were included. The athletes underwent clinical respiratory examination including lung function measurement, methacholine bronchial challenge for assessment of BHR, FENO, and skin prick testing. Asthma was diagnosed based on respiratory symptoms and clinical examination including objective measurements. Results. Asthma was more prevalent among winter athletes (50%) than summer athletes (20%). Thirty-three (52%) endurance athletes, 3 (6%) team sport athletes, and 7 (33%) technical sport athletes had medically diagnosed asthma. Significantly lower lung function (p<0.001) and higher prevalence of severe BHR (p<0.001) were found in asthmatic athletes compared with non-asthmatic athletes. Conclusion. Asthma is common among Norwegian elite athletes, with winter and endurance athletes showing the highest prevalence. Asthmatic athletes were characterized by lower lung function and more severe BHR compared with non-asthmatic counterparts. The high prevalence among winter and endurance athletes demonstrates a need for increased attention to prevent and reduce the prevalence of asthma among those athletes.

• Mühlen, Jan M.; Stang, Julie; Skovgaard, Esben Lykke; Júdice, Pedro B.; Molina-Garcia, Pablo & Johnston, William [Show all 15 contributors for this article] (2021). Recommendations for determining the validity of consumer wearable heart rate devices: Expert statement and checklist of the INTERLIVE Network. British Journal of Sports Medicine. ISSN 0306-3674. 55(14), p. 767–779. doi: 10.1136/bjsports-2020-103148. Full text in Research Archive Show summary

  Assessing vital signs such as heart rate (HR) by wearable devices in a lifestyle-related environment provides widespread opportunities for public health related research and applications. Commonly, consumer wearable devices assessing HR are based on photoplethysmography (PPG), where HR is determined by absorption and reflection of emitted light by the blood. However, methodological differences and shortcomings in the validation process hamper the comparability of the validity of various wearable devices assessing HR. Towards Intelligent Health and Well-Being: Network of Physical Activity Assessment (INTERLIVE) is a joint European initiative of six universities and one industrial partner. The consortium was founded in 2019 and strives towards developing best-practice recommendations for evaluating the validity of consumer wearables and smartphones. This expert statement presents a best-practice validation protocol for consumer wearables assessing HR by PPG. The recommendations were developed through the following multi-stage process: (1) a systematic literature review based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses, (2) an unstructured review of the wider literature pertaining to factors that may introduce bias during the validation of these devices and (3) evidence-informed expert opinions of the INTERLIVE Network. A total of 44 articles were deemed eligible and retrieved through our systematic literature review. Based on these studies, a wider literature review and our evidence-informed expert opinions, we propose a validation framework with standardised recommendations using six domains: considerations for the target population, criterion measure, index measure, testing conditions, data processing and the statistical analysis. As such, this paper presents recommendations to standardise the validity testing and reporting of PPG-based HR wearables used by consumers. Moreover, checklists are provided to guide the validation protocol development and reporting. This will ensure that manufacturers, consumers, healthcare providers and researchers use wearables safely and to its full potential.

• Illidi, Camilla Rønn; Stang, Julie; Melau, Jørgen; Hisdal, Jonny & Stensrud, Trine (2021). Does Cold-Water Endurance Swimming Affect Pulmonary Function in Healthy Adults? Sports. 9(1), p. 1–12. doi: 10.3390/sports9010007. Full text in Research Archive Show summary

  The acute effects of cold-water endurance swimming on the respiratory system have received little attention. We investigated pulmonary responses to cold-water endurance swimming in healthy recreational triathletes. Pulmonary function, alveolar diffusing capacity (DLCO), fractional exhaled nitric oxide (FENO) and arterial oxygen saturation by pulse oximetry (SpO2) were assessed in 19 healthy adults one hour before and 2.5 h after a cold-water (mean ± SD, 10 ± 0.9 °C) swim trial (62 ± 27 min). In addition, 12 out of the 19 participants measured pulmonary function, forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) 3, 10, 20 and 45 min post-swim by maximal expiratory flow volume loops and DLCO by the single breath technique. FVC and FEV1 were significantly reduced 3 min post-swim (p = 0.02) (p = 0.04), respectively, and five of 12 participants (42%) experienced exercise-induced bronchoconstriction (EIB), defined as a ≥ 10% drop in FEV1. No significant changes were observed in pulmonary function 2.5 h post-swim. However, mean FENO and DLCO were significantly reduced by 7.1% and 8.1% (p = 0.01) and (p < 0.001), respectively, 2.5 h post-swim, accompanied by a 2.5% drop (p < 0.001) in SpO2. The absolute change in DLCO correlated significantly with the absolute decline in core temperature (r = 0.52; p = 0.02). Conclusion: Cold-water endurance swimming may affect the lungs in healthy recreational triathletes lasting up to 2.5 h post-swim. Some individuals appear to be more susceptible to pulmonary impairments than others, although these mechanisms need to be studied further.

• Stensrud, Trine; Rossvoll, Øyvind; Mathiassen, Maria; Melau, Jørgen; Illidi, Camilla Rønn & Østgaard, Hege Nymo [Show all 8 contributors for this article] (2020). Lung function and oxygen saturation after participation in Norseman Xtreme Triathlon. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 30(6), p. 1008–1016. doi: 10.1111/sms.13651. Full text in Research Archive Show summary

  Objectives: To examine evidence of exercise-induced bronchoconstriction (EIB) defined as ≥10% reduction in forced expiratory volume in one second (FEV1 ) and exercise-induced arterial hypoxemia (EIAH) defined as ≥4% reduction in oxygen saturation (SpO2 ) from before to after participation in the Norseman Xtreme Triathlon. Secondarily, to assess whether changes in FEV1 and SpO2 are related to respiratory symptoms, training volume, and race time. Methods: In this quasi-experimental non-controlled study, we included 63 triathletes (50♂/13♀) aged 40.3 (±9.0) years (mean ± SD). Fifty-seven (46♂/11♀) measured lung function and 54 (44♂/10♀) measured SpO2 before the race, 8-10 minutes after the race (post-test 1) and the day after the race (post-test 2). Respiratory symptoms and training volume were recorded with modified AQUA questionnaire. ANOVA for repeated measures was used to detect differences in lung function and SpO2 . Statistical significance was accepted at 0.05 level. Results: Twenty-six participants (46%) presented with EIB at post-test 1 and 16 (28%) at post-test 2. Lung function variables were significantly reduced from baseline to post-test 1 and 2. Thirty-five participants (65%) showed evidence of mild to moderate EIAH. No significant correlations were observed except a weak correlation between maximal reduction in FEV1 and respiratory symptoms (r = 0.35, P = .016). Conclusion: Our results demonstrated that 46% of the participants presented with EIB and 65% showed evidence of EIAH after the Norseman Xtreme Triathlon. Changes in FEV1 and SpO2 were not correlated to weekly training hours or race time. We observed a weak correlation between maximal reduction in FEV1 and respiratory symptoms.

• Johnston, William; Júdice, Pedro B.; Molina-Garcia, Pablo; Mühlen, Jan M; Skovgaard, Esben Lykke & Stang, Julie [Show all 15 contributors for this article] (2020). Recommendations for determining the validity of consumer wearable and smartphone step count: Expert statement and checklist of the INTERLIVE network. British Journal of Sports Medicine. ISSN 0306-3674. doi: 10.1136/bjsports-2020-103147. Full text in Research Archive Show summary

  Consumer wearable and smartphone devices provide an accessible means to objectively measure physical activity (PA) through step counts. With the increasing proliferation of this technology, consumers, practitioners and researchers are interested in leveraging these devices as a means to track and facilitate PA behavioural change. However, while the acceptance of these devices is increasing, the validity of many consumer devices have not been rigorously and transparently evaluated. The Towards Intelligent Health and Well-Being Network of Physical Activity Assessment (INTERLIVE) is a joint European initiative of six universities and one industrial partner. The consortium was founded in 2019 and strives to develop best-practice recommendations for evaluating the validity of consumer wearables and smartphones. This expert statement presents a best-practice consumer wearable and smartphone step counter validation protocol. A two-step process was used to aggregate data and form a scientific foundation for the development of an optimal and feasible validation protocol: (1) a systematic literature review and (2) additional searches of the wider literature pertaining to factors that may introduce bias during the validation of these devices. The systematic literature review process identified 2897 potential articles, with 85 articles deemed eligible for the final dataset. From the synthesised data, we identified a set of six key domains to be considered during design and reporting of validation studies: target population, criterion measure, index measure, validation conditions, data processing and statistical analysis. Based on these six domains, a set of key variables of interest were identified and a ‘basic’ and ‘advanced’ multistage protocol for the validation of consumer wearable and smartphone step counters was developed. The INTERLIVE consortium recommends that the proposed protocol is used when considering the validation of any consumer wearable or smartphone step counter. Checklists have been provided to guide validation protocol development and reporting. The network also provide guidance for future research activities, highlighting the imminent need for the development of feasible alternative ‘gold-standard’ criterion measures for free-living validation. Adherence to these validation and reporting standards will help ensure methodological and reporting consistency, facilitating comparison between consumer devices. Ultimately, this will ensure that as these devices are integrated into standard medical care, consumers, practitioners, industry and researchers can use this technology safely and to its full potential.

• Brynjulfsen, Trine; Demmelmaier, Ingrid; Berntsen, Sveinung; Foyn, Tonje Hellum; Andersen, Oddbjørn Klomsten & Stang, Julie [Show all 11 contributors for this article] (2020). Motivation for physical activity in adolescents with asthma. Journal of Asthma. ISSN 0277-0903. doi: 10.1080/02770903.2020.1778025. Full text in Research Archive Show summary

  Objective: We explored motivation for physical activity (PA) and exercise in adolescents with asthma who entered and continued a 10-week play-based exercise intervention. Methods: Eighteen adolescents with asthma, aged 13–17 years, participated in a 10-week play- and interval-based indoor exercise intervention during winter and autumn months. Semi-structured focus group interviews were conducted in weeks 2 and 8, focusing on motivation for PA and exercise, as well as field observations of exercise sessions in weeks 2, 6, and 8. The first interview was analyzed separately from the second one and descriptive observational data were obtained using thematic analysis and self-determination theory as a framework. Results: In the first round of focus group interviews, participants (n = 18) described amotivation and motivation for PA within the following five themes: “teachers’ lack of asthma knowledge”, “embarrassment over asthma symptoms”, “not being able to keep pace with peers”, “seasonal challenges”, and “mastering fun physical activities”. Based on the second interview (n = 14) and descriptive observational data (n = 18), participants reported and revealed amotivation and motivation for PA within the following four themes: “understanding and relatedness”, “social support”, “competition”, and “mastering fun activities”. Conclusion: We conclude that play-based exercises designed for groups of adolescents with asthma can support motivation for PA and exercise and reduce social and asthma-specific barriers.

• Riiser, Amund; Stensrud, Trine; Stang, Julie & Andersen, Lars Bo (2020). Can β2-agonists have an ergogenic effect on strength, sprint or power performance? Systematic review and meta-analysis of RCTs. British Journal of Sports Medicine. ISSN 0306-3674. 54(22), p. 1351–1359. doi: 10.1136/bjsports-2019-100708. Full text in Research Archive Show summary

  Objectives: We aimed to examine the effect of β2-agonists on anaerobic performance in healthy non-asthmatic subjects. Design: Systematic review and meta-analysis. Eligibility criteria: We searched four databases (PubMed, Embase, SPORTDiscus and Web of Science) for randomised controlled trials, published until December 2019, examining the effect of β2-agonists on maximal physical performance lasting 1 min or shorter. Data are presented as standardised difference in mean (SDM) with 95% confidence intervals (95% CI). Results: 34 studies were included in the present meta-analysis. The studies include 44 different randomised and placebo-controlled comparisons with β2-agonists comprising 323 participants in crossover trials, and 149 participants in parallel trials. In the overall analyses, β2-agonists improved anaerobic performance by 5% (SDM 0.29, 95% CI 0.16 to 0.42), but the effect was related to dose and administration route. In a stratified analysis, the SDM was 0.14 (95% CI 0.00 to 0.28) for approved β2-agonists and 0.46 (95% CI 0.24 to 0.68) for prohibited β2-agonists, respectively. Furthermore, SDM was 0.16 (95% CI 0.02 to 0.30) for inhaled administration and 0.51 (95% CI 0.25 to 0.77) for oral administration, respectively, and 0.20 (95% CI 0.07 to 0.33) for acute treatment and 0.50 (95% CI 0.20 to 0.80) for treatment for multiple weeks. Analyses stratified for the type of performance showed that strength (0.35, 95% CI 0.15 to 0.55) and sprint (0.17, 95% CI 0.06 to 0.29) performance were improved by β2-agonists. Conclusion/implication: Our study shows that non-asthmatic subjects can improve sprint and strength performance by using β2-agonists. It is uncertain, however, whether World Anti-Doping Agency (WADA)-approved doses of β2-agonists improve performance. Our results support that the use of β2-agonists should be controlled and restricted to athletes with documented asthma.

• Riiser, Amund; Stensrud, Trine; Stang, Julie & Andersen, Lars Bo (2020). Aerobic performance among healthy (non-asthmatic) adults using beta2-agonists: a systematic review and meta-analysis of randomised controlled trials. British Journal of Sports Medicine. ISSN 0306-3674. doi: 10.1136/bjsports-2019-100984. Full text in Research Archive Show summary

  Objective: To examine the effect of beta2-agonists on aerobic performance in healthy, non-asthmatic study participants. Design: Systematic review and meta-analysis. Eligibility criteria: We searched four databases (PubMed, Embase, SPORTDiscus and Web of Science) for randomised controlled trials published until December 2019. Studies examining the effect of beta2-agonists on maximal physical performance lasting longer than 1 min were included in the meta-analysis. Data are presented as standardised difference in mean (SDM) with 95% CI. Results: The present meta-analysis includes 47 studies. The studies comprise 607 participants in cross-over trials, including 99 participants in three-way cross-over trials and 27 participants in a four-way cross-over trial. Seventy-three participants were included in parallel trials. Beta2-agonists did not affect aerobic performance compared with placebo (SDM 0.051, 95% CI −0.020 to 0.122). The SDM for the included studies was not heterogeneous (I2=0%, p=0.893), and the effect was not related to type of beta2-agonist, dose, administration route, duration of treatment or performance level of participants. Beta2-agonists had no effect on time trial performance, time to exhaustion or maximal oxygen consumption (p<0.218). Conclusion/implication: The present study shows that beta2-agonists do not affect aerobic performance in non-asthmatic subjects regardless of type, dose, administration route, duration of treatment or performance level of participants. The results of the present study should be of interest to WADA and to anyone who is interested in equal opportunities in competitive sports.

• Stang, Julie; Sikkeland, Liv Ingunn Bjoner; Tufvesson, Ellen; Holm, Are Martin; Stensrud, Trine & Carlsen, Kai-Håkon (2018). The Role of Airway Inflammation and Bronchial Hyperresponsiveness in Athlete's Asthma. Medicine & Science in Sports & Exercise. ISSN 0195-9131. 50(4), p. 659–666. doi: 10.1249/MSS.0000000000001478. Full text in Research Archive
• Stensrud, Trine; Stang, Julie; Thorsen, Einar & Bråten, Veslemøy (2016). Exhaled nitric oxide concentration in the period of 60 min after submaximal exercise in the cold. Clinical Physiology and Functional Imaging. ISSN 1475-0961. 36(2), p. 85–91. doi: 10.1111/cpf.12196. Full text in Research Archive Show summary

  Background Fractional expired nitric oxide (FENO) is decreased after exercise. The effect of exercise in the cold upon FENO is unknown. Purpose To examine changes in FENO after a short, high intensive exercise test in a cold and in a temperate environment. Methods Twenty healthy well-trained subjects (eight females) aged 18–28 years performed an 8-min exercise test at 18°C (SD = 1.0) and −10°C (SD = 1.2) ambient temperature. The tests were performed in a climate chamber in random order. The workload corresponded to 90–95% of peak heart rate (HRpeak) during the last 4 min. FENO was measured offline. Exhaled gas was sampled in Mylar® bags using a collector kit with a flow restrictor and analysed within 2 h. FENO was measured before exercise and repeatedly during the first hour after. ANOVA for repeated measures was used to compare differences in FENO after exercise between environments. Results There was no difference in baseline FENO. A significant difference in FENO between environments was found after warm-up and from 20 to 30 min after exercise, with FENO being lower after exercise in the cold (P<0.05). The maximal reduction in FENO was seen 5 min after exercise and was not different between environments. Conclusion Recovery of FENO was slower after exercising in −10°C compared with 18°C.

• Stang, Julie; Wiig, Håvard; Hermansen, Marte & Hansen, Ernst Albin (2016). Voluntary movement frequencies in submaximal one- and two-legged knee extension exercise and pedaling. Frontiers in Human Neuroscience. 10(2016). doi: 10.3389/fnhum.2016.00036. Full text in Research Archive Show summary

  Understanding of behavior and control of human voluntary rhythmic stereotyped leg movements is useful in work to improve performance, function, and rehabilitation of exercising, healthy, and injured humans. The present study aimed at adding to the existing understanding within this field. To pursue the aim, correlations between freely chosen movement frequencies in relatively simple, single-joint, one- and two-legged knee extension exercise were investigated. The same was done for more complex, multiple-joint, one- and two-legged pedaling. These particular activities were chosen because they could be considered related to some extent, as they shared a key aspect of knee extension, and because they at the same time were different. The activities were performed at submaximal intensities, by healthy individuals (n = 16, thereof eight women; 23.4 ± 2.7 years; 1.70 ± 0.11 m; 68.6 ± 11.2 kg). High and fair correlations (R-values of 0.99 and 0.75) occurred between frequencies generated with the dominant leg and the nondominant leg during knee extension exercise and pedaling, respectively. Fair to high correlations (R-values between 0.71 and 0.95) occurred between frequencies performed with each of the two legs in an activity, and the two-legged frequency performed in the same type of activity. In general, the correlations were higher for knee extension exercise than for pedaling. Correlations between knee extension and pedaling frequencies were of modest occurrence. The correlations between movement frequencies generated separately by each of the legs might be interpreted to support the following working hypothesis, which was based on existing literature. It is likely that involved central pattern generators (CPGs) of the two legs share a common frequency generator or that separate frequency generators of each leg are attuned via interneuronal connections. Further, activity type appeared to be relevant. Thus, the apparent common rhythmogenesis for the two legs appeared to be stronger for the relatively simple single-joint activity of knee extension exercise as compared to the more complex multi-joint activity of pedaling. Finally, it appeared that the shared aspect of knee extension in the related types of activities of knee extension exercise and pedaling was insufficient to cause obvious correlations between generated movement frequencies in the two types of activities.

• Stang, Julie; Stensrud, Trine; Mowinckel, Petter & Carlsen, Kai-Håkon (2016). Parasympathetic activity and bronchial hyperresponsiveness in athletes. Medicine & Science in Sports & Exercise. ISSN 0195-9131. 48(11), p. 2100–2107. doi: 10.1249/MSS.0000000000001008. Full text in Research Archive Show summary

  PURPOSE: A high prevalence of asthma and bronchial hyperresponsiveness (BHR) is reported in swimmers and cross-country skiers. It has been suggested that increased parasympathetic nervous activity is involved in asthma development in endurance athletes. We aimed to assess the associations of BHR to parasympathetic activity in healthy and asthmatic swimmers and cross-country skiers and healthy nonathletes. METHODS: Parasympathetic activity was measured by pupillometry and heart rate variability at the onset of exercise with the cardiac vagal index calculated in 28 cross-country skiers (♂18/♀10), 29 swimmers (♂17/♀12), and 30 healthy nonathlete controls (♂14/♀16) on two different days. All subjects performed a methacholine bronchial challenge with the provocation dose causing 20% decrease in the forced expiratory volume in 1 s calculated (PD20met). Data were analyzed by robust regression analysis and presented as β coefficients with 95% confidence intervals (CI). RESULTS: PD20met was negatively associated with cardiac vagal index (-13.9, 95% CI = -26.8 to -1.0) in all subjects. When adjusted to the type of sport, this association was stronger in swimmers (-8.3, 95% CI = -13.0 to -3.6) as compared with controls and nonsignificant in cross-country skiers. Percent pupil constriction was significantly associated with PD20met in swimmers (-9.4, 95% CI = -15.4 to -3.4) only after adjusting for the type of sport. Fourteen swimmers (48%) and 16 cross-country skiers (57%) had doctor-diagnosed asthma in combination with current BHR and/or current use of asthma drugs. Seventy-two percent swimmers, 44% cross-country skiers, and 39% controls had a PD20met ≤8 μmol (P = 0.015). Fourteen swimmers had a PD20met ≤2 μmol as compared with one cross-country skier (P < 0.001). CONCLUSION: Parasympathetic activity measured in the heart is more closely related to BHR as compared with parasympathetic activity measured in the pupils. The type of sport influences BHR severity and its relationship to parasympathetic activity.

• Stang, Julie; Couto, Mariana; Stensrud, Trine; Mowinckel, Petter; Moreira, André & Carlsen, Kai-Håkon (2016). Assessment of parasympathetic activity in athletes: Comparing two different methods. Medicine & Science in Sports & Exercise. ISSN 0195-9131. 48(2), p. 316–322. doi: 10.1249/MSS.0000000000000769. Full text in Research Archive Show summary

  Introduction: A variety of methods are used to assess parasympathetic activity in athletes targeting different organs; however the reliability of or interchangeability between measurement procedures is not clear. Objective: To identify the repeatability of two parasympathetic activity measurement procedures; heart rate variability (HRV) during a four second exercise test (4sET) and the contractile properties of the pupil (pupillometry), and to assess their agreement. Secondarily, to assess their relationship with the bronchodilating effect of inhaled ipratropium bromide (iIB), blocking parasympathetic signals to the lungs. Methods: Forty athletic subjects were enrolled in a cross sectional study. After 15 minutes resting in semi-darkness subjects underwent pupillometry (PLR-200(TM), NeurOptics Inc, CA, USA), followed by 4sET on a cycle ergometer. HRV was assessed by Polar Electro(R) heart rate monitor (RS-800CX/G3 - OY, Kempele, Finland). Both protocols were repeated after 5 minutes. Statistical analysis was performed according to Bland and Altman, and by Pearson's correlation coefficient and intra-class correlation (ICC). Lung function measurements by flow volume curves were performed before and 45 minutes after iIB. Results: Mean of differences was 1.21% ([limits of agreement] -3.59, 6.02) for pupil constriction and 0.05 mm (-0.28, 0.39) for pupil amplitude. The mean of differences for 4sET was 0.005 (-0.31, 0.32). A very weak ICC (r=-.01, p=.58) showed no agreement between the methods. No correlation was observed between pupillometry variables or 4sET with the change in lung function after iIB. Conclusion: Pupillometry showed better repeatability compared with the 4sET. There is poor agreement between parasympathetic activity levels measured in three different target organs of athletic subjects; the heart, the pupil and the lung. Thus, methods assessing parasympathetic activity in different target organs cannot be used interchangeably.

• Stang, Julie; Bråten, Veslemøy; Caspersen, Cecilie; Thorsen, Einar & Stensrud, Trine (2015). Exhaled nitric oxide after high-intensity exercise at 2800 m altitude. Clinical Physiology and Functional Imaging. ISSN 1475-0961. 35(5), p. 338–343. doi: 10.1111/cpf.12131. Full text in Research Archive Show summary

  Background: Nitric oxide (NO) concentration in exhaled gas is a marker of some inflammatory processes in the lung, and endogenous NO plays a role in the physiological responses to exercise and altitude. The aim of this study was to compare changes in exhaled NO concentration 5–60 mins after high-intensity exercise at 2800 m and at 180 m altitude. Methods: Twenty trained healthy volunteers (12 men), aged 19–28 years, were included in this open, crossover study. Subjects performed two exercise tests at different altitudes, 2800 m and 180 m, in a randomized order. The fraction of NO in exhaled gas (FENO) was measured 5 mins before and 5–60 mins after 8 mins of running on a treadmill at a heart rate (HR) of 90% of peak HR. Peak HR was assessed during a pretest at 180 m. Ambient temperature was 20·1°C (SD = 1·2) and relative humidity 40·2% (SD = 3·2). FENO measurements were corrected for altitude gas density effects and converted to partial pressure of NO (PENOcorr). Results: PENOcorr was reduced from 1·47 (1·21, 1·73) millipascal (mPa) at baseline to 1·11 (0·87, 1·34) mPa 5 mins after exercise at 2800 m and from 1·54 (1·24, 1·84) to 1·04 (0·87, 1·22) mPa 5 mins after exercise at 180 m. There was no difference in PENOcorr between exercise at 2800 m and 180 m, and PENOcorr was normalized within 20 mins. Conclusions: Exercise at 2800 m induces a similar acute reduction in exhaled nitric oxide concentration as compared with 180 m in healthy subjects.

• Couto, Mariana; Stang, Julie; Horta, Luis; Stensrud, Trine; Severo, Milton & Mowinckel, Petter [Show all 10 contributors for this article] (2015). Two distinct phenotypes of asthma in elite athletes identified by latent class analysis. Journal of Asthma. ISSN 0277-0903. 52(9), p. 897–904. doi: 10.3109/02770903.2015.1067321. Full text in Research Archive Show summary

  Introduction: Clusters of asthma in athletes have been insufficiently studied. Therefore, the present study aimed to characterize asthma phenotypes in elite athletes using latent class analysis (LCA) and to evaluate its association with the type of sport practiced. Methods: In the present cross-sectional study, an analysis of athletes’ records was carried out in databases of the Portuguese National Anti-Doping Committee and the Norwegian School of Sport Sciences. Athletes with asthma, diagnosed according to criteria given by the International Olympic Committee, were included for LCA. Sports practiced were categorized into water, winter and other sports. Results: Of 324 files screened, 150 files belonged to asthmatic athletes (91 Portuguese; 59 Norwegian). LCA retrieved two clusters: “atopic asthma” defined by allergic sensitization, rhinitis and allergic co-morbidities and increased exhaled nitric oxide levels; and “sports asthma”, defined by exercise-induced respiratory symptoms and airway hyperesponsiveness without allergic features. The risk of developing the phenotype “sports asthma” was significantly increased in athletes practicing water (OR = 2.87; 95%CI [1.82–4.51]) and winter (OR = 8.65; 95%CI [2.67–28.03]) sports, when compared with other athletes. Conclusion: Two asthma phenotypes were identified in elite athletes: “atopic asthma” and “sports asthma”. The type of sport practiced was associated with different phenotypes: water and winter sport athletes had three- and ninefold increased risk of “sports asthma”. Recognizing different phenotypes is clinically relevant as it would lead to distinct targeted treatments.

• Stang, Julie; Couto, Mariana; Carlsen, Kai-Håkon & Stensrud, Trine (2015). Increased bronchial parasympathetic tone in elite cross-country and biathlon skiers: a randomised crossover study. British Journal of Sports Medicine. ISSN 0306-3674. 49(1), p. 56–61. doi: 10.1136/bjsports-2014-094053. Full text in Research Archive Show summary

  Background: Increased parasympathetic activity in endurance-trained athletes has been reported by heart rate variability and pupillometry. Our primary objective was to assess parasympathetic activity and tone in the lower respiratory tract by investigating the effect of cholinergic antagonism by inhaled ipratropium bromide compared to the β2-receptor stimulating effect of inhaled salbutamol in elite cross-country and biathlon skiers. We also examined the medications’ relationship to cholinergic sensitivity as measured by bronchial responsiveness to methacholine (PD20met). Methods: In a randomised crossover study, 20 cross-country and two biathlon skiers (14♂/8♀) aged 20–37 years from the Norwegian national teams measured reversibility to inhaled ipratropium bromide and inhaled salbutamol and PD20met on three separate days. A positive reversibility test was defined as an increase in forced expiratory volume in 1 s (FEV1) of ≥12%. Spirometry was performed before and 45 and 15 min after inhaled ipratropium bromide and inhaled salbutamol, respectively. Bronchodilating medication was withheld according to the European Respiratory Society (ERS) guidelines. Correlations were assessed by Pearson's correlation coefficient (r). Results: Five athletes had significant reversibility after inhaled ipratropium bromide, and none after inhaled salbutamol. Twelve athletes (54.5%) had PD20met <8 μmol (1.57 mg). PD20met correlated negatively with ▵FEV1 after inhaled ipratropium bromide (r=−0.85, p<0.0001), but not after inhaled salbutamol (r=−0.308, p=0.16). Conclusions: In elite skiers, cholinergic sensitivity (PD20met) had a highly significant inverse correlation to the cholinergic antagonism of inhaled ipratropium bromide, but not at all to the bronchodilating inhaled salbutamol. This markedly increased bronchial parasympathetic tone may represent an important cholinergic role in the development of skier's asthma.

• Caspersen, Cecilie; Stang, Julie; Thorsen, Einar & Stensrud, Trine (2013). Exhaled nitric oxide concentration upon acute exposure to moderate altitude. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 23(2), p. e102–e107. doi: 10.1111/sms.12018. Full text in Research Archive Show summary

  The purpose of this study was to assess immediate changes in the partial pressure of nitric oxide (NO) in exhaled gas (PENO) in healthy trained subjects who were acutely exposed to moderate altitude. One group of nine and another group of 20 healthy subjects were exposed to an ambient pressure of 728 hPa (546 mmHg) corresponding to an altitude of 2800 m for 5 and 90 min, respectively, in an altitude chamber. PENO was measured offline by sampling exhaled gas in tight metal foil bags at 5, 30, 60, and 90 min. A correction for increased expiratory flow rate due to gas density effects at altitude was performed (PENOcorr). PENO was significantly decreased by 13–16%, while the fraction of NO in exhaled gas (FENO) was increased by 16–19% compared to sea level. There was no significant change in PENOcorr after exposure to altitude for 5, 30, 60, and 90 min. We conclude that there was no change in PENO upon arrival at altitude after correcting for gas density effects on expiratory flow rate. Corrections for altitude effects must be done before comparing measurements performed at different altitudes when using measurements of FENO to monitor athletes who have asthma during training at altitude.

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• Stang, Julie & Randa, Anders (2022). Respiratory health in former elite athletes. Full text in Research Archive
• Melsom, Helene Støle; Randa, Anders; Hisdal, Jonny; Stang, Julie & Stensrud, Trine (2022). Prevalence of asthma among Norwegian elite athletes. Full text in Research Archive
• Reier-Nilsen, Tonje; Stang, Julie; Flatsetøy, Hanne; Isachsen, Martine & Nordlund, Björn (2022). An app-based spirometer for detection of exercise-induced bronchoconstriction in athletes. Full text in Research Archive
• Isachsen, Martine; Reier-Nilsen, Tonje; Stang, Julie; Flatsetøy, Hanne & Nordlund, Björn (2022). The usability of app-based spirometry tests for detection of exercise-induced bronchoconstriction in athletes. Full text in Research Archive
• Isachsen, Martine; Reier-Nilsen, Tonje; Stang, Julie; Flatsetøy, Hanne & Nordlund, Björn (2022). The usability of app-based spirometry tests for detection of exercise-induced bronchoconstriction in athletes. European Clinical Respiratory Journal. 60, p. 3728–3728. doi: 10.1183/13993003.congress-2022.3728. Full text in Research Archive
• Westergren, Thomas; Stang, Julie; Stensrud, Trine; Andersen, Oddbjørn Klomsten; Sigdestad, Joakim Bordvik & Brynjulfsen, Trine [Show all 10 contributors for this article] (2019). Exercise adherence and psychological needs satisfaction in the PhysicaL activity and Asthma in Youth (PLAY) intervention. Full text in Research Archive
• Stang, Julie; Hem, Erlend Jan; Carlsen, Kai-Håkon; Couto, Mariana & Stensrud, Trine (2013). Increased Parasympathetic Tone and Bronchial Hyperresponsiveness In Elite Winter Sport Athletes. Medicine & Science in Sports & Exercise. ISSN 0195-9131. 45(5), p. 330–330. Full text in Research Archive
• Stang, Julie; Hem, Erlend Jan; Carlsen, Kai-Håkon & Stensrud, Trine (2012). Er astma hos toppidrettsutøvere assosiert med økt parasympatisk aktivitet? Norsk idrettsmedisin. ISSN 0806-9328. 27(3), p. 23–23. Full text in Research Archive
• Stang, Julie; Hem, Erlend Jan; Carlsen, Kai-Håkon & Stensrud, Trine (2012). Er astma hos toppidrettsutøvere assosiert med økt parasympatisk aktivitet. Full text in Research Archive
• Stang, Julie (2018). Why do athletes develop asthma?: Pathogenic mechanisms and asthma phenotypes. Norges idrettshøgskole. ISSN 9788250205499. Full text in Research Archive Show summary

  Paper III: Couto M, Stang J, Horta L, Stensrud T, Severo M, Mowinckel P, Moreira A, Carlsen KH. Two distinct phenotypes of asthma in elite athletes identified by latent class analysis. J Asthma. 2015;52(9):897-904.

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