Many comparisons of unresisted and resisted sprinting do not match running velocity. As such, differences may partly reflect velocity rather than resistance. This cross-sectional study examined kinetic and kinematic differences between unresisted and resisted sprinting accelerations at matched running velocities. Fourteen amateur sportsmen performed unresisted and resisted maximal overground sprints. Motorized resistance was applied via the waist and set at 20%, 40%, and 60% decreases in maximal unresisted velocity (V). Ground reaction forces and segment/joint angles were compared across velocity-matched steps between the conditions using ANOVA and statistical parametric mapping (SPM). Longer contact times were observed for resisted versus the unresisted condition, specifically 6.4% and 16.8% at 40% and 60% V (ES: -0.423; -0.851, respectively). Vertical impulse was 8.0%, 7.3%, and 14.6% greater in the resisted condition at 20%, 40%, and 60% V, (ES: -0.788; -0.551; and -0.862, respectively). Ankle range of motion was 5.8° greater at 60% V (ES: -1.064), and hip angle at toe-off was 2.8° and 8.3° greater at 40% and 60% V, (ES: -0.385; -0.987, respectively), compared to unresisted sprinting. No other statistically significant differences were observed. SPM analyses indicated differences only between kinetics at 20% V and ankle and trunk angles at 20% and 60% V. Our findings contrast the larger and consistent changes typically reported in resisted sprinting, indicating movement velocity may be a confounder. The comparatively modest remaining differences detected may reflect load-specific mechanisms that deserve future study.

This study aims to examine how landing biomechanics, including the contribution of joints and soft tissues, change throughout childhood and under increasing mechanical demand during double-legged landings. Children aged 3-12 years and adults performed landings from four heights: 10, 30, 50, and 70 cm. Ground reaction forces and full-body kinematics were used to calculate total mechanical work as well as the work performed by lower limb joints, upper limb joints and soft tissues. Biomechanical strategies were further assessed by estimating stiffness and damping throughout landing. Across all ages, participants performed a similar amount of total mechanical work and adjusted it appropriately with increasing mechanical demand. However, younger children relied more on soft tissues to dissipate energy, while the relative contribution of lower limb joints increased gradually with age until adulthood. Additionally, with increased mechanical demand, the relative contribution of lower limb joints decreased, whereas that of upper limb joints increased. This redistribution was accompanied by changes in biomechanical behavior: stiffness during the initial landing phase was greater in young children, while stiffness after peak force was independent of age but decreased as mechanical demand increased. In summary, although children as young as 3 years can land from a jump and adjust their behavior according to the mechanical demand, strategies continue to mature throughout childhood. Younger children exhibit stiffer behavior during the initial phase of landing and rely more on soft tissues to dissipate energy, whereas older children and adults show reduced stiffness and greater reliance on lower limb joints.

Age-related neuromuscular and cardiovascular declines may increase relative effort and thus fatigability during daily activities. Habitual physical activity (PA) may mitigate these alterations. This study examined the effects of age and PA on fatiguability in ecological conditions. Thirty-nine young men (YM, 22.1 ± 3.4 years), 34 old men (OM, 71.7 ± 4.1 years), and 23 very old men (VOM, 85.8 ± 2.7 years) performed a fatigue task. Increments were scaled in percentage body mass. Maximal knee extensor force (MVC), voluntary activation (VA), and twitch amplitude (Tw) were measured at baseline, after each stage and at task failure (TF). On a separate day, maximum oxygen consumption (V̇Omax) was quantified during a maximal ramp test. Results For a given workload (i.e., last common stage, LCS), MVC in percentage of baseline was lower in VOM (84.6% ± 9.2%) compared to YM (94.0% ± 7.0%; p < 0.001) and OM (91.7% ± 6.3%; p < 0.01). At LCS, Tw was lower in VOM (89.3% ± 12.7%) compared to OM (99.7% ± 10.5%; p < 0.05). MVC loss was greater in YM (-35.6% ± 14.5% of baseline) compared to VOM (-23.4% ± 11.3%; p < 0.01) at TF. No difference was found between YM and OM for loss in MVC and Tw. PA level was correlated with V̇Omax but did not affect fatigability. Tw loss at LCS was correlated with V̇Omax in VOM (r = 0.69; p < 0.05). VOM, but not OM, was more fatigued than YM for a given submaximal workload but the opposite was true at exhaustion. Fatigability in VOM was due to peripheral factors and was correlated with aerobic capacity. In VOM, unlike YM and OM, higher PA levels may be sufficient to improve aerobic capacity and reduce fatigability. Trial Registration: ClinicalTrials.gov identifier: NCT05413590.

Purpose Examine the efficacy of a virtually delivered, parent-focused physical literacy (PL) intervention for early childhood called PLAYshop and examine the level of and factors that influenced implementation. Methods A randomized controlled trial was conducted with 122 preschool-aged children (3-5 years) and their parents from western Canada. PLAYshop included a virtual workshop, educational and material resources, and follow-up support via an app with four booster lessons (1, 3, 5, 7 weeks post-workshop). Primary and secondary efficacy outcomes were measured at baseline and 2-month follow-up. Tertiary efficacy outcomes were also measured post-workshop (intervention group)/1-week post baseline questionnaire (control group). Tertiary implementation outcomes were measured via parental questionnaire and explored via parent and workshop leader interviews. Repeated measures Analysis of Covariance/Analysis of Variance and Generalized Estimating Equations were conducted. Results Intervention efficacy was not observed for children's PL (fundamental movement skills, motivation, enjoyment, confidence; primary outcome) or physical activity (PA; secondary outcome). Increases in other secondary and tertiary outcomes were observed in the intervention group, compared to the control group, including parent-child co-participation in PA (partial η = 0.062), parental PA modeling (partial η = 0.049) as well as parental capability (partial η = 0.039), opportunity (partial η = 0.089), and motivation (partial η = 0.026-0.045) to support children's PL development. High usefulness (87%) and satisfaction (96%) were reported by parents. Several themes were identified supporting the implementation of the intervention. Booster lesson completion was low (17%-30%). Conclusion Efficacy was observed for some parent but not child outcomes. Implementation was highly feasible at the delivery level but parent engagement in boosters had challenges. Trail Registration: NCT05255250 (Version 1: February 24, 2022; Version 3: December 7, 2022).

This study aimed to describe the incidence of head acceleration events (HAEs) during pitch-based in-season training and matches in professional male rugby league. Data were recorded using instrumented mouthguards from 108 players (70 forwards and 38 backs) at nine Super League teams (2024 season), resulting in 468 player-training sessions and 665 player-matches included. Peak linear and angular acceleration were calculated from each HAE and analyzed using generalized linear mixed-effects models. During the 468 player-training sessions, 814 HAEs above the lowest magnitude threshold (5 g and 400 rad.s) were observed and the mean HAE incidence rate per player-hour was 1.52 (95% confidence intervals; 1.34-1.70). This was substantially lower than matches (25.78 [23.28-28.27] per player-hour) with HAE incidence being 17 times greater during matches compared to training (incidence rate ratio 16.96 [14.92-19.01]). Higher magnitude HAEs had a lower incidence in both training and matches (e.g., > 25 g 0.04 [0.02-0.06] and 2.01 [1.79-2.24] per player-hour). Out of 468 player-training sessions, 307 (~66%) had no HAEs > 10 g and 441 (~94%) had no HAEs > 25 g. Overall, the incidence rates of HAEs during training were low and substantially lower than match-play. However, a small proportion of relatively high in magnitude HAEs do occur during training, which could be the target of prevention interventions in training. However, given the different HAE rates between training and matches, interventions targeting matches (e.g., law modifications or reduced exposure) would have a larger effect on reducing HAEs for players than training interventions.

This study aimed to investigate the effect of training intensity on contralateral adaptations following unilateral power-oriented resistance training (PT) in older adults. This secondary analysis of a within-person randomized controlled trial included 45 older adults (≥ 65 years; 25 women). After an 8-week control period (n = 45), part of the participants completed 12 weeks of a volume load-matched PT on one lower limb using either light loads (40% 1-RM, n = 9) or heavy loads (80% 1-RM, n = 10), while the contralateral limb did not exercise. Unilateral performance was assessed before and after each period through isometric tests (maximal isometric force, rate of force development, and muscle excitation) and dynamic tests (1-RM, maximal muscle power and maximal unloaded velocity determined through a force-velocity relationship test). Additionally, mid-thigh muscle mass and whole-body physical function were assessed. Linear mixed models were conducted to compare the effect (Cohen's d) of training intensity on the efficacy and magnitude of the contralateral adaptations and their impact on physical function. No contralateral adaptations were observed in any of the isometric tests. In contrast, untrained limbs showed comparable improvements in 1-RM (d = 0.35-0.42; p ≤ 0.001) and maximal muscle power (d = 0.49-0.54; p ≤ 0.001) regardless of PT intensity. Only heavy-load PT improved maximal unloaded velocity in the contralateral untrained limb (d = 0.68; p ≤ 0.001), while mid-thigh muscle mass (d = 0.24; p ≤ 0.013) and whole-body physical function assessed through the timed up-and-go test improved only after light-load PT (d = -0.74; p < 0.001). In conclusion, unilateral PT induced significant contralateral gains in dynamic muscle strength and power, regardless of training intensity, with heavier loads enhancing velocity-specific adaptations. Notably, light-load PT induced mild hypertrophy in the contralateral untrained limb and whole-body physical function, which might be particularly relevant for enhancing the intrinsic capacity of older adults. Trial Registration: ClinicalTrials.gov ID: NCT03724461.

The ketone bodies acetoacetate (AcAc) and β-hydroxybutyrate (βHB) have pleiotropic effects in multiple organs including the brain, heart, and skeletal muscle by serving as an alternative substrate for energy provision, and by acting as a signaling molecule modulating inflammation, oxidative stress, anabolic and catabolic processes, and gene expression. Ketogenic precursors such as 1,3-butanediol and medium-chain fatty acids, and ketone body-containing compounds such as ketone salts and ketone esters are commercially available and collectively termed exogenous ketone supplements (EKS). Ingestion of EKS produces an acute transient (1-2 h) increase in circulating AcAc and βHB concentrations, which has been termed "acute nutritional ketosis" or "intermittent exogenous ketosis". Many studies have failed to observe benefits of acute ingestion of EKS on various tests of exercise capacity and performance, but recent studies, albeit small in number, have suggested beneficial effects of EKS on recovery, sleep, overreaching, and adaptation to exercise training. This review describes the rationale and potential mechanistic basis for the proposed effects of EKS on these outcomes, as well as critically appraising the existing literature in this field, which at present is largely exploratory and requires more human studies with ecologically valid designs to address important knowledge gaps.

Despite growing interest in blood flow restriction (BFR) for enhancing training adaptations, its acute impacts on local and systemic physiological stress remain incompletely understood. This study compared the metabolic and perceptual responses of low-intensity cycling (LI) with BFR (LI + BFR) to both LI and high-intensity (HI) cycling without BFR, matched for time and external work. Ten males (26.9 ± 4.6 years) completed LI (20 min at 55% peak aerobic power output, PPO), LI + BFR (with 50% limb occlusion pressure), and HI (10 × 1 min at 90% PPO interspersed with 1-min recovery at 20% PPO) protocols in a randomized cross-over design. Interstitial metabolic responses were assessed via microdialysis in the vastus lateralis; systemic blood responses were evaluated via venous blood gas analysis. Cardiorespiratory responses, including heart rate, oxygen uptake, and ventilation, were continuously monitored during exercise. Serum creatine kinase (CK) and lactate dehydrogenase (LDH) were measured as indirect markers of muscle damage, and perceptual responses were documented. Muscle interstitial lactate and pyruvate were highest in HI, followed by LI + BFR, and lowest in LI (p < 0.05). Systemic blood and cardiorespiratory responses were comparable between LI + BFR and HI and exceeded LI (p < 0.05), while electrolyte shifts occurred across all conditions (p < 0.001) without between-condition differences. All protocols increased CK and LDH 24-48 h post-exercise, with the greatest increases in HI (p < 0.05). Perceived exertion and pain were higher in LI + BFR than in other conditions (p < 0.05). In conclusion, BFR intensifies local and systemic stress during LI and may be a potent strategy to promote muscle adaptive stimulus. However, when time and total external work are matched, high mechanical loading appears more effective in inducing local stress, which may be essential for further muscular adaptation processes.

This study tested whether a single 100 μg inhalation of salmeterol enhances 12-s sprint performance in both fresh and fatigued states in elite road cyclists. In a randomized crossover design, 16 well-trained, non-asthmatic male cyclists completed 2 trials 1 week apart. Participants inhaled either 100 μg salmeterol or placebo 1h before testing. Each trial involved: an initial 12-s sprint (fresh), a 1h race simulation (40%-95% peak power output) with heart rate, blood lactate concentration, and rating of perceived exertion (RPE) monitored, and a final 12-s sprint (fatigued). Peak and mean power, and vastus lateralis myoelectric activity were recorded during the sprints. Power declined from pre- to post-simulation in both conditions (p < 0.016), but the decrement was attenuated with salmeterol (peak: -7.5% vs. -18.2%; mean: -13.0% vs. -19.8%). Fatigued-sprint peak power was higher with salmeterol (915 ± 135 W) than placebo (831 ± 112 W; p = 0.030), as was mean power (692 ± 76 vs. 643 ± 92 W; p = 0.037). No effect of salmeterol was observed on fresh sprint performance and myoelectric activity. Blood lactate concentration and RPE rose similarly in both conditions (p < 0.001), while heart rate was higher with salmeterol during the first 20 min (p = 0.004). Acute inhalation of salmeterol attenuates muscle fatigue and enhances sprint performance at the end of a simulated race. These findings challenge the presumption of no enhancing effect of inhaled salmeterol at therapeutic doses in competitive road cycling, where final sprints often determine outcomes.

High-intensity interval exercise (HIIE) has been shown to improve motor skill consolidation when performed after physical practice (PP), but it remains unclear whether similar benefits extend to motor sequence learning (MSL) with both physical and motor imagery practice (MI). In this study, we examined the effects of HIIE on the consolidation of an explicit MSL task learned through PP or MI. Forty-eight participants were randomized into four groups based on the type of practice used to acquire the MSL task and whether they performed HIIE or rested before consolidation. Performance on the MSL task was assessed before and after acquisition, following HIIE or REST (early consolidation), and after 24 h and 7 days of late consolidation. Lactate and brain-derived neurotrophic factor (BDNF) levels, as well as corticospinal and intracortical excitability were examined to determine the mechanisms underpinning MSL acquisition and the effects of HIIE on consolidation. We found that both PP and MI increased performance during acquisition, with PP outperforming MI (p = 0.042), while both practices induced intracortical disinhibition right after acquisition (p = 0.02). Following HIIE, BDNF (p = 0.044) and lactate (p < 0.001) levels increased, but corticospinal and intracortical excitability remained unchanged. Importantly, our study suggests that MSL performance could be impaired by HIIE during both early and late consolidation (p < 0.01 and p < 0.05, respectively). Therefore, the HIIE-induced deterioration in MSL consolidation for both types of practice is likely due to the task's explicit demands, emphasizing the need to consider this factor when incorporating HIIE as an optimization approach into motor learning strategies in both sport and clinical contexts.

Childhood and adolescence are critical periods for the development of well-being, yet declines are commonly observed, particularly among youth from low socio-economic status backgrounds. This study examined the short-term (3.5 months) and long-term effects (16 months) on well-being of a residential multicomponent health promotion intervention at the Danish Christmas Seal Homes (DCSH), with and without the addition of the 11 for Health (11fH) programme. A randomized crossover design compared a Standard group (DCSH, n = 237) to a Standard+ group receiving the residential stay plus 11fH (combined football and health education sessions, n = 244). Well-being was assessed using the Pediatric Quality of Life Inventory (PedsQL 4.0 Generic) and KIDSCREEN-27. Multilevel modeling evaluated changes in well-being outcomes over time, accounting for repeated measurements nested within individuals. Participants in both groups reported well-being scores at or above normative values post-intervention, with these largely maintained at short- and long-term follow-ups. No significant group differences emerged over time. Physical Well-being declined over time, while Physical Functioning improved at short-term follow-up, but the increase was not sustained at the long-term follow-up. Females reported lower scores than males across several domains, including Physical Functioning, Emotional Functioning, Physical Well-being, and Psychological Well-being. Older age and higher pre-intervention scores were associated with lower well-being improvements. The results suggest that health-promoting interventions delivered in residential settings can help sustain well-being for socially vulnerable children. Moreover, consistent sex differences point to the need for ongoing support and tailored approaches for females. Trial Registration: This is a secondary analysis of a clinical trial, which has been registered on August 24, 2018: ClinicalTrials.gov ID: NCT03647007.

This study aimed to establish normative maximum mean power (MMP) values for elite cross-country mountain bike (XCO) cyclists across various durations (5 s to 5 min) under fresh and fatigued conditions, analyze differences in MMP between these states, and compare performance between Top 10 and Top 11-140 cyclists. A retrospective observational study analyzed power output data from 693 elite male XCO race files (2020-2024). Cyclists were categorized into Top 10 (n = 72) and Top 11-140 (n = 621) groups. MMP was measured in absolute (W) and relative (W kg) terms under fresh (early race) and fatigued (last lap) conditions, with cumulative energy expenditure (kJ) as a control variable. Data were cleaned for anomalies, non-parametric tests were used to assess differences, and correlations explored relationships between race result, energy expenditure, and MMP. Absolute MMP was higher under fresh conditions (first lap, mean energy expenditure: 188 ± 35 kJ) across all durations, with significant decreases in fatigued states (last lap, cumulative energy expenditure: 1250 ± 210 kJ; p < 0.001, effect size = 1.0). Top 10 cyclists outperformed the Top 11-140 group (p < 0.001, effect sizes = 0.3-0.6), showing greater energy expenditure (p < 0.001). Similar patterns were observed in relative terms, with some exceptions for very short efforts. Performance consistency was evident, with strong correlations between durations and conditions. Elite XCO cyclists exhibit distinct MMP profiles, with notable declines due to fatigue, particularly in short efforts. Top 10 cyclists demonstrate superior performance and workload capacity, highlighting the need for balanced anaerobic and aerobic training to excel in XCO racing, especially in the final lap.

The aim of this narrative review was to examine the effects and mechanisms of Post-Activation Performance Enhancement (PAPE) on sports and exercise performance, and to provide practical recommendations on its application. PAPE denotes the phenomenon of acute enhancements in contractile performance (e.g., enhanced strength, rate of force development or power) following a given conditioning activity (CA). PAPE can be utilized in a wide range of athletic disciplines, is manifested for both upper and lower body muscle exertions and may be exploited to boost performance during training and competition. Several physiological mechanisms have been proposed to underlie PAPE, including phosphorylation of contractile proteins and increased excitability of motor pathways in the nervous system. Other proposed mechanisms include transient alterations in muscle architecture, increased limb stiffness, and increases in skeletal muscle temperature. Repeated muscle contractions generate both acute fatigue and contractile potentiation, the net balance of which determines if physical performance subsequently is enhanced or attenuated. Decreases in performance are typically observed initially following CA, after which supercompensatory effects emerge typically at 4-9 min post CA. For conventional resistance exercise, CA protocols utilizing loading intensities ≥ 60% 1RM appear to induce the greatest magnitude of PAPE. Notably, a range of specific CA protocols can elicit PAPE, including conventional resistance training exercises, plyometric drills as well as blood flow restriction. In conclusion, when CA protocols are properly designed and executed, PAPE appears to enhance physical performance within both training and competition, and may be utilized during resistance training, jumping, and sprinting.

Given the challenges and concerns associated with the congested schedule dictated by the International Match Calendar (IMC), there is a need for a player-centric expert position statement with specific recommendations and guidance related to the key dimensions of the IMC in men's professional football. Following a review of scientific and occupational health literature and surveys of players and staff in professional football, 19 statements across 6 key dimensions of the IMC were formulated. The statements were then reviewed and refined through a three-round Delphi study, engaging experts to a consensus-based position statement. Expert consensus was reached on 12 statements across 5 key dimensions of the IMC: in-season rest and recovery, off-season break, mid-season break, travel, and young player workload. Although consensus was not reached on statements related to match workload, 69% of experts agreed on the need for a maximum limit of matches per player per season. The expert position statement provides recommendations and guidance on structural safeguards within the IMC that prioritize the long-term health and performance of players.

The effects of two short-haul air travel (SHAT) of different durations on sport-specific performance, sleep, and psychophysiological indices in highly trained football players were examined. Nineteen participants completed, in a randomized order, two simulated SHAT, 1 week apart, each lasting 4 h and 2 h, followed by a control condition (CON). Generic (10-m sprint, repeated sprint ability; RSA, countermovement jump; CMJ), sport-specific performance (Hoff Test, Loughborough Soccer Passing Test; LSPT), and psychophysiological responses (sleep, heart rate variability [HRV], salivary cortisol and immunoglobulin-A [sIgA], and perceptual recovery) were evaluated before (Baseline) and after each condition. Compared to Baseline, RSA and 10-m sprint declined by 3.5% and 6%, respectively, on the day after travel (D + 1) (p < 0.001 and p < 0.01). Likewise, CMJ and total distance covered during the Hoff test decreased by 5.5% at D + 1 (p < 0.001). LSPT performance decreased only after the 4 h flight (p < 0.05). Total sleep time was reduced the night before SHAT (p < 0.001) compared to Baseline. sIgA was reduced on the day of the travel (DT) and D + 1 after both SHAT, while HRV was decreased at DT only after the 4 h SHAT (p < 0.05). Mood states remained unaffected by travel, regardless of duration. We currently suggest that short-haul air travel, whether 4 or 2 h, induces psychophysiological perturbations and performance deterioration, likely due to the travel restrictive conditions and the inadequate sleep obtained the night before the flight. Since both flights were conducted early in the morning, more research is warranted to investigate the role of departure time on football performance.

This study assessed the safety of percutaneous muscle biopsy by analyzing over 2400 procedures performed between 2007 and 2025 in healthy individuals and patients with chronic diseases. We retrospectively reviewed biopsy-related adverse events among 1246 participants (471 healthy adults and 775 patients) to investigate whether health status or repeated sampling at the same site influenced complication rates. A total of 2435 biopsies were performed, primarily on the vastus lateralis muscle (97%). Overall, 80.6% of the procedures had no adverse events. The most common adverse events were erythema (6.6%), ecchymosis (4.1%), and pain (3.9%). Serious complications, including loss of consciousness (vasovagal syncope), were extremely rare (≤ 0.04%). Most adverse events occurred in isolation (74.9%) and did not preclude participation in subsequent research activities. Repeated biopsies modestly increased the risk of minor adverse events, particularly bleeding, erythema, and bruising. Notably, these were more frequently reported among healthy volunteers than among patients. In conclusion, percutaneous muscle biopsy is a safe and well-tolerated procedure, even when performed repeatedly or in individuals with chronic diseases. The minor adverse events were infrequent, transient, and clinically manageable. These findings support the continued use of this technique in both research and clinical settings.

Association between sleep and running-related injuries (RRI) risk remains still unclear. This prospective cohort study investigated whether sleep quality and quantity, along with training load and complementary recovery factors, were associated with the risk of RRI. Over a 26 week period, adult runners, with at least 1 year of running experience, weekly reported their RRI and completed the Hooper questionnaire assessing sleep (quality, quantity, latency), fatigue, muscle soreness, perceived stress, through a smartphone application. We also measured training load through participants' personal watches. We analyzed the association between RRI, Hooper variables, and training load using time-to-event models. We compared Hooper and training load through the 2 weeks preceding an RRI (RRI-1, RRI-2) and injury-free weeks using linear mixed models. A total of 339 runners (16.2% females, age: 43.4 ± 10.2, 92.9% competing regularly) from 24 countries were included. Lower sleep quality was significantly associated with an increased risk of RRI (HRR 1.36, 95% 1.04 to 1.78; p = 0.02). Compared to no-RRI weeks, muscle soreness was higher during RRI-2 (p = 0.02) and RRI-1 (p < 0.001), whereas fatigue was elevated during RRI-1 (p = 0.04). No further significant results were observed among the other factors. Poor sleep quality was associated with an increased risk of RRI and may represent an early warning sign. Elevated fatigue and muscle soreness may signal a heightened risk of injury in the weeks following this onset. While interpreted with caution, these findings highlight the importance for runners to improve sleep quality and regularly monitor recovery, to proactively reduce the likelihood of RRI.

The hamstrings are critical for athletic performance; however, no study has examined differences in hamstring muscle-tendon geometry (cross-sectional area/volume) and muscle typology (proportion of Type I/II fibers) between elite sprinters/jumpers and recreationally active individuals. This study aimed to compare hamstring geometry and typology between these groups and examine how these characteristics relate to sprint and strength performance. Elite sprint and jump athletes (n = 15, 3 female, 21.7 ± 2.2 y, 180.6 ± 9.9 cm, 72.2 ± 9.6 kg) and recreationally active individuals (n = 15, 4 female, 25.7 ± 3.0 y, 176.0 ± 9.5 cm, 76.3 ± 17.6 kg) completed sprint and eccentric knee flexor strength testing. Magnetic resonance imaging and spectroscopy were used to assess hamstring muscle-tendon geometry and typology, respectively. Compared to recreationally active individuals, elite athletes had larger hamstring muscles (all muscles, mean difference: 59.75-150.45 cm, p < 0.009), biceps femoris long head (BFlh) proximal aponeuroses (1.09 cm, p < 0.001), BF short head distal aponeuroses (1.24 cm, p = 0.002), semimembranosus proximal free tendons (0.75 cm, p = 0.024) and aponeuroses (2.29 cm, p < 0.001), semitendinosus distal free tendons (0.49 cm, p = 0.01) and BFlh proximal aponeurosis interface areas (10.43 cm, p < 0.001). Elite athletes also had 1.5 times greater estimated proportion of Type II fibers (p < 0.001). Medial hamstring geometry and muscle typology explained the greatest variance in maximal sprint speed (R = 0.65), while BFlh and semimembranosus muscle volumes with semitendinosus tendon volume explained the greatest variance in eccentric knee flexor strength (R = 0.59). Elite athletes had larger hamstring muscles, aponeuroses, and free tendons, and a greater estimated proportion of Type II fibers than recreationally active individuals. These structural and compositional differences likely contribute to their superior sprint and strength performance.

This study aimed to develop the first valid questionnaire to assess menstrual cycle (MC) and hormonal contraceptive (HC) knowledge in athletes and sports performance support staff. Questions were developed following a literature review and four knowledge domains were identified: (1) Normal MC Function, (2) MC Dysfunction, (3) Oral Contraceptive Pills, and (4) Other HCs. Experts (n = 6) reviewed the initial questionnaire, followed by pre-testing with athletes and support staff (n = 19). Validity (item analysis, construct validity) and reliability (test-retest, internal consistency) were assessed following questionnaire administration to athletes and staff without MC education ("Low Knowledge" [LK] group; n = 156) and "High Knowledge" [HK] participants (n = 30) with MC education. Most (n = 122) LK participants completed the questionnaire twice to assess test-retest reliability. Expert review showed good agreement (> 80%) on item clarity and relevancy and pre-testing indicated good content and face validity. The HK group scored significantly higher than LK participants across the questionnaire (43 ± 5 vs. 28 ± 10; p < 0.001; d = 1.48 [1.05, 1.90]) and all knowledge domains (p < 0.05). High item discrimination parameters were found for all domains, indicating effective discrimination between respondents with different knowledge levels. Test-retest reliability was excellent (intra-class correlation coefficient estimates from 0.93 [0.90, 0.95] to 0.98 [0.96, 0.99]), with all domains showing good-to-excellent reliability. Internal reliability (Cronbach's alpha) was considered acceptable (0.93 [0.92, 0.95]; α ≥ 0.7). This questionnaire delivers a valid and reliable tool to assess MC and HC knowledge amongst athletes and support staff and is recommended to guide and evaluate educational interventions to improve menstrual health literacy within sport.