Gender differences in strength and muscle fiber characteristics

The influence of sex and strength capacity on normalized low-back exposure during lifting: Insights from a joint power analysis

OBJECTIVE

Investigate the influence of sex, strength capacity, and relative load mass on low-back exposure and lower extremity joint power generation in backboard lifting.

BACKGROUND

Sex and strength have been shown to influence lifting strategy, but without load mass being scaled to strength it is unknown which factor influences low-back exposures, and whether there are interactions with load mass.

METHODS

Motion capture and force plate data from 28 participants were collected during backboard lifting at load masses scaled to strength capacity. Differences in normalized peak low-back moment, peak knee-to-hip power magnitude ratio and timing were tested as a function of sex, strength, and load mass.

RESULTS

Stronger participants had lower normalized peak low-back moments (average 32% change from low-capacity across all load masses), with no significant sex effect (p = 0.582). As load mass increased, normalized peak low-back moment, peak knee-to-hip power magnitude and synchronicity decreased.

CONCLUSION

Training to both increase strength capacity and hip-joint power generation may be a strategy to reduce low-back exposure in backboard lifting.

Gender and Age Differences in Performance of Over 70,000 Chinese Finishers in the Half- and Full-Marathon Events

(1) Background: The aim of the present study was to examine the characteristics of over 70,000 long-distance finishers over the last four years in Chinese half- and full-marathon events; (2) Methods: The available data of all finishers (n = 73,485; women, n = 17,134; men, n = 56,351) who performed half- and full-marathon events in Hangzhou from 2016 to 2019 were further analyzed for the characteristics of gender, age and average running speed; (3) Results: The total men-to-women ratio was the lowest in the half-marathon event (1.86) and the highest in the full-marathon event (17.42). Faster running performance in males than in females and faster average running speed in short-distance runners were shown. Gender and race distance were observed to have the most significant effects on average running speed (p < 0.01). For both male and female finishers, the slowest running speed was shown in older age groups (p < 0.01) during the full marathon. Our results indicated that the gender difference in performance was attenuated in the longer race distances and older age groups; (4) Conclusions: Understanding the participation and performances across different running distances would provide insights into physiological and biomechanical characteristics for training protocols and sports gear development in different groups.

Characterization of Musculoskeletal Injuries in Gymnastics Participants From 2013 to 2020

BACKGROUND

Many studies have analyzed gymnastics-related injuries in collegiate and elite athletes, but there is minimal literature analyzing the epidemiological characteristics of injuries in the greater gymnastics community.

HYPOTHESIS

A higher incidence of injuries in younger gymnasts between the ages of 6 and 15 years compared with those 16 years and older and a difference in the distribution of injuries between male and female gymnasts.

STUDY DESIGN

Retrospective cross-sectional study.

LEVEL OF EVIDENCE

Level 3.

METHODS

The National Electronic Injury Surveillance System (NEISS) was queried for all gymnastics-related musculoskeletal injuries presenting to the emergency department (ED) between 2013 and 2020. Incidence was calculated as per 100,000 person-years using the weighted estimates provided by NEISS and national participation data. Chi-square and column proportion z-testing was used to analyze where appropriate.

RESULTS

The incidence of gymnastics-related musculoskeletal injuries was 480.7 per 100,000 person-years. Most ED visits were children between the ages of 6 and 15 years (84.0%). Younger gymnasts (ages 6 to 10) were most likely to experience a lower arm fracture, while those over the age of 10 years were most likely to experience an ankle sprain (P < 0.01). Men and boys presented with a much greater proportion of shoulder injuries (8.0% vs 3.9%), while women and girls presented with a greater proportion of elbow injuries (9.9 % vs 5.9%) and wrist (10.5% vs 8.3%) injuries (P < 0.01).

CONCLUSION

As hypothesized, most gymnastics-related injuries between 2013 and 2020 were athletes between 6 and 15 years old. Many of these athletes are attempting new, more difficult, skills and are at increased risk of more acute injury when attempting skills they may be unfamiliar with.

CLINICAL RELEVANCE

With increased pressure to specialize at an early age to maintain competitiveness and learn new, higher-level skills compared with their peers, younger athletes are most susceptible to acute injury. New injury prevention strategies could be implemented to help this high-risk population compete and train safely.

Considerations for Sex-Cognizant Research in Exercise Biology and Medicine

As the fields of kinesiology, exercise science, and human movement developed, the majority of the research focused on male physiology and extrapolated findings to females. In the medical sphere, basing practice on data developed in only males resulted in the removal of drugs from the market in the late 1990s due to severe side effects (some life-threatening) in females that were not observed in males. In response to substantial evidence demonstrating exercise-induced health benefits, exercise is often promoted as a key modality in disease prevention, management, and rehabilitation. However, much like the early days of drug development, a historical literature knowledge base of predominantly male studies may leave the exercise field vulnerable to overlooking potentially key biological differences in males and females that may be important to consider in prescribing exercise (e.g., how exercise responses may differ between sexes and whether there are optimal approaches to consider for females that differ from conventional approaches that are based on male physiology). Thus, this review will discuss anatomical, physiological, and skeletal muscle molecular differences that may contribute to sex differences in exercise responses, as well as clinical considerations based on this knowledge in athletic and general populations over the continuum of age. Finally, this review summarizes the current gaps in knowledge, highlights the areas ripe for future research, and considerations for sex-cognizant research in exercise fields.

AR cooperates with SMAD4 to maintain skeletal muscle homeostasis

Androgens and androgen-related molecules exert a plethora of functions across different tissues, mainly through binding to the transcription factor androgen receptor (AR). Despite widespread therapeutic use and misuse of androgens as potent anabolic agents, the molecular mechanisms of this effect on skeletal muscle are currently unknown. Muscle mass in adulthood is mainly regulated by the bone morphogenetic protein (BMP) axis of the transforming growth factor (TGF)-β pathway via recruitment of mothers against decapentaplegic homolog 4 (SMAD4) protein. Here we show that, upon activation, AR forms a transcriptional complex with SMAD4 to orchestrate a muscle hypertrophy programme by modulating SMAD4 chromatin binding dynamics and enhancing its transactivation activity. We challenged this mechanism of action using spinal and bulbar muscular atrophy (SBMA) as a model of study. This adult-onset neuromuscular disease is caused by a polyglutamine expansion (polyQ) in AR and is characterized by progressive muscle weakness and atrophy secondary to a combination of lower motor neuron degeneration and primary muscle atrophy. Here we found that the presence of an elongated polyQ tract impairs AR cooperativity with SMAD4, leading to an inability to mount an effective anti-atrophy gene expression programme in skeletal muscle in response to denervation. Furthermore, adeno-associated virus, serotype 9 (AAV9)-mediated muscle-restricted delivery of BMP7 is able to rescue the muscle atrophy in SBMA mice, supporting the development of treatments able to fine-tune AR-SMAD4 transcriptional cooperativity as a promising target for SBMA and other conditions associated with muscle loss.

Sex Differences May Exist for Performance Fatigue but Not Recovery After Single-Joint Upper-Body and Lower-Body Resistance Exercise

ABSTRACT

Lewis, MH, Siedler, MR, Lamadrid, P, Ford, S, Smith, T, SanFilippo, G, Waddell, B, Trexler, ET, Buckner, S, and Campbell, BI. Sex differences may exist for performance fatigue but not recovery after single-joint upper-body and lower-body resistance exercise. J Strength Cond Res 36(6): 1498-1505, 2022-This study evaluated sex differences in performance recovery and fatigue during dynamic exercise. Twenty-eight resistance-trained males (n = 16) and females (n = 12) completed a repeated-measures, randomized, parallel-groups design. The protocol consisted of a baseline assessment, a recovery period (4, 24, or 48 hours), and a postrecovery assessment. The assessments were identical consisting of 4 sets of 10 repetition maximum (10RM) bicep curls and 4 sets of 10RM leg extensions to failure. Recovery was quantified as the number of total repetitions completed in the postrecovery bout. Fatigue was quantified as the number of repetitions completed set to set within the session. For analysis, we set the level of significance at p ≤ 0.05. No sex differences in performance recovery were observed across any of the investigated time periods for either exercise modality. Regarding fatigue, significant effects were observed for set (p < 0.001) and sex (p = 0.031) for bicep curls. Repetitions dropped in later sets, and females generally completed a greater number of repetitions than males (8.8 ± 0.5 vs. 7.2 ± 0.5). For leg extension, a significant sex × set interaction was observed (p = 0.003), but post hoc tests revealed these sex differences as marginal. Our results suggest that in dynamic bicep curls and leg extensions, other factors unrelated to sex may be more impactful on performance recovery. To optimize an athlete's desired adaptations, it may be more important to consider other variables unrelated to sex such as volume, perceived exertion, and training history when formulating training prescriptions for single-joint exercises.

Neuromuscular recruitment strategies of the vastus lateralis according to sex

AIM

Despite males typically exhibiting greater muscle strength and fatigability than females, it remains unclear if there are sex-based differences in neuromuscular recruitment strategies e.g. recruitment and modulation of motor unit firing rate (MU FR) at normalized forces and during progressive increases in force.

METHODS

The study includes 29 healthy male and 31 healthy female participants (18-35 years). Intramuscular electromyography (iEMG) was used to record individual motor unit potentials (MUPs) and near-fibre MUPs from the vastus lateralis (VL) during 10% and 25% maximum isometric voluntary contractions (MVC), and spike-triggered averaging was used to obtain motor unit number estimates (MUNE) of the VL.

RESULTS

Males exhibited greater muscle strength (P < .001) and size (P < .001) than females, with no difference in force steadiness at 10% or 25% MVC. Females had 8.4% and 6.5% higher FR at 10% and 25% MVC, respectively (both P < .03), while the MUP area was 33% smaller in females at 10% MVC (P < .02) and 26% smaller at 25% MVC (P = .062). However, both sexes showed similar increases in MU size and FR when moving from low- to mid-level contractions. There were no sex differences in any near-fibre MUP parameters or in MUNE.

CONCLUSION

In the vastus lateralis, females produce muscle force via different neuromuscular recruitment strategies to males which is characterized by smaller MUs discharging at higher rates. However, similar strategies are employed to increase force production from low- to mid-level contractions. These findings of similar proportional increases between sexes support the use of mixed sex cohorts in studies of this nature.

Differences in Fitness between Firefighter Trainee Academy Classes and Normative Percentile Rankings

Fire academy training classes may have trainees with a range of different fitness capabilities. Documentation of trainee fitness could indicate the need for flexibility in physical training emphases. Therefore, data from six academy classes (males = 274; females = 31) were analyzed, including: Illinois agility test (IAT), push-ups, pull-ups, leg tucks, multistage fitness test, backwards overhead 4.54 kg medicine ball throw (BOMBT), 10-repetition maximum deadlift, and 18 kg kettlebell farmers carry. A one-way ANOVA, with the Bonferroni post hoc test, calculated between-class fitness differences. Normative fitness test data were produced via percentile ranks. Classes 5 and 6 had the most females (n = 15). Class 1 completed the IAT faster than all classes (p ≤ 0.009). Classes 1 and 4 had a further BOMBT distance than Classes 5 and 6, and Class 3 outperformed Class 6 (p ≤ 0.044). Class 4 completed more leg tucks than Class 5 (p = 0.047). Class 1 had a greater deadlift than Classes 3, 4, and 6, and Class 2 outperformed Classes 3–6 (p ≤ 0.036). Class 3 was slower in the farmers carry compared to all classes (p ≤ 0.002). Percentile rankings showed that most females (48–100%) were in the 0–29% rank. Staff should implement individualized programs where appropriate for trainees as cohort fitness differences exist. Female trainees may need targeted maximal strength and power development.

Does caffeine ingestion affect the lower-body post-activation performance enhancement in female volleyball players?

Background

Post-activation performance enhancement (PAPE) is a physiological phenomenon that acutely improves voluntary muscular performance following a conditioning activity. A large and growing body of literature has investigated different strategies to induce a PAPE stimulus; however, little attention has been given to whether acute caffeine ingestion could augment the effect of PAPE on subsequent performance. This study evaluated the acute effects of caffeine ingestion and back squat conditioning activity on subsequent countermovement jump (CMJ) performance in female semi-professional volleyball players.

Methods

Fourteen resistance-trained female volleyball players (26 ± 3 years) performed 3 different testing conditions in randomized order: where each ingested 6 mg/kg of caffeine (CAF) or placebo (PLAC) and performed a single set of back squats at 80%1RM until mean movement velocity dropped by 10% as the conditioning activity or a control (CTRL) condition where participants did not ingest any supplement and did not perform the conditioning activity. CMJ height was examined at baseline and in 2 min intervals until 10 min postconditioning activity. Furthermore, due to the wide inter-individual variation in optimal recovery time of PAPE response, the baseline and best post-conditioning activity performance were also analyzed.

Results

The Friedman test revealed a significant difference in jump height within CTRL (p = 0.002) and CAF (p = 0.001) conditions, but no significant difference was found within the PAP condition. The post hoc showed a significant decrease in jump height in 8^th min in CTRL condition (p = 0.022, effect size [ES] = −0.31), a significant increase in jump height in 2^nd min in CAF condition (p = 0.013, ES = 0.3), without differences in PLAC condition in comparison to baseline values. Moreover, a significant jump height increases from baseline to best performance post conditioning activity value for CAF (p = 0.001, ES = 0.39) and PLAC (p = 0.001, ES = 0.3) condition, but no significant difference was found for the CTRL condition.

Conclusions

The single set of heavy-loaded back squats with controlled velocity used as a conditioning activity in the current study enhanced subsequent CMJ performance in female volleyball players with no additional effect of caffeine.

Do baseline physical fitness measures predict law enforcement academy graduation?

BACKGROUND: Law enforcement officers experience high stress levels and perform various physical tasks. Thus, law enforcement academies emphasize physical fitness training and assessment. OBJECTIVE: To examine fitness test-performances and determine which entry-level fitness components best predict likelihood of successful law enforcement academy graduation. METHODS: Recruits (151 males, 42 females) completed initial academy fitness testing: one-repetition maximum bench press, push-ups, sit-ups, pull-ups, sit-and-reach, 1.5-mile run, and work performance test. Chi-square and t-tests were used to examine gender differences. Correlation coefficients assessed relationships, while logistical regression determined the best fitness components for predicting graduation (p < 0.05). RESULTS: Males had greater fitness performances except pull-ups, sit-ups and sit and reach (p < 0.05). Distributions of below average fitness performances were similar between genders with majority of recruits performing below average on all tests. Gender, age, push-ups, and pull-ups explained 18% of the variance in graduation rates (p < 0.05). Males were 4.68 (p < 0.05) times more likely to graduate, but other predictors were not significant. CONCLUSIONS: No single fitness test predicted the likelihood of graduation and majority of performances were below average, suggesting the importance for proficiency across multiple fitness components. Considering lower fitness performances and graduation rates, females may further benefit from training programs prior to academy entrance.

Factors Associated with Handgrip Strength Among Older Adults in Malaysia

Purpose

Handgrip strength (HGS) is indicative of overall physical health among older adults. A decrease in HGS may be associated with an increased risk of disease. The aim of this study is to determine the factors associated with HGS among older adults in Malaysia.

Patients and Methods

One thousand two hundred four (1204) participants from urban and rural areas in Selangor state, Malaysia, were recruited. Sociodemographic and health-related conditions were gathered through a comprehensive face-to-face interview, followed by HGS assessments by a handgrip dynamometer. Subsequently, multiple linear regression was used to test the main association with the HGS.

Results

A total of 691 participants (57.4%) were male, and 513 (42.6%) were female. Males had a mean HGS of 30.0 (SD 7.53) kg, and females had a mean HGS of 19.4 (SD 5.28) kg. Males' handgrip strength was significantly reduced with increasing age, physically inactive, and diabetes (all at the level p<0.001) after adjusting for social-demographic characteristics and health-related variables. Meanwhile, for females, the HGS was significantly decreased with age (p<0.001), physically inactive (p<0.001) and hypertension (p=0.03). However, female HGS was positively related to BMI (p<0.001).

Conclusion

The study contributed to a better understanding of factors associated with HGS, and thus, the HGS is recommended as a section in the health evaluation among high-risk older adults as the strategy of disease control and prevention.

Gastrointestinal endoscopy and work-related injuries: an international survey

Background and study aims  Recently, the awareness of work-related musculoskeletal injuries (MSIs) among gastrointestinal endoscopists has increased because of their effect on the private and work life of clinicians as well as on the health care system. The high injury incidence (reported to range from 37 % to 89 %) has been correlated with the intensive muscular demand required during a procedure. Patients and methods  An online survey with 32 questions was conducted globally. Clinically active endoscopists (doctors and nurses) participated anonymously and voluntarily. The questionnaire included questions about endoscopist anthropometrics, experience of MSI, treatment, and preventive measures such as ergonomic training. Descriptive statistics were used to analyse the data. Results  Of 204 clinicians (78 % males; 81 % > 35 years of age), 107 (53 %) stated to have experienced a work-related MSI. The most frequent locations were in the neck (n = 49), shoulder and thumb (n = 39, both). Female clinicians resulted to be significantly more prone to develop MSI. In addition, endoscopists who performed more than 15 hours of endoscopy or more than 15 procedures per week reported a significantly higher rate of MSI. Conclusions  The high frequency of MSIs among gastrointestinal endoscopists highlights the importance of implementing ergonomic training. Including simple precautions before and during endoscopy may reduce the risk of developing an injury.

Neuromuscular recovery from severe- and extreme-intensity exercise in men and women

Maximal voluntary contraction force (MVC), potentiated twitch force (Q_pot), and voluntary activation (%VA) recover to baseline within 90 s following extreme-intensity exercise. However, methodological limitations mask important recovery kinetics. We hypothesized reductions in MVC, Q_pot, and %VA at task failure following extreme-intensity exercise would be less than following severe-intensity exercise, and Q_pot and MVC following extreme-intensity exercise would show significant recovery within 120 s but remain depressed following severe-intensity exercise. Twelve subjects (6 men) completed 2 severe-intensity (40, 50% MVC) and 2 extreme-intensity (70, 80% MVC) isometric knee-extension exercise bouts to task failure (T_lim). Neuromuscular function was measured at baseline, T_lim, and through 150 s of recovery. Each intensity significantly reduced MVC and Q_pot compared with baseline. MVC was greater at T_lim (p < 0.01) and at 150 s of recovery (p = 0.004) following exercise at 80% MVC compared with severe-intensity exercise. Partial recovery of MVC and Q_pot were detected within 150 s following T_lim for each exercise intensity; Q_pot recovered to baseline values within 150 s of recovery following exercise at 80% MVC. No differences in %VA were detected pre- to post-exercise or across recovery for any intensity. Although further analysis showed sex-specific differences in MVC and Q_pot, future studies should closely examine sex-dependent responses to extreme-intensity exercise. It is clear, however, that these data reinforce that mechanisms limiting exercise tolerance during extreme-intensity exercise recover quickly. Novelty: Severe- and extreme-intensity exercise cause independent responses in fatigue accumulation and the subsequent recovery time courses. Recovery of MVC and Q_pot occurs much faster following extreme-intensity exercise in both men and women.

Velocity-based resistance training: do women need greater velocity loss to maximize adaptations?

Purpose

Men and women typically display different neuromuscular characteristics, force–velocity relationships, and differing strength deficit (upper vs. lower body). Thus, it is not clear how previous recommendations for training with velocity-loss resistance training based on data in men will apply to women. This study examined the inter-sex differences in neuromuscular adaptations using 20% and 40% velocity-loss protocols in back squat and bench press exercises.

Methods

The present study employed an 8-week intervention (2 × week) comparing 20% vs. 40% velocity-loss resistance training in the back squat and bench press exercises in young men and women (~ 26 years). Maximum strength (1-RM) and submaximal-load mean propulsive velocity (MPV) for low- and high-velocity lifts in squat and bench press, countermovement jump and vastus lateralis cross-sectional area were measured at pre-, mid-, and post-training. Surface EMG of quadriceps measured muscle activity during performance tests.

Results

All groups increased 1-RM strength in squat and bench press exercises, as well as MPV using submaximal loads and countermovement jump height (P < 0.05). No statistically significant between-group differences were observed, but higher magnitudes following 40% velocity loss in 1-RM (g = 0.60) and in low- (g = 1.42) and high-velocity (g = 0.98) lifts occurred in women. Training-induced improvements were accompanied by increases in surface EMG amplitude and vastus lateralis cross-sectional area.

Conclusion

Similar increases in strength and power performance were observed in men and women over 8 weeks of velocity-based resistance training. However, some results suggest that strength and power gains favor using 40% rather than 20% velocity loss in women.

Validity of using perceived exertion to assess muscle fatigue during resistance exercises

BACKGROUND

The rating of perceived exertion (RPE) is correlated with physiological variables. The purpose of this study was to assess the validity of using the Borg CR-10 scale and velocity to predict muscle fatigue assessed by surface electromyography during single joint resistance exercises.

METHODS

Fifteen healthy males underwent different fatigue levels of unilateral elbow flexion (EF) and knee extension (KE), consisting of low, medium, and high volumes at 65% of their one-repetition maximum. The RPEs, spectral fatigue index (SFI), and mean velocity of the experimental exercises were assessed throughout the trials.

RESULTS

Significant differences in overall RPE (p < 0.001) and average SFI (p < 0.001) were observed between the conditions in both exercises. Significant changes in RPE and SFI (p < 0.001) were observed throughout the EF, whereas a SFI increase (p < 0.001) was only observed at the end point of KE. Multiple regression analyses revealed two significant models (p < 0.001) for the prediction of muscle fatigue during EF (R² = 0.552) and KE (R² = 0.377).

CONCLUSIONS

Muscle fatigue resulted in similar increases in perceptual responses, demonstrating that RPE is useful for assessing fatigue when resistance exercise is performed. However, velocity changes may not reflect muscle fatigue correctly when exercise is no longer performed in an explosive manner. We recommend combining RPE responses with velocity changes to comprehensively assess muscle fatigue during clinical and sports situations.

Is physical activity a future therapy for patients with Marfan syndrome?

Introduction

The international recommendations tend to avoid physical activity (PA) for patients with Marfan syndrome (MFS). However, exceptions have recently been made in the most recent recommendations for these patients, suggesting benefits from doing PA at low intensity only. Furthermore, there is no evidence that moderate aerobic or weight training can worsen the disease symptoms and increase mortality of MFS patients. The present review sums up the work carried out in the field of PA and MFS. The review aims to (1) identify the different types of exercise testing and training protocols and (2) discuss the feasibility and potentially beneficial nature of PA as an innovative way to manage MFS patients.

Methods

The scientific literature was reviewed using the following words: Marfan syndrome, training, physical activity, evaluation, weight training, arterial disease, aneurysms, lung damage, aortic dissection, rupture. A total of 345 studies were prospected and 43 studies were included.

Conclusions

A limited number of studies were done in humans, however one demonstrated the feasibility of the management of MFS patients with PA. There were potential beneficial effects of PA on arterial structures, but this review also showed deleterious effects when PA was conducted at high intensities, corresponding to 75–85% of the maximal oxygen uptake. However, these effects have only been reported in animal studies.

Sex Differences in Endurance Running

In recent years, there has been a significant expansion in female participation in endurance (road and trail) running. The often reported sex differences in maximal oxygen uptake (VO_2max) are not the only differences between sexes during prolonged running. The aim of this narrative review was thus to discuss sex differences in running biomechanics, economy (both in fatigue and non-fatigue conditions), substrate utilization, muscle tissue characteristics (including ultrastructural muscle damage), neuromuscular fatigue, thermoregulation and pacing strategies. Although males and females do not differ in terms of running economy or endurance (i.e. percentage VO_2max sustained), sex-specificities exist in running biomechanics (e.g. females have greater non-sagittal hip and knee joint motion compared to males) that can be partly explained by anatomical (e.g. wider pelvis, larger femur-tibia angle, shorter lower limb length relative to total height in females) differences. Compared to males, females also show greater proportional area of type I fibres, are more able to use fatty acids and preserve carbohydrates during prolonged exercise, demonstrate a more even pacing strategy and less fatigue following endurance running exercise. These differences confer an advantage to females in ultra-endurance performance, but other factors (e.g. lower O₂ carrying capacity, greater body fat percentage) counterbalance these potential advantages, making females outperforming males a rare exception. The present literature review also highlights the lack of sex comparison in studies investigating running biomechanics in fatigue conditions and during the recovery process.

Sex differences in endurance exercise capacity and skeletal muscle lipid metabolism in mice

Previous studies suggest that sex differences in lipid metabolism exist with females demonstrating a higher utilization of lipids during exercise, which is mediated partly by increased utilization of muscle triglycerides. However, whether these changes in lipid metabolism contribute directly to endurance exercise performance is unclear. Therefore, the objective of this study was to investigate the contribution of exercise substrate metabolism to sex differences in endurance exercise capacity (EEC) in mice. Male and female C57BL/6-NCrl mice were subjected to an EEC test until exhaustion on a motorized treadmill. The treadmill was set at a 10% incline, and the speed gradually increased from 10.2 m/min to 22.2 m/min at fixed intervals for up to 2.5 h. Tissues and blood were harvested in mice immediately following the EEC. A cohort of sedentary, non-exercised male and female mice were used as controls. Females outperformed males by ~25% on the EEC. Serum levels of both fatty acids and ketone bodies were ~50% higher in females at the end of the EEC. In sedentary female mice, skeletal muscle triglyceride content was significantly greater compared to sedentary males. Gene expression analysis demonstrated that genes involved in skeletal muscle fatty acid oxidation were significantly higher in females with no changes in genes associated with glucose uptake or ketone body oxidation. The findings suggest that female mice have a higher endurance exercise capacity and a greater ability to mobilize and utilize fatty acids for energy.

Expanding the Gap: An Updated Look Into Sex Differences in Running Performance

Males consistently outperform females in athletic endeavors, including running events of standard Olympic distances (100 m to Marathon). The magnitude of this percentage sex difference, i.e., the sex gap, has evolved over time. Two clear trends in sex gap evolution are evident; a narrowing of the gap during the 20th century, followed by a period of stability thereafter. However, an updated perspective on the average sex gap from top 20 athlete performances over the past two decades reveals nuanced trends over time, indicating the sex gap is not fixed. Additionally, the sex gap varies with performance level; the difference in absolute running performance between males and females is lowest for world record/world lead performances and increases in lower-ranked elite athletes. This observation of an increased sex gap with world rank is evident in events 400 m and longer and indicates a lower depth in female competitive standards. Explanations for the sex difference in absolute performance and competition depth include physical (physiological, anatomical, neuromuscular, biomechanical), sociocultural, psychological, and sport-specific factors. It is apparent that females are the disadvantaged sex in sport; therefore, measures should be taken to reduce this discrepancy and enable both sexes to reach their biological performance potential. There is scope to narrow the sex performance gap by addressing inequalities between the sexes in opportunities, provisions, incentives, attitudes/perceptions, research, and media representation.

Sex differences in semitendinosus muscle fiber-type composition

Sex differences in muscle fiber-type composition have been documented in several muscle groups while the hamstring muscle fiber-type composition has been poorly characterized. This study aimed to compare the semitendinosus muscle composition between men and women. Biopsy samples were obtained from the semitendinosus muscle of twelve men and twelve women during an anterior cruciate ligament reconstruction. SDH and ATPase activities as well as the size and the proportion of muscle fibers expressing myosin heavy chain (MyHC) isoforms were used to compare muscle composition between men and women. The proportion of SDH-positive muscle fibers was significantly lower (37.4 ± 11.2% vs. 49.3 ± 10.6%, p < 0.05), and the percentage of fast muscle fibers (i.e., based on ATPase activity) was significantly higher (65.8 ± 10.1% vs. 54.8 ± 8.3%, p < 0.05) in men versus women. Likewise, men muscles exhibited a lower percentage of the area that was occupied by MyHC-I labeling (35.6 ± 10.1% vs. 48.7 ± 8.9%; p < 0.05) and a higher percentage of the area that was occupied by MyHC-IIA (38.3 ± 6.7% vs. 32.5 ± 6.5%; p < 0.05) and MyHC-IIX labeling (26.1 ± 9.6% vs. 18.8 ± 8.5%; p = 0.06) as compared with women muscles. The cross-sectional area of MyHC-I, MyHC-IIA, and MyHC-IIX muscle fibers was 31%, 43%, and 50% larger in men as compared with women, respectively. We identified sex differences in semitendinosus muscle composition as illustrated by a faster phenotype and larger muscle size in men as compared with women. This sexual dimorphism might have functional consequences.

Level of exoskeleton support influences shoulder elevation, external rotation and forearm pronation during simulated work tasks in females

Despite growing literature, limited research details the influence of passive upper limb exoskeletons on upper limb kinematics. Two bolting tasks and a tracing task were completed at two heights (overhead and between waist and overhead height) for four exoskeleton conditions (no exoskeleton, and 3 levels of exoskeleton assistance) by female participants. Motion capture data, ratings of perceived exertion and discomfort, and task duration were recorded. Exoskeleton condition increased minimum shoulder elevation by 35-36% (Δ10.5-10.7°) at 1.81 kg and 2.72 kg of support, mean shoulder external rotation by 316% (Δ24.6°) at 0.91 kg of support and mean forearm pronation by 30.9% (Δ14.6°) at 0.91 kg of support. Exoskeleton condition reduced ratings of perceived exertion and discomfort, but not significantly. Task duration was unaffected. Exoskeleton use at any of three different settings modestly affected some joint kinematics for the tasks examined, which may merit consideration when deciding on occupational exoskeleton implementation.

Are Young Swimmers Short and Middle Distances Energy Cost Sex-Specific?

This study assessed the energy cost in swimming (C) during short and middle distances to analyze the sex-specific responses of C during supramaximal velocity and whether body composition account to the expected differences. Twenty-six swimmers (13 men and 13 women: 16.7 ± 1.9 vs. 15.5 ± 2.8 years old and 70.8 ± 10.6 vs. 55.9 ± 7.0 kg of weight) performed maximal front crawl swimming trials in 50, 100, and 200 m. The oxygen uptake (V˙O₂) was analyzed along with the tests (and post-exercise) through a portable gas analyser connected to a respiratory snorkel. Blood samples were collected before and after exercise (at the 1st, 3rd, 5th, and 7th min) to determine blood lactate concentration [La^–]. The lean mass of the trunk (LM_Trunk), upper limb (LM_UL), and lower limb (LM_LL) was assessed using dual X-ray energy absorptiometry. Anaerobic energy demand was calculated from the phosphagen and glycolytic components, with the first corresponding to the fast component of the V˙O₂ bi-exponential recovery phase and the second from the 2.72 ml × kg^–1 equivalent for each 1.0 mmol × L^–1 [La^–] variation above the baseline value. The aerobic demand was obtained from the integral value of the V˙O₂ vs. swimming time curve. The C was estimated by the rate between total energy releasing (in Joules) and swimming velocity. The sex effect on C for each swimming trial was verified by the two-way ANOVA (Bonferroni post hoc test) and the relationships between LM_Trunk, LM_UL, and LM_LL to C were tested by Pearson coefficient. The C was higher for men than women in 50 (1.8 ± 0.3 vs. 1.3 ± 0.3 kJ × m^–1), 100 (1.4 ± 0.1 vs. 1.0 ± 0.2 kJ × m^–1), and 200 m (1.0 ± 0.2 vs. 0.8 ± 0.1 kJ × m^–1) with p < 0.01 for all comparisons. In addition, C differed between distances for each sex (p < 0.01). The regional LM_Trunk (26.5 ± 3.6 vs. 20.1 ± 2.6 kg), LM_UL (6.8 ± 1.0 vs. 4.3 ± 0.8 kg), and LM_LL (20.4 ± 2.6 vs. 13.6 ± 2.5 kg) for men vs. women were significantly correlated to C in 50 (R²_adj = 0.73), 100 (R²_adj = 0.61), and 200 m (R²_adj = 0.60, p < 0.01). Therefore, the increase in C with distance is higher for men than women and is determined by the lean mass in trunk and upper and lower limbs independent of the differences in body composition between sexes.

Differences in Muscle Fatigability of Vastus Medialis between Sexes Using Surface Electromyographic Power Spectral Analysis in Healthy Adults

Objectives:

With a relatively high percentage of type I fibers in the vastus medialis (VM), its fatigability may be more sensitive to the effects of muscle activity in the quadriceps. However, sex-related differences in the muscle fatigability of the VM remain unknown. The purpose of the present study was to assess the differences in fatigability of the VM between healthy adult men and women.

Methods:

Surface electromyographic (EMG) activities of VM oblique (VMO) and VM long (VML) were recorded during sustained isometric contraction on a leg press machine. The results of EMG power spectral analysis were compared between healthy adult men and women. The decline in the median frequency (MF), defined as MF slope, was calculated using spectrum analysis after fast Fourier transform of the raw EMG signals of VMO and VML.

Results:

The endurance time and the MF slopes of the VMO and VML were significantly longer and lower, respectively, in women than in men. The present results demonstrated that both VMO and VML are more fatigue-resistant in women than in men.

Conclusions:

Understanding the sex differences in fatigability could help to design more effective exercise regimens for VMO and VML in healthy individuals. A similar approach should be considered when prescribing practical exercise regimens for patients with muscle atrophy.

Distribution of motor unit properties across human muscles

The purpose of our review was to compare the distribution of motor unit properties across human muscles of different sizes and recruitment ranges. Although motor units can be distinguished based on several different attributes, we focused on four key parameters that have a significant influence on the force produced by muscle during voluntary contractions: the number of motor units, average innervation number, the distributions of contractile characteristics, and discharge rates within motor unit pools. Despite relatively few publications on this topic, current data indicate that the most influential factor in the distribution of these motor unit properties between muscles is innervation number. Nonetheless, despite a fivefold difference in innervation number between a hand muscle (first dorsal interosseus) and a lower leg muscle (tibialis anterior), the general organization of their motor unit pools, and the range of discharge rates appear to be relatively similar. These observations provide foundational knowledge for studies on the control of movement and the changes that occur with aging and neurological disorders.

The Rise of the Female Warfighter: Physiology, Performance, and Future Directions

ABSTRACT

Since 1948, the United States military has been open to both men and women as permanent party service members. However, in the majority of the time since, there have been a subset of military occupational specialties (MOS), or job descriptions, open only to men. In particular, jobs requiring more intense physical and/or environmental strain were considered to be beyond the physiological capabilities of women. In the present analysis, we review the literature regarding neuromuscular, physical performance, and environmental physiology in women, to highlight that women have no inherent limitation in their capacity to participate in relevant roles and jobs within the military, within accepted guidelines to promote risk mitigation across sexes. First, we discuss performance and injury risk: both neuromuscular function and physical capabilities. Second, physiological responses to environmental stress. Third, we discuss risk as it relates to reproductive health and nutritional considerations. We conclude with a summary of current physiological, performance and injury risk data in men and women that support our overarching purpose, as well as suggestions for future directions.

Upper- vs. Lower-Body Exercise Performance in Female and Male Cross-Country Skiers

Purpose: To investigate the interaction between exercise modality (i.e., upper- and lower-body exercise) and sex in physiological responses and power output (PO) across the entire intensity spectrum (i.e., from low to maximal intensity).

Methods: Ten male and 10 female cross-country (XC) skiers performed a stepwise incremental test to exhaustion consisting of 5 min stages with increasing workload employing upper-body poling (UP) and running (RUN) on two separate days. Mixed measures ANOVA were performed to investigate the interactions between exercise modalities (i.e., UP and RUN) and sex in physiological responses and PO across the entire exercise intensity spectrum.

Results: The difference between UP and RUN (ΔUP−RUN), was not different in the female compared with the male XC skiers for peak oxygen uptake (18 ± 6 vs. 18 ± 6 mL·kg−1·min−1, p = 0.843) and peak PO (84 ± 18 vs. 91 ± 22 W, p = 0.207). At most given blood lactate and rating of perceived exertion values, ΔUP−RUN was larger in the male compared with the female skiers for oxygen uptake and PO, but these differences disappeared when the responses were expressed as % of the modality-specific peak.

Conclusion: Modality-differences (i.e., ΔUP−RUN) in peak physiological responses and PO did not differ between the female and male XC skiers. This indicates that increased focus on upper-body strength and endurance training in female skiers in recent years may have closed the gap between upper- and lower-body endurance capacity compared with male XC skiers. In addition, no sex-related considerations need to be made when using relative physiological responses for intensity regulation within a specific exercise modality.

Respiratory Function and Muscle Strength Vs. Past Work Type: a Cross-Sectional Study Among Retirees

Objectives

The aim of this cross-sectional study was to assess the effects of past occupational activity on muscle strength and respiratory function among retirees.

Methods

A total of 205 community-dwelling older adults participated in the study. Age (≥60 years) and cessation of professional activity (retirement) constituted the inclusion criteria. The International Standardized Classification of Occupations (ISCO-08) was used to stratify the participants into white- or blue-collar groups. Forced vital capacity (FVC), forced expiratory volume (FEV) in the first second, inspiratory vital capacity (IVC) parameters, and hand grip strength were tested.

Results

Statistically significant differences in IVC and FVC scores were found in white- and blue-collar workers after adjusting for sex and age (ANCOVA). White-collar men had significantly higher IVC as compared to blue-collar men.

Conclusions

Blue-collar male workers may be prone to deteriorating respiratory function in older age. It is vital to promote physical activity and educate blue-collar workers about the need to use respiratory protective equipment.

Quantitative analysis of approximate shapes in a myofiber cross-section and their relationship with myofiber cross-sectional area

[Purpose] Although the shapes observed in myofiber cross-sections have been subjectively identified as polygonal, precise methodologies to classify such shapes have not been elucidated previously. Therefore, we aimed to determine the approximate shapes found in myofiber cross-sections, and to elucidate their relationship with the myofiber cross-sectional area. [Materials and Methods] Soleus muscles of five 11-week-old male Wistar rats were collected as specimens. The muscle specimens were rapid-frozen in isopentane—cooled in dry ice and acetone—and sliced into 10-μm slices in a cryostat and stained with hematoxylin–eosin. The NIH ImageJ software was used to analyze the number of corners that were counted according to the proposed criteria and the myofiber cross-sectional areas of 500 myofibers. [Results] In assessments of the approximate shapes of myofiber cross-sections, the proportion of pentagons was 41%, which was the highest among polygons. A weak positive correlation was noted between the corner count and myofiber cross-sectional area, which indicated that polygons with more corners were associated with a larger myofiber cross-sectional area. [Conclusion] The myofiber cross-sections of the soleus muscle were considered to frequently show an approximately pentagonal shape. Moreover, a correlation was observed between the myofiber cross-section shape and myofiber cross-sectional area, suggesting that the area was also associated with the relevant functional features.

Physical fitness characteristics and performance in single-handed dinghy and 470 classes sailors

The purpose of this study was to investigate the differences in the physical fitness characteristics of Chinese single-handed dinghy and 470 sailors, predict the single-handed dinghy sailors' physical factors on the performance by equation to guide the training. The sample of this study consisted of one hundred and sixty-seven Chinese sailors who participated in the 2020 China National Sailing Championships, K Independent Samples Test was used to analyze the differences of different classes sailors, and the performance of Laser and Laser Radial sailors were analyzed by step multivariate linear regression. The results showed that the 470 helmsmen are shorter, lighter and have a lower BMI, 470 crew are similar in height to the single-handed dinghy sailors, but lower in weight and BMI. Laser sailors have better strength and flexibility than the ones of male 470. There is no significant difference in the physical fitness characteristics between the Laser Radial sailors and the female 470 crew, they both had better upper and lower body strength than female 470 helmsmen. The regression equation is possible to explain 65.5% of the performance of the sailors in Laser = 90.963-1.33 × sailing experience-0.461 × bench press-0.018 × cycling peak power out; The regression equation is possible to explain 76.7% of the performance of the sailors in Laser Radial = 27.433-0.391 × sailing experience+0.351 × vertical jump-0.329 × pull-up-0.027 × cycling peak power out. Performance in laser and Laser Radial sailors will be determined by the technique and tactics (sailing experience) as well as physical fitness.

Characterizing the Tapering Practices of United States and Canadian Raw Powerlifters

ABSTRACT

Travis, SK, Pritchard, HJ, Mujika, I, Gentles, JA, Stone, MH, and Bazyler, CD. Characterizing the tapering practices of United States and Canadian raw powerlifters. J Strength Cond Res 35(12S): S26-S35, 2021-The purpose of this study was to characterize the tapering practices used by North American powerlifters. A total of 364 powerlifters completed a 41-item survey encompassing demographics, general training, general tapering, and specific tapering practices. Nonparametric statistics were used to assess sex (male and female), competition level (regional/provincial, national, and international), and competition lift (squat, bench press, and deadlift). The highest training volume most frequently took place 5-8 weeks before competition, whereas the highest training intensity was completed 2 weeks before competition. A step taper was primarily used over 7-10 days while decreasing the training volume by 41-50% with varied intensity. The final heavy (>85% 1 repetition maximum [1RM]) back squat and deadlift sessions were completed 7-10 days before competition, whereas the final heavy bench press session was completed <7 days before competition. Final heavy lifts were completed at 90.0-92.5% 1RM but reduced to 75-80% 1RM for back squat and bench press and 70-75% for deadlift during the final training session of each lift. Set and repetition schemes during the taper varied between lifts with most frequent reports of 3 × 2, 3 × 3, and 3 × 1 for back squat, bench press, and deadlift, respectively. Training cessation durations before competition varied between deadlift (5.8 ± 2.5 days), back squat (4.1 ± 1.9 days), and bench press (3.9 ± 1.8 days). Complete training cessation was implemented 2.8 ± 1.1 days before competition and varied between sex and competition level. These findings provide novel insights into the tapering practices of North American powerlifters and can be used to inform powerlifting coaches and athlete's tapering decisions.

Effects of a Novel Rotator Cuff Rehabilitation Device on Shoulder Strength and Function

ABSTRACT

Savitzky, JA, Abrams, LR, Galluzzo, NA, Ostrow, SP, Protosow, TJ, Liu, SA, Handrakis, JP, and Friel, K. Effects of a novel rotator cuff rehabilitation device on shoulder strength and function. J Strength Cond Res 35(12): 3355-3363, 2021-The glenohumeral joint, a multiaxial ball and socket joint, has inherent instability counterbalanced by the muscular stability of the rotator cuff (RC) and connective tissue. Exercise has been shown to alleviate pain and disability arising from degenerative changes of the RC due to overuse, trauma, or poor posture. This study compared the training effects of ShoulderSphere (SS), an innovative device that uses resistance to centrifugal force, to TheraBand (TB), a traditional device that uses resistance to elasticity. Thirty-five healthy male and female adults (24.2 ± 2.4 years) were randomized into 3 groups: SS, TB, and control. Five outcomes were assessed before and after the twice-weekly, 6-week intervention phase: strength (shoulder flexion [Fx], extension [Ext], external rotation [ER], and internal rotation [IR]), proprioception (6 positions), posterior shoulder endurance (ShEnd), stability (Upper Quarter Y-Balance Test [YBal] (superolateral [YBalSup], medial [YBalMed], and inferolateral [YBalInf]), and power (seated shot put [ShtPt]). Data were analyzed using a 3 (group: SS, TB, and control) × 2 (time: pre and post) generalized estimating equation. Analyses demonstrated a main effect of time for all strength motions (p < 0.01): YBalInf (p < 0.0001), ShtPt (p < 0.05), and ShEnd (p < 0.0001) but no interaction effects of group × time. There were no main or interaction effects for proprioception. Both SS and TB groups had significant within-group increases in Ext, IR, YBalInf, and ShEnd. Only the SS group had significant increases in ER, Fx, and ShtPt. ShoulderSphere demonstrated comparable conditioning effects with TB and may afford additional strength gains in Fx and ER, and power. ShoulderSphere should be considered a viable alternative in RC conditioning.

The effect of body composition on strength and power in male and female students

PURPOSE

The aim of this study is to determine and to compare the effect of sex differences in percentage of body fat on the strength and power performances of the legs and arms during short maximal exercise.

METHODS

72 male and 64 female students aged 20 to 23 years were enrolled in this study. After assessing their morphological characteristics (body mass, height and percentage of fat mass), a squat jump test (SJ), a 5 successive jump test (5JT), a hand gripping (HG) and back strength (BS) tests have been conducted for each subject. Male students were re-tested after being weighed down with a weight equivalent to the mean differences in body fat recorded between the two sexes in the form of a loaded worn vest.

RESULTS

Male are 15.7% heavier and 7.4% taller and presented a percentage of fat mass (17.2 ± 1.8%) significantly (p < 0.001) lower than that of women subject (25.0 ± 2.5%) (difference male vs female for fat mass: -45.5%). HG, BS, 5JT and SJ performances were significantly higher in males (44 ± 5 kg, 141 ± 2 kg, 11 ± 1 m and 32.4 ± 2,7 cm, respectively) than in females (31.0 ± 4 kg, 81.6 ± 13 kg, 8.7 ± 0.7 m and 21.1 ± 1.9 cm, respectively). In the control (unloaded) condition, the relative difference between males and females represented 23.5% and 34.7% of the male performances for 5JT and SJ, respectively. In the weighted condition, the relative difference between weighted males and females still represented 11.7% and 23.8% of the weighted male performances for 5JT and SJ, respectively. Cancelling the sex difference in fat mass by adding weight in males reduced by 50.1% the sex difference during 5JT and 31.4% and 71.7% for hight and power results, respectively during SJ test.

CONCLUSION

During short and maximal exercise, male performed better with their hands, back and legs than female students. Excess fat for female students has a disadvantageous effect on vertical and horizontal jumps performances. The persistence of sex differences after weighting of male students indicates that body fat is responsible for 30 to 70% of the observed differences between sexes performances and power outcomes during jump tests.

Effect of gender, muscle type and skinfold thickness on myometric parameters in young people

Background

The aim of the study was to compare the mechanical properties of three human skeletal muscles: biceps brachii (BB), rectus femoris (RF), and tibialis anterior (TA) at rest measured by myoton device in males (n = 16, mean age 21.2 ± 0.6 years) and females (n = 16; 21.2 ± 0.9 years) and to investigate the influence of skin and subcutaneous tissue thickness (skinfold thickness, SFT) and gender on myometric parameters of the three skeletal muscles.

Methods

We measured the following mechanical and viscoelastic muscle properties using MyotonPRO^®: frequency (F [Hz]), decrement (D [log]), stiffness (S [N/m]), relaxation time (R [ms]) and creepability (C [De]). The values of SFT for all selected muscles were assessed by caliper. A mixed-design analysis of variance with gender as between subject comparison was used for assessing the differences between gender and muscles in SFT and each of the myometric parameters separately (F, D, S, R and C). Pearson correlation coefficient or Spearman’s rank correlation coefficient between SFT and myometric parameters was conducted for males, females and males and females together. The level of statistical significance was set at α ≤ 0.05 with Bonferroni correction for multiple comparisons.

Results

The SFT over the RF, TA, and BB muscles in women was statistically significantly larger compared with that of males. In females and males, the SFT over the RF was larger than over the TA and BB, and the SFT over the TA was larger compared with over the BB. The values of F and S recorded for the TA muscle were the highest among the three muscles, while D, C, and R were lowest in TA but highest in the RF muscle in men and women. The values of F and S were smaller in females than in males. Gender comparison of D, C, and R values showed that only D for the RF was significantly lower in females than in males, and C for the RF and TA was significantly larger in females than in males. Some correlation between SFT and myometric parameters were different between males and females. For example, there was a significant, negative correlation between SFT and F for all muscles in females, and a significant, positive correlation between these parameters for BB and TA (not for RF) in males. For pooled data (males and females together), a negative significant correlation between SFT and F was observed for RF and TA (not significant for BB muscle).

Discussion

It is concluded that the TA compared with the BB and RF has significantly greater F and S but the smallest D and C and the shortest R. Gender and muscle differences in the SFT may affect the measurements of muscle properties using MyotonPRO^®. The relationship between SFT and myometric parameters is different in males and females in the RF, TA, and BB muscles. Therefore, the myometric data should be analyzed in males and females separately.

Healthy Women and Men Do Not Show Differences in Tongue Strength and Regular Effort Saliva Swallows as Assessed by Piezo-Resistive Sensors: Results from a Reproducibility Study

The aim of this study was to establish the reproducibility of tongue strength measurements in healthy women and men during maximum anterior isometric pressure (MAIP) and regular effort saliva swallows (RESS). In this cross-sectional study, 30 healthy young adults were required to push with the tip of the tongue on a piezo-resistive sensor glued to the hard palate, immediately above the central incisor line. Tongue pressures exerted on the sensor during MAIP and spontaneous RESS were recorded. Participants underwent a retest procedure within the same session to verify the reproducibility of measurements, as determined by intraclass correlation coefficient (ICC), standard error of measurement (SEM), and minimum detectable change (MDC). Complete data were obtained from 30 subjects (15 women, 15 men; mean age 31.4 ± 7.8 years; mean weight 61.3 ± 9.4 kg). Compared to women, men showed a trend for generating larger MAIP (p = 0.06; d = 0.71) and RESS (p = 0.07; d = 0.69). After normalizing to body weight, height, and body mass index (BMI), such trends disappeared. At retest, MAIP and RESS proved stable and highly reliable (all ICCs ≥ 0.93) in men and women but associated to moderate variability as for SEM and MDC, with MAIP estimates associated to smaller SEM and MDC (SEM ranging 7.4-14.2%; MDC 18.6-20.9%) than RESS (SEM ranging 20.4-38.5%; MDC 52.5-55.6%). Piezo-resistive pressure sensors allow clinicians and researchers to perform reproducible measurements of tongue muscle performance. However, if therapeutic interventions are administered, measurement variability in tongue performance should be considered when appraising their clinical efficacy, especially for those populations who display impaired performance and may not be capable to generate high and stable forces. No gender-based differences emerged in the motor tasks tested.

Moving Past the One-Size-Fits-All Education-Training Model of Police Academies to the Self-Prescribed Individualized Exercise Prescription Model

Law enforcement agencies generally employ the "one-size-fits-all" education-training model. Its effectiveness compared to alternative training models has been under scrutiny. Physical fitness scores of Serbian male (n = 98) and female (n = 79) police cadets during their yearly evaluation were compared. Cadets trained for the first 3 years with the "one-size-fits-all" model. In the fourth year, they self-prescribed an individualized exercise program based on the obtained curriculum knowledge. A two-way MANOVA revealed a significant effect of academic years on combined variables (p < 0.001) and significant differences between academic years for deadlift, half squat, standing long jump, sit-ups and 12-min Cooper test time (p < 0.001). Sex also had a significant main effect on combined variables (p < 0.001) with males outscoring females on all of the fitness assessments. For pull-ups, there was a significant year * sex interaction (p = 0.01) with the third year to be pivotal for female and male performance, respectively. In conclusion, the use of a "one-size-fits-all" model, presented differences in physical fitness scores between the years one to three, pointing to its questionable effectiveness. On the contrary, the self-prescribed individualized exercise program of the fourth year elicited greater fitness scores, indicating the need to evaluate the applicability of such a training model more.

Skeletal muscle methylome and transcriptome integration reveals profound sex differences related to muscle function and substrate metabolism

Nearly all human complex traits and diseases exhibit some degree of sex differences, with epigenetics being one of the main contributing factors. Various tissues display sex differences in DNA methylation; however, this has not yet been explored in skeletal muscle, despite skeletal muscle being among the tissues with the most transcriptomic sex differences. For the first time, we investigated the effect of sex on autosomal DNA methylation in human skeletal muscle across three independent cohorts (Gene SMART, FUSION, and GSE38291) using a meta-analysis approach, totalling 369 human muscle samples (222 males and 147 females), and integrated this with known sex-biased transcriptomics. We found 10,240 differentially methylated regions (DMRs) at FDR < 0.005, 94% of which were hypomethylated in males, and gene set enrichment analysis revealed that differentially methylated genes were involved in muscle contraction and substrate metabolism. We then investigated biological factors underlying DNA methylation sex differences and found that circulating hormones were not associated with differential methylation at sex-biased DNA methylation loci; however, these sex-specific loci were enriched for binding sites of hormone-related transcription factors (with top TFs including androgen (AR), estrogen (ESR1), and glucocorticoid (NR3C1) receptors). Fibre type proportions were associated with differential methylation across the genome, as well as across 16% of sex-biased DNA methylation loci (FDR < 0.005). Integration of DNA methylomic results with transcriptomic data from the GTEx database and the FUSION cohort revealed 326 autosomal genes that display sex differences at both the epigenome and transcriptome levels. Importantly, transcriptional sex-biased genes were overrepresented among epigenetic sex-biased genes (p value = 4.6e−13), suggesting differential DNA methylation and gene expression between male and female muscle are functionally linked. Finally, we validated expression of three genes with large effect sizes (FOXO3A, ALDH1A1, and GGT7) in the Gene SMART cohort with qPCR. GGT7, involved in antioxidant metabolism, displays male-biased expression as well as lower methylation in males across the three cohorts. In conclusion, we uncovered 8420 genes that exhibit DNA methylation differences between males and females in human skeletal muscle that may modulate mechanisms controlling muscle metabolism and health.

Sex-Differences in the Oxygenation Levels of Intercostal and Vastus Lateralis Muscles During Incremental Exercise

This study aimed to examine sex differences in oxygen saturation in respiratory (SmO₂-m.intercostales) and locomotor muscles (SmO₂-m.vastus lateralis) while performing physical exercise. Twenty-five (12 women) healthy and physically active participants were evaluated during an incremental test with a cycle ergometer, while ventilatory variables [lung ventilation ( V . E), tidal volume (Vt), and respiratory rate (RR)] were acquired through the breath-by-breath method. SmO₂ was acquired using the MOXY^® devices on the m.intercostales and m.vastus lateralis. A two-way ANOVA (sex × time) indicated that women showed a greater significant decrease of SmO₂-m.intercostales, and men showed a greater significant decrease of SmO₂-m.vastus lateralis. Additionally, women reached a higher level of ΔSmO₂-m.intercostales normalized to V . E (L⋅min^-1) (p < 0.001), whereas men had a higher level of ΔSmO₂-m.vastus lateralis normalized to peak workload-to-weight (watts⋅kg^-1, PtW) (p = 0.049), as confirmed by Student's t-test. During an incremental physical exercise, women experienced a greater cost of breathing, reflected by greater deoxygenation of the respiratory muscles, whereas men had a higher peripheral load, indicated by greater deoxygenation of the locomotor muscles.

Trunk muscle endurance in individuals with and without patellofemoral pain: Sex differences and correlations with performance tests

OBJECTIVES

To compare trunk muscle endurance among females and males with and without patellofemoral pain (PFP), and to investigate the correlations between trunk muscle endurance and performance of the single leg hop test (SLHT) and forward step-down test (FSDT).

DESIGN

Cross-sectional.

SETTING

Laboratory-based study.

PARTICIPANTS

110 females and 38 males with PFP, 61 females and 31males without PFP.

MAIN OUTCOME MEASURES

Anterior and lateral trunk muscle endurance were assessed with the prone and bilateral side-bridge tests, respectively. Performance during the SLHT and FSDT was also assessed.

RESULTS

Lower anterior and lateral trunk muscle endurance were identified in females (p < .001; d = -0.74 to -0.86), but not in males (p ≥ .806; d = -0.04 to 0.05) with PFP as compared to sex-matched controls. Moderate to large, positive correlations between anterior and lateral trunk muscle endurance with performance in the SLHT and FSDT were identified in females (r = .27 to .50; p < .004) and males (r = 0.27 to 0.59; p < .031) with PFP and females without PFP (r = 0.26 to 0.40; p < .044).

CONCLUSION

Our findings highlight that assessing trunk muscle endurance is advised in females with PFP. Trunk muscle endurance of individuals with PFP may have a role in the performance of hopping and stepping down tasks.

Association of Performance in Strength and Plyometric Tests with Change of Direction Performance in Young Female Team-Sport Athletes

The change of direction (COD) ability is a task-specific skill dependent on different factors such as the degree of the turn, which has led to differentiating CODs as more force- (>90°) or velocity-oriented (<90°). Considering force and velocity requirements is of importance when designing sport-specific training programs for enhancing COD performance. Thus, 25 female handball and soccer players participated in this study, which investigated the association between three different strength and plyometric exercises and force- and velocity-oriented COD performance. By utilizing the median split analysis, the participants were further divided into a fast (n = 8) and a slow (n = 8) COD group, to investigate differences in step kinematics between fast and slow performers. The correlational analysis revealed that the bilateral back squat and unilateral quarter squat were significantly associated with several force- and velocity-oriented COD performance (r = -0.46 to -0.64), while the association between plyometric and COD performance was limited (r < 0.44). The fast COD group revealed higher levels of strength, jump height, peak velocities, higher step frequencies, shorter ground contact times, and greater acceleration and braking power (d > 1.29, p < 0.03). It was concluded that the observed correlation between strength and COD performance might be due to stronger athletes being able to produce more workload in a shorter time, which was supported by the step kinematics.

What Are the Risk Factors of Incurring Maxillofacial Fractures From Unarmed Hand-To-Hand Combat?

PURPOSE

The purpose of our study was to determine the risk factors of incurring maxillofacial fractures among individuals who engage in unarmed hand-to-hand combat.

METHODS

The following retrospective cohort study was competed using data from the Nationwide Inpatient Sample. The primary predictor variable was blood alcohol level. The primary outcome variable maxillofacial fracture. We used SPSS to conduct all statistical analyses.

RESULTS

Our final sample consisted of 9,441 patients injured from unarmed hand-to-hand combat. The mean age of the sample was 38.7 years. The most common age group was young adults (42.9%), followed closely by middle-aged adults (41.9%). The number of males was nearly 4 times that of females. The mandible was the most frequently fractured maxillofacial bone. Concerning the mandible per se, the angle (37.1%) was the most frequently fractured site, while the coronoid process (0.2%) was the least frequently fractured site. Relative to females, males were 2.7 times more likely to incur a craniomaxillofacial fracture (P < .5).

CONCLUSIONS

Males had an increased risk of maxillofacial fracture relative to females. The mandible, particularly the angle, was the most frequently fractured maxillofacial bone. We speculate this is because hooks are frequently thrown in unarmed hand-to-hand combat.

The interaction of aging with serum 25(OH)D and 1,25(OH)2 D status on muscle strength

BACKGROUND

To investigate the combination relationship of age with serum 25-hydroxyvitamin D (25(OH) D) and 1,25-(OH)2D3 levels on muscle strength.

METHODS

We performed a cross-sectional study on 270 subjects containing 115 men and 155 women. Serum concentration of 25(OH) D and 1,25-(OH)2D3 were assessed. Hand grip strength (HGS) was measured using a digital dynamometer.

RESULTS

There was no significant difference in mean of HGS among tertiles of 25(OH)D (P = .350) and 1,25(OH)₂ D (P = .467) before and after controlling for potential confounding factors. A significant difference in HGS was found between age categories in both crude (P < .001) and adjusted models (P = .018), where mean grip strength increased in the three first age categories, but decreased in the last group (48-69 years old). There was also a significant interaction between age and 25(OH) D (P = .049) and 1,25-(OH)2D3 (P = .047) on HGS, in which the combination effect increased the mean of muscle strength up to middle age after adjusting for confounders.

CONCLUSIONS

Serum 25(OH)D and 1,25(OH)₂ D were not related to muscle strength. However, age, and combination of age with both 25(OH)D and 1,25(OH)₂ D, significantly resulted in improving in muscle strength up to middle age.

The effect of gender on intramuscular pressure in patients with chronic exertional compartment syndrome of the lower leg

This study aimed to compare intramuscular pressure (IMP) in all four compartments of the lower leg between men and women in patients with suspected chronic exertional compartment syndrome (CECS), and to assess possible effects of gender in relation to covariation factors. A consecutive series of patients with exertional leg pain (n = 962, median age 27 years, 56.2% women) underwent IMP measurements between 2009 and 2019. The CECS diagnosis was confirmed (n = 491, 48% women) or ruled out (n = 471, 65% women) based on the patient's history, clinical examination, and IMP measurements. IMP values of the compartments were compared between genders. A multiple linear regression analysis was performed for IMP in the anterior and lateral compartments, where the number of patients was large enough to investigate the possible impact of other factors such as height, age, and duration of pain. Among those with a confirmed CECS diagnosis, one-minute post-exercise IMP was significantly lower in women than in men for all four muscle compartments: anterior (median [range] mmHg 44 [24-120] vs. 50 [24-130]), lateral (35 [20-89] vs. 40 [26-106]), deep posterior (31 [25-36] vs. 34 [24-53]), and superficial posterior (32 [27-39] vs. 37 [22-54]). In the multiple regression analysis, gender differences remained significant in the anterior compartment but not the lateral compartment, where only height remained a significant predictor of IMP. Gender should be considered when using cut-off values for IMP in diagnosing CECS, especially for the anterior compartment.

The Relation of Body Mass Index to Muscular Viscoelastic Properties in Normal and Overweight Individuals

Background: The body mass index (BMI) is closely related to fat tissue, which may have direct or indirect effects on muscle function. Previous studies have evaluated BMI and muscle viscoelastic properties in vivo in older people or individual sexes; however, the relationship between BMI and muscular viscoelastic properties is still unknown. Aims: The purpose of this study was to determine the correlation of BMI with muscular viscoelastic properties, and to compare these properties in a young sedentary population with normal and overweight individuals. Methods: A total of 172 healthy sedentary individuals (mean age, 26.00 ± 5.45 years) were categorized by sex (male and female) and BMI classification (normal (BMI, 18.50-24.99 kg/m²), overweight (BMI = 25.00-29.99 kg/m²)). Body weight was evaluated using an electronic scale, while height was measured using a standard stadiometer. BMI was calculated by dividing the weight in kilograms by the square of height in meters. The viscoelastic properties (tone, stiffness, and elasticity) of the biceps brachii (BB) and biceps femoris (BF) muscles were measured bilaterally using the MyotonPRO device at rest. Results: The bilateral BF tone and stiffness, right BB stiffness, and elasticity showed weak correlations with BMI in all participants. Furthermore, the bilateral BF tone and stiffness, right BB stiffness and elasticity, and left BB stiffness were weakly positively correlated with male sex. Only the right BB elasticity was weakly positively correlated with BMI in females (p < 0.05). No correlation with BMI was determined for other viscoelastic properties (p > 0.05). The overweight group showed increased bilateral BF stiffness and tone, right BB stiffness, and reduced bilateral BB elasticity compared to the normal-weight group (p < 0.05), while other viscoelastic properties were similar (p > 0.05). Greater bilateral BB tone, BF tone and stiffness, and lower BF elasticity were observed in males than in females (p < 0.05), but other viscoelastic properties were not significantly different (p < 0.05). No effect of BMI-sex interactions was found on viscoelastic properties (p > 0.05). Conclusions: The BB and BF viscoelastic properties were weakly correlated with BMI. Males showed greater muscle tone and stiffness, and lower elasticity. The overweight individuals showed increased stiffness and tone, particularly in lower extremities, and reduced elasticity in upper extremities. The effect of BMI-sex interactions on the viscoelastic properties was not clear. Higher BMI (increased mechanical load) might cause the human body to develop different muscular viscoelastic adaptations in the extremities.

Sex differences in skeletal muscle revealed through fiber type, capillarity, and transcriptomics profiling in mice

Skeletal muscle anatomy and physiology are sexually dimorphic but molecular underpinnings and muscle-specificity are not well-established. Variances in metabolic health, fitness level, sedentary behavior, genetics, and age make it difficult to discern inherent sex effects in humans. Therefore, mice under well-controlled conditions were used to determine female and male (n = 19/sex) skeletal muscle fiber type/size and capillarity in superficial and deep gastrocnemius (GA-s, GA-d), soleus (SOL), extensor digitorum longus (EDL), and plantaris (PLT), and transcriptome patterns were also determined (GA, SOL). Summed muscle weight strongly correlated with lean body mass (r2  = 0.67, p < 0.0001, both sexes). Other phenotypes were muscle-specific: e.g., capillarity (higher density, male GA-s), myofiber size (higher, male EDL), and fiber type (higher, lower type I and type II prevalences, respectively, in female SOL). There were broad differences in transcriptomics, with >6000 (GA) and >4000 (SOL) mRNAs differentially-expressed by sex; only a minority of these were shared across GA and SOL. Pathway analyses revealed differences in ribosome biology, transcription, and RNA processing. Curation of sexually dimorphic muscle transcripts shared in GA and SOL, and literature datasets from mice and humans, identified 11 genes that we propose are canonical to innate sex differences in muscle: Xist, Kdm6a, Grb10, Oas2, Rps4x (higher, females) and Ddx3y, Kdm5d, Irx3, Wwp1, Aldh1a1, Cd24a (higher, males). These genes and those with the highest "sex-biased" expression in our study do not contain estrogen-response elements (exception, Greb1), but a subset are proposed to be regulated through androgen response elements. We hypothesize that innate muscle sexual dimorphism in mice and humans is triggered and then maintained by classic X inactivation (Xist, females) and Y activation (Ddx3y, males), with coincident engagement of X encoded (Kdm6a) and Y encoded (Kdm5d) demethylase epigenetic regulators that are complemented by modulation at some regions of the genome that respond to androgen.