Physiological and molecular sex differences in human skeletal muscle in response to exercise training

Divergent multiomic acute exercise responses reveal the impact of sex as a biological variable

The majority of exercise physiology research has been conducted in males, resulting in a skewed biological representation of how exercise impacts the physiological system. Extrapolating male-centric physiological findings to females is not universally appropriate and may even be detrimental. Thus, addressing this imbalance and taking into consideration sex as a biological variable is mandatory for optimization of precision exercise interventions and/or regimens. Our present analysis focused on establishing multiomic profiles in young, exercise-naïve males (n = 23) and females (n = 17) at rest and following acute exercise. Sex differences were characterized at baseline and following exercise using skeletal muscle and extracellular vesicle transcriptomics, whole blood methylomics, and serum metabolomics. Sex-by-time analysis of the acute exercise response revealed notable overlap, and divergent molecular responses between males and females. An exploratory comparison of two combined exercise regimens [high-intensity tactical training (HITT) and traditional (TRAD)] was then performed using singular value decomposition, revealing latent data structures that suggest a complex dose-by-sex interaction response to exercise. These findings lay the groundwork for an understanding of key differences in responses to acute exercise exposure between sexes. This may be leveraged in designing optimal training strategies, understanding common and divergent molecular interplay guiding exercise responses, and elucidating the role of sex hormones and/or other sex-specific attributes in responses to acute and chronic exercise.NEW & NOTEWORTHY This study examined methylomics, transcriptomics, and metabolomics in circulation and/or skeletal muscle of young, healthy, exercise-naïve males and females before and after exposure to either traditional combined exercise (TRAD) and high-intensity tactical training (HITT). Across 40 young adults, we found an overlapping yet considerably sex-divergent response in the molecular mechanisms activated by exercise. These findings may provide insight into optimal training strategies for adaptation when considering sex as a biological variable.

A Randomized Crossover Trial on the Effects of Cadence on Calf Raise Test Outcomes: Cadence Does Matter

The calf raise test (CRT) is commonly used to assess triceps surae muscle-tendon unit function. Often, a metronome set to 60 beats/min (30 repetitions/min) is used to set the cadence of calf raise repetitions, but studies report using cadences ranging from 30 to 120 beats/min. We investigated the effect of cadence on CRT outcomes, accounting for the potential confounders of sex, age, body mass index, and physical activity. Thirty-six healthy individuals (50% female) performed single-leg calf raise repetitions to volitional exhaustion in 3 randomized cadence conditions, 7 days apart: 30, 60, and 120 beats/min. Repetitions, total vertical displacement, total work, peak height, and peak power were recorded using the validated Calf Raise application. Cadence significantly affected all CRT outcomes (P ≤ .008), except repetitions (P = .200). Post hoc analysis revealed 60 beats/min resulted in significantly greater total vertical displacement and work than 30 and 120 beats/min. Peak height was greater at 60 and 120 than 30 beats/min, and peak power was greater at 120 beats/min. Males generated greater work and peak power (P ≤ .001), whereas individuals with greater body mass index completed less repetitions (P = .008), achieved lower total vertical displacements (P = .003), and generated greater peak power (P = .005). CRT cadence is important to consider when interpreting CRT outcomes and comparing data between studies.

Exploring Gender-Specific Correlations Between Nutritional Intake, Body Composition, Psychological Skills, and Performance Metrics in Young Taekwondo Athletes

Objectives: Taekwondo performance is influenced by a complex and dynamic interplay of physical, nutritional, and psychological factors, all of which contribute to competitive success. However, the gender-specific relationships among these factors in young high-performance athletes remain understudied. This study aimed to fill in this knowledge gap. Methods: A cross-sectional study was conducted with 35 elite taekwondo athletes (male: n = 20, female: n = 15, age: 13 ± 1 years). Participants underwent anthropometric assessments, dietary evaluations, and psychological skill assessments during an 8-week training camp before the World Taekwondo Championships. Physical performance was assessed using the Frequency Speed of Kick Test (FSKTmult) and the Taekwondo-Specific Agility Test (TSAT). Statistical analyses included independent t-tests, correlation analyses, and regression models. Results: Males exhibited significantly higher fat-free mass (FFM: 42.8 ± 2.9 kg vs. 36.3 ± 1.6 kg, p < 0.001), skeletal muscle mass (SMM: 31.1 ± 2.2 kg vs. 28.2 ± 1.6 kg, p < 0.001), and energy intake (32.4 ± 4.6 kcal/kg vs. 29.3 ± 3.1 kcal/kg, p = 0.032) than females. Males also had greater dietary intakes of vitamin A, vitamin C, magnesium, and iron (all p < 0.05). There were no gender differences in any psychological attributes associated with emotional intelligence, sport success perception, and mental toughness. Although the total kick count in the FSKTmult was similar for male and female taekwondo athletes (100.2 ± 4.6 vs. 97.5 ± 5.9 kicks, p = 0.139), males outperformed females in round 4 (19.4 ± 1.1 vs. 18.6 ± 1.4 kicks, p = 0.048) and round 5 (18.2 ± 1.0 vs. 17.2 ± 1.0 kicks, p = 0.007) of this test, suggesting higher physical performance maintenance during the test. Regression models indicated that body mass (β = 0.901, p < 0.001) and calcium intake (β = 0.284, p = 0.011) predicted performance in males, while body mass (β = 1.372, p < 0.001), protein intake (β = 0.171, p = 0.012), and emotional regulation (β = 0.174, p = 0.012) were key predictors in females. Conclusions: These findings highlight the importance of an integrated approach to training, nutrition, and psychological preparation in optimizing taekwondo performance. While males and females demonstrated similar psychological resilience and total kick output in a taekwondo-specific test, males exhibited superior endurance in later test rounds of this test. Performance optimization in young elite taekwondo athletes may require the implementation of gender-specific training and nutrition strategies, emphasizing body weight control and calcium intake for males and protein intake for females.

Movement behaviors and cardiorespiratory fitness - a cross-sectional compositional data analysis among German adults

BACKGROUND

We investigated associations of movement behaviors (moderate-vigorous physical activity, light physical activity, and stationary time) with various parameters measured during cardiopulmonary exercise testing. We applied compositional data analysis to account for the relative contributions of different movement behaviors to the overall time budget of the waking day.

METHODS

We used data from 1,396 participants of the cross-sectional population-based Study of Health in Pomerania (SHIP-TREND-1), who provided valid accelerometer data worn on the hip for seven days during waking hours and participated in cardiopulmonary exercise testing on a cycle ergometer (n = 1,396 participants with a mean age of 57.1 (SD 13.2, 51% men). Linear regression models applying compositional data analysis were used to examine associations of proportions of movement behaviors (exposure) with parameters derived during cardiopulmonary exercise testing (outcome) normalized for body weight and stratified by sex. Models were adjusted for age, education, smoking, and partnership, except the %predicted VO2peak model, where age was omitted, as it is part of the calculation of the %predicted VO2peak. In models examining O2pulse or HRmax, individuals using beta blockers were excluded.

RESULTS

In males and females, more time spent in moderate-to-vigorous physical activity was associated with greater VO2VT1, VO2peak, and VO2 recovery after 60 s (all p < 0.01). Greater moderate-to-vigorous physical activity was also related to higher %predicted VO2peak and maximum heart rate in males and to higher VO2/work in females (all p < 0.01). In both sexes, more time in stationary time was associated with less %predicted VO2peak (p < 0.01). More light intensity physical activity was associated to higher %predicted VO2peak in both sexes and with lower VO2/work in women (all p < 0.01). Greater stationary time was related to less VO2/work, VO2VT1, and VO2peak in males and to less VO2 recovery after 60 s and O2pulse in females (p values < 0.05).

CONCLUSION

Moderate-to-vigorous physical activity (positive) and stationary time (inverse) influence parameters derived during cardiopulmonary exercise testing irrespective of age, smoking, and living in a relationship. The sex specific effects were rather small. Hence, promoting physical activity should be encouraged to increase cardiorespiratory fitness.

Malate or Not? Acute Effects of L-Citrulline Versus Citrulline Malate on Neuromuscular Performance in Young, Trained Adults: A Randomized, Double-Blind, Placebo-Controlled Crossover Trial

L-citrulline (CIT) supplementation seems to improve resistance training performance; yet, whether malate has additive ergogenic effects when combined with CIT is unknown. This randomized, double-blind, placebo-controlled crossover trial aimed to compare the acute effects of CIT versus citrulline malate (CMA) supplementation on neuromuscular performance and exertion and emotional perceptions in young, trained men and women. 43 (21 women; 24.2 ± 3.7 years) participants ingested a placebo, CIT (5.3 g of CIT), or CMA (5.3 g of CIT, 2.7 g of malate) 45 min before three experimental sessions in a counterbalanced manner. We evaluated the upper and lower limb maximal neuromuscular and ballistic performance through the two-point method and countermovement jump. Strength-endurance was assessed across three sets of 10 repetitions in the squat and bench press exercises. Exertion and emotional perceptions were evaluated before and after the assessment and during the strength-endurance assessment. CIT and CMA supplementation did not enhance maximal neuromuscular performance (all p ≥ .061, ηp2≤.066), or ballistic strength (all p ≥ .348, ηp2≤.025). Neither CIT nor CMA supplementation improved strength-endurance as observed in the total number of repetitions (all p ≥ .590, ηp2≤.013), repetitions before reaching velocity loss threshold (all p ≥ .623, ηp2≤.010), mean velocity (all p ≥ .792, ηp2≤.004), mean velocity decline (all p ≥ .293, ηp2≤.029), and mean velocity maintenance (all p ≥ .393 ηp2≤.022), or exertion and emotional perceptions (both p ≥ .306, ηp2≤.028). In conclusion, CIT and CMA supplementation may not increase the neuromuscular performance during low- to moderate-volume resistance training sessions in young, trained adults. This trial was registered at ClinicalTrials.gov (No. NCT05183893).

Sexual dimorphism in exercise-induced response on steroid hormones to a 24-week supervised concurrent training intervention

BACKGROUND

Steroid hormones are key mediators of adaptative responses to exercise, a stimulus that may concurrently affect their blood concentrations. However, the chronic endocrine adaptations and whether these potential changes are dependent on exercise intensity remain undetermined. Moreover, it is also unknown if the exercise-induced effects on steroid hormonal status are related to the participant' sex.

METHODS

This study aimed to investigate the intensity effects of a 24-week supervised concurrent training intervention on steroid hormones in sedentary young men and women. A total of 106 untrained young adults (68% women) aged 18-25 years were randomly assigned to one of the three groups: (I) Control group (no exercise; n = 35); (II) Ex-Moderate group (concurrent training at moderate intensity; n = 36); (III) Ex-Vigorous group (concurrent training at vigorous intensity; n = 35). Steroid hormones (i.e. cortisol, testosterone and dehydroepiandrosterone sulfate (DHEAS)) were measured in plasma through a chemiluminescent method. Body composition parameters were determined using a dual-energy X-ray absorptiometry scanner.

RESULTS

No significant changes in steroid hormones levels were observed after the intervention (all p ≥ .129). However, a time x group interaction was noted in the testosterone/cortisol ratio (T/C ratio) only in women (p = .044). Concretely, our data showed a significant decrement of T/C ratio in both the Ex-Moderate group and in the Ex-Vigorous compared with the control group (Δ = -24.2 ± 2.0% and Δ = -38.9 ± 45.4%, respectively).

CONCLUSION

Our 24-week supervised concurrent training intervention showed no significant changes in steroid hormone levels. However, a significant decrement of T/C ratio was observed only in women, indicating a sexual dimorphism in the effect on T/C ratio.

Genetic and metabolic insights into sexual dimorphism in the flexor carpi radialis of Asiatic toads (Bufo gargarizans) associated with amplexus behavior

BACKGROUND

Sexual dimorphism, a widespread phenomenon across the animal kingdom, encompasses differences between sexes in size, morphology, and physiological traits. In this study, we investigated sexual dimorphism in the flexor carpi radialis (FCR) muscle, which is critical for amplexus in Asiatic toads (Bufo gargarizans), using integrated transcriptomic and metabolomic approaches.

RESULTS

Male toads exhibited significantly larger FCR muscles, reflecting enhanced muscle function required for sustained amplexus. Transcriptomic analysis identified 818 differentially expressed genes (DEGs) between sexes, with 389 upregulated and 429 downregulated in males, predominantly associated with muscle contraction, sarcomere organization, and energy metabolism. Metabolomic profiling revealed 69 differentially expressed metabolites (DEMs), with male-biased enrichment in pathways involved in protein synthesis and degradation, energy metabolism, and material transport. Integrated analysis pinpointed key metabolic pathways-such as glycine, serine, and threonine metabolism; alanine, aspartate, and glutamate metabolism; fatty acid degradation; and the tricarboxylic acid (TCA) cycle-as central to the observed sexual dimorphism. Among these, the genes AGXT, ACADL, ACAT1, MDH2, and SUCLG2 emerged as pivotal regulators.

CONCLUSIONS

Collectively, these findings provide novel insights into the genetic and metabolic basis of sexual dimorphism in B. gargarizans, offering a deeper understanding of the evolutionary mechanisms driving sex-specific traits in vertebrates.

Vastus lateralis muscle architecture, quality, and stiffness are determinants of maximal performance in athletes?

Understanding intrinsic muscular adaptations more deeply can help clarify their relationships with sports performance. Therefore, the aim of this study was to determine if vastus lateralis muscle architecture, quality and stiffness can explain knee extensor maximal torque and countermovement and squat jump performance of athletes. One hundred and two athletes were evaluated based on the architecture, quality and stiffness of the vastus lateralis at rest. Furthermore, the knee extensor maximal voluntary isometric contraction and maximal concentric contraction at 60°/s and vertical jumps countermovement and squat jump performance were measured. Stepwise linear regression showed vastus lateralis echo intensity and muscle thickness determine knee extensor maximal voluntary isometric contraction (r2 = 0.435) and knee extensor maximal concentric contraction at 60°/s (r2 = 0.400) in athletes. Moreover, vastus lateralis echo intensity, muscle thickness and pennation angle can determine athletes' performance during countermovement (r2 = 0.439-0.578) and squat-jump (r2 = 0.459-0.570). The findings emphasize that vastus lateralis muscle architecture and quality is an important determinant of maximal knee extensor torque (40-44 %) and countermovement (44-58 %) and squat-jump (46-57 %) performance. Our results demonstrate that the muscle architecture and quality of the vastus lateralis are important determinants of torque and power output performance across various sports disciplines.

The Order of Concurrent Training Affects Acute Immunological Stress Responses and Measures of Muscular Fitness in Female Youth Judo Athletes

This study aimed to examine the acute effects of concurrent muscle strength and sport-specific endurance exercise order on immunological stress responses, metabolic response, muscular-fitness, and rating-of-perceived-exertion (RPE) in highly trained youth female judo athletes. Thirteen female participants randomly performed two concurrent training (CT) sessions; strength-endurance and endurance-strength. Immune response, metabolic response, muscular fitness (i.e., countermovement jump-derived force and power [CMJ-force and CMJ-power]), and RPE were measured at different time points (i.e., PRE, MID, POST, POST6h, and POST22h). There were significant time × order interactions for lymphocytes (p = 0.006, ES = 1.31), granulocyte-lymphocyte ratio (p = 0.002, ES = 1.56), and systemic inflammation index (p = 0.029, ES = 1.11), blood glucose and lactate (p < 0.001, ES = 2.09 and p = 0.0018, ES = 1.51, respectively), CMJ-force (p = 0.033, ES = 1.26), and CMJ-power (p = 0.007, ES = 1.40) as well as RPE (p < 0.001, ES = 2.05). CT-induced acute (i.e., POST) but not delayed (i.e., POST6h and POST22h) order-dependent immune cell count alterations in highly trained youth female judo athletes. All markers of the immune system went back to baseline values at POST22h. Metabolic responses were slightly higher following the endurance exercise (irrespective of the applied exercise order). CMJ-measures and RPE fluctuated during both CT sessions but returned to baseline 6 h post-exercise.

Impact of exercise with blood flow restriction on muscle hypertrophy and performance outcomes in men and women

Blood flow restriction training (BFRT) has been previously studied as an alternative form of resistance training to gain lean mass and improve performance outcomes. However, in all exercise studies of BFRT, the proportion of female participants represents only 17-29% of all research participants. This highlights a strong underrepresentation of females and the need for more knowledge on the impact of BFRT and sex differences. The primary objective was to compare the impact of 6-week BFRT on lean mass, strength, and performance outcomes between males and females. A total of 38 adults [age, 25.3 ±  3.1 years; female, n = 19 (50%)] performed whole-body resistance training program with blood flow restriction three times per week. Exercises were performed at 30% of 1-repetition maximum (1-RM) and blood flow restriction cuffs were set to 60% of each individual's limb occlusion pressure. Body composition was assessed via dual-energy x-ray absorptiometry and strength was measured using 1-RM. A significant increase in lean mass was observed in males (p = 0.009) and females (p = 0.023) with no difference in the change between groups (p = 0.279). Both males and females increased 1-RM for upper- and lower-body exercises, with significant interaction effects (time x sex) for chest press (p = 0.003), seated row (p = 0.038), knee flexion (p = 0.043), and knee extension (p = 0.035), suggesting males increased 1-RM more for these exercises. Furthermore, peak power was improved in males (p < 0.001) and females (p = 0.002) during a vertical squat jump, but a significant interaction (time x sex) effect was observed (p = 0.039), suggesting males increased to a greater extent. Males and females significantly increased lean body mass, to a similar degree, following six weeks of resistance training in combination with blood flow restriction. Likewise, both males and females improved muscle strength following 6-week BFRT, however males may improve strength to a greater extent than females.

Toward a Dynamic Model of Indispensable Amino Acid Requirements of the Adult Human: A Factorial Estimate of Oxidative Amino Acid Losses

BACKGROUND

Consensus regarding the required intake of indispensable amino acids (IDAAs) and protein [representing total amino acids (AAs)] in the adult is lacking. Oxidation is a major, although not exclusive, source of IDAA loss in humans body and a primary factor determining requirements; a quantitative understanding of oxidative IDAA losses is required.

OBJECTIVES

This study aimed to develop a factorial diurnal model of total oxidative IDAA and protein losses in the adult human.

METHODS

A factorial diurnal model of oxidative losses of protein and each IDAA at maintenance was developed by estimating the magnitude and variability of sources of oxidative loss from existing literature: inevitable catabolism (constitutive oxidation of each absorbed dietary AA), and protein turnover in the postprandial and postabsorptive states. Total oxidative losses were calculated by summing individual losses, validated against published independent nitrogen balance data and compared with current IDAA requirements.

RESULTS

The factorial model predicted minimum oxidative total AA losses of 390 ± 60 mg/kg BW/d, 59% of the estimated average requirement for protein. Inevitable AA oxidation and oxidation associated with postabsorptive protein turnover were the major sources of the oxidative loss for protein, at 40% and 44%, respectively. Summed oxidative IDAA losses ranged from 64% (isoleucine) to 91% (tryptophan) of current requirements. Total oxidative losses predicted by the model were significant predictors of actual experimental oxidative losses obtained by nitrogen balance (R2 = 0.66; P = 0.049).

CONCLUSIONS

The use of a factorial model for estimation of minimum IDAA and protein oxidative losses in the adult human provides an essential starting point for an updated understanding of protein and IDAA requirements. Further iterations of the model will estimate total protein and IDAA requirements, and account for variations in dietary protein quantity and quality, as well as different populations and physiologic states. Additional data, especially for inevitable oxidation in humans, and particularly with respect to individual IDAAs, are needed.

Neuromuscular Regeneration of Volumetric Muscle Loss Injury in Response to Agrin-Functionalized Tissue Engineered Muscle Grafts and Rehabilitative Exercise

Neuromuscular deficits compound the loss of contractile tissue in volumetric muscle loss (VML). Two avenues for promoting recovery are neuromuscular junction (NMJ)-promoting substrates (e.g., agrin) and endurance exercise. Although mechanical stimulation enhances agrin-induced NMJ formation, the two modalities have yet to be evaluated combinatorially. It is hypothesized that the implantation of human myogenic progenitor-seeded tissue-engineered muscle grafts (hTEMGs) in combination with agrin treatment and/or exercise will enhance neuromuscular recovery after VML. The hTEMGs alone transplant into VML defects promote significant regeneration with minimal scarring. A sex-appropriate, low-intensity continuous running exercise paradigm increases acetylcholine receptor (AChR) cluster density in male mice twofold relative to hTEMG alone after 7 weeks of treadmill training (p < 0.05). To further promote neuromuscular recovery, agrin is incorporated into the scaffolds via covalent tethering. In vitro, agrin increases the proliferation of hMPs, and trends toward greater myogenic maturity and AChR clustering. Upon transplantation, both hTEMGs + agrin and hTEMGs + exercise induce near 100% recovery of muscle mass and increase twitch and tetanic force output (p > 0.05). However, agrin treatment in combination with exercise produces no additional benefit. These data highlight the unprecedented regenerative potential of using hTEMGs together with either agrin or exercise supplementation to treat VML injuries.

Effect of Beetroot Juice Supplementation on Aerobic Capacity in Female Athletes: A Randomized Controlled Study

Background/Objectives: This study addresses the growing interest in nutritional supplements that improve athletic performance in endurance sports. Previous research suggests that nitrates in beetroot juice enhance blood vessel dilation and oxygen delivery to muscles. However, the effects of these nitrates on cardiopulmonary performance in female athletes remain underexplored. The aim of this study was to evaluate the effect of beetroot juice supplementation on aerobic work capacity in female endurance athletes. Methods: A cardiopulmonary exercise test (CPET) was conducted to assess aerobic work capacity. Eighteen healthy female endurance athletes (22.9 ± 5.6 years) participated in the study. The participants were randomly assigned to two groups: the control group (placebo group n = 9), which received a nitrate-free placebo beverage, and the experimental group (beetroot juice group n = 9), which consumed 50 mL of beetroot juice concentrate (~6.2 mmol nitrate) two and a half hours before the second test. Results: The results showed that the beetroot juice group demonstrated significant improvements in minute ventilation (VE), respiratory equivalents (VE/VO2 and VE/VCO2), and heart rate (HR) (p < 0.05). Maximal oxygen consumption (VO2 max) increased by 4.82% in the beetroot juice group (from 35.24 ± 5.07 to 36.94 ± 4.91 mL·min-1·kg-1), whereas a small decrease was observed in the placebo group. Conclusions: These findings indicate that beetroot juice may be an effective ergogenic aid, enhancing oxygen utilization and energy production during exercise in female athletes. In terms of practical applications, beetroot juice could contribute to improved athletic performance and serve as a valuable addition to athletes' nutritional plans. Future studies should explore the long-term effects, optimal dosages, and duration of supplementation in larger and more diverse populations.

Early life exercise impacts physiology and lifespan in a sex- and genotype-dependent manner in a Drosophila melanogaster exercise model

Exercise is a common strategy for disease prevention or management, including for diabetes and cardiac dysfunction. However, exercise response varies immensely between individuals, and in humans, the same exercise treatment can lead both to positive and negative responses. Drosophila melanogaster is an established model for exercise research that can be leveraged to understand this variation in exercise response. Here, we investigated how two early life exercise treatments differing in duration (5 and 20 days) impact the animals' health- and lifespan in four genotypes. Specifically, we measured lifespan, activity level, body condition, physical ability, and reproductive output in this exploratory study to gain insights into potential trade-offs. For most measures, we found both immediate and long-term effects, with some effects persisting weeks past the cessation of exercise. The effect of the exercise treatment was context-dependent, with treatment, sex, and genotype interactions determining phenotypes. For example, the 20-day treatment did not exhibit a consistently larger effect than the 5-day treatment. Similarly, neither the 5-day nor the 20-day treatment impacted lifespan, but two specific genotype/sex combinations showed altered lifespan after exercise. The 20-day treatment decreased climbing performance compared to controls up to several weeks after treatment ended in some genotypes. Together, our results highlight the complex, interacting factors controlling exercise response and demonstrate that early life exercise can have long-lasting effects in the Drosophila exercise model even though most individual groups show no response.

Sex differences in skeletal muscle metabolism in exercise and type 2 diabetes mellitus

This Review focuses on currently available literature describing sex differences in skeletal muscle metabolism in humans, as well as highlighting current research gaps within the field. These discussions serve as a call for action to address the current lack of sufficient sex-balanced studies in skeletal muscle research, and the resulting limitations in understanding sex-specific physiological and pathophysiological responses. Although the participation of women in studies has increased, parity between the sexes remains elusive, affecting the validity of conclusions drawn from studies with limited numbers of participants. Changes in skeletal muscle metabolism contribute to the development of metabolic disease (such as type 2 diabetes mellitus), and maintenance of skeletal muscle mass is a key component for health and the ability to maintain an independent life during ageing. Exercise is an important factor in maintaining skeletal muscle health and insulin sensitivity, and offers promise for both prevention and treatment of metabolic disease. With the increased realization of the promise of precision medicine comes the need to increase patient stratification and improve the understanding of responses in different populations. In this context, a better understanding of sex-dependent differences in skeletal muscle metabolism is essential.

Post-Lunch Napping as a Strategy to Enhance Physiological Performance and Cognitive Function in Elite Volleyball Players

Background and Objectives: Volleyball demands high levels of anaerobic strength, flexibility, agility, and mental focus. Adequate sleep has been shown to enhance athletic performance and cognitive function. This study investigates the impact of post-lunch naps of varying durations (25 and 45 min) on the physiological performance and cognitive focus of elite volleyball players. Materials and Methods: Sixteen elite volleyball players (8 male, 8 female) with at least 7 years of competitive experience participated in a randomized crossover study. They underwent three experimental conditions: no nap (No-Nap), a 25-min nap (N25), and a 45-min nap (N45). Physical performance was measured through counter-movement jumps (CMJ) and volleyball agility tests, while cognitive function was assessed using the D2 attention test. Statistical analysis included repeated measures ANOVA to examine the differences between nap conditions and gender-specific responses. Results: Significant improvements in both physical performance and cognitive focus were observed in the N25 and N45 conditions compared to the No-Nap condition (indicating the effectiveness of short naps in enhancing both physical and mental performance). Males outperformed females in most physical metrics, while females scored higher on the D2 attention test (suggesting possible gender-specific responses to napping). The 25-min nap showed slightly better results in terms of sleep quality and subsequent performance (confirming that shorter naps may be more beneficial). Conclusions: Post-lunch naps, especially of 25 or 45 min, enhance both physiological and cognitive performance in elite volleyball players. These findings suggest that integrating short naps into athletes' training regimens can improve performance and focus, with potential gender-specific benefits. Further research is needed to explore long-term effects and variations across other sports.

Sex differences in human performance

Sex as a biological variable is an underappreciated aspect of biomedical research, with its importance emerging in more recent years. This review assesses the current understanding of sex differences in human physical performance. Males outperform females in many physical capacities because they are faster, stronger and more powerful, particularly after male puberty. This review highlights key sex differences in physiological and anatomical systems (generally conferred via sex steroids and puberty) that contribute to these sex differences in human physical performance. Specifically, we address the effects of the primary sex steroids that affect human physical development, discuss insight gained from an observational study of 'real-world data' and elite athletes, and highlight the key physiological mechanisms that contribute to sex differences in several aspects of physical performance. Physiological mechanisms discussed include those for the varying magnitude of the sex differences in performance involving: (1) absolute muscular strength and power; (2) fatigability of limb muscles as a measure of relative performance; and (3) maximal aerobic power and endurance. The profound sex-based differences in human performance involving strength, power, speed and endurance, and that are largely attributable to the direct and indirect effects of sex-steroid hormones, sex chromosomes and epigenetics, provide a scientific rationale and framework for policy decisions on sex-based categories in sports during puberty and adulthood. Finally, we highlight the sex bias and problem in human performance research of insufficient studies and information on females across many areas of biology and physiology, creating knowledge gaps and opportunities for high-impact studies.

Sexual dimorphisms in skeletal muscle: current concepts and research horizons

The complex compositional and functional nature of skeletal muscle makes this organ an essential topic of study for biomedical researchers and clinicians. An additional layer of complexity is added with the consideration of sex as a biological variable. Recent research advances have revealed sexual dimorphisms in developmental biology, muscle homeostasis, adaptive responses, and disorders relating to skeletal muscle. Many of the observed sex differences have hormonal and molecular mechanistic underpinnings, whereas others have yet to be elucidated. Future research is needed to investigate the mechanisms dictating sex-based differences in the various aspects of skeletal muscle. As such, it is necessary that skeletal muscle biologists ensure that both female and male subjects are represented in biomedical and clinical studies to facilitate the successful testing and development of therapeutics for all patients.

Does sex matter in the cheetah? Insights into the skeletal muscle of the fastest land animal

The cheetah is considered the fastest land animal, but studies on their skeletal muscle properties are scarce. Vastus lateralis biopsies, obtained from male and female cheetahs as well as humans, were analysed and compared for fibre type and size, and metabolism. Overall, cheetah muscle had predominantly type IIX fibres, which was confirmed by the myosin heavy chain isoform content (mean±s.d. type I: 17±8%, type IIA: 21±6%, type IIX: 62±12%), whereas human muscle contained predominantly type I and IIA fibres (type I: 49±14%, type IIA: 43±8%, type IIX: 7±7%). Cheetahs had smaller fibres than humans, with larger fibres in the males compared with their female counterparts. Citrate synthase (16±6 versus 28±7 µmol min-1 g-1 protein, P<0.05) and 3-hydroxyacyl co-enzyme A dehydrogenase (30±11 versus 47±15 µmol min-1 g-1 protein, P<0.05) activities were lower in cheetahs than in humans, whereas lactate dehydrogenase activity was 6 times higher in cheetahs (2159±827 versus 382±161 µmol min-1 g-1 protein, P<0.001). The activities of creatine kinase (4765±1828 versus 6485±1298, P<0.05 µmol min-1 g-1 protein) and phosphorylase (111±29 versus 216±92 µmol min-1 g-1 protein) were higher in humans, irrespective of the higher type IIX fibres in cheetahs. Superoxide dismutase and catalase, markers of antioxidant capacity, were higher in humans, but overall antioxidant capacity was higher in cheetahs. To conclude, fibre type, fibre size and metabolism differ between cheetahs and humans, with limited differences between the sexes.

Characterising sex-related differences in lower- and higher-threshold motor unit behaviour through high-density surface electromyography

Emerging questions in neuromuscular physiology revolve around whether males and females share similar neural control in diverse tasks across a broad range of intensities. In order to explore these features, high-density electromyography was used to record the myoelectrical activity of biceps brachii during trapezoidal isometric contractions at 35% and 70% of maximal voluntary force (MVF) on 11 male and 13 female participants. Identified motor units were then classified as lower-threshold (recruited at ≤30%MVF) and higher-threshold (recruited at >30%MVF). The discharge rate, interspike interval variability, recruitment and derecruitment thresholds, and estimates of neural drive to motor neurons were assessed. Female lower-threshold motor units showed higher neural drive (P < 0.001), accompanied by higher discharge rate at recruitment (P = 0.006), plateau (P = 0.001) and derecruitment (P = 0.001). On the other hand, male higher-threshold motor units showed greater neural drive (P = 0.04), accompanied by higher discharge rate at recruitment (P = 0.005), plateau (P = 0.04) and derecruitment (P = 0.01). Motor unit discharge rate normalised by the recruitment threshold was significantly higher in female lower-threshold motor units (P < 0.001), while no differences were observed in higher-threshold motor units. Recruitment and derecruitment thresholds are higher in males across all intensities (P < 0.01). However, males and females have similar activation and deactivation strategies, as evidenced by similar recruitment-to-derecruitment ratios (P > 0.05). This study encompasses a broad intensity range to analyse motor unit sex-related differences, highlighting higher neural drive and discharge rates in female lower-threshold motor units, elevated recruitment and derecruitment thresholds in males, and convergences in activation and deactivation strategies. HIGHLIGHTS: What is the central question of the study? Do male and female motor units behave similarly in low- and high-intensity contractions? What is the main finding and its importance? Female motor units show higher discharge rates in low-intensity tasks and lower discharge rates in high-intensity tasks, with no differences in recruitment behaviour. A broader inter-spike interval variability was also observed in females. These findings underline that there are sex-specific differences concern the firing strategies based on task intensity.

Physical Activity, Fitness, and Long-Term Risk of Amyotrophic Lateral Sclerosis: A Prospective Cohort Study

BACKGROUND AND OBJECTIVES

Observational studies have demonstrated an increased amyotrophic lateral sclerosis (ALS) risk among professional athletes in various sports. For moderately increased levels of physical activity and fitness, the results are diverging. Through a cohort study, we aimed to assess the relationship between indicators of physical activity and fitness (self-reported physical activity and resting heart rate) and long-term ALS risk.

METHODS

From a large Norwegian cardiovascular health survey (1985-1999), we collected information on self-reported physical activity in leisure time, resting heart rate, and other cardiovascular risk factors. Patients with ALS were identified through health registries covering the whole population. We fitted Cox proportional hazard models to assess the risk of ALS according to levels of self-reported physical activity in 3 categories (1: sedentary; 2: minimum 4 hours per week of walking or cycling; 3: minimum 4 hours per week of recreational sports or hard training), and resting heart rate modeled both on the continuous scale and as quartiles of distribution.

RESULTS

Out of 373,696 study participants (mean 40.9 [SD 1.1] years at inclusion), 504 (41.2% women) developed ALS during a mean follow-up time of 27.2 (SD 5.0) years. Compared with participants with the lowest level of physical activity, the hazard ratio was 0.71 (95% CI 0.53-0.95) for those with the highest level. There were no clear associations between resting heart rate and ALS in the total sample. In men, the hazard ratio of ALS was 0.71 (95% CI 0.53-0.95) for those reporting moderate levels of physical activity and 0.59 (95% CI 0.42-0.84) for those reporting high levels, compared with those reporting low levels. Men with resting heart rate in the lowest quartile had 32% reduced risk of ALS (hazard ratio 0.68, 95% CI 0.49-0.94) compared with those in the second highest quartile. In women, no association was detected between neither self-reported levels of physical activity nor resting heart rate and ALS risk.

DISCUSSION

Indicators of high levels of physical activity and fitness are associated with a reduced risk of ALS more than 30 years later in men, but not in women.

The effects of plyometric training on physical fitness and skill-related performance in female basketball players: a systematic review and meta-analysis

Objective

This study aims to analyze the effects of plyometric training (PT) on physical fitness and skill-related performance in female basketball players.

Method

Five databases, including Web of Science, Scopus, PubMed, EBSCOhost, and Google Scholar, were used to select articles published up to 20 December 2023, using a combination of keywords related to PT and female basketball players. The risk of bias and the certainty of evidence in included articles were assessed using the Cochrane risk of bias (RoB2) tool and "The Grading of Recommendations Assessment, Development, and Evaluation" (GRADE).

Results

Ten studies were included for the systematic review, and eight for the meta-analysis, totalling 246 female basketball players aged 14.5-22.5 years. Most of these players were highly trained. Most of the included studies exhibited concerns regarding the risk of bias. The PT programs lasted 4-8 weeks, conducted 2-3 sessions per week, with sessions lasting 20-90 min and including 29-190 jumps. In the systematic review, most studies showed that PT significantly improved performance in countermovement jump (CMJ), squat jump (SJ), Sargent jump, standing long jump, lateral hop, medicine ball throw, t-Test, Illinois agility, lane agility drill, linear 20-m sprint, stable and dynamic leg balance, dribbling, passing, shooting, and various basketball-specific tests, as well as increased muscle volume and thigh cross-sectional area. However, some studies showed PT to induce no significant changes in performance during CMJ, t-Test, Illinois agility, knee extensor/flexor strength, linear sprint, and single leg balance tests. In the meta-analysis, CMJ height (ES = 0.37; p = 0.036), vertical jump (VJ) peak power (ES = 0.57; p = 0.015), VJ peak velocity (ES = 0.26; p = 0.004), and t-Test performance time (ES = 0.32; p = 0.004) were significantly improved with small effects following PT.

Conclusion

The effect of PT on performance in female basketball players was mixed. Most studies indicated that PT could improve various measures of physical fitness and skill-related performance, but performance remained unchanged in some tests. More studies with established tests are needed to investigate the effect of PT on female basketball players in the future.

Systematic Review Registration

https://inplasy.com/, Identifier INPLASY2023120078.

Hearts apart: sex differences in cardiac remodeling in health and disease

Biological sex is an important modifier of physiology and influences pathobiology in many diseases. While heart disease is the number one cause of death worldwide in both men and women, sex differences exist at the organ and cellular scales, affecting clinical presentation, diagnosis, and treatment. In this Review, we highlight baseline sex differences in cardiac structure, function, and cellular signaling and discuss the contribution of sex hormones and chromosomes to these characteristics. The heart is a remarkably plastic organ and rapidly responds to physiological and pathological cues by modifying form and function. The nature and extent of cardiac remodeling in response to these stimuli are often dependent on biological sex. We discuss organ- and molecular-level sex differences in adaptive physiological remodeling and pathological cardiac remodeling from pressure and volume overload, ischemia, and genetic heart disease. Finally, we offer a perspective on key future directions for research into cardiac sex differences.

Cerebral and muscle tissue oxygenation during exercise in healthy adults: A systematic review

BACKGROUND

Near-infrared spectroscopy (NIRS) technology has allowed for the measurement of cerebral and skeletal muscle oxygenation simultaneously during exercise. Since this technology has been growing and is now successfully used in laboratory and sports settings, this systematic review aimed to synthesize the evidence and enhance an integrative understanding of blood flow adjustments and oxygen (O2) changes (i.e., the balance between O2 delivery and O2 consumption) within the cerebral and muscle systems during exercise.

METHODS

A systematic review was conducted using PubMed, Embase, Scopus, and Web of Science databases to search for relevant studies that simultaneously investigated cerebral and muscle hemodynamic changes using the near-infrared spectroscopy system during exercise. This review considered manuscripts written in English and available before February 9, 2023. Each step of screening involved evaluation by 2 independent authors, with disagreements resolved by a third author. The Joanna Briggs Institute Critical Appraisal Checklist was used to assess the methodological quality of the studies.

RESULTS

Twenty studies were included, of which 80% had good methodological quality, and involved 290 young or middle-aged adults. Different types of exercises were used to assess cerebral and muscle hemodynamic changes, such as cycling (n = 11), treadmill (n = 1), knee extension (n = 5), isometric contraction of biceps brachii (n = 3), and duet swim routines (n = 1). The cerebral hemodynamics analysis was focused on the frontal cortex (n = 20), while in the muscle, the analysis involved vastus lateralis (n = 18), gastrocnemius (n = 3), biceps brachii (n = 5), deltoid (n = 1), and intercostal muscle (n = 1). Overall, muscle deoxygenation increases during exercise, reaching a plateau in voluntary exhaustion, while in the brain, oxyhemoglobin concentration increases with exercise intensity, reaching a plateau or declining at the exhaustion point.

CONCLUSION

Muscle and cerebral oxygenation respond differently to exercise, with muscle increasing O2 utilization and cerebral tissue increasing O2 delivery during exercise. However, at the exhaustion point, both muscle and cerebral oxygenation become compromised. This is characterized by a reduction in blood flow and a decrease in O2 extraction in the muscle, while in the brain, oxygenation reaches a plateau or decline, potentially resulting in motor failure during exercise.

Screening of aspiration pneumonia using the modified Mallampati classification tool in older adults

Pneumonia is a major cause of morbidity and mortality in older adults. In the aging society, screening methods for predicting aspiration pneumonia are crucial for its prevention. Changes in the oropharyngeal morphology and hyoid bone position may increase the risk of aspiration pneumonia. This multicenter study aimed to investigate a simple and effective screening method for predicting dysphagia and aspiration pneumonia. Overall, 191 older adults (aged 65 years or older) were randomly sampled using the simple random sampling technique. Oropharyngeal morphology was assessed using the modified Mallampati classification, which reflects the size of the tongue in the oropharyngeal cavity. The hyoid position was measured as the distance between the menton and laryngeal prominence to evaluate aging-related changes in the muscles of the laryngopharynx. Dysphagia was assessed using the repetitive saliva swallowing test (RSST), which measures the number of swallowing movements in 30 seconds; dysphasia is defined as less than 3 swallowing movements in 30 seconds. The aspiration signs were assessed based on history of choking or coughing reflex during eating or drinking and medical history of pneumonia. The study findings revealed that the modified Mallampati classification was significantly correlated with a medical history of pneumonia. A higher incidence of pneumonia was evident in the lower Mallampati classification, which shows the smaller size of the tongue base in the oropharyngeal cavity. The results of this study suggest that the modified Mallampati classification may be a possible screening method to predict the occurrence of pneumonia.

The impact of exercise on gene regulation in association with complex trait genetics

Endurance exercise training is known to reduce risk for a range of complex diseases. However, the molecular basis of this effect has been challenging to study and largely restricted to analyses of either few or easily biopsied tissues. Extensive transcriptome data collected across 15 tissues during exercise training in rats as part of the Molecular Transducers of Physical Activity Consortium has provided a unique opportunity to clarify how exercise can affect tissue-specific gene expression and further suggest how exercise adaptation may impact complex disease-associated genes. To build this map, we integrate this multi-tissue atlas of gene expression changes with gene-disease targets, genetic regulation of expression, and trait relationship data in humans. Consensus from multiple approaches prioritizes specific tissues and genes where endurance exercise impacts disease-relevant gene expression. Specifically, we identify a total of 5523 trait-tissue-gene triplets to serve as a valuable starting point for future investigations [Exercise; Transcription; Human Phenotypic Variation].

The Association of Age, Sex, and BMI on Lower Limb Neuromuscular and Muscle Mechanical Function in People with Multiple Sclerosis

(1) Background: The countermovement jump (CMJ) on a force plate could be a sensitive assessment for detecting early lower-limb muscle mechanical deficits in the early stages of multiple sclerosis (MS). CMJ performance is known to be influenced by various anthropometric, physiological, and biomechanical factors, mostly investigated in children and adult athletes. Our aim was to investigate the association of age, sex, and BMI with muscle mechanical function using CMJ to provide a comprehensive overview of lower-limb motor function in people with multiple sclerosis (pwMS). (2) Methods: A cross-sectional study was conducted with pwMS (N = 164) and healthy controls (N = 98). All participants performed three maximal CMJs on a force plate. Age, sex, and BMI were collected from all participants. (3) Results: Significant age, sex, and BMI effects were found for all performance parameters, flight time, and negative and positive power for pwMS and HC, but no significant interaction effects with the group (pwMS, HC) were detected. The highest significant effects were found for sex on flight time (η2 = 0.23), jump height (η2 = 0.23), and positive power (η2 = 0.13). PwMS showed significantly lower CMJ performance compared to HC in middle-aged (31-49 years), with normal weight to overweight and in both women and men. (4) Conclusions: This study showed that age, sex, and BMI are associated with muscle mechanical function in pwMS and HC. These results may be useful in developing reference values for CMJ. This is a crucial step in integrating CMJ into the diagnostic assessment of people with early MS and developing individualized and effective neurorehabilitative therapy.

Sex Differences in Neuromuscular Aging: The Role of Sex Hormones

Males and females experience different trajectories of neuromuscular function across the lifespan, with females demonstrating accelerated deconditioning in later life. We hypothesize that the menopause is a critical period in the female lifespan, during which the dramatic reduction in sex hormone concentrations negatively impacts synaptic input to the motoneuron pool, as well as motor unit discharge properties.

Low Response to Aerobic Training in Metabolic Disease: Role of Skeletal Muscle

Aerobic exercise is established to increase cardiorespiratory fitness (CRF), which is linked to reduced morbidity and mortality. However, people with metabolic diseases such as type 1 and type 2 diabetes may be more likely to display blunted improvements in CRF with training. Here, we present evidence supporting the hypothesis that altered skeletal muscle signaling and remodeling may contribute to low CRF with metabolic disease.

Sex differences in neuromuscular and biological determinants of isometric maximal force

AIM

Force expression is characterized by an interplay of biological and molecular determinants that are expected to differentiate males and females in terms of maximal performance. These include muscle characteristics (muscle size, fiber type, contractility), neuromuscular regulation (central and peripheral factors of force expression), and individual genetic factors (miRNAs and gene/protein expression). This research aims to comprehensively assess these physiological variables and their role as determinants of maximal force difference between sexes.

METHODS

Experimental evaluations include neuromuscular components of isometric contraction, intrinsic muscle characteristics (proteins and fiber type), and some biomarkers associated with muscle function (circulating miRNAs and gut microbiome) in 12 young and healthy males and 12 females.

RESULTS

Male strength superiority appears to stem primarily from muscle size while muscle fiber-type distribution plays a crucial role in contractile properties. Moderate-to-strong pooled correlations between these muscle parameters were established with specific circulating miRNAs, as well as muscle and plasma proteins.

CONCLUSION

Muscle size is crucial in explaining the differences in maximal voluntary isometric force generation between males and females with similar fiber type distribution. Potential physiological mechanisms are seen from associations between maximal force, skeletal muscle contractile properties, and biological markers.

Effects of chronic alcohol intoxication on aerobic exercise-induced adaptations in female mice

Chronic alcohol intoxication decreases muscle strength/function and causes mitochondrial dysfunction. Aerobic exercise training improves mitochondrial oxidative capacity and increases muscle mass and strength. Presently, the impact of chronic alcohol on aerobic exercise-induced adaptations was investigated. Female C57BL/6Hsd mice were randomly assigned to one of four groups: control sedentary (CON SED; n = 26), alcohol sedentary (ETOH SED; n = 27), control exercise (CON EX; n = 28), and alcohol exercise (ETOH EX; n = 25). Exercise mice had running wheel access for 2 h a day, 7 days a week. All mice were fed either control or an alcohol-containing liquid diet. Grip strength testing and EchoMRI were performed before and after the interventions. After 6 wk, hindlimb muscles were collected for molecular analyses. A subset of mice performed a treadmill run to fatigue (RTF), then abstained from alcohol for 2 wk and repeated the RTF. Alcohol decreased lean mass and forelimb grip strength compared with control-fed mice. Alcohol blunted the exercise-induced increase in muscle mass (plantaris and soleus), type IIa fiber percentage in the plantaris, and run time to fatigue. Mitochondrial markers (Citrate synthase activity and Complex I-IV, COXIV and Cytochrome C protein expression) were increased with exercise regardless of ETOH in the gastrocnemius but not tibialis anterior muscle. Two weeks of alcohol abstinence improved RTF time in ETOH EX but not in ETOH SED. These data suggest that alcohol impairs some exercise-induced adaptations in skeletal muscle, but not all were negatively affected, indicating that exercise may be a beneficial behavior even while consuming alcohol.NEW & NOTEWORTHY Alcohol consumption during an aerobic exercise training period prevented training-induced increases in run to fatigue time and grip strength. Cessation of alcohol allowed for recovery of endurance performance within 2 wk. The worsened exercise performance after alcohol was unrelated to impairments in markers of mitochondrial health. Therefore, some adaptations to exercise training are impaired with alcohol use (endurance performance, muscle growth, and strength), while others remain mostly unaffected (mitochondrial health).

Decreased sarcoplasmic reticulum phospholipids in human skeletal muscle are associated with metabolic syndrome

Metabolic syndrome affects more than one in three adults and is associated with increased risk of diabetes, cardiovascular disease, and all-cause mortality. Muscle insulin resistance is a major contributor to the development of the metabolic syndrome. Studies in mice have linked skeletal muscle sarcoplasmic reticulum (SR) phospholipid composition to sarcoplasmic/endoplasmic reticulum Ca2+-ATPase activity and insulin sensitivity. To determine if the presence of metabolic syndrome alters specific phosphatidylcholine (PC) and phosphatidylethanolamine (PE) species in human SR, we compared SR phospholipid composition in skeletal muscle from sedentary subjects with metabolic syndrome and sedentary control subjects without metabolic syndrome. Both total PC and total PE were significantly decreased in skeletal muscle SR of sedentary metabolic syndrome patients compared with sedentary controls, particularly in female participants, but there was no difference in the PC:PE ratio between groups. Total SR PC levels, but not total SR PE levels or PC:PE ratio, were significantly negatively correlated with BMI, waist circumference, total fat, visceral adipose tissue, triglycerides, fasting insulin, and homeostatic model assessment for insulin resistance. These findings are consistent with the existence of a relationship between skeletal muscle SR PC content and insulin resistance in humans.

Concurrent Strength and Endurance Training: A Systematic Review and Meta-Analysis on the Impact of Sex and Training Status

BACKGROUND

Many sports require maximal strength and endurance performance. Concurrent strength and endurance training can lead to suboptimal training adaptations. However, how adaptations differ between males and females is currently unknown. Additionally, current training status may affect training adaptations.

OBJECTIVE

We aimed to assess sex-specific differences in adaptations in strength, power, muscle hypertrophy, and maximal oxygen consumption ( V ˙ O2max) to concurrent strength and endurance training in healthy adults. Second, we investigated how training adaptations are influenced by strength and endurance training status.

METHODS

A systematic review and meta-analysis was conducted according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, and a Cochrane risk of bias was evaluated. ISI Web of science, PubMed/MEDLINE, and SPORTDiscus databases were searched using the following inclusion criteria: healthy adults aged 18-50 years, intervention period of ≥ 4 weeks, and outcome measures were defined as upper- and lower-body strength, power, hypertrophy, and/or V ˙ O2max. A meta-analysis was performed using a random-effects model and reported in standardized mean differences.

RESULTS

In total, 59 studies with 1346 participants were included. Concurrent training showed blunted lower-body strength adaptations in males, but not in females (male: - 0.43, 95% confidence interval [- 0.64 to - 0.22], female: 0.08 [- 0.34 to 0.49], group difference: P = 0.03). No sex differences were observed for changes in upper-body strength (P = 0.67), power (P = 0.37), or V ˙ O2max (P = 0.13). Data on muscle hypertrophy were insufficient to draw any conclusions. For training status, untrained but not trained or highly trained endurance athletes displayed lower V ˙ O2max gains with concurrent training (P = 0.04). For other outcomes, no differences were found between untrained and trained individuals, both for strength and endurance training status.

CONCLUSIONS

Concurrent training results in small interference for lower-body strength adaptations in males, but not in females. Untrained, but not trained or highly trained endurance athletes demonstrated impaired improvements in V ˙ O2max following concurrent training. More studies on females and highly strength-trained and endurance-trained athletes are warranted.

CLINICAL TRIAL REGISTRATION

PROSPERO: CRD42022370894.

Real World Interstitial Glucose Profiles of a Large Cohort of Physically Active Men and Women

The use of continuous glucose monitors (CGMs) in individuals living without diabetes is increasing. The purpose of this study was to profile various CGM metrics around nutritional intake, sleep and exercise in a large cohort of physically active men and women living without any known metabolic disease diagnosis to better understand the normative glycemic response to these common stimuli. A total of 12,504 physically active adults (age 40 ± 11 years, BMI 23.8 ± 3.6 kg/m2; 23% self-identified as women) wore a real-time CGM (Abbott Libre Sense Sport Glucose Biosensor, Abbott, USA) and used a smartphone application (Supersapiens Inc., Atlanta, GA, USA) to log meals, sleep and exercise activities. A total of >1 M exercise events and 274,344 meal events were analyzed. A majority of participants (85%) presented an overall (24 h) average glucose profile between 90 and 110 mg/dL, with the highest glucose levels associated with meals and exercise and the lowest glucose levels associated with sleep. Men had higher mean 24 h glucose levels than women (24 h-men: 100 ± 11 mg/dL, women: 96 ± 10 mg/dL). During exercise, the % time above >140 mg/dL was 10.3 ± 16.7%, while the % time <70 mg/dL was 11.9 ± 11.6%, with the remaining % within the so-called glycemic tight target range (70-140 mg/dL). Average glycemia was also lower for females during exercise and sleep events (p < 0.001). Overall, we see small differences in glucose trends during activity and sleep in females as compared to males and higher levels of both TAR and TBR when these active individuals are undertaking or competing in endurance exercise training and/or competitive events.

Remodeling of the human skeletal muscle proteome found after long-term endurance training but not after strength training

Exercise training has tremendous systemic tissue-specific health benefits, but the molecular adaptations to long-term exercise training are not completely understood. We investigated the skeletal muscle proteome of highly endurance-trained, strength-trained, and untrained individuals and performed exercise- and sex-specific analyses. Of the 6,000+ proteins identified, >650 were differentially expressed in endurance-trained individuals compared with controls. Strikingly, 92% of the shared proteins with higher expression in both the male and female endurance groups were known mitochondrial. In contrast to the findings in endurance-trained individuals, minimal differences were found in strength-trained individuals and between females and males. Lastly, a co-expression network and comparative literature analysis revealed key proteins and pathways related to the health benefits of exercise, which were primarily related to differences in mitochondrial proteins. This network is available as an interactive database resource where investigators can correlate clinical data with global gene and protein expression data for hypothesis generation.

The Impact of Gender-Affirming Hormone Therapy on Physical Performance

CONTEXT

The inclusion of transgender people in elite sport has been a topic of debate. This narrative review examines the impact of gender-affirming hormone therapy (GAHT) on physical performance, muscle strength, and markers of endurance.

EVIDENCE ACQUISITION

MEDLINE and Embase were searched using terms to define the population (transgender), intervention (GAHT), and physical performance outcomes.

EVIDENCE SYNTHESIS

Existing literature comprises cross-sectional or small uncontrolled longitudinal studies of short duration. In nonathletic trans men starting testosterone therapy, within 1 year, muscle mass and strength increased and, by 3 years, physical performance (push-ups, sit-ups, run time) improved to the level of cisgender men. In nonathletic trans women, feminizing hormone therapy increased fat mass by approximately 30% and decreased muscle mass by approximately 5% after 12 months, and steadily declined beyond 3 years. While absolute lean mass remains higher in trans women, relative percentage lean mass and fat mass (and muscle strength corrected for lean mass), hemoglobin, and VO2 peak corrected for weight was no different to cisgender women. After 2 years of GAHT, no advantage was observed for physical performance measured by running time or in trans women. By 4 years, there was no advantage in sit-ups. While push-up performance declined in trans women, a statistical advantage remained relative to cisgender women.

CONCLUSION

Limited evidence suggests that physical performance of nonathletic trans people who have undergone GAHT for at least 2 years approaches that of cisgender controls. Further controlled longitudinal research is needed in trans athletes and nonathletes.

Impaired communication at the neuromotor axis during Degenerative Cervical Myelopathy

Degenerative Cervical Myelopathy (DCM) is a progressive neurological condition characterized by structural alterations in the cervical spine, resulting in compression of the spinal cord. While clinical manifestations of DCM are well-documented, numerous unanswered questions persist at the molecular and cellular levels. In this study, we sought to investigate the neuromotor axis during DCM. We use a clinically relevant mouse model, where after 3 months of DCM induction, the sensorimotor tests revealed a significant reduction in both locomotor activity and muscle strength compared to the control group. Immunohistochemical analyses showed alterations in the gross anatomy of the cervical spinal cord segment after DCM. These changes were concomitant with the loss of motoneurons and a decrease in the number of excitatory synaptic inputs within the spinal cord. Additionally, the DCM group exhibited a reduction in the endplate surface, which correlated with diminished presynaptic axon endings in the supraspinous muscles. Furthermore, the biceps brachii (BB) muscle exhibited signs of atrophy and impaired regenerative capacity, which inversely correlated with the transversal area of remnants of muscle fibers. Additionally, metabolic assessments in BB muscle indicated an increased proportion of oxidative skeletal muscle fibers. In line with the link between neuromotor disorders and gut alterations, DCM mice displayed smaller mucin granules in the mucosa layer without damage to the epithelial barrier in the colon. Notably, a shift in the abundance of microbiota phylum profiles reveals an elevated Firmicutes-to-Bacteroidetes ratio-a consistent hallmark of dysbiosis that correlates with alterations in gut microbiota-derived metabolites. Additionally, treatment with short-chain fatty acids stimulated the differentiation of the motoneuron-like NSC34 cell line. These findings shed light on the multifaceted nature of DCM, resembling a synaptopathy that disrupts cellular communication within the neuromotor axis while concurrently exerting influence on other systems. Notably, the colon emerges as a focal point, experiencing substantial perturbations in both mucosal barrier integrity and the delicate balance of intestinal microbiota.

Pain-sensorimotor interactions: New perspectives and a new model

How pain and sensorimotor behavior interact has been the subject of research and debate for many decades. This article reviews theories bearing on pain-sensorimotor interactions and considers their strengths and limitations in the light of findings from experimental and clinical studies of pain-sensorimotor interactions in the spinal and craniofacial sensorimotor systems. A strength of recent theories is that they have incorporated concepts and features missing from earlier theories to account for the role of the sensory-discriminative, motivational-affective, and cognitive-evaluative dimensions of pain in pain-sensorimotor interactions. Findings acquired since the formulation of these recent theories indicate that additional features need to be considered to provide a more comprehensive conceptualization of pain-sensorimotor interactions. These features include biopsychosocial influences that range from biological factors such as genetics and epigenetics to psychological factors and social factors encompassing environmental and cultural influences. Also needing consideration is a mechanistic framework that includes other biological factors reflecting nociceptive processes and glioplastic and neuroplastic changes in sensorimotor and related brain and spinal cord circuits in acute or chronic pain conditions. The literature reviewed and the limitations of previous theories bearing on pain-sensorimotor interactions have led us to provide new perspectives on these interactions, and this has prompted our development of a new concept, the Theory of Pain-Sensorimotor Interactions (TOPSMI) that we suggest gives a more comprehensive framework to consider the interactions and their complexity. This theory states that pain is associated with plastic changes in the central nervous system (CNS) that lead to an activation pattern of motor units that contributes to the individual's adaptive sensorimotor behavior. This activation pattern takes account of the biological, psychological, and social influences on the musculoskeletal tissues involved in sensorimotor behavior and on the plastic changes and the experience of pain in that individual. The pattern is normally optimized in terms of biomechanical advantage and metabolic cost related to the features of the individual's musculoskeletal tissues and aims to minimize pain and any associated sensorimotor changes, and thereby maintain homeostasis. However, adverse biopsychosocial factors and their interactions may result in plastic CNS changes leading to less optimal, even maladaptive, sensorimotor changes producing motor unit activation patterns associated with the development of further pain. This more comprehensive theory points towards customized treatment strategies, in line with the management approaches to pain proposed in the biopsychosocial model of pain.

Muscle miRNAs are influenced by sex at baseline and in response to exercise

BACKGROUND

Sex differences in microRNA (miRNA) expression profiles have been found across multiple tissues. Skeletal muscle is one of the most sex-biased tissues of the body. MiRNAs are necessary for development and have regulatory roles in determining skeletal muscle phenotype and have important roles in the response to exercise in muscle. Yet there is limited research into the role and regulation of miRNAs in the skeletal muscle at baseline and in response to exercise, a well-known modulator of miRNA expression. The aim of this study was to investigate the effect of sex on miRNA expression in the skeletal muscle at baseline and after an acute bout of high-intensity interval exercise. A total of 758 miRNAs were measured using Taqman®miRNA arrays in the skeletal muscle of 42 healthy participants from the Gene SMART study (23 males and 19 females of comparable fitness levels and aged 18-45 years), of which 308 were detected. MiRNAs that differed by sex at baseline and whose change in expression following high-intensity interval exercise differed between the sexes were identified using mixed linear models adjusted for BMI and Wpeak. We performed in silico analyses to identify the putative gene targets of the exercise-induced, sex-specific miRNAs and overrepresentation analyses to identify enriched biological pathways. We performed functional assays by overexpressing two sex-biased miRNAs in human primary muscle cells derived from male and female donors to understand their downstream effects on the transcriptome.

RESULTS

At baseline, 148 miRNAs were differentially expressed in the skeletal muscle between the sexes. Interaction analysis identified 111 miRNAs whose response to an acute bout of high-intensity interval exercise differed between the sexes. Sex-biased miRNA gene targets were enriched for muscle-related processes including proliferation and differentiation of muscle cells and numerous metabolic pathways, suggesting that miRNAs participate in programming sex differences in skeletal muscle function. Overexpression of sex-biased miRNA-30a and miRNA-30c resulted in profound changes in gene expression profiles that were specific to the sex of the cell donor in human primary skeletal muscle cells.

CONCLUSIONS

We uncovered sex differences in the expression levels of muscle miRNAs at baseline and in response to acute high-intensity interval exercise. These miRNAs target regulatory pathways essential to skeletal muscle development and metabolism. Our findings highlight that miRNAs play an important role in programming sex differences in the skeletal muscle phenotype.

Impact of biological sex and sex hormones on molecular signatures of skeletal muscle at rest and in response to distinct exercise training modes

Substantial divergence in cardio-metabolic risk, muscle size, and performance exists between men and women. Considering the pivotal role of skeletal muscle in human physiology, we investigated and found, based on RNA sequencing (RNA-seq), that differences in the muscle transcriptome between men and women are largely related to testosterone and estradiol and much less related to genes located on the Y chromosome. We demonstrate inherent unique, sex-dependent differences in muscle transcriptional responses to aerobic, resistance, and combined exercise training in young and older cohorts. The hormonal changes with age likely explain age-related differential expression of transcripts. Furthermore, in primary human myotubes we demonstrate the profound but distinct effects of testosterone and estradiol on amino acid incorporation to multiple individual proteins with specific functions. These results clearly highlight the potential of designing exercise programs tailored specifically to men and women and have implications for people who change gender by altering their hormone profile.

Sex differences and athletic performance. Where do trans individuals fit into sports and athletics based on current research?

There are well known sex differences in parameters of physical fitness/performance due to changes occurring during sexual development. Thus, many sport and athletic events have regulations separating male and female participants. However, the inclusion or exclusion of transgender individuals in athletics has recently received outsized attention despite relatively few cases of transgender athletes. When determining which athletic gender category trans individuals should be permitted to compete in, it is important to understand the level of physical fitness/performance these individuals possess relative to their cisgender counterparts. Unfortunately, there are few studies investigating this topic, and several complications that confound this research. The current review seeks to discuss sex and gender as concepts, review sex differences in fitness/performance and how they develop, and then, consider how current evidence suggests that trans individuals compare to cis individuals. Finally, this review seeks to offer considerations for whether trans individuals should be excluded from sports and athletics, and how future research should proceed to better understand this marginalized population.

Physiological responses to treadmill exercise in size- and fitness-matched male and female firefighter applicants

Physiological responses during a standardised treadmill test for structural firefighting employment were compared in 41 pairs of size-matched, male and female applicants. Applicants wore personal exercise clothing, running shoes, and fire protective ensemble with self-contained breathing apparatus (added mass 21.2 ± 1.0 kg). Applicants walked at 1.56 m·s-1, completing a 5-min warm-up, 8-min at 10% grade, and then, progressive 1-min stages to exhaustion. The cut-score required completion of 13-min of exercise. Up to the cut-score, no differences in heart rate, oxygen uptake or minute ventilation were detected between sexes. At time 12:30-13:00 min, V̇O2 was 45.7 ± 0.6 vs. 44.2 ± 0.5 mL·kg-1·min-1 (body mass) for males and females, respectively. Despite similar physiological responses at minute 13, females worked at higher fractions of peak than males (p < 0.05). A second analysis compared a subset of 27 fitness-matched (V̇O2peak) male-female pairs. Fitness-matching further reduced or eliminated most observed differences in physiological responses, except small differences in breathing pattern. Practitioner Summary: Physiological responses during a standardised treadmill test for firefighter applicants were investigated in male and female applicants matched on size and fitness. Absolute responses to exercise were the same for both sexes when size-matched, but relative intensity was higher for females. Fitness-matching reduced or eliminated most previously observed differences. Abbreviations: NFPA: National Fire Protection Association; V̇O2: rate of oxygen consumption; V̇O2peak: rate of oxygen consumption at peak exercise; PAR-Q+: Physical Activity Readiness Questionnaire Plus; SCBA: self-contained breathing apparatus; ANOVA: analysis of variance; V̇E: minute ventilation; V̇Epeak: minute ventilation at peak exercise; V̇E/V̇O2: ventilatory equivalent for oxygen.

Sex differences in muscle protein expression and DNA methylation in response to exercise training

BACKGROUND

Exercise training elicits changes in muscle physiology, epigenomics, transcriptomics, and proteomics, with males and females exhibiting differing physiological responses to exercise training. However, the molecular mechanisms contributing to the differing adaptations between the sexes are poorly understood.

METHODS

We performed a meta-analysis for sex differences in skeletal muscle DNA methylation following an endurance training intervention (Gene SMART cohort and E-MTAB-11282 cohort). We investigated for sex differences in the skeletal muscle proteome following an endurance training intervention (Gene SMART cohort). Lastly, we investigated whether the methylome and proteome are associated with baseline cardiorespiratory fitness (maximal oxygen consumption; VO2max) in a sex-specific manner.

RESULTS

Here, we investigated for the first time, DNA methylome and proteome sex differences in response to exercise training in human skeletal muscle (n = 78; 50 males, 28 females). We identified 92 DNA methylation sites (CpGs) associated with exercise training; however, no CpGs changed in a sex-dependent manner. In contrast, we identified 189 proteins that are differentially expressed between the sexes following training, with 82 proteins differentially expressed between the sexes at baseline. Proteins showing the most robust sex-specific response to exercise include SIRT3, MRPL41, and MBP. Irrespective of sex, cardiorespiratory fitness was associated with robust methylome changes (19,257 CpGs) and no proteomic changes. We did not observe sex differences in the association between cardiorespiratory fitness and the DNA methylome. Integrative multi-omic analysis identified sex-specific mitochondrial metabolism pathways associated with exercise responses. Lastly, exercise training and cardiorespiratory fitness shifted the DNA methylomes to be more similar between the sexes.

CONCLUSIONS

We identified sex differences in protein expression changes, but not DNA methylation changes, following an endurance exercise training intervention; whereas we identified no sex differences in the DNA methylome or proteome response to lifelong training. Given the delicate interaction between sex and training as well as the limitations of the current study, more studies are required to elucidate whether there is a sex-specific training effect on the DNA methylome. We found that genes involved in mitochondrial metabolism pathways are differentially modulated between the sexes following endurance exercise training. These results shed light on sex differences in molecular adaptations to exercise training in skeletal muscle.

Skinfold Thickness as a Cardiometabolic Risk Predictor in Sedentary and Active Adult Populations

Studies report that increased body fat can lead to health risks for individuals. However, some methods used for analyzing adiposity did not identify its distribution in the human body because they are typically measured using bioimpedance scales. This study aims to associate the presence of cardiometabolic risk factors in sedentary and active adult populations through anthropometric methods based on skinfold thickness measurements. A cross-sectional study was conducted on 946 adults aged between 18 and 79 years with prior informed consent. Clinical, anthropometric, and biochemical parameters, as well as some cardiometabolic risk factors, were evaluated. Almost half of the population (45.1%; n = 427) is sedentary. A significant association was found between the sum of the skinfolds (bicipital, tricipital, subscapular, and suprailiac) and the cardiometabolic risk factors evaluated, highlighting the cardiovascular risk associated with abdominal obesity, risk of insulin resistance, as well as the development of hyperglycemia, and hypertriglyceridemia. The bicipital fold was thicker (19.67 mm) in the population with a sedentary lifestyle than in the physically active population (18.30 mm). Furthermore, the skinfolds that predict higher metabolic risks were suprailiac and subscapular in sedentary and active populations. Thus, these skinfold measurements could be considered in assessing the adult population for early cardiometabolic risk detection, even in healthy and physically active people.

Gender similarities and differences in skeletal muscle and body composition: an MRI study of recreational cyclists

Objectives

This study aims to quantitatively evaluate whether there are muscle mass differences between male and female recreational cyclists and compare muscle quality and body composition in the pelvis region between two well-matched groups of fit and healthy male and female adults.

Methods

This cross-sectional study involved 45 female and 42 male recreational cyclists. The inclusion criteria for both groups were to have cycled more than 7000 km in the last year, have an absence of injuries and other health problems, have no contraindication to MRI, and be 30-65 years old. Our main outcome measures were fat fraction, as a measure of intramuscular fat (IMF) content, and volume of the gluteal muscles measured using Dixon MRI. The gluteal subcutaneous adipose tissue (SAT) volume was evaluated as a secondary measure.

Results

We found that there were no gender differences in the IMF content of gluteus maximus (GMAX, p=0.42), gluteus medius (GMED, p=0.69) and gluteus minimus (GMIN, p=0.06) muscles, despite women having more gluteal SAT (p<0.01). Men had larger gluteal muscles than women (p<0.01), but no differences were found when muscle volume was normalised by body weight (GMAX, p=0.54; GMED, p=0.14; GMIN, p=0.19).

Conclusions

Our study shows that despite the recognised hormonal differences between men and women, there is gender equivalence in the muscle mass and quality of the gluteal muscles when matched for exercise and body weight. This new MRI study provides key information to better understand gender similarities and differences in skeletal muscle and body composition.

The Effect of Omega-3 Fatty Acids on Sarcopenia: Mechanism of Action and Potential Efficacy

Sarcopenia, a progressive disease characterized by a decline in muscle strength, quality, and mass, affects aging population worldwide, leading to increased morbidity and mortality. Besides resistance exercise, various nutritional strategies, including omega-3 polyunsaturated fatty acid (n-3 PUFA) supplementation, have been sought to prevent this condition. This narrative review summarizes the current evidence on the effect and mechanism of n-3 PUFA on musculoskeletal health. Despite conflicting evidence, n-3 PUFA is suggested to benefit muscle mass and volume, with more evident effects with higher supplementation dose (>2 g/day). n-3 PUFA supplementation likely improves handgrip and quadriceps strength in the elderly. Improved muscle functions, measured by walking speed and time-up-to-go test, are also observed, especially with longer duration of supplementation (>6 months), although the changes are small and unlikely to be clinically meaningful. Lastly, n-3 PUFA supplementation may positively affect muscle protein synthesis response to anabolic stimuli, alleviating age-related anabolic resistance. Proposed mechanisms by which n-3 PUFA supplementation improves muscle health include 1. anti-inflammatory properties, 2. augmented expression of mechanistic target of rapamycin complex 1 (mTORC1) pathway, 3. decreased intracellular protein breakdown, 4. improved mitochondrial biogenesis and function, 5. enhanced amino acid transport, and 6. modulation of neuromuscular junction activity. In conclusion, n-3 PUFAs likely improve musculoskeletal health related to sarcopenia, with suggestive effect on muscle mass, strength, physical performance, and muscle protein synthesis. However, the interpretation of the findings is limited by the small number of participants, heterogeneity of supplementation regimens, and different measuring protocols.

Female cardiovascular biology and resilience in the setting of physiological and pathological stress

For years, females were thought of as smaller men with complex hormonal cycles; as a result, females have been largely excluded from preclinical and clinical research. However, in the last ten years, with the increased focus on sex as a biological variable, it has become clear that this is not the case, and in fact, male and female cardiovascular biology and cardiac stress responses differ substantially. Premenopausal women are protected from cardiovascular diseases, such as myocardial infarction and resultant heart failure, having preserved cardiac function, reduced adverse remodeling, and increased survival. Many underlying biological processes that contribute to ventricular remodeling differ between the sexes, such as cellular metabolism; immune cell responses; cardiac fibrosis and extracellular matrix remodeling; cardiomyocyte dysfunction; and endothelial biology; however, it is unclear how these changes afford protection to the female heart. Although many of these changes are dependent on protection provided by female sex hormones, several of these changes occur independent of sex hormones, suggesting that the nature of these changes is more complex than initially thought. This may be why studies focused on the cardiovascular benefits of hormone replacement therapy in post-menopausal women have provided mixed results. Some of the complexity likely stems from the fact that the cellular composition of the heart is sexually dimorphic and that in the setting of MI, different subpopulations of these cell types are apparent. Despite the documented sex-differences in cardiovascular (patho)physiology, the underlying mechanisms that contribute are largely unknown due to inconsistent findings amongst investigators and, in some cases, lack of rigor in reporting and consideration of sex-dependent variables. Therefore, this review aims to describe current understanding of the sex-dependent differences in the myocardium in response to physiological and pathological stressors, with a focus on the sex-dependent differences that contribute to post-infarction remodeling and resultant functional decline.

Effects of Sex and Cuff Pressure on Physiological Responses during Blood Flow Restriction Resistance Exercise in Young Adults

PURPOSE

The purpose of this study was to examine the physiological responses resulting from an acute blood flow restriction resistance exercise bout with two different cuff pressures in young, healthy men and women.

METHODS

Thirty adults (18-30 yr) completed a bilateral leg extension blood flow restriction bout consisting of four sets (30-15-15-15 repetitions), with cuffs applied at pressures corresponding to 40% and 60% of the minimum arterial occlusion pressure (AOP) needed to completely collapse the femoral arteries. During each of these conditions (40% and 60% AOP), physiological measures of near-infrared spectroscopy (NIRS) and EMG amplitude (EMG AMP) were collected from the dominant or nondominant vastus lateralis. After each set, ratings of perceived exertion (RPE) were collected, whereas only at baseline and at the end of the bout, mean arterial pressure (MAP) was assessed. Separate mixed-factorial ANOVA models were used to examine mean differences in the change in EMG AMP and NIRS parameters during each set. The absolute RPE and MAP values were also examined with separate ANOVAs. A P value ≤0.05 was considered statistically significant.

RESULTS

Regardless of sex or cuff pressure, the change in EMG AMP was lower in set 1 (14.8%) compared with the remaining sets (22.6%-27.0%). The 40% AOP condition elicited the greatest changes in oxy[heme] and deoxy[heme], while also providing lower RPEs. For MAP, there was an effect for time such that MAP increased from preexercise (87.5 ± 4.3 mm Hg) to postexercise (104.5 ± 4.1 mm Hg).

CONCLUSIONS

The major findings suggested that the 40% AOP condition permitted the greatest amount of recovery during the interset rest. In addition, there did not seem to be any meaningful sex-related difference in this sample of young healthy adults.