Physiological characteristics predictive of passing military physical employment standard tasks for ground close combat occupations in men and women.

Challenges for some women meeting the physical employment standards (PES) for ground close combat (GCC) roles stem from physical fitness and anthropometric characteristics. The purpose of this study was to identify the modifiable and nonmodifiable characteristics predictive of passing GCC-based PES tasks and determine the modifiable characteristics suitable to overcome nonmodifiable limitations. 107 adults (46 women) underwent multiday testing assessing regional and total lean mass (LM), percent body fat (BF%), aerobic capacity (V̇O2peak), strength, power, and PES performance. Predictors with p-value <0.200 were included in stepwise logistic regression analysis or binary logistic regression when outcomes among sexes were insufficient. Relative and absolute arm LM (OR: 4.617-8.522, p < 0.05), leg LM (OR: 2.463, p < 0.05), and upper body power (OR: 2.061, p < 0.05) predicted medicine ball chest throw success. Relative and absolute arm LM (OR: 3.734-11.694, p < 0.05), absolute trunk LM (OR: 2.576, p < 0.05), and leg LM (OR: 2.088, p < 0.05) predicted casualty drag success. Upper body power (OR: 3.910, p < 0.05), absolute trunk LM (OR: 2.387, p < 0.05), leg LM (OR: 2.290, p < 0.05), and total LM (OR: 1.830, p < 0.05) predicted maximum single lift success. Relative and absolute arm LM (OR: 3.488-7.377, p < 0.05), leg LM (OR: 1.965, p < 0.05), and upper body power (OR: 1.957, p < 0.05) predicted water can carry success. %BF (OR: 0.814, p = 0.007), V̇O2peak (OR: 1.160, p = 0.031), and lower body strength (OR: 1.059, p < 0.001) predicted repeated lift and carry success. V̇O2peak (OR: 1.540, p < 0.001) predicted 2-km ruck march success. Modifiable characteristics were the strongest predictors for GCC-based PES task success to warrant their improvement for enhancing PES performance for women.

Effect of Menstrual Cycle and Hormonal Contraception on Musculoskeletal Health and Performance: Protocol for a Prospective Cohort Design and Cross-Sectional Comparison.

BACKGROUND: Women of reproductive age experience cyclical variation in the female sex steroid hormones 17ß-estradiol and progesterone during the menstrual cycle that is attenuated by some hormonal contraceptives. Estrogens perform a primary function in sexual development and reproduction but have nonreproductive effects on bone, muscle, and sinew tissues (ie, ligaments and tendons), which may influence injury risk and physical performance. OBJECTIVE: The purpose of the study is to understand the effect of the menstrual cycle and hormonal contraceptive use on bone and calcium metabolism, and musculoskeletal health and performance. METHODS: A total of 5 cohorts of physically active women (aged 18-40 years) will be recruited to participate: eumenorrheic, nonhormonal contraceptive users (n=20); combined oral contraceptive pill (COCP) users (n=20); hormonal implant users (n=20); hormonal intrauterine system users (n=20); and hormonal injection users (n=20). Participants must have been using the COCP and implant for at least 1 year and the intrauterine system and injection for at least 2 years. First-void urine samples and fasted blood samples will be collected for biochemical analysis of calcium and bone metabolism, hormones, and metabolic markers. Knee extensor and flexor strength will be measured using an isometric dynamometer, and lower limb tendon and stiffness, tone, and elasticity will be measured using a Myoton device. Functional movement will be assessed using a single-leg drop to assess the frontal plane projection angle and the qualitative assessment of single leg loading. Bone density and macro- and microstructure will be measured using ultrasound, dual-energy x-ray absorptiometry, and high-resolution peripheral quantitative computed tomography. Skeletal material properties will be estimated from reference point indentation, performed on the flat surface of the medial tibia diaphysis. Body composition will be assessed by dual-energy x-ray absorptiometry. The differences in outcome measures between the hormonal contraceptive groups will be analyzed in a one-way between-group analysis of covariance. Within the eumenorrheic group, the influence of the menstrual cycle on outcome measures will be assessed using a linear mixed effects model. Within the COCP group, differences across 2 time points will be analyzed using the paired-samples 2-tailed t test. RESULTS: The research was funded in January 2020, and data collection started in January 2022, with a projected data collection completion date of August 2024. The number of participants who have consented at the point of manuscript submission is 66. It is expected that all data analysis will be completed and results published by the end of 2024. CONCLUSIONS: Understanding the effects of the menstrual cycle and hormonal contraception on musculoskeletal health and performance will inform contraceptive choices for physically active women to manage injury risk. TRIAL REGISTRATION: ClinicalTrials.gov NCT05587920; https://classic.clinicaltrials.gov/ct2/show/NCT05587920. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/50542.

Iron status is associated with tibial structure and vitamin D metabolites in healthy young men.

The influence of iron on collagen synthesis and vitamin D metabolism has implications for bone health. This cross-sectional observational study investigated associations between markers of iron status and tibial structure, vitamin D metabolites, and circulating biochemical markers of bone metabolism in young healthy men. A total of 343 male British Army recruits participated (age 22 ± 3 y, height 1.77 ± 0.06 m, body mass 75.5 ± 10.1 kg). Circulating biochemical markers of iron status, vitamin D metabolites, and bone metabolism, and tibial structure and density by high-resolution peripheral quantitative computed tomography scans (HRpQCT) were measured in participants during week 1 of basic military training. Associations between markers of iron status and HRpQCT outcomes, bone metabolism, and vitamin D metabolites were tested, controlling for age, height, lean body mass, and childhood exercise volume. Higher ferritin was associated with higher total, trabecular, and cortical volumetric bone mineral density, trabecular volume, cortical area and thickness, stiffness, and failure load (all p ≤ 0.037). Higher soluble transferrin receptor (sTfR) was associated with lower trabecular number, and higher trabecular thickness and separation, cortical thickness, and cortical pore diameter (all p ≤ 0.033). Higher haemoglobin was associated with higher cortical thickness (p = 0.043). Higher ferritin was associated with lower ßCTX, PINP, total 25(OH)D, and total 24,25(OH)2D, and higher 1,25(OH)2D:24,25(OH)2D ratio (all p ≤ 0.029). Higher sTfR was associated with higher PINP, total 25(OH)D, and total 24,25(OH)2D (all p ≤ 0.025). The greater density, size, and strength of the tibia, and lower circulating concentrations of markers of bone resorption and formation with better iron stores (higher ferritin) are likely as a result of the direct role of iron in collagen synthesis.

Circulating extracellular vesicle characteristics differ between men and women following 12 weeks of concurrent exercise training.

Concurrent resistance and endurance exercise training (CET) has well-studied benefits; however, inherent hormonal and genetic differences alter adaptive responses to exercise between sexes. Extracellular vesicles (EVs) are factors that contribute to adaptive signaling. Our purpose was to test if EV characteristics differ between men and women following CET. 18 young healthy participants underwent 12-weeks of CET. Prior to and following CET, subjects performed an acute bout of heavy resistance exercise (AHRET) consisting of 6 × 10 back squats at 75% 1RM. At rest and following AHRET, EVs were isolated from plasma and characteristics and miRNA contents were analyzed. AHRET elevated EV abundance in trained men only (+51%) and AHRET-induced changes were observed for muscle-derived EVs and microvesicles. There were considerable sex-specific effects of CET on EV miRNAs, highlighted by larger variation following the 12-week program in men compared to women at rest. Pathway analysis based on differentially expressed EV miRNAs predicted that AHRET and 12 weeks of CET in men positively regulates hypertrophy and growth pathways more so than in women. This report highlights sex-based differences in the EV response to resistance and concurrent exercise training and suggests that EVs may be important adaptive signaling factors altered by exercise training.

Skeletal muscle adaptations to high-intensity, low-volume concurrent resistance and interval training in recreationally active men and women.

This study compared the structural and cellular skeletal muscle factors underpinning adaptations in maximal strength, power, aerobic capacity, and lean body mass to a 12-week concurrent resistance and interval training program in men and women. Recreationally active women and men completed three training sessions per week consisting of high-intensity, low-volume resistance training followed by interval training performed using a variety upper and lower body exercises representative of military occupational tasks. Pre- and post-training vastus lateralis muscle biopsies were analyzed for changes in muscle fiber type, cross-sectional area, capillarization, and mitochondrial biogenesis marker content. Changes in maximal strength, aerobic capacity, and lean body mass (LBM) were also assessed. Training elicited hypertrophy of type I (12.9%; p = 0.016) and type IIa (12.7%; p = 0.007) muscle fibers in men only. In both sexes, training decreased type IIx fiber expression (1.9%; p = 0.046) and increased total PGC-1α (29.7%, p < 0.001) and citrate synthase (11.0%; p < 0.014) content, but had no effect on COX IV content or muscle capillarization. In both sexes, training increased maximal strength and LBM but not aerobic capacity. The concurrent training program was effective at increasing strength and LBM but not at improving aerobic capacity or skeletal muscle adaptations underpinning aerobic performance.

Sex differences in energy balance, body composition, and metabolic and endocrine markers during prolonged arduous military training.

This study investigated sex differences in energy balance, body composition, and metabolic and endocrine markers during prolonged military training. Twenty-three trainees (14 women) completed 44-wk military training (three terms of 14 wk with 2-wk adventurous training). Dietary intake and total energy expenditure were measured over 10 days during each term by weighed food and doubly labeled water. Body composition was measured by dual-energy X-ray absorptiometry (DXA) at baseline and at the end of each term. Circulating metabolic and endocrine markers were measured at baseline and at the end of terms 2 and 3. Absolute energy intake and total energy expenditure were higher, and energy balance was lower, for men than women (P ≤ 0.008). Absolute energy intake and balance were lower, and total energy expenditure was higher, during term 2 than terms 1 and 3 (P < 0.001). Lean mass did not change with training (P = 0.081). Fat mass and body fat increased from term 1 to terms 2 and 3 (P ≤ 0.045). Leptin increased from baseline to terms 2 and 3 in women (P ≤ 0.002) but not in men (P ≥ 0.251). Testosterone and free androgen index increased from baseline to term 3 (P ≤ 0.018). Free thyroxine (T4) decreased and thyroid-stimulating hormone (TSH) increased from baseline to term 2 and term 3 (P ≤ 0.031). Cortisol decreased from baseline to term 3 (P = 0.030). IGF-I and total triiodothyronine (T3) did not change with training (P ≥ 0.148). Men experienced greater energy deficits than women during military training due to higher total energy expenditure.NEW & NOTEWORTHY Energy deficits are common in military training and can result in endocrine and metabolic disturbances. This study provides first investigation of sex differences in energy balance, body composition, and endocrine and metabolic markers in response to prolonged and arduous military training. Men experienced greater energy deficits than women due to higher energy expenditure, which was not compensated for by increased energy intake. These energy deficits were not associated with decreases in fat or lean mass or metabolic or endocrine function.

Acute Resistance Exercise Modifies Extracellular Vesicle miRNAs Targeting Anabolic Gene Pathways: A Prospective Cohort Study.

BACKGROUND: Resistance training confers numerous health benefits that are mediated in part by circulating factors. Toward an enhanced molecular understanding, there is growing interest in a class of signaling biomarkers called extracellular vesicles (EV). EVs support physiological adaptations to exercise by transporting their cargo (e.g., microRNA (miRNA)) to target cells. Previous studies of changes in EV cargo have focused on aerobic exercise, with limited data examining the effects of resistance exercise. We examined the effect of acute resistance exercise on circulating EV miRNAs and their predicted target pathways. METHODS: Ten participants (5 men; age, 26.9 ± 5.5 yr; height, 173.4 ± 10.5 cm; body mass, 74.0 ± 11.1 kg; body fat, 25.7% ± 11.6%) completed an acute heavy resistance exercise test (AHRET) consisting of six sets of 10 repetitions of back squats using 75% one-repetition maximum. Pre-/post-AHRET, EVs were isolated from plasma using size exclusion chromatography, and RNA sequencing was performed. Differentially expressed miRNAs between pre- and post-AHRET EVs were analyzed using Ingenuity Pathway Analysis to predict target messenger RNAs and their target biological pathways. RESULTS: Overall, 34 miRNAs were altered by AHRET ( P < 0.05), targeting 4895 mRNAs, with enrichment of 175 canonical pathways ( P < 0.01), including 12 related to growth/metabolism (p53, IGF-I, STAT3, PPAR, JAK/STAT, growth hormone, WNT/ß-catenin, ERK/MAPK, AMPK, mTOR, and PI3K/AKT) and 8 to inflammation signaling (TGF-ß, IL-8, IL-7, IL-3, IL-6, IL-2, IL-17, IL-10). CONCLUSIONS: Acute resistance exercise alters EV miRNAs targeting pathways involved in growth, metabolism, and immune function. Circulating EVs may serve as significant adaptive signaling molecules influenced by exercise training.

Effect of acute resistance exercise on bone turnover in young adults before and after concurrent resistance and interval training.

Weight-bearing physical activity can stimulate bone adaptation. This investigation explored the effect of an acute bout of resistance exercise before and after resistance+interval training on circulating biomarkers of bone metabolism and muscle-bone crosstalk. Healthy young male and female participants (n = 21 male, 28 ± 4 years; n = 17 female, 27 ± 5 years) performed a 6 × 10 squat test (75% 1RM) before and after a 12-week resistance+interval training program. Before and after completion of the training program, blood samples were collected at rest, immediately postexercise, and 2 h postexercise. Blood samples were analyzed for ßCTX, P1NP, sclerostin, osteocalcin, IGF-1, and irisin. Significant effects of acute exercise (main effect of time) were observed as increases in concentrations of IGF-1, irisin, osteocalcin, and P1NP from rest to postexercise. A sex*time interaction indicated a greater decline in ßCTX concentration from rest to 2 h postexercise and a greater increase in sclerostin concentration from rest to immediately postexercise in male compared with female participants. Sex differences (main effect of sex) were also observed for irisin and P1NP concentrations. In summary, changes in concentrations of biochemical markers of bone metabolism and muscle-bone crosstalk were observed in males and females after an acute bout of resistance exercise and following 12 weeks of resistance+interval training.

Hormonal contraceptive use is associated with altered bone structural and metabolic responses to military training in women: An observational cohort study.

Military training increases tibial density and size. Female sex hormones may influence the adaption of bone to loading, but it is unknown if women using different hormonal contraceptives adapt similarly to military training. One hundred and sixteen women (57 women not using hormonal contraceptives [non-users], 38 combined oral contraceptive pill [COCP] users, 21 depot medroxyprogesterone acetate [DMPA] users) completed this study. Tibial volumetric bone mineral density (vBMD) and geometry were measured by peripheral quantitative computed tomography (4 %, 14 %, 38 %, and 66 % sites) at the start (week 1) and end (week 14) of British Army basic training. Circulating markers of bone and calcium metabolism were measured at weeks 1, 2, 4, 6, 10, and 14. Training increased trabecular vBMD at the 4 % site, periosteal perimeter at the 14 % and 66 % sites, and total area, cortical area, cortical thickness, and bone strength at all sites (0.1 to 1.6 %, p ≤ 0.009), with no differences between hormonal contraceptive groups (p ≥ 0.127). Trabecular vBMD increased at the 14 % site in non-users (0.8 %, p = 0.005), but not in COCP or DMPA users (p ≥ 0.205). Periosteal perimeter increased at the 38 % site in COCP (0.4 %, p < 0.001) and DMPA (0.5 %, p < 0.001) users, but not in non-users (p = 0.058). Training had no effect on periosteal perimeter at the 4 % site or cortical vBMD or endosteal perimeter at any site (p ≥ 0.168). ßCTX decreased and PINP increased during training with no difference between hormonal contraceptive groups. Training increased iPTH in non-users, but not COCP or DMPA users. Hormonal contraceptives may exert site-specific effects on the mechanobiology of bone, with higher endogenous oestradiol promoting trabecularisation and inhibiting periosteal expansion in non-users compared with hormonal contraceptive users.

Sex differences in iron status during military training: a prospective cohort study of longitudinal changes and associations with endurance performance and musculoskeletal outcomes.

This study investigated sex differences in Fe status, and associations between Fe status and endurance and musculoskeletal outcomes, in military training. In total, 2277 British Army trainees (581 women) participated. Fe markers and endurance performance (2·4 km run) were measured at the start (week 1) and end (week 13) of training. Whole-body areal body mineral density (aBMD) and markers of bone metabolism were measured at week 1. Injuries during training were recorded. Training decreased Hb in men and women (mean change (-0·1 (95 % CI -0·2, -0·0) and -0·7 (95 % CI -0·9, -0·6) g/dl, both P < 0·001) but more so in women (P < 0·001). Ferritin decreased in men and women (-27 (95 % CI -28, -23) and -5 (95 % CI -8, -1) µg/l, both P ≤ 0·001) but more so in men (P < 0·001). Soluble transferrin receptor increased in men and women (2·9 (95 % CI 2·3, 3·6) and 3·8 (95 % CI 2·7, 4·9) nmol/l, both P < 0·001), with no difference between sexes (P = 0·872). Erythrocyte distribution width increased in men (0·3 (95 % CI 0·2, 0·4)%, P < 0·001) but not in women (0·1 (95 % CI -0·1, 0·2)%, P = 0·956). Mean corpuscular volume decreased in men (-1·5 (95 % CI -1·8, -1·1) fL, P < 0·001) but not in women (0·4 (95 % CI -0·4, 1·3) fL, P = 0·087). Lower ferritin was associated with slower 2·4 km run time (P = 0·018), sustaining a lower limb overuse injury (P = 0·048), lower aBMD (P = 0·021) and higher beta C-telopeptide cross-links of type 1 collagen and procollagen type 1 N-terminal propeptide (both P < 0·001) controlling for sex. Improving Fe stores before training may protect Hb in women and improve endurance and protect against injury.

Eating Disorder Risk and Common Mental Disorders in British Servicewomen: A Cross-Sectional Observational Study.

PURPOSE: Servicewomen are at increased risk of common mental disorders compared with servicemen and their female civilian counterparts. The prevalence of eating disorder risk and common mental disorders, and associated risk factors in British servicewomen are poorly understood. METHODS: All women younger than 45 yr in the UK Armed Forces were invited to complete a survey about demographics, exercise behaviors, eating behaviors, and common mental disorders. RESULTS: A total of 3022 women participated; 13% of participants were at high risk of an eating disorder based on Brief Eating Disorder in Athletes Questionnaire and Female Athlete Screening Tool scores. Twenty-five percent of participants had symptoms of anxiety (seven-item Generalized Anxiety Disorder Assessment score ≥10), and 26% had symptoms of depression (nine-item Patient Health Questionnaire score ≥10). Older age was associated with a lower risk, and heavier body mass was associated with a higher risk, of eating disorders ( P ≤ 0.043). Older age and higher rank were associated with a lower risk of symptoms of anxiety and depression ( P ≤ 0.031), and a heavier body mass was associated with a higher risk of symptoms of depression ( P ≤ 0.012). Longer habitual sleep duration was associated with a lower risk of eating disorders and symptoms of anxiety and depression ( P ≤ 0.028). A higher volume of field exercise was associated with a lower risk, and a higher volume of military physical training and personal physical training was associated with a higher risk, of eating disorders ( P ≤ 0.024). Job role and deployment history were not associated with any outcome. CONCLUSIONS: Sleeping and training habits provide potential novel targets for exploring how common mental disorders can be managed in British servicewomen.

Vitamin D Metabolites Are Associated With Musculoskeletal Injury in Young Adults: A Prospective Cohort Study.

The relationship between vitamin D metabolites and lower body (pelvis and lower limb) overuse injury is unclear. In a prospective cohort study, we investigated the association between vitamin D metabolites and incidence of lower body overuse musculoskeletal and bone stress injury in young adults undergoing initial military training during all seasons. In 1637 men and 530 women (aged 22.6 ± 7.5 years; body mass index [BMI], 24.0 ± 2.6 kg/m- 2 ; 94.3% white ethnicity), we measured serum 25-hydroxyvitamin D (25(OH)D) and 24,25-dihydroxyvitamin D (24,25(OH)2 D) by high-performance liquid chromatography tandem mass spectrometry, and 1,25-dihydroxyvitamin D (1,25(OH)2 D) by immunoassay during week 1 of training. We examined whether the relationship between 25(OH)D and 1,25(OH)2 D:24,25(OH)2 D ratio was associated with overuse injury. During 12 weeks of training, 21.0% sustained ≥1 overuse musculoskeletal injury, and 5.6% sustained ≥1 bone stress injury. After controlling for sex, BMI, 2.4 km run time, smoking, bone injury history, and Army training course (Officer, standard, or Infantry), lower body overuse musculoskeletal injury incidence was higher for participants within the second lowest versus highest quartile of 24,25(OH)2 D (odds ratio [OR] = 1.62; 95% confidence interval [CI] 1.13-2.32; p = 0.009) and lowest versus highest cluster of 25(OH)D and 1,25(OH)2 D:24,25(OH)2 D (OR = 6.30; 95% CI 1.89-21.2; p = 0.003). Lower body bone stress injury incidence was higher for participants within the lowest versus highest quartile of 24,25(OH)2 D (OR = 4.02; 95% CI 1.82-8.87; p < 0.001) and lowest versus highest cluster of 25(OH)D and 1,25(OH)2 D:24,25(OH)2 D (OR = 22.08; 95% CI 3.26-149.4; p = 0.001), after controlling for the same covariates. Greater conversion of 25(OH)D to 24,25(OH)2 D, relative to 1,25(OH)2 D (ie, low 1,25(OH)2 D:24,25(OH)2 D), and higher serum 24,25(OH)2 D were associated with a lower incidence of lower body overuse musculoskeletal and bone stress injury. Serum 24,25(OH)2 D may have a role in preventing overuse injury in young adults undertaking arduous physical training. © 2023 Crown copyright and The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR). This article is published with the permission of the Controller of HMSO and the King's Printer for Scotland.

Distal Tibial Bone Properties and Bone Stress Injury Risk in Young Men Undergoing Arduous Physical Training.

Trabecular microarchitecture contributes to bone strength, but its role in bone stress injury (BSI) risk in young healthy adults is unclear. Tibial volumetric BMD (vBMD), geometry, and microarchitecture, whole-body areal BMD, lean and fat mass, biochemical markers of bone metabolism, aerobic fitness, and muscle strength and power were measured in 201 British Army male infantry recruits (age 20.7 [4.3] years, BMI 24.0 ± 2.7 kg·m2) in week one of basic training. Tibial scans were performed at the ultra-distal site, 22.5 mm from the distal endplate of the non-dominant leg using High Resolution Peripheral Quantitative Computed Tomography (XtremeCT, Scanco Medical AG, Switzerland). Binary logistic regression analysis was performed to identify associations with lower body BSI confirmed by MRI. 20 recruits (10.0%) were diagnosed with a lower body BSI. Pre-injured participants had lower cortical area, stiffness and estimated failure load (p = 0.029, 0.012 and 0.011 respectively) but tibial vBMD, geometry, and microarchitecture were not associated with BSI incidence when controlling for age, total body mass, lean body mass, height, total 25(OH)D, 2.4-km run time, peak power output and maximum dynamic lift strength. Infantry Regiment (OR 9.3 [95%CI, 2.6, 33.4]) Parachute versus Line Infantry, (p ≤ 0.001) and 2.4-km best effort run time (1.06 [95%CI, 1.02, 1.10], p < 0.033) were significant predictors. Intrinsic risk factors, including ultradistal tibial density, geometry, and microarchitecture, were not associated with lower body BSI during arduous infantry training. The ninefold increased risk of BSI in the Parachute Regiment compared with Line Infantry suggests that injury propensity is primarily a function of training load and risk factors are population-specific.

Twelve weeks of concurrent resistance and interval training improves military occupational task performance in men and women.

In the British Army, ground close combat roles have opened to women, however, they must pass the newly developed, gender-neutral Role Fitness Tests for Soldiers (RFT(S)). Due to physiological differences between sexes, training that optimally prepares both sexes for military occupational demands and the RFT(S) is needed. The purpose of this study was to determine the efficacy of a 12-week periodized strength and power programme with concurrent interval training on RFT(S) performance and determine if performance adaptations differed between sexes. 39 recruit-aged (18-35 yrs) participants, including 21 men (29 ± 1 yrs) and 18 women (27 ± 1 yrs), completed the study. Participants performed 3 training sessions per week that included strength and power resistance training followed by interval training. Pre- to post-training, improvements were observed for seated medicine ball throw (4.5%, p < 0.001), casualty drag (29.8%, p < 0.001), single lift (8.9%, p < 0.001), water can carry (13.8%, p = 0.012), repeated lift and carry (6.5%, p < 0.001), 2-km load carriage (7.2%, p < 0.001) and 2-km run (3.2%, p = 0.021). Pre- to post-training improvements were also observed for maximal squat (27.0%, p < 0.001), bench press (8.9%, p < 0.001) and deadlift (24.6%, p < 0.001) maximal strength, but not upper body power or aerobic capacity. No differences in RFT(S) improvements were observed between sexes, however men performed better than women in all RFT(S) and physical performance measures. Concurrent resistance and interval training improves military occupational performance in men and women; however, women may need more training than men to pass the gender-neutral RFT(S).

Twelve weeks of concurrent resistance and interval training improved seated medicine ball throw, casualty drag, single lift, water can carry, repeated lift and carry, 2-km load carriage and 2-km run performance, military occupational performance measures that comprise the British Army Role Fitness Test for Soldiers (RFT(S)).Men and women demonstrated similar military occupational performance improvements from pre- to post-training, however, men performed better than women in all measures.Simple linear regression analyses between improvements in RFT(S) tasks and measures of physical fitness (one-repetition maximal strength, upper body power, lower body power, aerobic capacity) demonstrated limited significant associations suggesting that military occupational performance improvement relies on simultaneous development of multiple fitness domains.

The effect of calcium supplementation on calcium and bone metabolism during load carriage in women: protocol for a randomised controlled crossover trial.

BACKGROUND: Military field exercises are characterised by high volumes of exercise and prolonged periods of load carriage. Exercise can decrease circulating serum calcium and increase parathyroid hormone and bone resorption. These disturbances to calcium and bone metabolism can be attenuated with calcium supplementation immediately before exercise. This randomised crossover trial will investigate the effect of calcium supplementation on calcium and bone metabolism, and bone mineral balance, during load carriage exercise in women. METHODS: Thirty women (eumenorrheic or using the combined oral contraceptive pill, intrauterine system, or intrauterine device) will complete two experimental testing sessions either with, or without, a calcium supplement (1000 mg). Each experimental testing session will involve one 120 min session of load carriage exercise carrying 20 kg. Venous blood samples will be taken and analysed for biochemical markers of bone resorption and formation, calcium metabolism, and endocrine function. Urine will be collected pre- and post-load carriage to measure calcium isotopes for the calculation of bone calcium balance. DISCUSSION: The results from this study will help identify whether supplementing women with calcium during load carriage is protective of bone and calcium homeostasis. TRIAL REGISTRATION: NCT04823156 (clinicaltrials.gov).

Current risks factors and emerging biomarkers for bone stress injuries in military personnel.

INTRODUCTION: Bone stress injuries (BSIs) have plagued the military for over 150 years; they afflict around 5 to 10% of military recruits, more so in women, and continue to place a medical and financial burden on defence. While the tibia generally adapts to the rigours of basic military training, the putative mechanisms for bone maladaptation are still unclear. METHODS: This paper provides a review of the published literature on current risk factors and emerging biomarkers for BSIs in military personnel; the potential for biochemical markers of bone metabolism to monitor the response to military training; and, the association of novel biochemical 'exerkines' with bone health. RESULTS: The primary risk factor for BSI in military (and athletic) populations is too much training, too soon. Appropriate physical preparation before training will likely be most protective, but routine biomarkers will not yet identify those at risk. Nutritional interventions will support a bone anabolic response to training, but exposure to stress, sleep loss, and medication is likely harmful to bone. Monitoring physiology using wearables-ovulation, sleep and stress-offer potential to inform prevention strategies. CONCLUSIONS: The risk factors for BSIs are well described, but their aetiology is very complex particularly in the multi-stressor military environment. Our understanding of the skeletal responses to military training is improving as technology advances, and potential biomarkers are constantly emerging, but sophisticated and integrated approaches to prevention of BSI are warranted.

The effect of sex and protein supplementation on bone metabolism during a 36-h military field exercise in energy deficit.

This study investigated sex differences in, and the effect of protein supplementation on, bone metabolism during a 36-h military field exercise. Forty-four British Army Officer cadets (14 women) completed a 36-h field exercise. Participants consumed either their habitual diet [n = 14 women (Women) and n = 15 men (Men Controls)] or the habitual diet with an additional 46.6 g·day-1 of protein for men [n = 15 men (Men Protein)]. Women and Men Protein were compared with Men Controls to examine the effect of sex and protein supplementation. Circulating markers of bone metabolism were measured before, 24 h after (postexercise), and 96 h after (recovery) the field exercise. Beta C-telopeptide cross links of type 1 collagen and cortisol were not different between time points or Women and Men Controls (P ≥ 0.094). Procollagen type I N-terminal propeptide decreased from baseline to postexercise (P < 0.001) and recovery (P < 0.001) in Women and Men Controls. Parathyroid hormone (PTH) increased from baseline to post-exercise (P = 0.006) and decreased from postexercise to recovery (P = 0.047) in Women and Men Controls. Total 25(OH)D increased from baseline to postexercise (P = 0.038) and recovery (P < 0.001) in Women and Men Controls. Testosterone decreased from baseline to post-exercise (P < 0.001) and recovery (P = 0.007) in Men Controls, but did not change for Women (all P = 1.000). Protein supplementation in men had no effect on any marker. Men and women experience similar changes to bone metabolism-decreased bone formation and increased PTH-following a short-field exercise. Protein had no protective effect likely because of the energy deficit.NEW & NOTEWORTHY Energy deficits are common in arduous military training and can cause disturbances to bone metabolism. This study provides first evidence that short periods of severe energy deficit and arduous exercise-in the form of a 36-h military field exercise-can suppress bone formation for at least 96 h, and the suppression in bone formation was not different between men and women. Protein feeding does not offset decreases in bone formation during severe energy deficits.

Menstrual Function, Eating Disorders, Low Energy Availability, and Musculoskeletal Injuries in British Servicewomen.

PURPOSE: This study aimed to investigate associations between menstrual function, eating disorders, and risk of low energy availability with musculoskeletal injuries in British servicewomen. METHODS: All women younger than 45 yr in the UK Armed Forces were invited to complete a survey about menstrual function, eating behaviors, exercise behaviors, and injury history. RESULTS: A total of 3022 women participated; 2% had a bone stress injury in the last 12 months, 20% had ever had a bone stress injury, 40% had a time-loss musculoskeletal injury in the last 12 months, and 11% were medically downgraded for a musculoskeletal injury. Menstrual disturbances (oligomenorrhea/amenorrhea, history of amenorrhea, and delayed menarche) were not associated with injury. Women at high risk of disordered eating (Female Athlete Screening Tool score >94) were at higher risk of history of a bone stress injury (odds ratio (OR; 95% confidence interval (CI)), 2.29 (1.67-3.14); P < 0.001) and time-loss injury in the last 12 months (OR (95% CI), 1.56 (1.21-2.03); P < 0.001) than women at low risk of disordered eating. Women at high risk of low energy availability (Low Energy Availability in Females Questionnaire score ≥8) were at higher risk of bone stress injury in the last 12 months (OR (95% CI), 3.62 (2.07-6.49); P < 0.001), history of a bone stress injury (OR (95% CI), 2.08 (1.66-2.59); P < 0.001), a time-loss injury in the last 12 months (OR (95% CI), 9.69 (7.90-11.9); P < 0.001), and being medically downgraded with an injury (OR (95% CI), 3.78 (2.84-5.04); P < 0.001) than women at low risk of low energy availability. CONCLUSIONS: Eating disorders and risk of low energy availability provide targets for protecting against musculoskeletal injuries in servicewomen.

Measurement of Energy Intake Using the Principle of Energy Balance Overcomes a Critical Limitation in the Assessment of Energy Availability.

Prolonged low energy availability, which is the underpinning aetiology of the Relative Energy Deficiency in Sport and the Female and Male Athlete Triad frameworks, can have unfavourable impacts on both health and performance in athletes. Energy availability is calculated as energy intake minus exercise energy expenditure, expressed relative to fat free mass. The current measurement of energy intake is recognized as a major limitation for assessing energy availability due to its reliance on self-report methods, in addition to its short-term nature. This article introduces the application of the energy balance method for the measurement of energy intake, within the context of energy availability. The energy balance method requires quantification of the change in body energy stores over time, with concurrent measurement of total energy expenditure. This provides an objective calculation of energy intake, which can then be used for the assessment of energy availability. This approach, the Energy Availability - Energy Balance (EAEB) method, increases the reliance on objective measurements, provides an indication of energy availability status over longer periods and removes athlete burden to self-report energy intake. Implementation of the EAEB method could be used to objectively identify and detect low energy availability, with implications for the diagnosis and management of Relative Energy Deficiency in Sport and the Female and Male Athlete Triad.

Gender data gap in military research: a review of the participation of men and women in military musculoskeletal injury studies.

Servicewomen are at increased risk of musculoskeletal injuries compared with their male counterparts, but women are under-represented in sports medicine research. The aim of this review was to assess the representation of women in military musculoskeletal injury studies. PubMed was searched for human original research studies using the terms Military OR Army OR Navy OR 'Air Force' AND 'musculoskeletal injury' Each study was categorised as epidemiology (basic training), epidemiology (trained personnel), risk factors, interventions and other. The number of male and female participants was retrieved from each study. A total of 262 studies were included: 98 (37%) studies only included men, 17 (6%) studies only included women and 147 (56%) studies included both men and women. A total of 8 051 778 participants were included in these studies (men: 6 711 082, 83%; women: 1 340 696, 17%). The study theme with the greatest proportion of women was musculoskeletal injury epidemiology studies in a basic training population (20% of participants) with the lowest proportion of women in intervention trials (6% of participants). These data suggest women are not under-represented in military musculoskeletal injury studies when considering the gender representation of most militaries. Our data are, however, biased by large epidemiological trials and women were under-represented in intervention trials. The under-representation of women in intervention trials could be due to difficulties in controlling for the effects of female sex steroids on musculoskeletal outcomes, or a focus on interventions in the most arduous military roles where injury risk is highest and women have been previously excluded.