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.

IMUs Can Estimate Hip and Knee Range of Motion during Walking Tasks but Are Not Sensitive to Changes in Load or Grade.

The ability to estimate lower-extremity mechanics in real-world scenarios may untether biomechanics research from a laboratory environment. This is particularly important for military populations where outdoor ruck marches over variable terrain and the addition of external load are cited as leading causes of musculoskeletal injury As such, this study aimed to examine (1) the validity of a minimal IMU sensor system for quantifying lower-extremity kinematics during treadmill walking and running compared with optical motion capture (OMC) and (2) the sensitivity of this IMU system to kinematic changes induced by load, grade, or a combination of the two. The IMU system was able to estimate hip and knee range of motion (ROM) with moderate accuracy during walking but not running. However, SPM analyses revealed IMU and OMC kinematic waveforms were significantly different at most gait phases. The IMU system was capable of detecting kinematic differences in knee kinematic waveforms that occur with added load but was not sensitive to changes in grade that influence lower-extremity kinematics when measured with OMC. While IMUs may be able to identify hip and knee ROM during gait, they are not suitable for replicating lab-level kinematic waveforms.

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. Towards an enhanced molecular understanding, there is growing interest in a class of signaling biomarkers called extracellular vesicles (EVs). Extracellular vesicles 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 y, height: 1.7 ± 0.1 m, 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 (DE) 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 4,895 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 eight 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.

Utility of HR-pQCT in detecting training-induced changes in healthy adult bone morphology and microstructure.

Healthy bone adjusts its traits in an exceptionally coordinated, compensatory process. Recent advancements in skeletal imaging via High-Resolution Peripheral Quantitative Computed Tomography (HR-pQCT) allows for the in vivo 3-dimensional and longitudinal quantification of bone density, microarchitecture, geometry, and parameters of mechanical strength in response to varying strain stimuli including those resulting from exercise or military training. Further, the voxel size of 61 microns has the potential to capture subtle changes in human bone in as little as 8 weeks. Given the typical time course of bone remodeling, short-term detection of skeletal changes in bone microstructure and morphology is indicative of adaptive bone formation, the deposition of new bone formation, uncoupled from prior resorption, that can occur at mechanistically advantageous regions. This review aims to synthesize existing training-induced HR-pQCT data in three distinct populations of healthy adults excluding disease states, pharmacological intervention and nutritional supplementation. Those included are: 1) military basic or officer training 2) general population and 3) non-osteoporotic aging. This review aims to further identify similarities and contrasts with prior modalities and cumulatively interpret results within the scope of bone functional adaptation.

Hydrodynamic Flow Characteristics of a Recirculating Pool: Examining the Ecological Validity for Training and Testing.

ABSTRACT: Krajewski, KT, Beethe, AZ, Dever, DE, Johnson, CD, Nindl, BC, Lovalekar, MT, Flanagan, SD, and Connaboy, C. Hydrodynamic flow characteristics of a recirculating pool: examining the ecological validity for training and testing. J Strength Cond Res 37(10): 2023-2031, 2023-Recirculating swimming flumes (RSFs) with elliptical multifeature designs have grown in popularity due to their multifunctionality for rehabilitation and training. Because of their smaller footprint, laboratories have adopted their use to investigate swimming and underwater treadmill running. However, little is known about the hydrodynamic characteristics of these RSFs and how they might influence outcomes. The purpose was to determine hydrodynamic flow characteristics of an RSF at the manufacturers' set "speeds" around the centroid of flow projection. Hydrodynamic velocity profiles were collected through a 3D profiling velocimeter, sampling at 200 Hz in an RSF. Data were collected 0.5 and 1.5 m from the projection channel at designated flume "speeds" of 30-95 (+99) in 5-unit increments. Velocity data were collected for 1 minute per trial (location × speed) to determine mean flow velocity (MFV) for 10, 20, 30, and 40 cm2 cross-sectional areas (CSAs). A two-way ANOVA was conducted comparing CSAs from the surface by distance from the current channel (4 × 2). Separate ANOVAs were conducted to assess differences in MFV across each CSA. Significant differences between flow CSAs indicated that MFV is less for a larger area at the same speed, indicative of variable and turbulent flow characteristics across the respective CSAs. Mean flow velocity was further diminished by distance from the flow channel as supported by the main effect, thus exposing an individual to variant flow velocities simultaneously. Limited stability of the flow velocity centroid could affect swim mechanics making the movement pattern no longer analogous to traditional pool and open water swimming, rather resembling swimming upstream in a river with turbulent flow.

Association of clinically-measured and dynamic ankle dorsiflexion assessed by markerless motion capture during the drop-jump task on landing biomechanics and risk of ankle injury in military personnel undergoing 10 weeks of physical training.

OBJECTIVES: Determine the influence of clinically-measured maximum dorsiflexion, dynamic peak dorsiflexion and percent of clinically-measured maximum dorsiflexion used during a drop-jump task on landing biomechanics and risk of ankle injury in military personnel. DESIGN: Prospective cohort study. METHODS: 672 participants (122 women) enrolled. The weightbearing lunge test assessed clinically-measured maximum dorsiflexion averaged across limbs (degrees). Markerless motion capture and force plates collected lower extremity kinematic and kinetic data during a drop-jump task. Percent of clinically-measured maximum dorsiflexion used during landing was calculated as dynamic peak dorsiflexion divided by clinically-measured value, multiplied by 100 (%). De-identified injury data was derived from military physical therapists. Simple linear regression analysis determined the association between dorsiflexion measures and landing biomechanics. Simple binary logistic regression analyses identified predictors of ankle injuries. Statistical significance was set at α = 0.05. RESULTS: Eighteen participants sustained a traumatic ankle injury from a landing. All measures of dorsiflexion were associated with movement patterns that countered the stiff-legged landing strategy with dynamic measures showing a higher predictive value. Protective factors against ankle injury included height (odds ratio: 0.818, p = 0.006) and weight (odds ratio: 0.824, p = 0.023) for women. Relative braking impulse was a risk factor for men (odds ratio: 1.890, p = 0.001). CONCLUSIONS: Greater clinically-measured and dynamic measures of dorsiflexion were associated with movement patterns that countered the stiff-legged landing strategy but neither measure of dorsiflexion predicted ankle injury risk. Resultant biomechanics and anthropometrics influenced ankle injury risk to warrant recognition for injury prevention initiatives.

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.

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.

Predictive utility of commercial grade technologies for assessing musculoskeletal injury risk in US Marine Corps Officer candidates.

Recently, commercial grade technologies have provided black box algorithms potentially relating to musculoskeletal injury (MSKI) risk and functional movement deficits, in which may add value to a high-performance model. Thus, the purpose of this manuscript was to evaluate composite and component scores from commercial grade technologies associations to MSKI risk in Marine Officer Candidates. 689 candidates (Male candidates = 566, Female candidates = 123) performed counter movement jumps on SPARTA™ force plates and functional movements (squats, jumps, lunges) in DARI™ markerless motion capture at the start of Officer Candidates School (OCS). De-identified MSKI data was acquired from internal OCS reports for those who presented to the Physical Therapy department for MSKI treatment during the 10 weeks of training. Logistic regression analyses were conducted to validate the utility of the composite scores and supervised machine learning algorithms were deployed to create a population specific model on the normalized component variables in SPARTA™ and DARI™. Common MSKI risk factors (cMSKI) such as older age, slower run times, and females were associated with greater MSKI risk. Composite scores were significantly associated with MSKI, although the area under the curve (AUC) demonstrated poor discrimination (AUC = .55-.57). When supervised machine learning algorithms were trained on the normalized component variables and cMSKI variables, the overall training models performed well, but when the training models were tested on the testing data the models classified MSKI "by chance" (testing AUC avg = .55-.57) across all models. Composite scores and component population specific models were poor predictors of MSKI in candidates. While cMSKI, SPARTA™, and DARI™ models performed similarly, this study does not dismiss the use of commercial technologies but questions the utility of a singular screening task to predict MSKI over 10 weeks. Further investigations should evaluate occupation specific screening, serial measurements, and/or load exposure for creating MSKI risk models.

Epidemiology of Musculoskeletal Injuries Among Naval Special Warfare Personnel.

BACKGROUND: Musculoskeletal injuries (MSIs) are an important cause of morbidity in the military, especially among Special Forces. The aim of this analysis was to describe MSIs among two groups of Naval Special Warfare (NSW) personnel-Special Warfare Combatant-Craft Crewman (SWCC) Operators and Crewman Qualification Training (CQT) students. METHODS: In this cross-sectional study, we describe self-reported MSIs that occurred during a one-year period and the calculated financial costs of MSIs. Group comparisons were conducted using Fisher's exact tests and independent samples t tests. RESULTS: Data were available for 142 SWCC Operators (26.9 ± 5.9 years, 1.8 ± 0.1 meters, 85.4 ± 10.4 kilograms) and 187 CQT students (22.8 ± 3.2 years, 1.8 ± 0.2 meters, 81.4 ± 8.9 kilograms). The one-year cumulative MSI incidence was significantly lower among SWCC Operators (21.1%) compared to CQT students (37.4%, p = 0.002). The most common anatomic location for MSIs was the lower extremity (SWCC: 50.0% of MSIs, CQT: 66.3%). Physical training was the predominant activity when MSIs occurred (SWCC: 31.6%, CQT: 77.6%). The lifetime cost of all the MSIs included in the analysis was approximately $580,000 among 142 SWCC Operators and $1.2 million among 187 CQT students. CONCLUSION: MSIs, especially those affecting the lower extremity and occurring during physical training, cause considerable morbidity and financial burden among NSW personnel. Many of the musculoskeletal injuries are to musculotendinous tissue, which typically results from tissue overload or inadequate recovery. Further investigation of the preventable causes of these MSIs and development of a customized, evidence-based MSI prevention program is required to reduce the burden of these MSIs.

Reliability and Validity of a Flume-Based Maximal Oxygen Uptake Swimming Test.

A mode-specific swimming protocol to assess maximal aerobic uptake (VO2maxsw) is vital to accurately evaluate swimming performance. A need exists for reliable and valid swimming protocols that assess VO2maxsw in a flume environment. The purpose was to assess: (a) reliability and (b) "performance" validity of a VO2maxsw flume protocol using the 457-m freestyle pool performance swim (PS) test as the criterion. Nineteen males (n = 9) and females (n = 10) (age, 28.5 ± 8.3 years.; height, 174.7 ± 8.2 cm; mass, 72.9 ± 12.5 kg; %body fat, 21.4 ± 5.9) performed two flume VO2maxsw tests (VO2maxswA and VO2maxswB) and one PS test [457 m (469.4 ± 94.7 s)]. For test-retest reliability (Trials A vs. B), moderately strong relationships were established for VO2maxsw (mL·kg-1·min-1)(r= 0.628, p = 0.002), O2pulse (mL O2·beat-1)(r = 0.502, p = 0.014), VEmax (L·min-1) (r = 0.671, p = 0.001), final test time (sec) (0.608, p = 0.004), and immediate post-test blood lactate (IPE (BLa)) (0.716, p = 0.001). For performance validity, moderately strong relationships (p < 0.05) were found between VO2maxswA (r =-0.648, p = 0.005), O2pulse (r= -0.623, p = 0.008), VEmax (r = -0.509 p = 0.037), and 457-m swim times. The swimming flume protocol examined is a reliable and valid assessment of VO2maxsw., and offers an alternative for military, open water, or those seeking complementary forms of training to improve swimming performance.

Military tactical adaptive decision making during simulated military operational stress is influenced by personality, resilience, aerobic fitness, and neurocognitive function.

Laboratory-based studies designed to mimic combat or military field training have consistently demonstrated deleterious effects on warfighter's physical, cognitive, and emotional performance during simulated military operational stress (SMOS). Purpose: The present investigation sought to determine the impact of a 48-h simulated military operational stress (SMOS) on military tactical adaptive decision making, and the influence of select psychological, physical performance, cognitive, and physiological outcome measures on decision making performance. Methods: Male (n = 48, 26.2 ± 5.5 years, 177.7 ± 6.6 cm, 84.7 ± 14.1 kg.) subjects currently serving in the U.S. military were eligible to participate in this study. Eligible subjects completed a 96-h protocol that occurred over five consecutive days and four nights. Day 2 (D2) and day 3 (D3) consisted of 48-h of SMOS wherein sleep opportunity and caloric needs were reduced to 50%. Differences in SPEAR total block score from baseline to peak stress (D3 minus D1) were calculated to assess change in military tactical adaptive decision making and groups were stratified based on increase (high adaptors) or decrease (low adaptors) of the SPEAR change score. Results: Overall, military tactical decision-making declined 1.7% from D1 to D3 (p < 0.001). High adaptors reported significantly higher scores of aerobic capacity (p < 0.001), self-report resilience (p = 0.020), extroversion (p < 0.001), and conscientiousness (p < 0.001). at baseline compared to low adaptors, while low adaptors reported greater scores in Neuroticism (p < 0.001). Conclusion: The present findings suggest that service members whose adaptive decision making abilities improved throughout SMOS (i.e., high adaptors) demonstrated better baseline psychological/self-reported resilience and aerobic capacity. Further, changes in adaptive decision-making were distinct from those of lower order cognitive functions throughout SMOS exposure. With the transition of future military conflicts placing higher priority on enhancing and sustaining cognitive readiness and resiliency, data presented here demonstrates the importance of measuring and categorizing baseline measures inherent to military personnel, in order to change and train one's ability to suffer less of a decline during high stress conditions.

A Minimal Sensor Inertial Measurement Unit System Is Replicable and Capable of Estimating Bilateral Lower-Limb Kinematics in a Stationary Bodyweight Squat and a Countermovement Jump.

This study aimed to validate a 7-sensor inertial measurement unit system against optical motion capture to estimate bilateral lower-limb kinematics. Hip, knee, and ankle sagittal plane peak angles and range of motion (ROM) were compared during bodyweight squats and countermovement jumps in 18 participants. In the bodyweight squats, left peak hip flexion (intraclass correlation coefficient [ICC] = .51), knee extension (ICC = .68) and ankle plantar flexion (ICC = .55), and hip (ICC = .63) and knee (ICC = .52) ROM had moderate agreement, and right knee ROM had good agreement (ICC = .77). Relatively higher agreement was observed in the countermovement jumps compared to the bodyweight squats, moderate to good agreement in right peak knee flexion (ICC = .73), and right (ICC = .75) and left (ICC = .83) knee ROM. Moderate agreement was observed for right ankle plantar flexion (ICC = .63) and ROM (ICC = .51). Moderate agreement (ICC > .50) was observed in all variables in the left limb except hip extension, knee flexion, and dorsiflexion. In general, there was poor agreement for peak flexion angles, and at least moderate agreement for joint ROM. Future work will aim to optimize methodologies to increase usability and confidence in data interpretation by minimizing variance in system-based differences and may also benefit from expanding planes of movement.

Physiological biomarker monitoring during arduous military training: Maintaining readiness and performance.

OBJECTIVES: Physiological and psychological stressors can degrade soldiers' readiness and performance during military training and operational environments. Integrative and holistic assessments of biomarkers across diverse human performance optimization domains during multistressor training can be leveraged to provide actionable insight to military leadership regarding service member health and readiness. DESIGN/METHOD: A broad categorization of biomarkers, to include biochemical measures, bone and body composition, psychometric assessments, movement screening, and physiological load can be incorporated into robust analytical pipelines for understanding the complex factors that impact military human performance. RESULTS: In this perspective commentary we overview the rationale, selection, and methodologies for monitoring biomarker domains that are relevant to military research and specifically highlight methods that have been incorporated in a research program funded by the Office of Naval Research, Code 34 Biological and Physiological Monitoring and Modeling of Warfighter Performance. CONCLUSIONS: The integration of screening and continuous monitoring methodologies via robust analytical approaches will provide novel insight for military leaders regarding health, performance, and readiness outcomes during multistressor military training.

Prevention of Lower Extremity Musculoskeletal Injuries in Tactical and First Responder Populations: A Systematic Review and Meta-Analysis of Randomized Trials From 1955 to 2020.

ABSTRACT: Sinnott, AM, Krajewski, KT, LaGoy, AD, Beckner, ME, Proessl, F, Canino, MC, Nindl, BC, Turner, RL, Lovalekar, MT, Connaboy, C, and Flanagan, SD. Prevention of lower extremity musculoskeletal injuries in tactical and first responder populations: A systematic review and meta-analysis of randomized trials from 1955 to 2020. J Strength Cond Res 37(1): 239-252, 2023-Lower extremity musculoskeletal injuries (LEMSIs) impose a significant burden on tactical and first responder populations. To determine the effectiveness of LEMSI prevention strategies, we performed a systematic review and meta-analysis of randomized controlled trials published in English from 1955 to 2020 (PROSPERO: CRD42018081799). MEDLINE, EMBASE, Cochrane, CINAHL, ProQuest, and DTIC databases were searched for trials that assigned military service members, police, firefighters, or paramedics to LEMSI prevention interventions with a minimum surveillance period of 12 weeks. Evidence was synthesized as odds ratios (OR) for LEMSI occurrence between individuals assigned to interventions and those assigned to standard activities. Risk of bias was assessed with the Cochrane Risk of Bias tool 2.0. Random-effects meta-analyses were conducted for (a) physical training and (b) footwear modifications to reduce LEMSI and (c) footwear modifications to reduce stress fractures specifically. Certainty in the body of evidence was determined with the GRADE approach. Of 28,499 records, 18 trials comprised of more than 11,000 subjects were synthesized. Interventions included physical training (8, N = 6,838), footwear modifications (8, N = 3,792), nutritional supplementation (1, N = 324), and training modifications (1, N = 350). Overall risk of bias was generally moderate ( N = 7 of 18) or high ( N = 9 of 18). Physical training (OR = 0.87, 95% CI [0.71, 1.08], p = 0.22, I 2 = 58.4%) and footwear modification (OR = 1.13, 95% CI [0.85, 1.49], p = 0.42, I 2 = 0.0%) did not reduce LEMSI or stress fractures (OR = 0.76, 95% CI [0.45, 1.28], p = 0.30, I 2 = 70.7%). Our results indicate that there is weak evidence to support current LEMSI prevention strategies. Future efforts will benefit from longer surveillance periods, assessment of women and nonmilitary populations, improved methodological rigor, and a greater breadth of approaches.

Decreased Percent Body Fat but Not Body Mass is Associated with Better Performance on Combat Fitness Test in Male and Female Marines.

ABSTRACT: Pletcher, ER, Lovalekar, M, Coleman, LC, Beals, K, Nindl, BC, and Allison, KF. Decreased percent body fat but not body mass is associated with better performance on the Marine Corps Combat Fitness Test. J Strength Cond Res 37(4): 887-893, 2023-The military uses a variety of physical fitness tests to assess physical readiness. The Marine Corps designed the Combat Fitness Test (CFT) to emphasize functional fitness related to operational demands. The purpose of this study was to investigate the association between body mass (BM), fat free mass (FFM), and percent body fat (BF%) measured via air displacement plethysmography with CFT performance in male and female marines. Two-hundred 10 male (22.4 ± 2.6 years) and 84 female (22.6 ± 2.8 years) marines were grouped into quintiles according to BM (in kilograms), FFM (in kilograms), and BF%. Kruskal-Wallis test or 1-way analysis of variance were used to determine if significant differences in CFT total and component scores existed between the groups of subjects classified into quintiles of BM, FFM, and BF%. No significant differences in CFT scores were observed between BM quintile in either men or women. No significant differences in CFT scores were observed between FFM quintiles in men. Total CFT score ( p = 0.002), movement to contact (MTC; p = 0.014), maneuver under fire (MANUF; p = 0.008), and ammunition lift (AL; p = 0.014) were all significantly different among FFM quintiles in women. Total CFT score ( p = 0.007), MTC ( p = 0.001), and MANUF ( p = 0.022) were significantly different among BF% quintiles in men. Total CFT score ( p = 0.008), MTC ( p = 0.033), and AL ( p = 0.016) were significantly different among BF% quintiles in women. Male and female marines in the quintile with lowest BF% had better CFT scores than those in higher quintiles. Targeted physical training and nutrition considerations to optimize BF% may help improve military task performance.

Less daytime sleepiness and slow wave activity during sleep predict better physical readiness in military personnel.

BACKGROUND: Military personnel must maintain physical performance despite exposure to operational stressors such as sleep loss, caloric restriction and high cognitive load. Habitual sleep and specific sleep features are positively associated with fitness and may contribute to physical performance in operational settings. Further, by affecting muscle recovery, sleep may contribute to the ability to maintain performance across multiple days of exposure to operational stressors. OBJECTIVES: We examined the role of individual differences in baseline sleep on baseline physical performance and on change in physical performance throughout exposure to simulated military operational stress (SMOS). METHODS: Military personnel (36 male, 9 female, 26.3 ± 5.3 years) completed a 5-day SMOS protocol during which they completed a tactical mobility test daily. Sleep questionnaires were administered at intake and sleep was monitored each night with polysomnography. Lasso regressions were used to identify meaningful predictors of physical performance at baseline and of change in physical performance across SMOS. RESULTS: Better aerobic fitness, lower daytime sleepiness (Epworth Sleepiness Scale), and lower absolute slow wave activity (0.5-4 Hz) predicted better physical performance at baseline (66.1% of variance explained), but did not relate to changes in performance. CONCLUSIONS: Collectively, higher daytime sleepiness and slow wave activity may reflect more chronic exposure to insufficient sleep and higher baseline sleep drive, which in turn led to compromised physical performance. The findings suggest that low self-report sleepiness and low objective slow wave activity may reflect two quantifiable markers of healthy sleep behaviors that have implications for operational performance.

Changes in eating pathology symptoms during initial military training in men and women and associations with BMI and injury risk.

Nutritional fitness, which comprises food choices, meal timing, and dietary intake behaviors, is an important component of military service member health and performance that has garnered recent attention. This study utilized generalized linear mixed effects modeling (GLMM) to investigate changes in eating pathology symptoms in men and women during initial military training (Marine Corps Officer Candidates School (OCS)). Associations among eating pathology, musculoskeletal injury risk and BMI were also assessed. This investigation includes data from the Eating Pathology Symptoms Inventory (EPSI) and BMI at the start of OCS (n = 598: Male n = 469, Female n = 129) and end of the 10-week program (n = 413: Male n = 329, Female n = 84), and injury surveillance throughout. At baseline, female candidates presented with greater body dissatisfaction, binge eating, purging, and restricting, but lower negative attitudes toward obesity compared to male candidates (p < 0.001). Eating symptoms changed during military training indicated by decreased body dissatisfaction in women (p = 0.003), decreased excessive exercise and negative attitudes toward obesity in men (p < 0.001), decreased cognitive restraint (p < 0.001), restricting (p < 0.001), purging (p = 0.013), and muscle building (p < 0.001) and increased binge eating (p < 0.001) in both sexes. Changes in restricting were significantly related to changes in BMI during training (p < 0.05). The likelihood of future injury was 108 % higher in female candidates than males and decreased by 5 % for each unit increase in excessive exercise. Eating attitudes and behaviors change during military training environments and are associated with military health and readiness outcomes including BMI and injury risk.