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Insulin-like growth factor (IGF)-I is a ubiquitous peptide hormone involved in a host of critical physiological processes (e.g., protein synthesis and glucose homeostasis) and has been suggested to be a biomarker reflecting health and metabolic status. In most cases (muscle, bone, tendon, body composition, and cognitive function), elevated IGF-I concentrations are considered beneficial; however, cancer remains a notable exception. While the fact that both increased and decreased IGF-I can be considered reflective of favorable and beneficial health outcomes may appear as a paradox, it is important to emphasize that, in both cases, measured IGF-I concentrations do offer important insight into physiological processes. The effects of military operational field training on the circulating IGF-I system are discussed within the context of novel measurement technologies that (1) are field expedient and (2) provide more meaningful information. Prospective experimental approaches involving physical activity that sample and measure IGF-I in the body's various biocompartments will provide greater insight into the complex role that IGF-I possesses. Minimally invasive technologies that are field expedient, cost-effective, and allow for continuous and real-time feedback will have the greatest likelihood of being adapted and used in military environments.

Teamwork is an essential element in the majority of critical Army lifting tasks. Therefore, an understanding of the relationship between individual and team lifting capacity is of great tactical importance. Twenty-three male and 17 female U.S. Army soldiers were randomly assigned to single- and mixed-gender teams of two, three, and four persons. Individual lifting strength was the one-repetition-maximum (1RM) load lifted from floor to knuckle height using a weight bar. A square-shaped bar was used for two- and four-person lifting, and a triangular-shaped bar was used for three-person lifting. Team lifting strength as a percentage of the sum of individual lifting strength (%sum) did not change with team size. The %sum for teams of men (87.3%) was less than for teams of women (91.1%, p < 0.05). The %sums for both single-gender teams (all men and all women) were greater (p < 0.01) than for mixed-gender teams (80.2%). The number of people lifting a large object was increased to four with no decrease in the effectiveness of the individual lifter beyond that found for two persons. The 1RM loads presented in this paper were lifted under ideal conditions by young soldiers and do not represent norms for an industrial population.

Purpose: The purpose of this study was to look at the effect of additional individual physical training (PT) in addition to mandatory unit PT as well as other risk factors on physical fitness. Design: A cross-sectional design. Setting: This study was conducted on a US military installation. Participants: Participants were 6290 male and 558 female active duty US Army soldiers in 3 light infantry brigades. Measures: Participants completed self-administered questionnaires asking about individual characteristics, PT, and physical fitness. Cut points were established for soldiers scoring within the top 33% for each of the 3 Army Physical Fitness Test events (2-mile run, sit-ups, and push-ups) and top 50% in each of the tests combined for overall performance. Analysis: Odds ratios and 95% confidence intervals from multivariate analyses were calculated. Results: Variables impacting physical fitness performance of men and women included increased body mass index, leading unit PT sessions, and individual distance running mileage. Other variables impacting physical performance for men included increased age, smoking, and individual resistance training. Conclusion: Soldiers performing additional individual PT demonstrated a positive influence on fitness compared to unit PT participation alone. Increased age and being overweight/obese negatively influenced physical fitness. To enhance fitness performance through unit PT, running by ability groups and resistance training should be encouraged by leadership.

CONTEXT: Ankle injury is one of the most common conditions in athletics and military activities. Strength asymmetry (SA) and imbalance may represent a risk factor for injury, but past investigations have produced ambiguous conclusions. Perhaps one explanation for this ambiguity is the fact that these authors used univariate models to predict injury. OBJECTIVE: To evaluate the predictive utility of SA and imbalance calculations for ankle injury in univariate and multivariate prediction models. DESIGN: Prospective cohort study. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 140 male US Air Force Special Forces. MAIN OUTCOME MEASURE(S): Baseline testing consisted of body composition, isometric strength, and aerobic and anaerobic capacity. A clinician conducted medical chart reviews 365 days posttesting to document the incidence of ankle injury. Strength asymmetries were calculated based on the equations most prevalent in the literature along with known physiological predictors of injury in the military: age, height, weight, body composition, and aerobic capacity. Simple logistic regression was conducted using each predictor, and backward stepwise logistic regression was conducted with each equation method and the physiological predictors entered initially into the model. RESULTS: Strength asymmetry or imbalance or both, as a univariate predictor, was not able to predict ankle injury 365 days posttesting. Body mass (P = .01) and body mass index (P = .01) significantly predicted ankle injury. Strength asymmetry or imbalance or both significantly predicted ankle injury when considered with body mass (P = .002–.008). CONCLUSIONS: As a univariate predictor, SA did not predict ankle injury. However, SA contributed significantly to predicting ankle injury in a multivariate model using body mass. Interpreting SA and imbalance in the presence of other physiological variables can help elucidate the risk of ankle injury.

Objectives: To provide an overall perspective on musculoskeletal injury (MSI) epidemiology, risk factors, and preventive strategies in military personnel. Design: Narrative review. Methods: The thematic session on MSIs in military personnel at the 5th International Congress on Soldiers' Physical Performance (ICSPP) included eight presentations on the descriptive epidemiology, risk factor identification, and prevention of MSIs in military personnel. Additional topics presented were bone anabolism, machine learning analysis, and the effects of non-steroidal anti-inflammatory drugs (NSAIDs) on MSIs. This narrative review focuses on the thematic session topics and includes identification of gaps in existing literature, as well as areas for future study. Results: MSIs cause significant morbidity among military personnel. Physical training and occupational tasks are leading causes of MSI limited duty days (LDDs) for the U.S. Army. Recent studies have shown that MSIs are associated with the use of NSAIDs. Bone MSIs are very common in training; new imaging technology such as high resolution peripheral quantitative computed tomography allows visualization of bone microarchitecture and has been used to assess new bone formation during military training. Physical activity monitoring and machine learning have important applications in monitoring and informing evidence-based solutions to prevent MSIs. Conclusions: Despite many years of research, MSIs continue to have a high incidence among military personnel. Areas for future research include quantifying exposure when determining MSI risk; understanding associations between health-related components of physical fitness and MSI occurrence; and application of innovative imaging, physical activity monitoring and data analysis techniques for MSI prevention and return to duty.

Extracellular vesicles (EVs) transport biological content between cells to mediate physiological processes. The association between EVs and resilience, the ability to cope with stress, is unknown. Using unbiased machine learning approaches, we aimed to identify a biological profile of resilience. Twenty servicemen (27.8 ± 5.9 years) completed the Connor Davidson Resilience (CD‐RISC) questionnaire and were exposed to daily physical and cognitive exertion with 48‐hr sleep and caloric restriction. Blood samples from baseline and the second day of stress were analyzed for neuroendocrine biomarkers impacted by military stress. EVs were isolated from plasma and stained with antibodies associated with exosomes (CD63), microvesicles (VAMP3), and apoptotic bodies (THSD1). Individuals were separated into high (n = 10, CD‐RISC > 90) and low (n = 10, CD‐RISC < 79) resilience. EV features were stratified by size, then down‐selected using regression trees and compared between groups. Diagnostic accuracy was assessed using receiver operating characteristic curves. Compared to low resilience, high resilience demonstrated a greater increase in variability of THSD1 local bright spot intensities among large‐sized EVs in response to stress (p = 0.002, Hedges' g = 1.59). Among medium‐sized EVs, high resilience exhibited a greater decrease in side scatter intensity (p = 0.014, Hedges' g = 1.17). Both features demonstrated high to moderate diagnostic accuracy for high resilience (AUC = 0.90 and 0.79). In contrast, neuroendocrine biomarker concentrations were similar between groups. The increase in variability among THSD1 + EVs in high, but not low, resilient individuals following stress may suggest high resilience is accompanied by stress‐triggered apoptotic adaptations to the environment that are not detected in neuroendocrine biomarkers.

Musculoskeletal injuries (MSKI) are a significant burden on the military healthcare system. Movement strategies, genetics, and fitness level have been identified as potential contributors to MSKI risk. Screening measures associated with MSKI risk are emerging, including novel technologies, such as markerless motion capture (mMoCap) and force plates (FP) and allow for field expedient measures in dynamic military settings. The aim of the current study was to evaluate movement strategies (i.e., describe variables) of the countermovement jump (CMJ) in Marine officer candidates (MOCs) via mMoCap and FP technology by clustering variables to create distinct movement strategies associated with MSKI sustained during Officer Candidates School (OCS). 728 MOCs were tested and 668 MOCs (Male MOCs = 547, Female MOCs = 121) were used for analysis. MOCs performed 3 maximal CMJs in a mMoCap space with FP embedded into the system. De-identified MSKI data was acquired from internal OCS reports for those who presented to the OCS Physical Therapy department for MSKI treatment during the 10 weeks of OCS training. Three distinct clusters were formed with variables relating to CMJ kinetics and kinematics from the mMoCap and FPs. Proportions of MOCs with a lower extremity and torso MSKI across clusters were significantly different (p < 0.001), with the high-risk cluster having the highest proportions (30.5%), followed by moderate-risk cluster (22.5%) and low-risk cluster (13.8%). Kinetics, including braking rate of force development (BRFD), braking net impulse and propulsive net impulse, were higher in low-risk cluster compared to the high-risk cluster (p < 0.001). Lesser degrees of flexion and shorter CMJ phase durations (braking phase and propulsive phase) were observed in low-risk cluster compared to both moderate-risk and high-risk clusters. Male MOCs were distributed equally across clusters while female MOCs were primarily distributed in the high-risk cluster. Movement strategies (i.e., clusters), as quantified by mMoCap and ...

The purpose of this research was to determine the effects of high intensity endurance training (ET) and resistance training (RT) alone and in combination on various military tasks. Thirty-five male soldiers were randomly assigned to one of four training groups: total body resistance training plus endurance training (RT + ET), upper body resistance training plus endurance training [UB + ET), RT only, and ET only. Training was performed 4 days per week for 12 weeks. Testing occurred before and after the 12-week training regimen. All groups significantly improved push-up performance, whereas only the RT + ET group did not improve sit-up performance. The groups that included ET significantly decreased 2-mile run time, however, only RT + ET and UB + ET showed improved loaded 2-mile run time. Leg power increased for groups that included lower body strengthening exercises (RT and RT + ET). Army Physical Fitness Test performance, loaded running, and leg power responded positively to training, however, it appears there is a high degree of specificity when concurrent training regimens are implemented.

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.