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Background: Military personnel in combat roles observe a high prevalence of knee osteoarthritis. Knee total joint moment (KTJM) and the knee adduction moment percentage contribution (KAM%) of KTJM have been linked to knee osteoarthritis. It is postulated that sex, load carriage, and imposed locomotion patterns such as forced marching (FM) alter mechanics of the knee. The purpose of this study was to determine the effects of “military-relevant” load magnitudes, locomotion patterns, and sex on KTJM and its planar percentage contributions in recruit-aged adults during short-duration gait tasks. Hypothesis: The greatest load magnitude and FM will significantly increase KAM contribution to KTJM compared with lower magnitudes or no load. Additionally, women will exhibit greater KAM contribution to KTJM compared with men regardless of experimental condition. Study Design: Controlled laboratory study. Methods: Twenty healthy recruit-aged (18-35 years) adults (10 male, 10 female) executed trials of running and FM with no load (BW), an additional load of 45% of BW, and an additional load of 55% of BW. KTJM was calculated along with each plane of motion percentage contribution: knee flexion moment (KFM%), KAM%, and knee rotation moment (KRM%). A 3 × 2 × 2 mixed model analysis of variance was used to evaluate the effects of load carriage, locomotion pattern, and sex on KTJM, KFM%, KAM%, and KRM% at multiple gait events of stance phase. Results: FM exhibited a greater (P < .001) KTJM than running at heel strike. Running had greater KAM% (P = .01) and KRM% (P < .001) compared with FM. At midstance, running exhibited greater (P < .001) KTJM than FM for each load condition; however, FM had greater KAM% (P < .001) and KRM% (P = .002) compared with running at peak vertical ground reaction force and midstance. Men exhibited greater KAM% at heel strike (P = .02) independent of locomotion pattern and at midstance (P = .04) for FM. Conclusion: Load carriage increases KAM% to a magnitude similarly observed in populations with knee osteoarthritis, especially when executing FM. Interestingly, men exhibited greater KAM% than women, suggesting differing strategies to motor execution with relative load carriage. Clinical Relevance: Screening recruits for greater KAM% during loaded gait tasks may identify individuals in need of specialized training to reduce the risk of knee osteoarthritis development.

Background/Objectives: The purpose of this study was to evaluate the association between risk-taking behaviors, vestibular symptoms/impairment and perception–action coupling behavior in recently concussed adolescents. Methods: This study utilized a cross-sectional design to evaluate the early effects of concussion on 12–18-year-old adolescents (n = 47) recruited from a concussion specialty clinic at their presenting clinical appointment. The Perception–Action Coupling Task (PACT) was used to assess action boundary perception by evaluating the participant’s ability to quickly and accurately determine whether a virtual “ball” fits in a virtual “hole”. Accuracy, response time and inverse efficiency were evaluated at the 0.8 and 1.2 ratios of ball–hole pairings, where 0.8 indicates the ball was slightly smaller than the hole and 1.2 indicates the ball was slightly larger than the hole. The Balloon Analog Risk Task (BART) is a computerized test which measures risk-taking behavior by “pumping” up a balloon. Each pump provides a small amount of virtual money into their bank; the goal is to make as much money as possible without popping the virtual balloon. The Vestibular Ocular Motor Screening (VOMS) tool is a brief screening tool designed to identify ocular or vestibular dysfunction following sport-related concussion, where horizontal/vertical vestibular ocular reflex (VOR) and visual motion sensitivity (VMS) are the primary vestibular outcomes. Pearson correlation matrices were developed to evaluate the association between BART, VOMS and PACT outcomes within the study cohort of concussed adolescents. Results: PACT inverse efficiency at the 1.2 ball–hole ratio was significantly correlated with all three VOMS outcomes (r = 0.33–0.37). The standard deviation of pump reaction time during BART was significantly correlated with accuracy (r = −0.47) and inverse efficiency (r = 0.42) at the 1.2 ratio. The standard deviation of the total number of pumps during BART was significantly correlated with PACT response time at the 1.2 ratio (r = 0.34). Horizontal VOR correlated with balloons collected (r = −0.30) and balloons popped (r = −0.30). Conclusions: The results of this study suggest that risk-taking behaviors and vestibular symptoms/impairment are associated with worse action boundary perception in adolescents following concussion. This relationship is more pronounced in male adolescents than females.

Soldiers are challenged with interpreting information in unpredictable contexts, while maintaining high levels of job-specific performance. Virtual reality (VR) provides a controlled, immersive environment to evaluate military-relevant tasks under stress. This study determined psychological, physical, and cognitive associations with military-relevant VR task performance. Twenty-five male active-duty soldiers completed baseline psychological and cognitive assessments and then returned twice to complete VR-based Recognition Memory (RMT), Spatial Orienting (SOT), and Decision-Making (DMT) tasks under conditions of stress (active threat of torso electric shock) or no stress (torso vibration only). Baseline measures were categorized into 13 domains and standardized via z-scores. Generalized estimating equations were run with experimental condition (shock vs. vibrate) as the within-subject variable. Variables associated with correct object identification during the RMT include coping skills (e.g., acceptance), physical fitness (e.g., 2-mile run time), social intelligence, and personality traits (e.g., conscientiousness). Other coping skills (e.g., denial) decreased the odds of correct identification. Variables associated with accurate orienting on the SOT include coping skills (e.g., restraint), neurocognitive function (e.g., working memory), and prior video game experience. Additional measures of neurocognitive function (e.g., spatial orientation) reduced the odds of correct orientation. Variables associated with distinguishing targets during the DMT include coping skills (e.g., acceptance) and neurocognitive function (e.g., spatial orientation). Other coping skills (e.g., disengagement coping styles) reduced these odds. Coping skills, specifically higher acceptance, are associated with performance on military-relevant VR tasks and should be examined further to better understand how military performance could benefit from interventions targeting modifiable characteristics.

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.

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 βCTX, 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 βCTX 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.

ObjectivesMusculoskeletal injuries (MSI) are an important concern in military populations. The purpose of this study was to describe the burden of MSI and associated financial cost, in a sample of US Air Force Special Operations Command Special Tactics Operators.MethodsIn this cross-sectional study, medical records of the Operators were reviewed during the years 2014–2015. MSI that occurred during a 1-year period prior to the date of review were described. MSI attributes described included incidence, anatomic location, cause, activity when MSI occurred, type and lifetime cost of MSI estimated using the Web-based Injury Statistics Query and Reporting System.ResultsA total of 130 Operators participated in the study (age: 29.1±5.2 years). The 1-year cumulative incidence of MSI was 49.2 injured Operators/100 Operators/year. The most frequent anatomic location and sublocation for MSI were the lower extremity (40.9% of MSI) and shoulder (20.9%), respectively. Lifting was a common cause of MSI (21.8%). A large per cent of MSI (55.5%) occurred while Operators were engaged in either physical or tactical training. Common MSI types were pain/spasm/ache (44.5%). Many MSI (41.8%) were classified as potentially preventable by an injury prevention training programme. The total lifetime cost of these MSI was estimated to be approximately US$1.2 million.ConclusionMSI are an important cause of morbidity and financial cost in this sample of Air Force Special Tactics Operators. There is a need to develop a customised injury prevention programme to reduce the burden and cost of MSI in this population.

Background: Musculoskeletal injuries at the shoulder are highly prevalent and place a large burden on United States Special Forces personnel. Literature is lacking regarding the risk factors for these types of injuries. Purpose/Hypothesis: The purpose of this study was to evaluate the association of shoulder strength and kinematic characteristics, which have shown retrospective associations with shoulder conditions/injuries, with prospectively collected shoulder injuries. We hypothesized that lower strength and abnormal kinematics would be predictive of future shoulder injury. Study Design: Case-control study; Level of evidence, 3. Methods: A total of 140 male Special Forces operators underwent a musculoskeletal evaluation of the shoulder that included a scapular kinematic assessment during a humeral elevation task and isokinetic strength testing of the scapular protractors/retractors, external/internal rotators, and elevators of the shoulder. From strength assessments, ipsilateral strength ratios and bilateral strength asymmetries were also calculated. Musculoskeletal injuries of the shoulder were collected prospectively by use of medical chart reviews at 365 days following the evaluation. Separate generalized estimating equations (GEEs) and simple logistic regressions were used to analyze the association between baseline predictors and development of shoulder injury. Results: Results of the GEEs showed no significant prediction of shoulder injury by shoulder strength (odds ratio [OR], 1.00-1.03), ipsilateral strength ratios (OR, 0.43-2.12), or scapular kinematics (OR, 0.99-1.01). Logistic regression indicated that none of the bilateral asymmetries were significantly predictive of shoulder injury (OR, 1.00-1.04). Conclusion: The results indicate that shoulder strength and kinematic characteristics are not risk factors for shoulder injury in the Special Forces population. These findings are in opposition to the general findings of previous research using a retrospective analysis.

Introduction As humans’ advance towards a Mars mission, ensuring astronaut safety, well-being, and performance becomes increasingly critical. Long-duration space exploration presents several challenges for human sleep, including altered photoperiods, prolonged confinement, and monotony. Antarctica provides an ideal analog for understanding how these and other stressors impact sleep over time. Prior studies among Antarctic cohorts have found reduced total sleep, increased sleep onset, and circadian phase delay. However, day-to-day regularity of sleep-wake patterns in the Antarctic over prolonged periods has not been studied. Methods Crew members (N= 110) at a coastal (McMurdo: MM, n = 88) and an inland Antarctic station (South Pole: SP, n = 22) were studied longitudinally for up to 9-months. Sleep was monitored continuously with actigraphy (Actiwatch Spectrum, Philips Respironics) and examined in relation to cumulative time on station and calendar month (photoperiod). Self-reported mental health symptoms were also examined monthly using The Mental Health Checklist (MHCL). The Sleep Regularity Index (SRI; Phillips et al., 2017) which calculates the percentage probability of an individual being in the same state (sleep vs. wake) at any two time-points 24 hours apart was calculated to examine sleep regularity over time. Results Controlling for time on station prior to participation, we observed no significant changes in monthly SRI over a 6-month period at MM where photoperiod alterations are less extreme. At SP, SRI remained very stable during months of total daylight but declined during winter months in the absence of sunlight. SRI scores were significantly different between month-8 and month-9 and with large effect sizes across month-7, month-8, and month-9. Participants with lower month-7 SRI scores had significantly higher MHCL poor self-regulation scores at the end of the mission. Conclusion Day-to-day variability in sleep–wake patterns is an important predictor of health and safety. Our findings show reductions in sleep regularity during prolonged Antarctic residence particularly at the SP station, where sunlight is absent for 6 months of the year. Less sleep regularity predicted worse mental health functioning. These findings suggest that mitigation the impact of altered light-dark cycles on sleep is critical for a Mars mission. Support (if any) NASA award #NNX15AC13G S014 to the last author.

Forced-marching with heavy loads is a typical task for warfighters. Unfortunately, injury incidence is high during these tasks with the most common mechanism of injury being a slip, trip, or fall. Given that individuals are less stable in the mediolateral plane we sought to understand how load carriage, sex and task completion impacts parameters of mediolateral stability during forced-marching. Twenty-four (12F, 12 M) recruit-aged adults (18–35 years) completed trials of forced-marching unloaded and with a load 55 % of bodyweight. Mean and standard deviation of center of mass position (zB), heading (ΔzB), step-width (w), and trunk impulse (JTrunk) were calculated. Detrended fluctuation analysis and direct control analysis were performed on time-series of each parameter. Only JTrunk mean and variability changed between conditions, increasing with load (p = 0.006; p < 0.001). Load had no effect on zB and ΔzB control with the former being minimally controlled and the latter tightly regulated. The addition of load decreased (p = 0.004) control of w and JTrunk but the latter was still tightly regulated. There were no effects of sex but individuals who failed to complete the loaded trial had greater (p = 0.038) JTrunk compared to those who did. The continued strict regulation of JTrunk when loaded suggests an attempt to reduce large magnitude deviations. Larger JTrunk of individuals unable to complete the task may indicate limited trunk muscle strength/endurance to restrict impulse. Alternatively, these individuals may utilize a coordinative pattern poorly suited for constraining trunk movement. Therefore, JTrunk may represent an important parameter of assessment to identify individuals of greater risk.