The test-retest reliability of physiological and perceptual responses during treadmill load carriage.

PURPOSE: Understanding the test-retest reliability of physiological responses to load carriage influences the interpretation of those results. The aim of this study was to determine the test-retest reliability of physiological measures during loaded treadmill walking at 5.5 km h-1 using the MetaMax 3B. METHODS: Fifteen Australian Army soldiers (9 male, 6 female) repeated two 12-min bouts of treadmill walking at 5.5 km h-1 in both a 7.2 kg Control condition (MetaMax 3B, replica rifle) and a 23.2 kg Patrol condition (Control condition plus vest) across three sessions, separated by one week. Expired respiratory gases and heart rate were continuously collected, with the final 3 min of data analysed. Ratings of Perceived Exertion and Omnibus-Resistance Exercise Scale were taken following each trial. Reliability was quantified by coefficient of variation (CV), intra-class correlation coefficients (ICC), smallest worthwhile change (SWC), and standard error of the measurement. RESULTS: Metabolic and cardiovascular variables were highly reliable (≤ 5% CV; excellent-moderate ICC), while the respiratory variables demonstrated moderate reliability (< 8% CV; good-moderate ICC) across both conditions. Perceptual ratings had poorer reliability during the Control condition (12-45% CV; poor ICC) than the Patrol condition (7-16% CV; good ICC). CONCLUSIONS: The test-retest reliability of metabolic and cardiovascular variables was high and relatively consistent during load carriage. Respiratory responses demonstrated moderate test-retest reliability; however, as the SWC differed with load carriage tasks, such data should be interpreted independently across loads. Perceptual measures demonstrated poor to moderate reliability during load carriage, and it is recommended that they only be employed as secondary measures.

Sleep of recruits throughout basic military training and its relationships with stress, recovery, and fatigue.

OBJECTIVE: Studies in basic military training (BMT) examining sleep are largely cross-sectional, and do not investigate relationships between sleep, stress, recovery and fatigue. The aims of this study were to (1a) quantify changes in recruits' sleep quantity and quality over 12 weeks of BMT; (1b) quantify changes in recruits' perceptions of stress, fatigue and recovery over BMT; and (2) explore relationships between sleep, and perceptions of stress, fatigue and recovery. METHODS: 45 recruits (37 male; 8 female, age: 25.2 ± 7.2 years, height: 176.2 ± 10.0 cm, mass: 76.8 ± 15.0 kg) wore ActiGraph GT9X's for 12 weeks of BMT, collecting sleep duration, efficiency and awakenings. Subjective sleep quality, fatigue were measured daily, with stress and recovery measured weekly. Multi-level models assessed relationships between sleep, and stress, recovery, and fatigue. RESULTS: Objective daily means for sleep duration were 6.3 h (± 1.2 h) and 85.6% (± 5.5%) for sleep efficiency. Main effects were detected for all mean weekly values (p < 0.05). Sleep quality showed the strongest relationships with stress, recovery and fatigue. The best model to explain relationships between, stress, recovery and fatigue, included sleep quality, sleep duration, sleep efficiency and awakenings. CONCLUSIONS: The reported mean sleep duration of 6.3 h per night may negatively impact training outcomes across BMT. Combining both subjective and objective measures of sleep best explained relationships between sleep metrics stress, fatigue and recovery. Perceived sleep quality was most strongly related to change in stress, recovery, or post-sleep fatigue.

Overnight sleeping heart rate variability of Army recruits during a 12-week basic military training course.

PURPOSE: This study aimed to quantify sleeping heart rate (HR) and HR variability (HRV) alongside circulating tumor necrosis factor alpha (TNFα) concentrations during 12-week Basic Military Training (BMT). We hypothesised that, despite a high allostatic load, BMT would increase cardiorespiratory fitness and HRV, while lowering both sleeping HR and TNFα in young healthy recruits. METHODS: Sixty-three recruits (18-43 years) undertook ≥ 2 overnight cardiac frequency recordings in weeks 1, 8 and 12 of BMT with 4 h of beat-to-beat HR collected between 00:00 and 06:00 h on each night. Beat-to-beat data were used to derive HR and HRV metrics which were analysed as weekly averages (totalling 8 h). A fasted morning blood sample was collected in the equivalent weeks for the measurement of circulating TNFα concentrations and predicted VO2max was assessed in weeks 2 and 8. RESULTS: Predicted VO2max was significantly increased at week 8 (+ 3.3 ± 2.6 mL kg-1 min-1; p < 0.001). Sleeping HR (wk1, 63 ± 7 b min-1) was progressively reduced throughout BMT (wk8, 58 ± 6; wk12, 55 ± 6 b min-1; p < 0.01). Sleeping HRV reflected by the root mean square of successive differences (RMSSD; wk1, 86 ± 50 ms) was progressively increased (wk8, 98 ± 50; wk12, 106 ± 52 ms; p < 0.01). Fasted circulating TNFα (wk1, 9.1 ± 2.8 pg/mL) remained unchanged at wk8 (8.9 ± 2.5 pg/mL; p = 0.79) but were significantly reduced at wk12 (8.0 ± 2.4 pg/mL; p < 0.01). CONCLUSION: Increased predicted VO2max, HRV and reduced HR during overnight sleep are reflective of typical cardiorespiratory endurance training responses. These results indicate that recruits are achieving cardiovascular health benefits despite the high allostatic load associated with the 12-week BMT.

Recovery of Cognitive Performance Following Multi-Stressor Military Training.

OBJECTIVE: This project aimed to assess the impact of an 8-day military training exercise on cognitive performance, and track its recovery in periods of reduced training load and partially restored sleep. BACKGROUND: Military personnel often work in challenging multi-stressor environments, where sleep loss is inevitable. Sleep loss can impair multiple cognitive domains, which can have disastrous consequences in military contexts. METHOD: A total of 57 male and female soldiers undergoing the Australian Army combat engineer Initial Employment Training course were recruited and tracked over a 16-day study period which included an 8-day field-based military training exercise. Cognitive performance was assessed via a computerised battery at seven time points across four sequential study periods; 1) baseline (PRE), 2) military field training exercise which included total sleep deprivation (EX-FIELD), 3) training exercise at simulated base with restricted sleep opportunities (EX-BASE), and 4) a 3-day recovery period (REC). Subjective load, fatigue, and sleep were evaluated continuously via questionnaire and actigraphy. RESULTS: Psychomotor speed, reaction time, visual tracking and vigilance were impaired following the EX-FIELD period (p < 0.05). The majority of affected measures recovered 2 days following EX-FIELD, being no different in EX-BASE compared to PRE. CONCLUSION: The sensitivity of the cognitive tests to sleep restriction, and recovery, indicates they can help assess operational readiness in military personnel. Future studies should explore other indicators of, and strategies to preserve, operational readiness in military personnel. APPLICATION: This study highlights the impact of work-induced fatigue on cognitive performance, and would interest authorities seeking to preserve operational readiness.

Comparison of Military Recruit and Incumbent Physical Characteristics and Performance: Potential Implications for Through-Career Individual Readiness and Occupational Performance.

ABSTRACT: Drain, JR, Debenedictis, T, Bulmer, S, and Michael, S. comparison of military recruit and incumbent physical characteristics and performance: Potential implications for through-career individual readiness and occupational performance. J Strength Cond Res 36(9): 2536-2543, 2022-After basic military training, physical training practices among incumbent personnel differ substantially, potentially precipitating varied physical capacity and operational readiness. The purpose of this retrospective investigation was to compare physical characteristics and physical performance between recruits and incumbent personnel. Data were collected for 222 army recruits (REC: 197 men/25 women) nearing completion of basic training and 280 incumbent army personnel from combat arms (CA: 142 men) and noncombat arms trades (NCA: 113 men/25 women). Height, mass, and body mass index (BMI) were recorded together with performance measures including predicted V̇ o2 max and 1 repetition maximum box lift. Compared with REC, male incumbents were older (21.8 ± 0.6 vs. 27.6 ± 1.2 years; mean ± 95% confidence interval), had greater body mass (77.6 ± 1.3 vs. 82.6 ± 1.5 kg) and BMI (24.2 ± 0.3 vs. 25.8 ± 0.5 kg·m -2 ), similar relative V̇ o2 max, and lower box lift (49.7 ± 1.4 vs. 47.2 ± 2.4 kg). Male CA demonstrated greatest physical performance while male NCA demonstrated the highest BMI and poorest physical performance. Compared with REC, female incumbents were older (22.8 ± 1.6 vs. 31.9 ± 4.4 years), had similar body mass, higher BMI (24.1 ± 0.7 vs. 26.1 ± 2.4 kg·m -2 ), as well as lower V̇ o2 max (42.0 ± 1.3 vs. 37.9 ± 2.1 ml·kg· -1 ·min -1 ) and box lift (27.8 ± 2.1 vs. 23.3 ± 2.4 kg). More than 97% of men and approximately 75% of women were able to achieve the box lift and V̇ o2 max baseline standards. The older age category (26 + vs. 18-25 years) typically demonstrated higher BMI and lower physical performance. Through-career maintenance of physical capacity is important for military personnel to support individual readiness and occupational performance, preserve health, and mitigate musculoskeletal injury risk.

Monitoring stress and allostatic load in first responders and tactical operators using heart rate variability: a systematic review.

BACKGROUND: Awareness of the cumulative stress placed on first responders and tactical operators is required to manage acute fatigue, which can impair occupational performance, and may precipitate negative chronic health outcomes. The aim of this review was to investigate the utility of heart rate variability (HRV) to monitor stress and allostatic load among these populations. METHODS: A systematic search of Academic Search Complete, MEDLINE complete, PsycINFO, SPORTDiscus and Scopus databases was conducted. Eligibility criteria: original peer reviewed research articles, written in English, published between 1985 and 2020, using human participants employed as a first responder or tactical operator, free from any psychological disorder. RESULTS: Of the 360 articles screened, 60 met the inclusion criteria and were included for full text assessment. Articles were classified based on single or repeated stressor exposure and the time of HRV assessment (baseline, during stressor, post stressor). Singular stressful events elicited a reduction in HRV from baseline to during the event. Stressors of greater magnitude reduced HRV for extended durations post stressor. Lower resting HRV was associated with lower situational awareness and impaired decision-making performance in marksmanship and navigation tasks. There were insufficient studies to evaluate the utility of HRV to assess allostatic load in repeated stressor contexts. CONCLUSION: A reduction in HRV occurred in response to acute physical and cognitive occupational stressors. A slower rate of recovery of HRV after the completion of acute occupational stressors appears to occur in response to stressors of greater magnitude. The association between lower HRV and lower decision-making performance poses as a useful tool but further investigations on within subject changes between these factors and their relationship is required. More research is required to investigate the suitability of HRV as a measure of allostatic load in repeated stress exposures for fatigue management in first responder and tactical operators.

Associations between inflammatory markers and well-being during 12 weeks of basic military training.

PURPOSE: Stress, anxiety and physical exertion are all closely linked to well-being, and each can alter immune function. Diminished well-being has been observed during military training, however there is mixed evidence regarding whether concomitant changes in inflammatory markers occur, with these phenomena indicating potential maladaptive responses to imposed training loads. The aims of this project were (1) assess changes in inflammation and subjective well-being across a 12-week basic military training (BMT) program, and (2) evaluate relationships between circulating inflammatory markers and well-being. METHODS: A total of 37 men and women undergoing 12 weeks of BMT in Australia were recruited. Well-being was assessed via questionnaire (DASS-21), and plasma samples were collected for the analysis of inflammatory cytokines [interleukin (IL)-4, IL-6, IL-1ß, IL-8, IL-10, and tumor necrosis factor (TNF)-α] at weeks 1, 4, 8 and 12. Data were analysed using general linear mixed models. RESULTS: Depression, anxiety and stress subscale scores all significantly improved (all P ≤ 0.001), and TNF-α decreased (P = 0.031) across time. Compared to baseline (week 1), significant decreases in associations between depression and IL-10, anxiety and IL-10, and stress and IL-10, IL-4 IL-6 and TNF-α (all P < 0.05), were detected across BMT. CONCLUSION: The BMT program appears to support improved well-being over the 12 weeks, with minimal perturbation to inflammatory markers. Biomarkers and well-being displayed consistent associations and may have utility as psychophysiological indicators of health status in military research, however for now, subjective measures may represent more cost-effective proxies for ongoing monitoring of military personnel.

Is muscular strength a critical physical attribute for the apprehension of a simulated non-compliant suspect?

This investigation determined the influence of technique and experience on arm retraction force required to apprehend a non-compliant suspect. Phase-One: Nine experienced RAAF military-police completed four apprehension simulations, peak arm retraction force was measured; i) Control(CON), ii) Pressure-Point(PP), iii) Targeted-Striking(TS) and iv) 2-Person(2Per) techniques. Phase-Two: Experienced (EXP, n = 8) or Inexperienced (INEXP, n = 22) military-police completed CON, PP and Pressure-Point + Coaching(PP + C). Strength was assessed in INEXP. EXP produced more force (178.7 N ± 25.9) than INEXP during CON, but no participant successfully apprehended the suspect. All EXP were successful with PP, arm retraction force 357 N (CI: 233.7,480.2) was lower compared to CON, but no difference was observed between PP and CON for INEXP. PP + C, 82% of INEXP were successful, force declined 138.2 N (CI: 67.8,208.5) compared to CON. All EXP required PP for successful apprehension. INEXP required PP + C for apprehension success. Muscular strength had a limited relationship with arm retraction force. Practitioner summary: For law enforcement personnel, apprehension of a suspect is a critical and physically demanding task, where success is associated with muscular strength and technique. We observed success in the apprehension of a simulated suspect by military law enforcement personnel was primarily determined by participant skill and experience and not muscular strength.

Treadmill load carriage overestimates energy expenditure of overground load carriage.

This study compared physiological and biomechanical responses between treadmill and overground load carriage. Thirty adults completed six 10-minute walking trials across three loads (0, 20, and 40% body mass) and two surfaces (treadmill and overground). Relative oxygen consumption was significantly greater on the treadmill for 20% (1.54 ± 0.20 mL⋅kg-1⋅min-1) and 40% loads (1.08 ± 0.20 mL⋅kg-1⋅min-1). All other physiological and perceptual responses were significantly higher in the treadmill condition and with increases in load. Stance time was longer (0%: 0.05 s; 20%: 0.02 s, 40%: 0.05 s, p < 0.001) and cadence was lower (0%: 1 step·min-1; 20%: 2 steps·min-1; 40%: 3 steps·min-1, p < 0.05) on the treadmill. Peak lower limb joint angles were similar between surfaces except for ankle plantar flexion, which was 8˚ greater on the treadmill. The physiological responses to treadmill-based load carriage are generally not transferable to overground load carriage and caution must be taken when conducting treadmill-based load carriage research to inform operational-based scenarios. Practitioner Summary: Literature is limited when comparing the physiological and biomechanical responses to treadmill and overground load carriage. Using a repeated measures design, it was shown that although walking kinematics are generally similar between surfaces, there was a greater physiological demand while carrying a load on a treadmill when compared with overground. Abbreviations: BM: body mass; e.g: for example; HR: heart rate; HRmax: heart rate maximum; Hz: hertz; kg: kilograms; km·h-1: kilometres per hour; L⋅min-1: litres per minute; m: metres; MD: mean difference; mL·kg-1·min-1: millilitres per kilogram per minute; mL⋅min-1: millilitres per minute; η2p: partial-eta squared; OG: overground; RPE: rating of perceived exertion; s: seconds; SD: standard deviation; SE: standard error; steps·min-1: steps per minute; TM: treadmill; V̇CO2: volume of carbon dioxide; V̇E: ventilation; V̇O2: volume of oxygen; V̇O2max: maximum volume of oxygen; y: years.

No physiological or biomechanical sex-by-load interactions during treadmill-based load carriage.

This study investigated whether physiological demand or gait mechanics differ between sexes during treadmill load carriage. Female (n = 15) and male (n = 15) military recruit-type participants with no load carriage experience completed three 10-minute walking trials at a self-selected speed with increasing relative body-borne loads (0%, 20%, and 40% body weight). A range of cardiorespiratory, perceptual and biomechanical variables were measured. Self-selected walking speed was similar between sexes (4.6-4.8 km·h-1, p > .05) and there were no significant sex-by-load interactions for any variables. Absolute VO2 and VCO2 were greater in males (difference 175-178 mL·min-1, p < .001), however, when relative to body mass, VO2 was similar between sexes (p > .05). Across all loads, cadence was 7 ± 2 steps·min-1 faster (p = .004) and stance time was 0.06 ± 0.02 s shorter (p = .013) in females. Increasing load resulted in greater physiological demand, cadence, % stance time, and step length (p < .05). Practitioner summary: Literature comparing physiological and biomechanical variables between sexes during load carriage is scarce. Physiological and biomechanical sex differences were limited to relative measures associated with physical size (height and mass). Future research may pool male and female participants when conducting trials up to ten minutes in length. Abbreviations: BW: body weight; COM: centre of mass; HR: heart rate; HRmax: maximum heart rate; RER: respiratory exchange ratio; RPE: rating of perceived exertion; VCO2: volume of carbon dioxide; VE: ventilation; VO2: volume of oxygen; VO2max: maximum volume of oxygen.

The Effectiveness of Basic Military Training To Improve Functional Lifting Strength in New Recruits.

Australian Army recruits are required to meet the incumbent baseline physical employment standards (PES) during basic military training. A box lift and place (BLP) assessment is included in the PES, and it assesses the ability to perform essential muscular strength tasks. Therefore, basic military training must provide sufficient training stimulus to enable recruits to achieve the baseline BLP standard. A study was undertaken to investigate changes in the performance of 1-repetition maximum BLP in male (n = 154; age, 21.4 years) and female (n = 20; age, 23.1 years) recruits over the first 8 weeks of a 12-week basic military training course. Both male and female recruits showed modest improvements (2.2 ± 5.9 kg and 3.0 ± 3.1 kg, respectively; p ≤ 0.05) in maximal BLP performance, and there were no differences between genders. The female recruits showed greater relative improvements compared with the male recruits (14.7 ± 7.8% vs. 6.5 ± 2.3%). Despite the modest improvements in BLP performance, 70% of female and 100% of male recruits achieved the baseline BLP standard (25 kg) during week 8. The 30% failure rate for female recruits, however, suggests that the basic training program should be improved. A training program that yields greater gains in muscular strength would likely increase female recruit BLP pass rates. Augmented muscular strength would also likely increase the number of recruits capable of achieving higher BLP standards for more physically demanding employment categories. A training program that yields greater improvements in muscular strength may also enable lower entry standards, thereby increasing the recruit pool.

Lower limb kinematics and physiological responses to prolonged load carriage in untrained individuals.

The aim of this study was to simultaneously assess the changes in physiology, and kinematic and spatiotemporal features of gait, during prolonged load carriage in individuals without load carriage experience. Eleven males, representative of new military recruits, walked for 120 min at 5.5 km h(- 1), 0% grade, on a motorised treadmill while carrying a 22 kg load. The load ( ≤ 30% body mass) was distributed over a weighted vest, combat webbing and replica model firearm, to reflect a patrol order load. Oxygen consumption and heart rate increased throughout the trial; however, apart from a minor increase in step length, there were no changes in the kinematic or spatiotemporal parameters, despite an increase in perceived exertion and discomfort. These data suggest that individuals with no experience in load carriage are able to maintain normal gait during 2 h of fixed speed walking, while carrying a patrol order load ≤ 30% body mass.

Characterising the physical demands of critical tasks across the Royal Australian Air Force.

BACKGROUND: Militaries have historically utilised generic physical fitness tests to assess physical readiness, but there has been a recent shift to develop physical employment standards (PES) based on actual job demands. OBJECTIVE: The purpose of this investigation was to characterise the physical demands of critical tasks performed by Royal Australian Air Force (RAAF) personnel to inform PES development. METHODS: Job task analysis were performed for 27 RAAF trades. Criterion tasks were identified through a systematic approach involving workshops and field-observations. The identified tasks were assessed for dominant physical capacity and grouped into movement-based clusters. Psychophysiological measures were collected from personnel performing the tasks. RESULTS: Of 87 criterion tasks, 92% were characterised as manual handling dominant. Across these 87 tasks the principal physical capacities were: muscular strength (59%), muscular endurance (52%) and cardiorespiratory endurance (39%). The most common movement clusters were Lift to Platform (44%) and Lift and Carry (38%). Lift to Platform tasks required lifting to a median height of 1.32 m (1.20 -1.65 m) and a median mass of 25.0 kg (21.0 -28.9 kg) per person. Median carry mass was 25.0 kg (22.4 -36.1 kg) per person and distance was 26.0 m (17.5 -50.0 m). Median task mean 'Vdot;O2, HR and RPE were 1.8 L.min- 1 (1.5-2.2 L.min- 1), 137 b.min- 1 (120-144) and 13 (12-14). CONCLUSIONS: The high proportion of manual handling criterion tasks emphasises the importance of these activities and the underlying physical capacities for RAAF personnel. Current fitness assessments are unlikely to predict job task performance.

Subjective Measures of Workload and Sleep in Australian Army Recruits; Potential Utility as Monitoring Tools.

INTRODUCTION: Subjective measures may offer practitioners a relatively simple method to monitor recruit responses to basic military training (BMT). Yet, a lack of agreement between subjective and objective measures may presents a problem to practitioners wishing to implement subjective monitoring strategies. This study therefore aims to examine associations between subjective and objective measures of workload and sleep in Australian Army recruits. MATERIALS AND METHODS: Thirty recruits provided daily rating of perceived exertion (RPE) and differential RPE (d-RPE) for breathlessness and leg muscle exertion each evening. Daily internal workloads determined via heart rate monitors were expressed as Edwards training impulse (TRIMP) and average heart rate. External workloads were determined via global positioning system (PlayerLoadTM) and activity monitors (step count). Subjective sleep quality and duration was monitored in 29 different recruits via a customized questionnaire. Activity monitors assessed objective sleep measures. Linear mixed-models assessed associations between objective and subjective measures. Akaike Information Criterion assessed if the inclusion of d-RPE measures resulted in a more parsimonious model. Mean bias, typical error of the estimate (TEE) and within-subject repeated measures correlations examined agreement between subjective and objective sleep duration. RESULTS: Conditional R2 for associations between objective and subjective workloads ranged from 0.18 to 0.78, P < 0.01, with strong associations between subjective measures of workload and TRIMP (0.65-0.78), average heart rate (0.57-0.73), and PlayerLoadTM (0.54-0.68). Including d-RPE lowered Akaike Information Criterion. The slope estimate between objective and subjective measures of sleep quality was not significant. A trivial relationship (r = 0.12; CI -0.03, 0.27) was observed between objective and subjective sleep duration with subjective measures overestimating (mean bias 25 min) sleep duration (TEE 41 min). CONCLUSIONS: Daily RPE offers a proxy measure of internal workload in Australian Army recruits; however, the current subjective sleep questionnaire should not be considered a proxy measure of objective sleep measures.

Overnight heart rate variability responses to military combat engineer training.

The study aimed to determine if overnight heart rate variability (HRV) is reflective of workload and stress during military training. Measures of cognitive load, perceived exertion, physical activity, nocturnal HRV, cognitive performance and sleep were recorded for a 15-day assessment period in 32 combat engineers. The assessment period consisted of 4 phases, PRE, FIELD, BASE and RECOVERY that exposed trainees to periods of sleep deprivation and restriction. The FIELD phase was characterised by an increase in mood disturbance, perceived exertion, physical activity, HRV and a reduction in sleep quantity (p < 0.05). Measures of HRV returned to PRE-values quicker than subjective wellbeing responses. The combination of sleep duration (ß = -0.002, F = 13.42, p < 0.001) and physical activity (metabolic equivalents, ß = -0.483, F = 5.95, p = 0.017), the main stressors of the exercise, provided a significant effect in the best predictive model of HRV. The different recovery rates of HRV and subjective wellbeing suggest a different physiological and psychological response.

The physiological demand of a task simulation varies when developed by independent groups of experiential experts.

OBJECTIVE: To investigate the disparity in the specification and physiological demand of a task simulation when developed by two independent panels of experiential experts. DESIGN: Independent groups design. METHODS: Two groups of experiential experts from the Royal Australian Air Force (RAAF) worked independently to design, and then complete a simulation of a generic occupational task; the establishment of a security control point. Task duration, oxygen consumption, and cardiac frequency were measured whilst each panel completed the task simulation. Maximal acceptable work duration (MAWD) and the percentage of MAWD (%MAWD) were also calculated. Independent t-tests were used to determine differences (P < 0.05) between the measured variables. RESULTS: No differences were observed in the average oxygen consumption (1.26 ± 0.25 L min-1 and 1.28 ± 0.29 L min-1 respectively; P = 0.84), or cardiac frequency (134 ± 16.4 beats·min-1 and 125 ± 8.5 beats·min-1 respectively; P = 0.12) between Panel 1 and Panel 2. However, there was a significant difference between panels with respect to task duration (Panel 1: 15.5 ± 3.68 min; Panel 2: 34.20 ± 9.60 min; P < 0.01), and the %MAWD (Panel 1: 5.32 ± 3.17%, Panel 2: 12.15 ± 9.40%, P = 0.04). CONCLUSIONS: The physiological demand of a task simulation is dependent upon the group of experts consulted to develop the simulation. It is critical that input from a wide representation of experiential experts is considered when developing task simulations to avoid bias towards the perceptions of the experts consulted.

Monitoring Responses to Basic Military Training with Heart Rate Variability.

INTRODUCTION: Heart rate variability (HRV) has shown sensitivity to the acute stressors experienced by defense personnel. This study examines the suitability of overnight HRV as a repeated measure of allostatic load in defense personnel. METHODS: Daily measures of sleep, cognitive load, and perceived exertion were reported for the 12-wk duration of basic military training (BMT) in 48 recruits. Physical activity, subjective well-being, and HRV were measured weekly. The natural log of the root mean square of successive differences of interbeat intervals (Ln RMSSD) and the Ln RMSSD to interbeat interval ratio (Ln RMSSD:RRi ratio) during predicted slow wave sleep were used for HRV. Physical performance was assessed via the 20-m shuttle run and maximal push-up test in weeks 2 and 8 of BMT with predicted V̇O 2 peak values calculated. RESULTS: Predicted V̇O 2 peak increased from 42.6 ± 4.5 to 48.0 ± 2.7 mL·kg -1 ·min -1 ( P < 0.001). Ln RMSSD was elevated in weeks 7 and 10, and the Ln RMSSD:RRi ratio was elevated in week 10 above all other weeks ( P < 0.05). An increase in perceived exertion ( F = 9.10, P = 0.003) and subjective fatigue ( F = 6.97, P = 0.009), as well as a reduction in V̇O 2 peak ( F = 7.95, P = 0.009), individually predicted an increase in Ln RMSSD. The best predictive model of Ln RMSSD included perceived exertion ( F = 8.16, P = 0.005), subjective fatigue ( F = 8.49, P = 0.004), the number of awakenings during sleep ( F = 7.79, P = 0.006), and the change in V̇O 2 peak ( F = 19.110, P < 0.001). CONCLUSIONS: HRV was predicted by subjective recruit responses to BMT workloads rather than objective measures of physical activity. Improvements in cardiorespiratory fitness depicted recruits who experienced enough stress to facilitate physiological adaptation, which was reflected by a reduction in HRV during BMT. Monitoring HRV and HRV in relation to interbeat interval length may provide a better tool for determining allostatic load than HRV alone.

Mechanical Differences between Men and Women during Overground Load Carriage at Self-Selected Walking Speeds.

Few studies have directly compared physical responses to relative loading strategies between men and women during overground walking. This study aimed to compare gait mechanics of men and women during overground load carriage. A total of 30 participants (15 male, 15 female) completed three 10-min walking trials while carrying external loads of 0%, 20% and 40% of body mass at a self-selected walking speed. Lower-body motion and ground reaction forces were collected using a three-dimensional motion capture system and force plates, respectively. Female participants walked with a higher cadence (p = 0.002) and spent less absolute time in stance (p = 0.010) but had similar self-selected walking speed (p = 0.750), which was likely due to the female participants being shorter than the male participants. Except for ankle plantarflexion moments, there were no sex differences in spatiotemporal, kinematic, or kinetic variables (p > 0.05). Increasing loads resulted in significantly lower self-selected walking speed, greater stance time, and changes in all joint kinematics and kinetics across the gait cycle (p < 0.05). In conclusion, there were few differences between sexes in walking mechanics during overground load carriage. The changes identified in this study may inform training programs to increase load carriage performance.

Factors Predicting Training Delays and Attrition of Recruits during Basic Military Training.

Ensuring a balance between training demands and recovery during basic military training (BMT) is necessary for avoiding maladaptive training responses (e.g., illness or injury). These can lead to delays in training completion and to training attrition. Previously identified predictors of injury and attrition during BMT include demographic and performance data, which are typically collected at a single time point. The aim of this study was to determine individual risk factors for injury and training delays from a suite of measures collected across BMT. A total of 46 male and female recruits undertaking the 12-week Australian Army BMT course consented to this study. Injury, illness, attrition, and demographic data were collected across BMT. Objective measures included salivary cortisol and testosterone, step counts, cardiorespiratory fitness, and muscular endurance. Perceptions of well-being, recovery, workload, fatigue, and sleep were assessed with questionnaires. Baseline and mean scores across BMT were evaluated as predictors of injury and attrition using generalized linear regressions, while repeated-measures ANOVA was used for the group comparisons. From the 46 recruits, 36 recruits completed BMT on time; 10 were delayed in completion or discharged. Multiple risk factors for injury during BMT included higher subjective ratings of training load, fatigue, and stress, lower sleep quality, and higher cortisol concentrations. Higher ratings of depression, anxiety, and stress, and more injuries were associated with a higher risk of delayed completion. Higher concentrations of testosterone and higher levels of fitness upon entry to BMT were associated with reduced risk of injury and delayed completion of BMT. Ongoing monitoring with a suite of easily administered measures may have utility in forewarning risk of training maladaptation in recruits and may complement strategies to address previously identified demographic and performance-based risk factors to mitigate injury, training delays, and attrition.

A Comprehensive Analysis of Injuries During Army Basic Military Training.

INTRODUCTION: The injury definitions and surveillance methods commonly used in Army basic military training (BMT) research may underestimate the extent of injury. This study therefore aims to obtain a comprehensive understanding of injuries sustained during BMT by employing recording methods to capture all physical complaints. MATERIALS AND METHODS: Six hundred and forty-six recruits were assessed over the 12-week Australian Army BMT course. Throughout BMT injury, data were recorded via (1) physiotherapy reports following recruit consultation, (2) a member of the research team (third party) present at physical training sessions, and (3) recruit daily self-reports. RESULTS: Two hundred and thirty-five recruits had ≥1 incident injury recorded by physiotherapists, 365 recruits had ≥1 incident injury recorded by the third party, and 542 recruits reported ≥1 injury-related problems via the self-reported health questionnaire. Six hundred twenty-one, six hundred eighty-seven, and two thousand nine hundred sixty-four incident injuries were recorded from a total of 997 physiotherapy reports, 1,937 third-party reports, and 13,181 self-reported injury-related problems, respectively. The lower extremity was the most commonly injured general body region as indicated by all three recording methods. Overuse accounted for 79% and 76% of documented incident injuries from physiotherapists and the third party, respectively. CONCLUSIONS: This study highlights that injury recording methods impact injury reporting during BMT. The present findings suggest that traditional injury surveillance methods, which rely on medical encounters, underestimate the injury profile during BMT. Considering accurate injury surveillance is fundamental in the sequence of injury prevention, implementing additional injury recording methods during BMT may thus improve injury surveillance and better inform training modifications and injury prevention programs.