Influence of Soldiers' Cardiorespiratory Fitness on Physiological Responses and Dropouts During a Loaded Long-distance March.

INTRODUCTION: In military service, marching is an important, common, and physically demanding task. Minimizing dropouts, maintaining operational readiness during the march, and achieving a fast recovery are desirable because the soldiers have to be ready for duty, sometimes shortly after an exhausting task. The present field study investigated the influence of the soldiers' cardiorespiratory fitness on physiological responses during a long-lasting and challenging 34 km march. MATERIALS AND METHODS: Heart rate (HR), body core temperature (BCT), total energy expenditure (TEE), energy intake, motivation, and pain sensation were investigated in 44 soldiers (20.3 ± 1.3 years, 178.5 ± 7.0 cm, 74.8 ± 9.8 kg, body mass index: 23.4 ± 2.7 kg × m-2, peak oxygen uptake ($\dot{\rm{V}}$O2peak): 54.2 ± 7.9 mL × kg-1 × min-1) during almost 8 hours of marching. All soldiers were equipped with a portable electrocardiogram to record HR and an accelerometer on the hip, all swallowed a telemetry pill to record BCT, and all filled out a pre- and post-march questionnaire. The influence of aerobic capacity on the physiological responses during the march was examined by dividing the soldiers into three fitness groups according to their $\dot{\rm{V}}$O2peak. RESULTS: The group with the lowest aerobic capacity ($\dot{\rm{V}}$O2peak: 44.9 ± 4.8 mL × kg-1 × min-1) compared to the group with the highest aerobic capacity ($\dot{\rm{V}}$O2peak: 61.7 ± 2.2 mL × kg-1 × min-1) showed a significantly higher (P < .05) mean HR (133 ± 9 bpm and 125 ± 8 bpm, respectively) as well as peak BCT (38.6 ± 0.3 and 38.4 ± 0.2 °C, respectively) during the march. In terms of recovery ability during the break, no significant differences could be identified between the three groups in either HR or BCT. The energy deficit during the march was remarkably high, as the soldiers could only replace 22%, 26%, and 36% of the total energy expenditure in the lower, middle, and higher fitness group, respectively. The cardiorespiratory fittest soldiers showed a significantly higher motivation to perform when compared to the least cardiorespiratory fit soldiers (P = .002; scale from 1 [not at all] to 10 [extremely]; scale difference of 2.3). A total of nine soldiers (16%) had to end marching early: four soldiers (21%) in the group with the lowest aerobic capacity, five (28%) in the middle group, and none in the highest group. CONCLUSION: Soldiers with a high $\dot{\rm{V}}$O2peak showed a lower mean HR and peak BCT throughout the long-distance march, as well as higher performance motivation, no dropouts, and lower energy deficit. All soldiers showed an enormous energy deficit; therefore, corresponding nutritional strategies are recommended.

Validation of ambulatory monitoring devices to measure energy expenditure and heart rate in a military setting.

Objectives.To investigate the validity of different devices and algorithms used in military organizations worldwide to assess physical activity energy expenditure (PAEE) and heart rate (HR) among soldiers.Design.Device validation study.Methods. Twenty-three male participants serving their mandatory military service accomplished, firstly, nine different military specific activities indoors, and secondly, a normal military routine outdoors. Participants wore simultaneously an ActiHeart, Everion, MetaMax 3B, Garmin Fenix 3, Hidalgo EQ02, and PADIS 2.0 system. The PAEE and HR data of each system were compared to the criterion measures MetaMax 3B and Hidalgo EQ02, respectively.Results. Overall, the recorded systematic errors in PAEE estimation ranged from 0.1 (±1.8) kcal.min-1to -1.7 (±1.8) kcal.min-1for the systems PADIS 2.0 and Hidalgo EQ02 running the Royal Dutch Army algorithm, respectively, and in the HR assessment ranged from -0.1 (±2.1) b.min-1to 0.8 (±3.0) b.min-1for the PADIS 2.0 and ActiHeart systems, respectively. The mean absolute percentage error (MAPE) in PAEE estimation ranged from 29.9% to 75.1%, with only the Everion system showing an overall MAPE <30%, but all investigated devices reported overall MAPE <1.4% in the HR assessment.Conclusions. The present study demonstrated poor to moderate validity in terms of PAEE estimation, but excellent validity in all investigated devices in terms of HR assessment. Overall, the Everion performed among the best in both parameters and with a device placement on the upper arm, the Everion system is particularly useful during military service, as it does not interfere with other relevant equipment.

Development of physical fitness performance in young Swiss men from 2006 to 2015.

From 1980 to 2000, physical fitness decreased and body mass index (BMI) increased in the population of many industrialized countries. Little is known about these trends after the year 2000. This study aimed to investigate physical fitness performance, physical activity (PA) behavior, and BMI of young, male Swiss adults between 2006 and 2015. For this purpose, results from the Swiss Armed Forces mandatory recruitment were used. A total of 306 746 male conscripts provided complete fitness test data, mean ± SD (range from 5th to 95th percentile): 20 ± 1 (18-21) years, 178 ± 7 (168-189) cm; 74 ± 13 (58-97) kg, predicted maximal oxygen consumption of 49.9 ± 4.6 (41.8-56.9) mL/kg/min (Conconi test), 125 ± 58 (43-232) seconds in trunk muscle strength test (prone bridge), 2.31 ± 0.24 (1.90-2.66) m in standing long jump, 6.46 ± 0.73 (5.30-7.70) m in seated shot put (2 kg medical-ball shot) and 45.6 ± 12.2 (29.9-66.7) seconds in one-leg standing test (sum of both legs; eyes closed after 10 seconds and head tilted back after 20 seconds). In the investigated population, 73.8% fulfilled basic PA recommendations, 46.2% were classified as regularly vigorously active. Performances in aerobic endurance and muscle power did not show secular changes over time. However, core stability performance and PA behavior increased, while balance ability decreased over this 10-year period. Average BMI increased by 2.0% between 2006 and 2010 and did not change thereafter. Male Swiss adults are at least as physically fit as they were a decade ago. The secular trends of decreasing physical performances and increasing BMI have stopped, and self-reported sport participation and leisure time PA have been increased in the observed population over the last 10 years.

Factors That Influence the Rating of Perceived Exertion After Endurance Training.

PURPOSE: Session rating of perceived exertion (sRPE) is an often-used measure to assess athletes' training load (TL). However, little is known about which factors could optimize the quality of data collection thereof. The aim of this study was to investigate the effects of the survey methods and the time points when sRPE was assessed on the correlation between subjective (sRPE) and objective (heart-rate training impulse; TRIMP) assessment of TL. METHODS: In the first part of the study, 45 well-trained subjects (30 men and 15 women) performed 20 running sessions with a heart-rate monitor and reported sRPE 30 min after training cessation. For the reporting, the subjects were grouped into 3 groups (paper-pencil, online questionnaire, and mobile device). In the second part of the study, another 40 athletes (28 men and 12 women) performed 4 × 5 running sessions with the 4 time points to report the sRPE randomly assigned (directly after training cessation, 30 min postexercise, in the evening of the same day, and the next morning directly after waking up). RESULTS: The assessment of sRPE is influenced by time point, survey method, TRIMP, sex, and training type. It is recommended to assess sRPE values via a mobile device or online tool, as the paper survey method displayed lower correlations between sRPE and TRIMP. CONCLUSIONS: Subjective TL measures are highly individual. When compared with the same relative intensity, lower sRPE values were reported by women for the training types representing slow runs and for time points with greater duration between training cessation and sRPE assessment. The assessment method for sRPE should be kept constant for each athlete, and comparisons between athletes or sexes are not recommended.

An evaluation of measurement systems estimating gait speed during a loaded military march over graded terrain.

This study aimed to evaluate the accuracy of three measurement systems estimating gait speed during a loaded military march over graded terrain. Systems developed by the Swiss and Netherlands Armed Forces and a commercial wrist-based device were evaluated in comparison to a Global Positioning System. The first part of the paper focuses on the development of the Dutch system, where speed is estimated from a chest worn accelerometer and body measurements. For this validation study 36 subjects were walking or running 13 laps of 200 m at different speeds. Results showed that walking and running speed can be estimated with a R2adj of 0.968 and 0.740, respectively. In the second part of this paper, data from 64 soldiers performing a 35 km march were used to evaluate the accuracy of three measurement systems in estimating speed. Data showed that estimating gait speed with a single accelerometer can be accurate for military activity, even without prior individual calibration measurements. However, predictions should be corrected for confounders such as body size and shoe type to be accurate. Both, downhill and uphill walking led to changes in gait characteristics and to an overestimation of speed by up to 10%. Correcting for slope or gradient using altimetry in future algorithms/experiments could improve the estimation of gait speed.

Validity of sports watches when estimating energy expenditure during running.

BACKGROUND: The aim of this study was to assess the accuracy of three different sport watches in estimating energy expenditure during aerobic and anaerobic running. METHODS: Twenty trained subjects ran at different intensities while wearing three commercial sport watches (Suunto Ambit2, Garmin Forerunner920XT, and Polar V800). Indirect calorimetry was used as the criterion measure for assessing energy expenditure. Different formulas were applied to compute energy expenditure from the gas exchange values for aerobic and anaerobic running. RESULTS: The accuracy of the energy expenditure estimations was intensity-dependent for all tested watches. During aerobic running (4-11 km/h), mean absolute percentage error values of -25.16% to +38.09% were observed, with the Polar V800 performing most accurately (stage 1: -12.20%, stage 2: -3.61%, and stage 3: -4.29%). The Garmin Forerunner920XT significantly underestimated energy expenditure during the slowest stage (stage 1: -25.16%), whereas, the Suunto Ambit2 significantly overestimated energy expenditure during the two slowest stages (stage 1: 38.09%, stage 2: 36.29%). During anaerobic running (14-17 km/h), all three watches significantly underestimated energy expenditure by -21.62% to -49.30%. Therefore, the error in estimating energy expenditure systematically increased as the anaerobic running speed increased. CONCLUSIONS: To estimate energy expenditure during aerobic running, the Polar V800 is recommended. By contrast, the other two watches either significantly overestimated or underestimated energy expenditure during most running intensities. The energy expenditure estimations generated during anaerobic exercises revealed large measurement errors in all tested sport watches. Therefore, the algorithms for estimating energy expenditure during intense activities must be improved before they can be used to monitor energy expenditure during high-intensity physical activities.

Physical fitness level affects perception of chronic stress in military trainees.

This study investigated whether physical fitness affects the perception of chronic stress in military trainees while controlling for established factors influencing stress perception. The sample consisted of 273 men (20.23 ± 1.12 years, 73.56 ± 10.52 kg, 1.78 ± 0.06 m). Physical fitness was measured by progressive endurance run (maximum oxygen uptake; VO2 max), standing long jump, seated shot put, trunk muscle strength, and one leg standing test. Perceived stress was measured using the Perceived Stress Questionnaire in Weeks 1 and 11 of basic military training (BMT). VO2 max and four influencing variables (perceived stress in Week 1, neuroticism, transformational leadership style, and education level) explained 44.44% of the variance of the increase in perceived stress during 10 weeks of BMT (R2  = 0.444, F = 23.334, p < .001). The explained variance of VO2 max was 4.14% (R2  = 0.041), with a Cohen's f2 effect size of 0.045 (assigned as a small effect by Cohen, ). The results indicate a moderating influence of good aerobic fitness on the varied level of perceived stress. We conclude that it is advisable to provide conscripts with a specific endurance training program prior to BMT for stress prevention reasons.

Aerobic Fitness Level Affects Cardiovascular and Salivary Alpha Amylase Responses to Acute Psychosocial Stress.

BACKGROUND: Good physical fitness seems to help the individual to buffer the potential harmful impact of psychosocial stress on somatic and mental health. The aim of the present study is to investigate the role of physical fitness levels on the autonomic nervous system (ANS; i.e. heart rate and salivary alpha amylase) responses to acute psychosocial stress, while controlling for established factors influencing individual stress reactions. METHODS: The Trier Social Stress Test for Groups (TSST-G) was executed with 302 male recruits during their first week of Swiss Army basic training. Heart rate was measured continuously, and salivary alpha amylase was measured twice, before and after the stress intervention. In the same week, all volunteers participated in a physical fitness test and they responded to questionnaires on lifestyle factors and personal traits. A multiple linear regression analysis was conducted to determine ANS responses to acute psychosocial stress from physical fitness test performances, controlling for personal traits, behavioural factors, and socioeconomic data. RESULTS: Multiple linear regression revealed three variables predicting 15 % of the variance in heart rate response (area under the individual heart rate response curve during TSST-G) and four variables predicting 12 % of the variance in salivary alpha amylase response (salivary alpha amylase level immediately after the TSST-G) to acute psychosocial stress. A strong performance at the progressive endurance run (high maximal oxygen consumption) was a significant predictor of ANS response in both models: low area under the heart rate response curve during TSST-G as well as low salivary alpha amylase level after TSST-G. Further, high muscle power, non-smoking, high extraversion, and low agreeableness were predictors of a favourable ANS response in either one of the two dependent variables. CONCLUSIONS: Good physical fitness, especially good aerobic endurance capacity, is an important protective factor against health-threatening reactions to acute psychosocial stress.

Training Methods and Training Instructors' Qualification Are Related to Recruits' Fitness Development During Basic Military Training.

Adequate physical fitness is essential for successful military service. Military organizations worldwide therefore make continuous efforts to improve their army's physical training (PT) programs. To investigate the effect of the training methods and the qualification of PT instructors on the development of recruits' physical fitness, the present study compared the outcomes of 2 training groups. Both study groups participated in approximately 145 minutes per week of PT. The control group executed the standard army PT prepared and supervised by army PT instructors. Content of the PT in the intervention group was similar to that of the control group, but their training sessions' methods were different. Their training sessions were organized, prepared, and delivered by more and better-qualified supervisors (tertiary-educated physical education teachers). After 10 weeks of training, the participants of the intervention group experienced a significantly greater physical fitness improvement than those of the control group (positive change in endurance 32 and 17%, balance 30 and 21%, and core strength 74 and 45%, respectively). In both groups, the recruits with the lowest initial fitness levels significantly increased their performance. In the intervention group, but not the control, one-third of the recruits with the highest initial fitness levels were able to further improve their general fitness performance. This study demonstrates that the training methods and quality of instruction during PT sessions are relevant for recruits' fitness development in basic military training.

Musculoskeletal Injuries and Training Patterns in Junior Elite Orienteering Athletes.

Findings about the relation between musculoskeletal injuries and training patterns in orienteering athletes are sparse. Therefore, the musculoskeletal injuries and training patterns of 31 Swiss elite orienteering athletes aged 18-19 years were analyzed in a retrospective study. Individual training diaries and medical records were used to assess training data and injury history, respectively. Group comparisons and a multiple linear regression (MLR) were performed for statistical analysis. The junior elite orienteering athletes performed 7.38 ± 2.00 training sessions weekly, with a total duration of 455.75 ± 98.22 minutes. An injury incidence rate (IIR) of 2.18 ± 2.13 injuries per 1000 hours of training was observed. The lower extremity was affected in 93% of all injuries, and the knee (33%) was the most commonly injured location. The MLR revealed that gender and six training variables explained 60% of the variance in the injury severity index in this study. Supported by the low IIR in the observed age group, the training protocol of the junior elite orienteering athletes was generally adequate. In comparison to elite track, marathon, and orienteering athletes, the junior elite athletes performed less high-intensity interval training (HIIT). However, more frequent HIIT seems to be a protective factor against injuries.

Adapted marching distances and physical training decrease recruits' injuries and attrition.

There is evidence that progressive loading of physical demands at the beginning of basic military service and specific physical training can reduce injury incidences. Therefore, aim of this study was to measure the effects of a progressive increase in marching distances and an adapted physical training program on injury incidence and attrition rate in a Swiss Army infantry training school. One company reduced the distances covered on foot during the first 4 weeks of basic military training. A second company performed an adapted physical training program for 10 weeks. A third company participated in both interventions combined, and a fourth company served as a control group without any intervention. The injury incidences and attrition rates of 651 male recruits were registered during 21 weeks of military service. Several predictor variables for injury and attrition, such as physical fitness, previous injuries, level of previous physical activity, smoking, motivation, and socioeconomic factors, were assessed as well. The data were analyzed using binary logistic backward regressions. Each intervention separately had a favorable effect on injury prevention. However, combining the 2 interventions resulted in the greatest reduction in injury incidence rate (-33%). Furthermore, the adapted physical training successfully reduced the military service attrition rates (-53%).

Hair cortisol concentration is unaffected by basic military training, but related to sociodemographic and environmental factors.

The analysis of hair cortisol concentrations (HCC) is a promising new biomarker for retrospective measurement of chronic stress. The effect of basic military training (BMT) on chronic stress has not yet been reported. The aim of this study was to investigate the effect of 10-week BMT on HCC, while further exploring the role of known and novel covariates. Young healthy male recruits of the Swiss Army participated twice, 10 weeks apart, in data collection (1st examination: n = 177; 2nd examination: n = 105). On two occasions, we assessed HCC, perceived stress and different candidate variables that may affect HCC (e.g. socioeconomic status, meteorological data). Military training increased perceived stress from the first to the second examination, but did not affect HCC. In line with this, there was no correlation between HCC and perceived stress ratings. This could be interpreted as a missing influence of mainly physical stress (e.g. exercise) on HCC. In contrast, significant correlations were found between HCC and ambient temperature, humidity and education. Future studies should control for meteorological data and educational status when examining HCC.

Impact of training patterns on injury incidences in 12 Swiss Army basic military training schools.

Non-battle injury rates are a major health problem in the armed forces today. Injury rates are related to physical demands of daily military routine. The aim of this study is to investigate the impact of different physical training patterns on incidences of injuries in 12 Swiss Army basic military training schools. Therefore, injury data of 1,676 voluntary participant recruits and objective sensor data on physical demands of 50 volunteers at each of 12 trainings schools were assembled. Multiple linear regression showed that high physical demands, decreasing development of distances covered on foot, monotony in weekly physical demands, little time spent on sport-related physical training, and little time for night rest were significant risk factors for injuries. Together, those variables describe 98.8% of the variances of total injury incidence rate between military training schools. The new method used to objectively assess training demands allowed this study to investigate the impact of training patterns on injury incidence in a large number of training schools. The results of this study are important for future interventions to reduce injury incidence rates in a military setting by quantifying the injury risk potential of a large number of training patterns.

Analysis of the multi-segmental postural movement strategies utilized in bipedal, tandem and one-leg stance as quantified by a principal component decomposition of marker coordinates.

Postural control research describes ankle-, hip-, or multi-joint strategies as mechanisms to control upright posture. The objectives of this study were, first, development of an analysis technique facilitating a direct comparison of the structure of such multi-segment postural movement patterns between subjects; second, comparison of the complexity of postural movements between three stances of different difficulty levels; and third, investigation of between-subject differences in the structure of postural movements and of factors that may contribute to these differences. Twenty-nine subjects completed 100-s trials in bipedal (BP), tandem (TA) and one-leg stance (OL). Their postural movements were recorded using 28 reflective markers distributed over all body segments. These marker coordinates were interpreted as 84-dimensional posture vectors, normalized, concatenated from all subjects, and submitted to a principal component analysis (PCA) to extract principal movement components (PMs). The PMs were characterized by determining their relative contribution to the subject's entire postural movements and the smoothness of their time series. Four, eight, and nine PM were needed to represent 90% of the total variance in BP, TA, and OL, respectively, suggesting that increased task difficulty is associated with increased complexity of the movement structure. Different subjects utilized different combinations of PMs to control their posture. In several PMs, the relative contribution of a PM to a subject's overall postural movements correlated with the smoothness of the PM's time series, suggesting that utilization of specific postural PMs may depend on the subject's ability to control the PM's temporal evolution.