Factors of trainability and predictability associated with military physical fitness test success

Unsupervised Machine Learning in Countermovement Jump and Isometric Mid-Thigh Pull Performance Produces Distinct Combat and Physical Fitness Clusters in Male and Female U.S. Marine Corps Recruits

INTRODUCTION

Several challenges face the U.S. Marine Corps (USMC) and other services in their efforts to design recruit training to augment warfighter mobility and resilience in both male and female recruits as part of an integrated model. Strength and power underpin many of the physical competencies required to meet the occupational demands one might face in military. As the military considers adopting force plate technology to assess indices of strength and power, an opportunity presents itself for the use of machine learning on large datasets to deduce the relevance of variables related to performance and injury risk. The primary aim of this study was to determine whether cluster analysis on baseline strength and power data derived from countermovement jump (CMJ) and isometric mid-thigh pull (IMTP) adequately partitions men and women entering recruit training into distinct performance clusters. The secondary aim of this study is then to assess the between-cluster frequencies of musculoskeletal injury (MSKI).

MATERIALS AND METHODS

Five hundred and sixty-five males (n = 386) and females (n = 179) at the Marine Corps Recruit Depots located at Parris Island and San Diego were enrolled in the study. Recruits performed CMJ and IMTP tests at the onset of training. Injury data were collected via medical chart review. Combat fitness test (CFT) and physical fitness test (PFT) results were provided to the study team by the USMC. A k-means cluster analysis was performed on CMJ relative peak power, IMTP relative peak force, and dynamic strength index. Independent sample t-tests and Cohen's d effect sizes assessed between-cluster differences in CFT and PFT performance. Differences in cumulative incidence of lower extremity %MSKIs were analyzed using Fisher's exact test. Relative risk and 95% confidence intervals (CIs) were also calculated.

RESULTS

The overall effects of cluster designation on CMJ and IMTP outcomes ranged from moderate (relative peak power: d = -0.68, 95% CI, -0.85 to -0.51) to large (relative peak force: d = -1.69, 95% CI, -1.88 to -1.49; dynamic strength index: d = 1.20, 95% CI, 1.02-1.38), indicating acceptable k-means cluster partitioning. Independent sample t-tests revealed that both men and women in cluster 2 (C2) significantly outperformed those in cluster 1 (C1) in all events of the CFT and PFT (P < .05). The overall and within-gender effect of cluster designation on both CFT and PFT performance ranged from small (d > 0.2) to moderate (d > 0.5). Men in C2, the high-performing cluster, demonstrated a significantly lower incidence of ankle MSKI (P = .04, RR = 0.2, 95% CI, 0.1-1.0). No other between-cluster differences in MSKI were statistically significant.

CONCLUSIONS

Our results indicate that strength and power metrics derived from force plate tests effectively partition USMC male and female recruits into distinct performance clusters with relevance to tactical and physical fitness using k-means clustering. These data support the potential for expanded use of force plates in assessing readiness in a cohort of men and women entering USMC recruit training. The ability to pre-emptively identify high and low performers in the CFT and PFT can aid in leadership developing frameworks for tailoring training to enhance combat and physical fitness with benchmark values of strength and power.

The Influence of Previous Lifestyle on Occupational Physical Fitness in the Context of Military Service

The Estonian Defense Forces are the basis of military service, mandatory for all male citizens of the Republic of Estonia who are at least 17 years old. The physical load in military service, especially in the first stage, is significantly greater than for men in everyday life. Therefore, it is important to know if health promotion in civilian life adequately prepares young people for military service and to what extent pre-military health behaviors affect physical performance during service. The purpose of this work was to examine conscripts' physical fitness at different stages of military service and its relationships with previous lifestyle. Soldiers' physical fitness was estimated three times during military service using three tests: sit-ups, push-ups and 2-mile run. Lifestyle and socio-economic background data was collected by a web-based questionnaire (n = 235). Linear regression analysis was performed using Army Physical Fitness Test (APFT) scores as dependent variables and questionnaire data as independent variables. The socio-economic background variables had no effect on physical fitness scores throughout the training period (p > 0.05). Young men that were physically more active daily, did sports, had healthier diet and did not smoke before entering military service showed better physical fitness test results throughout the period of service (p < 0.05). The effect of participation in sports was evident, as the conscripts with previous sports experiences demonstrated higher fitness tests scores (p < 0.01). These findings show that health promotion initiatives or programs for promoting physical activity and healthy diet, and preventing obesity and tobacco use, can also have a positive effect on the physical performance of young men during military service.

Field-Based Performance Tests Are Related to Body Fat Percentage and Fat-Free Mass, But Not Body Mass Index, in Youth Soccer Players

The primary aim of this study was to determine the association between body composition and performance outcomes in youth soccer players. Twenty-five competitive male youth soccer players (age = 13.7 ± 0.8 years, height = 167.4 ± 9.7 cm, weight = 57.6 ± 12.1 kg) volunteered to participate in this study. Height and weight were used to calculate body mass index (BMI). Body fat percentage (BF%) and fat-free mass (FFM) were determined with dual-energy X-ray absorptiometry. Each athlete performed the Pacer test, vertical jump, and t-test drill. Participants were predominantly normal weight (20.4 ± 2.7 kg·m-2). The body composition results were 20.3 ± 4.9% for BF% and 46.5 ± 8.7 kg for FFM. The results of the performance tests indicated a mean ± standard deviation (SD) of 1418 ± 332 m for Pacer, 57.2 ± 7.4 cm for vertical jump, 11.6 ± 0.7 s for t-test. Body mass index was not associated with any performance measure (r = 0.02 to -0.21, all p > 0.05). Body fat percentage was associated with the Pacer, vertical jump, and t-test (r = -0.62, -0.57, 0.61, respectively; all p < 0.01) and remained after accounting for BMI. Fat-free mass was only significantly related to t-test (r = -0.43, p < 0.01). However, after controlling for BMI, FFM was related to all three performance tests. Body fat percentage and FFM are associated with performance in youth soccer players, with stronger relationships reported in the former metric. The findings highlight the need for accurate body composition measurements as part of an assessment battery in young athletes.

External Responsiveness and Intrasession Reliability of the Rope-Climbing Test

Dhahbi, W, Chamari, K, Chèze, L, Behm, DG, and Chaouachi, A. External responsiveness and intrasession reliability of the rope-climbing test. J Strength Cond Res 30(10): 2952-2958, 2016-Although the rope-climbing test (RCT) has been validated for upper-body power assessment of Commando soldiers, the external responsiveness and intrasession reliability of the RCT have not been reported. To examine RCT external responsiveness and intrasession reliability, this study consisted of 2 separate phases. Forty male soldiers belonging to the special units of the National Guard, selected on the basis of their training and specialty operations levels, participated in the first phase of the study to identify the discriminant ability of RCT. This group was then divided into anti-terrorism Commandos (21 soldiers) and Intervention-Brigade (19 soldiers). Only the anti-terrorism Commandos participated in the intrasession reliability study. The Commandos were significantly better than the Intervention-Brigade soldiers on execution time (ET), absolute power output (APO), and relative power output (RPO; p < 0.001). The areas under the receiver operator characteristics curves were all higher than 0.70: 0.91, 0.85, and 0.90 for ET, APO, and RPO, respectively. The RCT provided good external responsiveness; thus, RCT was considered to indicate "good" discriminative ability. No significant difference was found between groups in posttest rating of perceived exertion. The intrasession reliability coefficients were excellent for ET, APO, and RPO (intraclass correlation coefficient [3,1] > 0.90). The standard errors of measurement values for the ET, APO, and RPO were all less than 5% (range: 1.29-1.47%). The main findings of this study suggest that RCT is a tool with both high sensitivity and intrasession reliability, allowing the consistent detection of differences in upper-limb power performance between the 2 military groups of different operational capacity levels.

Rank, job stress, psychological distress and physical activity among military personnel

Background

Physical fitness is one of the most important qualities in armed forces personnel. However, little is known about the association between the military environment and the occupational and leisure-time dimensions of the physical activity practiced there. This study assessed the association of rank, job stress and psychological distress with physical activity levels (overall and by dimensions).

Methods

This a cross-sectional study among 506 military service personnel of the Brazilian Army examined the association of rank, job stress and psychological distress with physical activity through multiple linear regression using a generalized linear model.

Results

The adjusted models showed that the rank of lieutenant was associated with most occupational physical activity (β = 0.324; CI 95% 0.167; 0.481); “high effort and low reward” was associated with more occupational physical activity (β = 0.224; CI 95% 0.098; 0.351) and with less physical activity in sports/physical exercise in leisure (β = −0.198; CI 95% −0.384; −0.011); and psychological distress was associated with less physical activity in sports/exercise in leisure (β = −0.184; CI 95% −0.321; −0.046).

Conclusions

The results of this study show that job stress and rank were associated with higher levels of occupational physical activity. Moreover job stress and psychological distress were associated with lower levels of physical activity in sports/exercises. In the military context, given the importance of physical activity and the psychosocial environment, both of which are related to health, these findings may offer input to institutional policies directed to identifying psychological distress early and improving work relationships, and to creating an environment more favorable to increasing the practice of leisure-time physical activity.