Impact of physical fitness and body composition on injury risk among active young adults: A study of Army trainees.

OBJECTIVES

To determine the combined effects of physical fitness and body composition on risk of training-related musculoskeletal injuries among Army trainees.

DESIGN

Retrospective cohort study.

METHODS

Rosters of soldiers entering Army basic combat training (BCT) from 2010 to 2012 were linked with data from multiple sources for age, sex, physical fitness (heights, weights (mass), body mass index (BMI), 2 mile run times, push-ups), and medical injury diagnoses. Analyses included descriptive means and standard deviations, comparative t-tests, risks of injury, and relative risks (RR) and 95% confidence intervals (CI). Fitness and BMI were divided into quintiles (groups of 20%) and stratified for chi-square (χ) comparisons and to determine trends.

RESULTS

Data were obtained for 143,398 men and 41,727 women. As run times became slower, injury risks increased steadily (men=9.8-24.3%, women=26.5-56.0%; χ trends (p<0.00001)). For both genders, the relationship of BMI to injury risk was bimodal, with the lowest risk in the average BMI group (middle quintile). Injury risks were highest in the slowest groups with lowest BMIs (male trainees=26.5%; female trainees=63.1%). Compared to lowest risk group (average BMI with fastest run-times), RRs were significant (male trainees=8.5%; RR 3.1, CI: 2.8-3.4; female trainees=24.6%; RR 2.6, CI: 2.3-2.8). Trainees with the lowest BMIs exhibited highest injury risks for both genders and across all fitness levels.

CONCLUSIONS

While the most aerobically fit Army trainees experience lower risk of training-related injury, at any given aerobic fitness level those with the lowest BMIs are at highest risk. This has implications for recruitment and retention fitness standards.