Associations of age, aerobic fitness, and body mass index with injury in an operational Army brigade.

OBJECTIVES: To investigate the effects of age, aerobic fitness, and body mass index (BMI) on injury risk in operational Army soldiers.

DESIGN: Retrospective cohort study.

METHODS: Male soldiers from an operational Army brigade were administered electronic surveys regarding personal characteristics, physical fitness, and injuries occurring over the last 12 months. Injury risks were stratified by age, 2-mile run time, and BMI. Analyses included descriptive incidence, a Mantel-Haenszel χ2 test to determine trends, a multivariable logistic regression to determine factors associated with injury, and a one-way analysis of variance (ANOVA).

RESULTS: Forty-seventy percent of 1099 respondents reported at least one injury. A linear trend showed that as age, 2-mile run time, and BMI increased, so did injury risk (p<0.01). When controlling for BMI, the most significant independent injury risk factors were older age (odd ratio (OR) 30years-35years/≤24years=1.25, 95%CI: 1.08-2.32), (OR≥36years/≤24years=2.05, 95%CI: 1.36-3.10), and slow run times (OR≥15.9min/≤13.9min=1.91, 95%CI: 1.28-2.85). An ANOVA showed that both run times and BMI increased with age.

CONCLUSIONS: The stratified analysis and the multivariable logistic regression suggested that older age and poor aerobic fitness are stronger predictors of injury than BMI.