MULTIVARIATE ANALYSIS OF INTRINSIC INJURY RISK FACTORS IN A COHORT OF US ARMY BASIC TRAINEES

Abstract

Previous studies of injuries in basic combat training (BCT) have predominately examined only individuals completing the training. In this study we used survival analysis to adjust for time at risk of injury so the entire BCT population could be examined regardless of whether or not the individual completed training. Potential intrinsic injury risk factors were examined among 675 men participating in the newly lengthened 9-week BCT cycle during the summer of the year 2000. Injury data were obtained from a review of the subjects' medical records at the conclusion of training. Potential injury risk factors were obtained prospectively from records in the basic training units. Data were analyzed using Cox regression, with time to the first time-loss injury as the dependent variable. Continuous risk factor variables were converted into quartiles (Q). Only 12 percent of the cohort experienced time-loss injury. Univariate Cox regressions showed that push-up performance on entry to BCT, 2-mile run performance on entry to BCT, exercise history prior to BCT, and cigarette smoking history were related to time to injury (p < 0.01); age, stature, body mass, body mass index, and sit-up performance were not (p>0.10). Stepwise multivariate Cox regression showed that slower 2-mile run performance and cigarette smoking history were independently related to time to injury. Adjusted risk ratios and 95 percent confidence intervals (in parentheses) from the multivariate analysis were as follows: 2-mile run performance - Q1 = 1.0, Q2 = 1.5(0.6–3.6), Q3 = 3.6(1.6–7.9)*, Q4(slow) = 3.4(1.6–7.6)*; cigarette smoking in year before BCT - None = 1.0, Quit = 2.1(1.0–4.1)*, < 10 cig/day = 1.6(0.8–3.3), > 10 cig/day = 2.1(1.2–3.7)* [where * indicates p < 0.05 compared to level with risk ratio of 1.0]. These data indicate that aerobic endurance and cigarette smoking history are independent risk factors for time loss injury among men participating in a 9-week US Army BCT cycle.