Purpose: The purpose of this study was to compare body mass index (BMI) and abdominal circumference (AC) in discriminating individual musculoskeletal injury risk within a large population. We also sought to determine whether age or sex modulate the interaction between body habitus and injury risk.
Methods: We conducted a retrospective cohort study involving 67,904 United States Air Force personnel from 2005 to 2011. Subjects were stratified by age, sex, BMI, adjusted BMI (aBMI), and abdominal circumference (AC). New musculoskeletal injuries were recorded relative to body habitus and time elapsed from start of study.
Results: Cox proportional hazard regression revealed increased hazard ratios (HR) for musculoskeletal injury in those with high-risk AC (males: >39in., females >36in.) compared to low-risk AC (males: <=35in., females: <=32in.) in all age categories (18-24 years: HR=1.567, 95% Confidence Interval (CI) 1.327-1.849; 25-34 years: HR=2.089, 95% CI: 1.968-2.218; 35+ years: HR=1.785, 95% CI: 1.651-1.929). Hazard ratios for obese (BMI>=30kg/m2) compared to normal individuals (BMI<25kg/m2) were less elevated. Kaplan-Meier curves showed a dose-response relationship in all age groups, but most prominently in 25-34 year-olds. Time to injury was consistently lowest in 18-24 year-olds. Score chi-square values, indicating comparative strength of each model for injury risk estimation in our cohort, were higher for AC than for BMI or aBMI within all age groups.
Conclusions: AC is a better predictor of musculoskeletal injury risk than BMI in a large military population. Although absolute injury risk is greatest in 18-24 year-olds, the effect of obesity on injury risk is greatest in 25-34 year-olds. There is a dose-response relationship between obesity and musculoskeletal injury risk, an effect seen with both BMI and AC.
(C) 2014 American College of Sports Medicine