Abstract
BACKGROUND: Body composition influences physical fitness (PF) and risk of musculoskeletal injury (MSKI). Assessing the relationship between body fat (BF), PF and MSKI risk in a large diverse military population may provide evidence basis informing health-care policies, practices, and programs for military and civilian populations. OBJECTIVE: Evaluate the validity of expedient methods to estimate BF (e.g., circumference-based equation (CBE) and bioelectrical impedance analysis (BIA)) and investigate relationships between BF and PF with MSKI risk in a large diverse population. METHODS: Participants were 1904 active-duty Soldiers (643 F) representing Army demographics sex, race/ethnicity (R/E), and age. PF, defined as the most recent Army Combat Fitness Test (ACFT) score and incidence of MSKI, were obtained from Army records. BF was determined by dual-energy x-ray absorptiometry (%BF(DXA)), bioelectrical impedance analysis (%BF(BIA)), and CBE using 3-site (Hodgdon, %BF(HE)) and 1-site (Taylor-McClung, %BF(TM)) equations. Results were stratified by race and sex, to evaluate differences in accuracy of estimated %BF (weighted root mean squared error from %BF(DXA)). Associations of BF and PF with MSKI risk were evaluated with logistic regression. RESULTS: CBE and BIA underestimated %BF compared to %BF(DXA). %BF(BIA) differed from %BF(DXA) overall and by sex. %BF(TM) underestimation was uniform across both sex and R/E compared to %BF(DXA). Mean differences from %BF(DXA) by sex (M;F) were lower when measured by %BF(TM) (4.38; 4.59) compared to %BF(HE) (5.88; 4.39). Individuals had a greater likelihood of MSKI if they failed BF standards (odds ratio 1.32). Scoring ≥ 540 total on ACFT exhibited a 31% (95% CI: 0.52, 0.92) lower MSKI risk during the following 12 months than those with a lower score. CONCLUSIONS: A single-site BF equation (%BF(TM)) maintained similar accuracy across the Soldier population by sex, age, and R/E. Implementing a PF score threshold in lieu of passing Army BF standards was associated with lower MSKI risk.