Science behind policy: implementing a modern circumference-based body fat equation with a physical fitness threshold is associated with lower musculoskeletal injury risk.

McClung, Holly L; Bartlett, P Matthew; Spiering, Barry A; Foulis, Stephen A; Oliver, Tyler E; Walker, Leila A; Nguyen, Vy T; Proctor, Susan P et al. · Int J Obes (Lond) · 2025

prospective_cohort · Level II

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Abstract

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. 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. 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<sub>DXA</sub>), bioelectrical impedance analysis (%BF<sub>BIA</sub>), and CBE using 3-site (Hodgdon, %BF<sub>HE</sub>) and 1-site (Taylor-McClung, %BF<sub>TM</sub>) equations. Results were stratified by race and sex, to evaluate differences in accuracy of estimated %BF (weighted root mean squared error from %BF<sub>DXA</sub>). Associations of BF and PF with MSKI risk were evaluated with logistic regression. CBE and BIA underestimated %BF compared to %BF<sub>DXA</sub>. %BF<sub>BIA</sub> differed from %BF<sub>DXA</sub> overall and by sex. %BF<sub>TM</sub> underestimation was uniform across both sex and R/E compared to %BF<sub>DXA</sub>. Mean differences from %BF<sub>DXA</sub> by sex (M;F) were lower when measured by %BF<sub>TM</sub> (4.38; 4.59) compared to %BF<sub>HE</sub> (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. A single-site BF equation (%BF<sub>TM</sub>) 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.

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