The Science Behind The Modern Army Body Composition Policy

BACKGROUND: Body composition influences both physical fitness (PF) and the risk of musculoskeletal injury (MSKI) in healthy Soldiers. Assessing the interrelationships between body fat (BF), PF and MSKI risk in a large diverse Soldier population can help inform data-driven policy for the Army. PURPOSE: To update Army BF assessment policy through use of efficient sex-specific circumference-based equations (CBE) while accounting for the relationship between BF and PF to MSKI risk in a demographically diverse and physically active Soldier population. METHODS: The study population was 1904 active-duty Soldiers (1261 M, 643 F) representing modern Army demographics by sex, race/ethnicity (R/E) and age. PF, defined as the most recent Army Combat Fitness Test (ACFT) score within 6 months of BF assessment, and history of MSKI were attained from Army records. BF was determined by dual-energy x-ray absorptiometry (%BFDXA), and by CBE using a 3-site equation (Hodgdon, %BFHE) and a single-site equation (Taylor-McClung, %BFTM). BF values for CBE were classified “Acceptable” if complying with Army %BF standards (AR 600-9). PF scores were classified as “high pass” if scores >540 and 80 points on each ACFT event. Accuracy of %BF estimation was assessed via weighted root mean squared error from the %BFDXA. Logistic regression was used to evaluate effects of BF and a high pass PF on MSKI risk. RESULTS: Both CBE methods underestimated %BF compared to %BFDXA. %BFTM underestimation (~3%) was similar across both sex and R/E compared to %BFDXA. Mean differences across sex (RMSE, M;F) were less when measured by %BFTM (4.382; 4.594) compared to %BFHE (5.886; 4.395). Both “high pass” PF individuals and those who passed the %BFTM assessment exhibited a 24.5% reduction in MSKI risk during the following 12 months. CONCLUSION: A single-site BF equation (%BFTM) is accurate across the Soldier population by sex, age and R/E. Using a “high pass” PF score threshold is a valid addition to BF assessment to mitigate MSKI risk. Disclaimer: The views expressed in this abstract are those of the authors and do not reflect the official policy of the Department of Army, Department of Defense, or the U.S. Government.