Body Composition Changes During 8 Weeks Of Military Training Are Not Accurately Captured By Circumference-based Assessments

The U.S. Army has body fat standards to promote physical readiness and prevent obesity. Currently, body fat percentage (%BF) is estimated using separate, sex-based formulas, based on circumference measurements. Notably, both predictive equations underestimate %BF in Soldiers with high %BF. The %BF equations were last evaluated based on data from 1993 and, given the prevalence of overweight and obesity in the general population, and the heightened focus on optimizing body composition during U.S. Army Basic Combat Training (BCT), how well the existing circumference-based equations estimate %BF at the start and end of BCT should be evaluated. PURPOSE: To determine the accuracy of circumference-based %BF equations at the start and end of BCT METHODS: Dual-energy X-ray absorptiometry (DXA) and circumference-based measures of %BF were obtained in women (n = 481) and men (n = 926) at the start and end of 8 weeks of BCT. Repeated-measure ANOVAs were used to assess difference between DXA and circumferences at baseline and for the change during BCT. RESULTS: Pre-BCT, %BF was underestimated with circumference relative to DXA, with mean errors of -6.0% ± 4.4% for women and -6.0% ± 3.5% for men (p < 0.01 for both), with no difference between sexes (p = 0.77). DXA detected a -4.0% ± 2.4% and -3.3% ± 2.8% change in %BF for women and men in response to BCT, respectively (p < 0.01 for both), whereas circumference estimates of %BF indicated no change 0.0% ± 3.3% (p = 0.86) in women and 2.2% ± 3.3% (p < 0.01) change in men. CONCLUSION: Circumference-based measures underestimated %BF at that start of BCT in both sexes, as compared to DXA. Circumference measures underestimated changes in %BF during BCT in men and did not detect changes in women. These findings suggest that circumference-based %BF metrics may not be an appropriate tool to track changes in body composition during U.S. Army BCT.