Body composition changes during 8 weeks of military training are not accurately captured by circumference-based assessments

In 1981, the US military adopted body fat standards to promote physical readiness and prevent obesity. Separate circumference-based equations were developed for women and men. Both predictive equations were known to underestimate % BF. However, it was not known how well these abdominal circumference-based methods tracked changes in %BF. This study examined the validity of the circumference-based %BF equations for assessing changes in %BF in young adult recruits during Army Basic Combat Training (BCT). 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 (pre-BCT) and end (post-BCT) of 8 weeks of BCT. Repeated-measure ANOVAs were used to assess differences between DXA and circumference pre-BCT and for the change during BCT. Pre-BCT, circumferences underestimated %BF relative to DXA, with mean errors of -6.0% +/- 4.4% for women and -6.0% +/- 3.5% for men (both p < 0.01), and no difference between sexes was observed (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 (both p < 0.01), whereas circumference estimates of %BF indicated a 0.0% +/- 3.3% (p = 0.86) change in women and a - 2.2% +/- 3.3% (p < 0.01) change in men (sex difference by technique p < 0.01). In conclusion, circumference-based measures underestimated %BF at the 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 short duration training.

Automated summary

In 1981, the US military implemented body fat standards to improve physical readiness and prevent obesity. This study examined the accuracy of circumference-based equations in assessing changes in body fat percentage (BF%) during Army Basic Combat Training (BCT) in young adult recruits. The results showed that circumference measures underestimated BF% at the start of BCT in both genders. Additionally, circumference measures did not accurately detect changes in BF% during BCT in women and underestimated the changes in men.