Body mass does not reflect the body composition changes in response to similar physical training in young women and men

Abstract

Introduction U.S. Army Basic Combat Training (BCT) prepares new recruits to meet soldier physical demands. It also serves as a model of physical changes in healthy young nonobese women and men during an intensive 10-week training program without diet restriction. In this prospective observational study, we quantified the changes in lean mass and body fat induced by BCT in a large sample of men and women undergoing the same physical training program. Methods Young women (n = 573) and men (n = 1071) meeting Army health and fitness recruitment standards volunteered to provide DXA-derived body composition data at the beginning and end of BCT. Results During BCT, there was no change in body mass in women and a 1.7-kg loss in men. Relative body fat (%BF) declined by an average of 4.0 ± 2.4 and 3.4 ± 2.8 percentage points (±SD) for women and men, respectively. The greatest predictor of change in %BF during BCT for both sexes was %BF at the beginning of training. Women and men gained an average 2.7 ± 1.6 kg and 1.7 ± 2.0 kg of lean mass during BCT. Conclusions Army BCT produced significant effects on body composition despite minimal changes in total body mass. These findings demonstrate the ability of a 10-week sex-integrated physical training program to positively alter body composition profiles of young adults.