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Pre- and post-test changes in the factors that influence computed body density changes.

Abstract Individual changes in the body density of 62 young men who participated in a 10-week physical conditioning program were found to be more closely related to changes in residual lung volume (r = .49), than to changes in body weight (r = .31) or underwater weight (r = .26). Thus, the computed changes in body density for individual subjects were related as much to individual changes in residual lung volume as to changes in underwater weight or body weight. There was a mean decrease in body weight (1.3%) and residual lung volume (4.5%), while underwater weight increased 1.2% and the resulting body density increased .0008 density units. It was concluded that if an assumed constant value of residual volume is used to compute density, then observed changes in body density for an individual subject due to an experimental treatment such as physical conditioning may be masked by large changes in residual lung volume.