Variability of body density in ambulatory subjects measured at different days

The variability of weight in air and underwater, residual lung volume and body density was studied in ambulatory men who were advised to maintain a constant diet and level of physical activity for four days (group I) and 60 days (group II). It was assumed that data obtained from group I which included volunteers familiar with the densitometric procedure would yield more reliable information than from group II which consisted of inexperienced subjects. Weight underwater and residual lung volume were the most variable measurements. The precision in body density varied from 0.0008 to 0.0018 g.ml-1, equivalent to 0.32 and 0.73% body fat in groups I and II, respectively. The data suggest that familiarity with the technique did not influence the reliability of body density measurement. Body composition as indicated by body density appears to remain constant over relatively long periods during which diet and levels of physical activity are controlled.