APPARENT BODY DENSITY AND VARIABILITY DURING UNDERWATER WEIGHING

A study was conducted to determine the minimum number of trials necessary to establish “true” underwater weight during body density measurements on 86 college females. Nine to 10 trials of underwater weight were recorded for each subject. The results showed a significant upward trend of a curved nature during successive trials of weighing. As subjects became accustomed to making a maximum expiration while submerged underwater, the amount of air expired increased progressively between trials 1 and 10. Thus underwater weight increased during consecutive trials which affected body density values by .001–.003 density units. Similar changes have been reported by others and attributed to physical training and conditioning programs. In 42% of the subjects highest underwater weights were observed during the first five trials. The magnitude of error associated with these trials was considerably higher than for the last several trials. This was due to an 85% reduction in within-individual variability (i.e., the variability of the average individual about her own mean). This represented a large increase in the consistency of the measurement. In order to obtain the most representative underwater weight for an individual 9 to 10 trials were necessary. The average value calculated from the last three trials was used to establish “true” underwater weight. © 1968 Taylor & Francis Group, LLC.