Measurement of Body Composition in the Dehydrated State

Abstract

The purpose of the study is to examine the effect of exercise-induced dehydration on body composition using three indirect methods: bioelectrical impedance analysis (BIA), skinfold thickness (SF), and underwater weighing (UWW).Method: Thirty healthy, physically active subjects with normal weight (22 males) participated as study subjects. After baseline body composition measurements using the above three methods were obtained, the subjects began to dehydrate by exercise until an average of 1.5% body weight loss was accomplished. Within 10 minutes post-exercise, the subjects’ body composition measurements using the same measurement methods were repeated. Results: There was a significant (p<0.05) difference between the three methods for determining fat free mass (FFM), fat mass (FM), and percent body fat (%BF). The %BF and FM measurements using the BIA method were significantly (p<0.05) affected by exercise-induced dehydration, but not the UWW or the SF method. Compared to the UWW method before dehydration, the SF method significantly (p<0.05) under-estimated FM, %BF, and over-estimated FFM, whereas the BIA method significantly (p<0.05) over-estimated FM and % BF, and under-estimated FFM. These observations also occur after exercise-induced dehydration. Comparing genders, the BIA method produced higher %BF and FM values in the female subjects than in the male subjects both before and after dehydration. Conclusion: We concluded that exercise-induced dehydration of 1.5% weight loss significantly (p<0.05) limits the usefulness of the BIA method for determining human body composition in physically active and normal weight adults, whereas dehydration induced an insignificant effect on the SF or UWW method.