USE OF BIOELECTRICAL-IMPEDANCE ANALYSIS MEASUREMENTS AS PREDICTORS OFPHYSICAL PERFORMANCE

Through its association with fat-free mass (FFM), bioelectrical impeda nce analysis (BIA) offers an alternative to physical performance testi ng. We examined the relations between stature(2)/resistance (S-2/R), F FM, and muscular strength in data from three studies of young military men and women. Resistance was measured at 50 kHz by using the convent ional tetrapolar electrode method. FFM was based on skinfold thickness es, and estimated with the regression equations of Durnin and Womersle y. Strength was measured as a one-repetition maximum on an incremental lift test (IL1RM), which is widely used by the military services to p redict overall body strength. Although there was an association betwee n IL1RM and S-2/R in each of these studies (correlations ranged from 0 .35 to 0.53), correlations were strongest between FFM and S-2/R (R = 0 .53 to 0.85), indicating that BIA and FFM derived from skinfold thickn esses are better correlated with each other than are the relations of either of these with physical performance. Modest increases in FFM and strength in one 8-wk training study correlated with S-2/R; however, l arge decreases in FFM and strength in another study (with weight losse s of 10 kg in 8 wk) were not reflected by changes in S-2/R. Thus, BIA is not particularly useful for performance prediction despite its mode rate relation to FFM. BIA is especially problematic with large changes in body composition, for which there are apparent deviations in hydra tion status; expedient methods such as skinfold predictions will be mo re resistant to such effects.