Negligible effects of previous moderate physical activity and changes in environmental temperature on whole body electrical impedance.

Several studies have shown that the predictive power of various linear combinations of anthropometric data (body weight, height, sex, age, etc.) to estimate fat free mass is improved after inclusion of measurements of electrical impedance (see eg Khaled et al., 1988). Published algorithms are based on measurements performed under fairly standardized conditions with the subjects at stationary conditions of rest, of environmental temperature and of body fluids. Use of the method under less standardized conditions raises the question of possible effects of deviations from these standard conditions. Hydration and dehydration by 1-2 l of fluid increased or decreased, respectively, the electrical resistance by about 14 per cent and the effects persisted for more than 1 h (Khaled et al., 1988). A change in environmental temperature by 21 degrees C from 35 degrees C to 14 degrees C (with almost constant relative humidity) during 90 min caused an increase in the resistance of about 9 per cent (Caton et al., 1988). The perturbations used in the studies quoted above are fairly drastic and not likely to occur under reasonably controlled field conditions. Therefore, we report here results of measurements of whole body electrical impedance before, during and after a period of 10 degrees C increased environmental temperature and before and after a 5-min period of light to moderate physical exercise.