THE USE OF BIO-ELECTRICAL IMPEDENCE ANALYSIS TO ESTIMATE CHANGES IN TOTAL BODY WATER AFTER RAPID REHYDRATION

Abstract

1622 Recent reports suggest that bio-electrical impedence analysis (BIA) is useful in monitoring hydration status after altitude exposure (Piccoli et al., Med. SCi. Sports Exer. 1996 ). The present study was designed to evaluate changes in total body water using BIA, over a 10 h period, when subjects were rapidly rehydrated after having been dehydrated to (meanpmS.E.M.) 2.6pm0.6% B.M.. BIA measures were taken when subjects were euhydrated (EU), dehydrated (DE), and rehydrated at 3- (RE3) and 10 h (RE10). Changes in body mass were also measured at these time points. Subjects rapidly rehydrated over the first 3 h with a 5% glucose-electrolyte solution, of which they ingested a volume equal to 150% of that lost as sweat. Following dehydration body mass decreased by 2.0pm0.3 kg but was restored over the initial 3 h rehydration period (EU, 81.5pm3.9 kg; RE3, 81.3pm4.0 kg, p>0.05). BIA measures of total body water were not different between EU and RE3 (46.1pm2.0 l; 45.5pm2.1 l, p>0.05). After a further 7 h body mass had decreased by 1.6pm0.2 kg and was now significantly lower than EU (79.3pm3.8 kg, P<0.01). Total body water was estimated to be 1.0pm0.4 l lower than EU, however, this failed to reach significance (P=0.06). Based on the changes in body mass it would appear that under the present conditions changes in total body water are slightly underestimated when measured by BIA. This, however, may be a consequence of the frequency (50 Hz) at which the measurements were made since 50 Hz frequency is reported to measure extracellular water.