A comparison of the effects of milk and a carbohydrate-electrolyte drink on the restoration of fluid balance and exercise capacity in a hot, humid environment

To determine the effect of skimmed milk (MILK) and a sports drink (CHO-E) in restoring fluid balance following exercise-induced dehydration and on subsequent exercise performance. Seven physically active males cycled intermittently in the heat until 2% body mass was lost. During a 1h rehydration period a CHO-E (23mmol Na+/L) or MILK (32mmol Na+/L) was consumed in a volume equivalent to 150% of body mass loss. Following a 3h recovery period, subjects cycled to exhaustion at 61% VO2peak in hot-humid conditions (35°C, 63%). Participants were in positive fluid balance at the end of the 3h recovery period when MILK (191 ± 162 mL) was consumed and euhydrated on CHO-E (-135 ± 392 mL). This difference in fluid balance (326 ± 354 mL), equivalent to 0.4% BM, approached significance (P=0.051). No differences were observed in plasma volume between trials but serum osmolality and stomach fullness were higher on MILK than CHO-E (P<0.05). Rectal temperature was higher on MILK at the onset of the exercise capacity test, but no differences in skin temperature, RPE, heart rate or exercise capacity were observed between MILK (39.7 ± 8.1min) and CHO-E (39.6 ± 7.3min). The results suggest that despite the positive effect on fluid balance, the ingestion of MILK following exercise-induced dehydration did not improve exercise capacity compared to a CHO-E