The effects of rehydration on cycling performance after exercise-induced dehydration

The effects of 7.6% carbohydrate-electrolyte solution (CES) and placebos (P) on rehydration (R) after exercise-induced dehydration and on a subsequent time-trial (TT) of cycling performance were studied. Thirteen male subjects exercised in a thermally-controlled environment (28 degrees C, 63% RH) until 3% of their body weight was lost. After exercise, the subjects moved to a neutral environment (22 degrees C) and rested for 30 minutes prior to a 2-hour R period. During R, subjects were fed CES or P to a maximum volume of 120% of previous body mass loss at 0, 30, and 60 minutes, in bolus-doses of 50%, 40% and 30% respectively. After R, subjects performed a 1-hour TT with no further fluid intake. % R with CES was significantly higher than with P (70 +/- 3% vs 60 +/- 5%; p < 0.01). During the TT, blood glucose dropped in the CES group but not in the P group. It was found that, despite a more effective R with CES, the performance results did not differ between groups (65.1 +/- 2.2 minutes and 65.2 +/- 2.3 minutes for CES and P respectively). It is suggested that an insulin-mediated rebound effect on CHO metabolism during TT, in which no further CHO was supplied, nullified the benefits of rehydration.