Mora-Rodríguez, R., Coso, J. D., Estevez, E., Hamouti, N., & Ortega, J. F. (2007). Effects of oral rehydration on thermoregulation of trained and untrained subjects exercising at different intensities. ACSM Annual Meeting New Orleans, Presentation Number 728.

This study determined the thermoregulatory and cardiovascular effects of oral rehydration during exercise in the heat in trained (N = 10) and untrained (N = 10) males at different exercise intensities. Ss pedaled in a hot-dry environment (36ºC) at three intensities (40, 60, and 80% of VO2peak). Ss performed the same total work at a load appropriate for training status and task in all trials for three exercise durations (120, 60, and 45 minutes). Trials were performed replacing 80% of fluid losses with a 6% carbohydrate fluid or without fluids in a random order.

Rehydration had a cooling effect (lower rectal temperature) during low and moderate exercise intensities (40% and 60% VO2peak) in both trained and untrained Ss, but was not effective at 80% VO2peak in either group despite an increased sweat rate. Trained Ss exhibited cardiovascular benefits (lower heart rate) from rehydration when exercising at high intensity in the heat.

Implication. Rehydration is beneficial at low to moderate exercise intensities in both trained and untrained Ss. Heart rate is lower in higher-intensity exercise when hydration has occurred only in trained Ss.

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