How important are euhydration and rehydration prior to, and during exercise respectively? It appears that they are essential.
Data from Cheung et al. (2000) demonstrate that subjects exercised in hot conditions at constant pace for 106min when euhydrated AND rehydrated with water at a rate of 1L per hour. However, when the test was repeated, time to fatigue dropped to 93min when the subjects were euhydrated BUT NOT rehydrated during exercise, and dropped to 87min when hyophydrated by 2% body mass and rehydrated at 1L per hour fluid replacement.
The results here demonstrate the prehydration and rehydration during exercise are essential to maintaining exercise performance and limiting endurance fatigue during hot conditions.