Effects of exercise in the heat on body fluid distribution.

Experimental findings as to body fluid shifts during exercise appear to be greatly influenced by the mode of exercise (bicycle ergometer, treadmill, etc) and by the state of subject hydration. Endurance training has been shown to increase resting plasma (blood) volume. Also, endurance training results in modification of vascular volume dynamics during exercise, i.e. for a set task, plasma volume becomes stabilized. In the untrained individual, heat exposure exaggerates body fluid shifts during exercise. With training, stability of vascular volume is attained during heat exposure, but maximum protective responses towards exercise in heat is only gained upon heat acclimatization. Two items benefit the individual: an increase in the capacity of the sweat mechanism and an expansion of plasma volume. Benefits of training as to body fluid shifts are probably a result of metabolic changes within the active muscle mass.