Effect of training and heat acclimation on exercise responses of sedentary females

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Abstract
In an attempt to explain why females experience greater strain than males during exercise in the heat, we studied the responses of nine females to moderate exercise (40% VO2 max) on a cycle ergometer in a cool (16--20 degrees C, 30% rh) and a hot (45 degrees C, 30% rh) environment. Venous blood was sampled during rest, at the 40th min of exercise, and 25 min after exercise. Test runs were then performed during a 4-wk training program (phase 2) and during heat acclimation (phase 3). Except for K+, changes in plasma constituents during exercise were not altered by training or acclimation. A greater mean decrease in plasma volume occurred during exercise in a hot (11.9%) than in a cool (3.9%) environment. Plasma osmolality and protein concentration increased due to the loss of plasma water. The most striking response to training was a significant expansion of resting plasma volume (9.7%) and total protein content (11.6%). During acclimation, sweat rates increased and mean skin temperatures significantly decreased. Hemodilution reported in heat-acclimated men was not seen. The factor primarily responsible for improved cardiovascular fitness in these women during acclimation may have been the maintenance of a larger central blood volume.