Journal of Applied Physiology, Vol 47, Issue 5 978-984, Copyright © 1979 by American Physiological Society
Effect of training and heat acclimation on exercise responses of sedentary females
S. M. Fortney and L. C. Senay Jr
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.
