EFFECTS OF EXERCISE-HEAT ACCLIMATION ON FLUID, ELECTROLYTE, AND ENDOCRINE RESPONSES DURING TILT AND +GZ ACCELERATION IN WOMEN AND MEN

  • 1 January 1985
    • journal article
    • research article
    • Vol. 56  (7) , 683-689
Abstract
Plasma fluid, electrolyte, protein, renin, and vasoactive hormone (epinephrine, norepinephrine, vasopressin) responses were measured in 6 women (21-23 yr) and 4 men (21-38 yr) before and immediately following an orthostatic tolerance test (70 head-up tilt) and a +Gz (positive linear) (head-to-foot) acceleration tolerance test (0.5 G .cntdot. min-1 linear ramp to grayout). These tests were conducted before and after 12 consecutive days of exercise-heat acclimation when the subjects exercised on a cycle ergometer at a relative oxygen uptake of 44% to 49% peak oxygen uptake in at a hot environment (Ta = 40.degree. C, 42% rh). During acclimation plasma volume increased by 10.6% (P < 0.05) in the women and by 11.9% (P < 0.05)in the men; in both groups exercise heart rate decreased significantly. After acclimation, acceleration tolerance was unchanged in both groups (range 3.1 to 3.4 G); the women''s tilt tolerance was unchanged (range 33.6 to 39.5 min), but the men''s tilt tolerance increased from 30.4 min before to 58.3 min (.DELTA. = 91%, P < 0.05) after acclimation. Since the pattern of fluid, electrolyte, and protein shifts and acceleration tolerances in the women and men were virtually the same, the hormone responses were highly variable, and the men''s tilt tolerance increased significantly after acclimation, it is clear that responses to tilting cannot be used to predict responses to acceleration. Analysis of data from the present study and the literature suggests that current exercise training regimes should be unrestricted for astronauts who have not previously been highly endurance trained. Until proven otherwise, care should be taken in the selection of astronauts and in the type and intensity of the exercise training programs engaged in by those who have been or are highly endurance-trained athletes.