Heat acclimation, physical fitness, and responses to exercise in temperate and hot environments

Abstract

Three groups of men with different .ovrhdot.VO2 max (60.1, 47.7 and 35.6 ml .cntdot. kg-1 .cntdot. min-1) were administered 2 submaximal tests at 23.degree. C, at 41 and 82 W, before and after 8 days of heat acclimation (3 h work at 41 W at 39.4.degree. C dry bulb, 30.3.degree. C wet bulb). A control group with .ovrhdot.VO2 max of 45.3 ml .cntdot. kg1-11 .cntdot. min-1 was tested at 23.degree. C and in heat before and after 6 days of exercise at 23.degree. C. Trained subjects with the highest .ovrhdot.VO2 max showed the best responses, the lowest .ovrhdot.VO2 max group showed the worst responses at 23.degree. C and in heat (differences in heart rates and rectal temperatures but not in sweat rates and O2 consumption responses). Heat acclimation resulted in substantial improvements in responses at 23.degree. C and in heat of the acclimation groups, with very minor changes shown by the control group. Changes at 23.degree. C were characterized by decreases in heart rate, rectal temperature (0.3-0.5.degree. C), O2 consumption, sweat rate (25-30%) and increases of 13% and 23% in .ovrhdot.VO2 max in the groups with average and low .ovrhdot.VO2 max, respectively. .ovrhdot.VO2 max correlated r = -0.62 and -0.65 with rectal temperatures at 23.degree. C and in heat, respectively. Exercise rectal temperature at 23.degree. C was mainly a function of heat acclimatization, as well as .ovrhdot.VO2 max and surface area/mass ratio. Heat acclimation presented an effective method of physical training, and .ovrhdot.VO2 max was partially related to heat tolerance.