Physiological and Hematological Responses of Matched Older and Younger Men during Dry-Heat Acclimation

摘要

Nine younger and nine older men were matched for body weight, surface area, surface area-to-weight ratio, percent body fat and maximal aerobic power, but differed in age by 25 years and regular weekly aerobic activity. After evaluation in a comfortable environment (22 C,50% rh), these subjects were concurrently heat acclimated by treadmill walking for two to 50-min exercise bouts separated by 10-min rest for 10 consecutive days in a hot-dry environment. During the first day of heat exposure, performance time was 27 min longer for the older men while final rectal and skin temperatures and heart rate were lower, and final total body sweat loss higher when compared to the younger men. These physiological advantages for the older men persisted for the first few days of exercise-heat acclimation. By the end of acclimation, no physiological or performance time differences were observed between groups. Final rated perceived exertion was generally higher for the younger men throughout the acclimation period while final thermal sensation was higher only on the first acclimation day. Sweating sensitivity, esophageal temperature at sweating onset, and the sweating onset time did not differ between groups either pre- or post-acclimation. Both plasma volume and total circulating protein increased from pre- to post-acclimation with no differences between groups. Greater regular weekly aerobic activity for the older men was associated with their better initial performance during exercise in the heat; however, heat acclimation negated this advantage.