INTERINDIVIDUAL VARIABILITY IN PHYSIOLOGICAL RESPONSES TO A 9-DAY COURSE OF HOT-HUMID HEAT ACCLIMATION 1069:

Introduction. Responses to heat stress vary according to the environment and work rate as well as the physiological baseline of the individual. Interindividual variability (IV) in physiological responses to heat stress has been recognized, but the effects of heat acclimation (HA) on IV has not been adequately investigated. Therefore, we tested our hypothesis that IV would decrease over a well controlled course of HA. Methods. 8 males (age 27.2±4.8 yrs, weight 72.3±8.4 kg, VO2 max 55.1±6.6 ml O2·kg-1·min-1) completed heat tolerance tests (HTT 1 and 2) before and after 9 consecutive days of HA. Both the HTT and HA trials consisted of 100 minute walks at 25% VO2 max in 43.1±0.1°C db, 50.0±0.1% rh. Subjects were fluid replaced(102±4%) during all trials. Rectal temperature (Tre), heart rate (HR), VO2, and sweat sensitivity (SS) were measured during the HTT and HA trials 3, 5 and 9. Results. Subjects achieved HA as indicated by HTT 2 vs 1. However, the variability data (coefficient of variation (CV) = SD·Mean-1·100) did not support the hypothesis as IV generally remained high for all variables except Tre at HA 9 and HTT 2.Table Conclusion. It appears that the IV in physiological responses to heat stress remains high over a rigorous course of HA.