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Decay of heat acclimation.

Ashley-CD; Ferron-J; Bernard-TE
Med Sci Sports Exerc 2005 May; 37(5)(Suppl 1):S401
Acclimation can have a positive impact on heat tolerance. A period of time away from heat can result in the loss of the physiological adaptations of acclimation increasing the risk of heat illness, injury and death. The decay of acclimation has not been determined. PURPOSE: To examine the decay pattern of acclimation to heat. MEHODS: Participants (6 M, 6 F; BSA = 2.11 & 1.74 m2; max VO2 = 38.45 & 35.53 ml/kg/min) underwent an acclimation period by walking on a treadmill in a climatic chamber. Environmental conditions of the chamber were set at 50 degrees C and 20% rh. The treadmill speed and grade was set to elicit a moderate metabolic rate of approximately 40% max VO2. A 3-day plateau in core temperature (Tre) was used as evidence of acclimation. Participants were then randomly assigned to one of 2 decay groups. Group A returned for 1 acclimation session at 1,3 and 5 weeks post-acclimation. Group B returned for 1 acclimation session at 2,4 and 6 weeks post-acclimation. A repeated measures ANOVA was performed with levels of decay as the independent variable and end Tre, end heart rate (HR), sweat rate (SR) and tolerance time (TT) as the dependent variables. A trend analysis was used to examine the relationship between the independent and dependent variables. RESULTS: Average time for acclimation was 7 days. Tolerance time increased from the first to the final acclimation session (TT=88 & 112 min). There was a trend for a decrease in TT with increasing time away from the heat with TT equivalent for the first acclimation session and decay week 6. Other independent variables were not significant although there was a trend for an increase in end Tre with increased time away from heat. CONCLUSIONS: Complete decay of acclimation occurs after 6 weeks away from heat as evidenced by a decrease in TT and an increase in Tre.
Heat; Heat-stress; Environmental-exposure; Acclimatization; Heat-exposure; Heat-tolerance; Humans; Men; Women; Physical-fitness; Physical-exercise; Physical-reactions; Physiological-function; Physiological-effects; Physiology; Risk-factors; Injuries
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Medicine and Science in Sports and Exercise
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University of South Florida
Page last reviewed: May 5, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division