Effects of 5-Day Heat Acclimation on Workers Wearing Personal Protective Clothing.

Introduction: Elevated ambient temperature and personal protective clothing (PPC) induce physiological strain which may be counteracted by heat acclimation. The purpose of this study was to determine if 5-day heat acclimation training (HAT) improves thermal and perceptual responses while wearing chemical, biological, radiological, and nuclear (CBRN) PPC. Methods: Nine healthy men completed a heat stress test (walking for one hour with CBRN PPC) in 35°C and 50% relative humidity (RH) before and after 5-day HAT. The HAT consisted of five consecutive days of two 45-minute cycling sessions (50% VO2max) wearing athletic clothing separated by a 15 min rest in 45°C and 20% RH. Results of the pre- and post-HAT heat stress tests were compared. Results: Heat acclimation was seen through 5-day HAT; however, thermoregulatory responses did not improve while wearing CBRN PPC. Improvement (p<0.05, day 1 vs. day 5 HAT) in skin temperature (38.0±0.5°C vs. 37.6±0.5°C), body temperature (38.6±0.4°C vs. 38.3±0.4°C), sweat rate (2.26±0.3kg vs. 2.64±0.3kg), RPE (15.8±2.4 vs. 13.9±3.1), and heat perception (5.7±0.6 vs. 4.9±1.0) were noted. However, no physiological or perceptual improvements (p>0.05) were found in the post-HAT heat stress test. Conclusions: Heat acclimation adaptations may be blunted by CBRN PPC, thus requiring differing or extended HAT.