Increased air velocity reduces young and older males\u2019 thermal strain similarly despite humidity and clothing

摘要

During exercise in dry heat, older adults have a lower evaporative heat loss capacity than younger adults when full evaporation is permitted, potentially putting older workers at greater risk for heat related injuries. However, it is unknown how increased air velocity alters the thermoregulatory responses when evaporative heat loss is restricted (i.e., high humidity, clothing insulation), and whether age-related differences in thermoregulation remain evident under such conditions.PURPOSE: To examine the heat stress responses of young and older males during intermittent exercise in humid heat under two levels of air velocity which modify the level of evaporative cooling.METHODS: Under 0.5 (Low) and 3.0 m/s (High) air velocity, 10 young (Mean\ub1SE; Y: 24\ub11 yrs) and 10 older (O: 59\ub11 yrs) active males, matched for body surface area, cycled 4 x 15 min (15 min rest, 30 min final rest) at a fixed rate of heat production (400 W) wearing coveralls in humid heat (35\ub0C, 60% relative humidity). Rectal (Tre) and visceral (Tvisc) temperatures, heart rate (HR), and local sweat rate (LSR) on the forearm were measured continuously.RESULTS: At the end of the 4th exercise bout, no age-related differences were observed between the low and high air velocity conditions for Tre (Low: Y = 38.28\ub10.11, O = 38.31\ub10.08; High: Y = 37.94\ub10.08, O = 37.87\ub10.08\ub0C), Tvisc (Low: Y = 38.36\ub10.13, O = 38.26\ub10.07; High: Y = 37.93\ub10.10, O = 37.87\ub10.11\ub0C), % of max HR (Low: Y = 79.9\ub12.8, O = 77.3\ub11.2; High: Y = 67.6\ub12.6, O = 72.4\ub12.2%), or LSR (Low: Y = 1.20\ub10.10, O = 1.17\ub10.10; High: Y = 1.15\ub10.11, O = 1.10\ub10.11 mg\ub7min-1\ub7cm-2). For both Young and Older males, Tre, Tvisc, HR, and LSR were reduced during the High compared to Low air velocity condition.CONCLUSION: Following moderate intensity intermittent exercise in humid heat wearing work coveralls, young and older males showed similar levels of thermal and cardiovascular strain under Low and High air velocity levels. Increased air velocity reduced the thermal and cardiovascular strain to a similar extent in both young and older males. This Project was funded by research grants provided by the Workplace Safety and Insurance Board (Ontario), Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation (all G.P. Kenny), MITACS Accelerate (H.E. Wright).