Young versus older males\u2019 thermoregulatory responses to exercise in humid heat under two air velocities

Older adults have less evaporative heat loss than younger adults during exercise performed at a fixed rate of heat production under conditions which permit full sweat evaporation. However, when evaporative heat loss is restricted (i.e., high humidity, clothing insulation), such differences may not lead to expected differences in the level of thermal strain. Despite a greater evaporative capacity in younger adults, excessive sweat dripping that would result under such conditions may not provide any additional cooling benefit.PURPOSE: To examine the effects of exercise in warm/humid heat under two different levels of air velocity to modify the level of evaporative cooling, on the heat stress responses of young versus older adults.METHODS: Ten young (Mean\ub1SE; Y: 24\ub11 yrs) and 10 older (O: 59\ub11 yrs) males, matched for body surface area and wearing work coveralls, performed 4 successive 15 min cycling bouts (15 min rest) at a fixed rate of heat production (400 W) in humid heat (35\ub0C, 60% relative humidity) with 0.5 (Low) and 3.0 m/s (High) air velocity. Rectal temperature (Tre) was measured continuously. Blood and urine were analyzed prior to exercise (PRE) and the end of final recovery for hemoglobin, hematocrit, and Interleukin (IL)-6, and urine specific gravity (USG), respectively.RESULTS: The change (\u394) in Tre (PRE-end of exercise) was similar between age groups under Low (Y: 1.11\ub10.09, O: 1.28\ub10.10\ub0C) and High (Y: 0.76\ub10.08, O: 0.96\ub10.10\ub0C) air velocities, however was greater in Low than High for both groups. Plasma volume \u394 was similar between Y and O, however were greater under Low (Y: -10.9\ub11.3, O: -10.8\ub11.0%) than High (Y: -5.7\ub10.7, O: -6.9\ub10.8%). Despite elevated PRE IL-6 in O, no age-related differences were seen for the \u394 IL-6 during Low (Y n=9: 4.47\ub11.04, O n=7: 3.72\ub10.98 pg/mL) or High (Y: 1.04\ub10.37, O: 1.32\ub10.38 pg/mL). IL-6 \u394 was greater under Low than High. No age or condition differences in USG were seen.CONCLUSION: Preliminary data indicate that young and older males show similar thermal strain and changes in hydration status following intermittent exercise in humid heat. High air velocity was effective in reducing strain within both age groups. Support: Workplace Safety and Insurance Board of Ontario & Canada Foundation for Innovation-Leaders Opportunity Fund (G.P. Kenny), MITACS Accelerate (H.E. Wright).Peer reviewed: YesNRC publication: N