Aging Impairs Whole-Body Heat Loss in Females under Both Dry and Humid Heat Stress.

PURPOSE: This study was designed to determine whether age-related impairments in whole-body heat loss, which are known to exist in dry heat, also occur in humid heat in females. METHODS: To evaluate this possibility, ten young (25+/-4 years) and ten older (51+/-7 years) females matched for body surface area (Young: 1.69+/-0.11; Older: 1.76+/-0.14 m2, P=0.21) and peak oxygen consumption (Young: 38.6+/-4.6; Older: 34.8+/-6.6 mL[BULLET OPERATOR]kg-1[BULLET OPERATOR]min-1, P=0.15) performed four 15-min bouts of cycling at a fixed metabolic heat production rate (300 W; equivalent to ~45% V[Combining Dot Above]O2peak), each separated by a 15-min recovery, in dry (35[degrees]C, 20% relative humidity) and humid heat (35[degrees]C, 60% relative humidity). Total heat loss (evaporative +/- dry heat exchange) and metabolic heat production were measured using direct and indirect calorimetry, respectively. Body heat storage was measured as the temporal summation of heat production and loss. RESULTS: Total heat loss was lower in humid compared to dry conditions during all exercise bouts in both groups (all P

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