| Abstract | Aging is associated with a reduction in the body’s capacity to dissipate heat as evidenced by an attenuated skin blood flow and sweating response during passive heat exposure. To date
however, few studies have examined age-related changes in thermoregulatory function during exercise in the heat in older adults, especially in older females.
PURPOSE: To investigate the effects of age progression on whole-body heat loss during intermittent exercise in the heat in young and older females.
METHODS: Direct and indirect calorimetry was used to measure changes in body heat content and metabolic heat production (M-W). Core temperature (Trec) was measured continuously.
Five young (Y) (24±3 years) and five older (O) (54±9 years) healthy females matched for body surface area (Y: 1.61±0.04, O: 1.65±0.09) performed four successive bouts of 15-min cycling
(Ex1, Ex2, Ex3, Ex4) at a constant rate of heat production (300 W) at 35°C and 20% relative humidity. Each exercise bout was separated by 15 minutes of rest (R1, R2, R3) with a final rest
period of one hour (R4).
RESULTS: Body heat content (kJ) during Ex1 (Y: 114±9, O: 130±10), Ex2 (Y: 78±8, O: 91±7), Ex3 (Y: 72±7, O: 88±8) and Ex4 (Y: 76±6, O: 89±6) were greater in older versus younger
females. The older females also had a greater net change in body heat content following each exercise/rest cycle; Ex1/R1 (Y; 93±10, O; 114±11), Ex2/R2 (Y: 41±8, O; 56±7), Ex3/R3 (Y:
31±12, O; 43±10) and Ex4/R4 (Y: 5±19, O; 46±13). The changes in body heat content were paralleled by a larger increase in core temperature from baseline in the older group at the end of
Ex4 (Y: +0.59±0.09, O: +0.68±0.07) and following the 1-hour recovery period (Y: +0.22±0.08, O: +0.40±0.05).
CONCLUSIONS: These findings suggest that older females matched for weight and body composition have a lower capacity for whole body heat loss compared to younger females during
intermittent exercise in the heat performed at a fixed rate of metabolic heat production |
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