• Joanie Larose, Heather E Wright, Ronald J Sigal, Pierre Boulay, Stephen Hardcastle, and Glen P Kenny.
• 1Human and Environmental Physiology Research Unit, Faculty of Health Sciences, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, CANADA; 2Clinical Epidemiology Program, Ottawa Health Research Institute, Ottawa, Ontario, CANADA; 3Faculties of Medicine and Kinesiology, Departments of Medicine, Cardiac Sciences and Community Health Sciences, University of Calgary, Calgary, Alberta, CANADA; 4Faculty of Physical Education and Sports, University of Sherbrooke, Sherbrooke, Quebec, CANADA; and 5CanmetMINING, Natural Resources Canada, Sudbury, Ontario, CANADA.
• Med Sci Sports Exerc. 2013 Dec 1;45(12):2265-76.

IntroductionAging is associated with a reduction in the body's capacity to dissipate heat. To date, few studies have examined age-related changes in thermoregulatory function during short exercise periods in the heat in older females.PurposeThis study aimed to investigate the effects of age on whole-body heat loss during intermittent exercise in the heat in young and older females.MethodsDirect and indirect calorimetry was used to measure whole-body evaporative heat loss (EHL), change in body heat content, and metabolic heat production. Eleven young (Y) (mean ± SD age = 24 ± 4 yr) and 13 older (O) (51 ± 8 yr) females matched for body surface area (Y, 1.72 ± 0.15; O, 1.75 ± 0.12 m²) and fitness (V(˙)O(2max)) (Y, 36.7 ± 6.8 mL O₂·kg⁻¹·min⁻¹; O, 33.8 ± 8.0 mL O₂·kg⁻¹·min⁻¹) performed four bouts of 15-min cycling (Ex1, Ex2, Ex3, and Ex4) at a constant rate of heat production (300 W) at 35°C and 20% relative humidity. Each exercise bout was separated by 15 min of rest.ResultsEHL was reduced in O compared with Y during Ex1 (O, 199 ± 6 W; Y, 240 ± 9 W; P = 0.001), Ex2 (O, 238 ± 4 W; Y, 261 ± 9 W, P = 0.023), and Ex3 (O, 249 ± 4 W; Y, 274 ± 11 W; P = 0.040). EHL was not different between groups during Ex4 or during the recovery periods. Older females had a greater change in body heat content compared with young females (O, 270 ± 20 kJ; Y, 166 ± 20 kJ; P = 0.001).ConclusionThese findings suggest that older females have a lower capacity for whole-body EHL compared with younger females during short intermittent exercise in the heat performed at a fixed rate of metabolic heat production.

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