title: Age-related differences in heat loss capacity occur under both dry and humid heat stress conditions.
abstract: This study examined the progression of impairments in heat dissipation as a function of age and environmental conditions. Sixty men (n = 12 per group; 20-30, 40-44, 45-49, 50-54, and 55-70 yr) performed four intermittent exercise/recovery cycles for a duration of 2 h in dry (35°C, 20% relative humidity) and humid (35°C, 60% relative humidity) conditions. Evaporative heat loss and metabolic heat production were measured by direct and indirect calorimetry, respectively. Body heat storage was measured as the temporal summation of heat production and heat loss during the sessions. Evaporative heat loss was reduced during exercise in the humid vs. dry condition in age groups 20-30 (-17%), 40-44 (-18%), 45-49 (-21%), 50-54 (-25%), and 55-70 yr (-20%). HE fell short of being significantly different between groups in the dry condition, but was greater in age group 20-30 yr (279 ± 10 W) compared with age groups 45-49 (248 ± 8 W), 50-54 (242 ± 6 W), and 55-70 yr (240 ± 7 W) in the humid condition. As a result of a reduced rate of heat dissipation predominantly during exercise, age groups 40-70 yr stored between 60-85 and 13-38% more heat than age group 20-30 yr in the dry and humid conditions, respectively. These age-related differences in heat dissipation and heat storage were not paralleled by significant differences in local sweating and skin blood flow, or by differences in core temperature between groups. From a whole body perspective, combined heat and humidity impeded heat dissipation to a similar extent across age groups, but, more importantly, intermittent exercise in dry and humid heat stress conditions created a greater thermoregulatory challenge for middle-aged and older adults.
authors.affiliation: Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada;
authors.forename: Joanie
authors.initials: J
authors.lastname: Larose
authors.affiliation: Faculty of Physical Education and Sports, University of Sherbrooke, Sherbrooke, Quebec, Canada;
authors.forename: Pierre
authors.initials: P
authors.lastname: Boulay
authors.affiliation: Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada;
authors.forename: Heather E
authors.initials: HE
authors.lastname: Wright-Beatty
authors.affiliation: Departments of Medicine, Cardiac Sciences, and Community Health Sciences, Faculties of Medicine and Kinesiology, University of Calgary, Calgary, Alberta, Canada; and.
authors.forename: Ronald J
authors.initials: RJ
authors.lastname: Sigal
authors.affiliation: CanmetMining, Natural Resources Canada, Sudbury, Ontario, Canada.
authors.forename: Stephen
authors.initials: S
authors.lastname: Hardcastle
authors.affiliation: Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada; gkenny@uottawa.ca.
authors.forename: Glen P
authors.initials: GP
authors.lastname: Kenny
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D001831:Body Temperature / Q000502:physiology*; D001833:Body Temperature Regulation / Q000502:physiology*; D002153:Calorimetry, Indirect / Q000379:methods; D015444:Exercise / Q000502:physiology; D018882:Heat Stress Disorders / Q000503:physiopathology*; D006358:Hot Temperature; D006801:Humans; D006813:Humidity; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology; D012867:Skin / Q000098:blood supply / Q000503:physiopathology; D013546:Sweating / Q000502:physiology; D022722:Thermogenesis / Q000502:physiology; D055815:Young Adult
keywords: aging; calorimetry; exercise; heat loss; humidity