Whole body heat loss is reduced in older males during short bouts of intermittent exercise

Abstract

Hardcastle S, Kenny GP. Whole body heat loss is reduced in older males during short bouts of intermittent exercise. Am J Physiol Regul Integr Comp Physiol 305: R619 -R629, 2013. First published July 24, 2013 doi:10.1152/ajpregu.00157.2013.-Studies in young adults show that a greater proportion of heat is gained shortly following the start of exercise and that temporal changes in whole body heat loss during intermittent exercise have a pronounced effect on body heat storage. The consequences of short-duration intermittent exercise on heat storage with aging are unclear. We compared evaporative heat loss (HE) and changes in body heat content (⌬Hb) between young (20 -30 yr), middle-aged (40 -45 yr), and older males (60 -70 yr) of similar body mass and surface area, during successive exercise (4 ϫ 15 min) and recovery periods (4 ϫ 15 min) at a fixed rate of heat production (400 W) and under fixed environmental conditions (35°C/20% relative humidity). HE was lower in older males vs. young males during each exercise (Ex1: 283 Ϯ 10 vs. 332 Ϯ 11 kJ, Ex2: 334 Ϯ 10 vs. 379 Ϯ 5 kJ, Ex3: 347 Ϯ 11 vs. 392 Ϯ 5 kJ, and Ex4: 347 Ϯ 10 vs. 387 Ϯ 5 kJ, all P Ͻ 0.02), whereas HE in middle-aged males was intermediate to that measured in young and older adults (Ex1: 314 Ϯ 13, Ex2: 355 Ϯ 13, Ex3: 371 Ϯ 13, and Ex4: 365 Ϯ 8 kJ). HE was not significantly different between groups during the recovery periods. The net effect over 2 h was a greater ⌬Hb in older (267 Ϯ 33 kJ; P ϭ 0.016) and middle-aged adults (245 Ϯ 16 kJ; P ϭ 0.073) relative to younger counterparts (164 Ϯ 20 kJ). As a result of a reduced capacity to dissipate heat during exercise, which was not compensated by a sufficiently greater rate of heat loss during recovery, both older and middle-aged males had a progressively greater rate of heat storage compared with young males over 2 h of intermittent exercise. evaporative heat loss; aging; calorimetry; thermal transients A NUMBER OF STUDIES HAVE EXAMINED age-related differences in thermoregulatory control during prolonged exercise (range 30 -90 min) in the heat [range: 30 -49°C/20 -60% relative humidity (RH)] (4, 11-13, 20, 23, 26, 29, 33, 34). Some studies reported no differences in thermoregulatory function (4,20,23,29,33), whereas others found significant age-related impairments in heat loss capacity (e.g., reduced local sweating rate/onset/sensitivity and/or greater increments in core and skin temperatures) (11-13, 26, 34). It is possible that these discrepancies reflect that in some studies, older adults were able to achieve heat balance, while in other studies, heat load exceeded their physiological maximal sweating capacity; hence, differences in local sweat rate and/or core temperature were evident. What these studies did not examine, however, is whether age-related impairments in heat loss capacity occur during exercise of short duration (i.e., 15 min) when the rate of heat storage has been shown to be the greatest (21).At the onset of exercise, the rate of metabolic heat production increases immediately and is not i...

Heat Waves, Aging, and Human Cardiovascular Health

“…Regional sweating patterns also change with aging, with the largest reductions in sweating occurring in the abdomen and less significant reductions occurring in the lower back, thigh, and arm (60). An attenuated evaporative heat loss results in greater heat storage in older men and women (41, 42) which can exacerbate the cardiovascular strain described above. Even though the sweating response in the aged is often attenuated, prolonged sweating during long duration heat stress causes a significant reduction in plasma volume.…”

Increasing age is a major risk factor for susceptibility to heat stress during physical activity

“…To date, research has demonstrated several factors -primarily age, cardiorespiratory fitness, and body fat -to influence wholebody heat loss (WBHL) and therefore alter susceptibility to heat stress in otherwise healthy adults (Larose et al 2013b;Stapleton et al 2015;Dervis et al 2016). Specifically, recent reports depict impairments in WBHL in physically active adults as young as 40 years of age (Larose et al 2013a(Larose et al , 2013b, although these studies isolated aging from other factors (i.e., participants were matched for body morphology and fitness).…”

“…Specifically, recent reports depict impairments in WBHL in physically active adults as young as 40 years of age (Larose et al 2013a(Larose et al , 2013b, although these studies isolated aging from other factors (i.e., participants were matched for body morphology and fitness). Cardiorespiratory fitness has yielded contradictory evidence in smaller studies (Jay 2014); however, it was found to have a critical role in attenuating the agerelated decrements in WBHL (Stapleton et al 2015).…”

Temperature of Ingested Water during Exercise Does Not Affect Body Heat Storage

“…Additionally, it is unknown whether modula tions in local and whole-body heat loss would parallel the observations in the present study with exercise performed under uncompensable conditions (i.e., increased ambient humidity and/or when clothing is worn). Furthermore, our results are specific to young males and our findings may not necessarily be replicated in populations that have a re duced capacity to dissipate heat as has been shown with females (8), older individuals (17,18), and individuals with chronic health disorders such as type 1 and 2 diabetes (3,14).…”