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

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 (\u394Hb) 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 7 15 min) and recovery periods (4 7 15 min) at a fixed rate of heat production (400 W) and under fixed environmental conditions (35 \ub0C/20% relative humidity). HE was lower in older males vs. young males during each exercise (Ex1: 283 \ub1 10 vs. 332 \ub1 11 kJ, Ex2: 334 \ub1 10 vs. 379 \ub1 5 kJ, Ex3: 347 \ub1 11 vs. 392 \ub1 5 kJ, and Ex4: 347 \ub1 10 vs. 387 \ub1 5 kJ, all P less than 0.02), whereas HE in middle-aged males was intermediate to that measured in young and older adults (Ex1: 314 \ub1 13, Ex2: 355 \ub1 13, Ex3: 371 \ub1 13, and Ex4: 365 \ub1 8 kJ). HE was not significantly different between groups during the recovery periods. The net effect over 2 h was a greater \u394Hb in older (267 \ub1 33 kJ; P = 0.016) and middle-aged adults (245 \ub1 16 kJ; P = 0.073) relative to younger counterparts (164 \ub1 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.Peer reviewed: YesNRC publication: N