Thermal responses to exercise in children.

Abstract

The thermal responses to exercise in eight athletic pre-pubertal boys (mean age 12·8 years) and five young athletic adolescent girls (mean age 1·38 years) were studied in a moderate environment {T db = 21°C, T db = 17°C) and the results compared with data collected on eight adult athletes (mean age 36 years). The maximal aerobic power output (VO 2max) for the three groups averaged 66·7, 63·6 and 68·6 ml kg−1 min−1 respectively. At the same relative work load (%VO 2max), the metabolic heat production (M) was approximately 44% less in the children than the adults, but rectal temperature at the sixtieth min of exercise was the same in the two groups. The major difference between the subjects was in the mean skin temperature (T¯sk) and evaporative sweat loss (mdot;sk). Evaporative sweat loss was lower in children and T¯ sk was approximately 3°C higher, for the same environmental conditions, than in adults. The children were able to lose equal amounts of their total heat production (W)by physical (convection and radiation) and physiological (evaporation ofsweat) means compared with the adults who dissipated less than one third of their H by non-evaporative pathways. Thus, due to the possible advantage of their high body surface area to weight ratio, it would seem that young children are excellent convectors and radiators of heat, and in consequence have a relatively poorly developed and/or insensitive sweat mechanism. For these reasons it is suggested, contrary to the conclusions of Gullestad (1975), that the thermal responses of children are quantitatively different from young adults, and they must be regarded separately during exercise.