The effect of water temperature on the hormonal response to prolonged swimming

Abstract

The relationship between thermoreception, hormonal secretion and muscular activity was studied. 6 men swam 60 min in 21, 27 and 33°C water at a speed requiring 68 % of Vo_a max (determined in 27°C water). Rectal temperature increased in 33°C (1.3 ± 0.2°C, mean and S.E.) and 27°C (0.7 ± 0.1°C) expts. but decreased in 21°C expts. (0.8 ± 0.3°C). Changes in esophageal and muscle temperatures parallelled changes in rectal temperature. Plasma noradrenaline was higher in 33°C than in 27°C expts. and growth hormone, Cortisol and glucagon concentrations increased in 27°C and 33°C expts. only. Insulin concentrations were uniformly depressed during swimming at the different water temperatures. In 21°C expts. noradrenaline and adrenaline concentrations were higher than in 27°C expts. V_O2, carbohydrate combustion and peak lactate were slightly lower in 33°C expts. Plasma glucose decreased slightly and FFA and glycerol concentrations increased identically in all expts. Heart rate increased continuously during swimming in 27°C and 33°C expts., but not in 21°C expts. In conclusion the rise in body temperatures normally observed during exercise enhances the exercise induced increases in the plasma concentrations of noradrenaline, Cortisol, growth hormone and glucagon. Decreased body temperatures may elicit catecholamine secretion as a direct consequence of thermoreception. Shivering may account for previously observed decreases in insulin secretion during cold stress but not for increases in Cortisol and growth hormone.