Effects of various beverages on the hormones involved in energy metabolism during exercise in the heat in previously dehydrated subjects

Abstract

The objective of our study was to examine the effects of beverage content on hormone responses involved in fuel substrate metabolism (catecholamines, insulin and glucagon) in previously dehydrated subjects exercising at a moderate intensity in the heat. Six healthy men walked for 60-min on five occasions at 50% maximal oxygen uptake in a warm environment (dry bulb temperature 35 ± 0.2°C, relative humidity 20%). On each occasion, the subjects were dehydrated before exercise (loss of 2% body mass) by passive controlled hyperthermia, which led to a reduction in plasma volume (PV) of about −5% to −9%. In one session, the subjects exercised without rehydration (Dh). In the other sessions, four beverages (650 ml) were given just before the exercise: mineral water (W), a 60 g · l⁻¹ glucose and 1.2 g · l⁻¹ NaCl solution (GS), a 60 g · l⁻¹ maltodextrin solution, and a 60 g · l⁻¹ maltodextrin and 1.2 g · l⁻¹ NaCl solution. Compared to Dh and W, carbohydrate supply with or without NaCl induced a higher glycaemia (P < 0.05), a reduced increase in plasma adrenaline concentration (P < 0.05) and a higher plasma insulin concentration (P < 0.05), which lowered plasma free fatty acids and glycerol concentrations (P < 0.05). The lesser increase in plasma noradrenaline concentrations observed during GS compared to Dh and W sessions can be explained by a larger correction in PV which might have induced better haemodynamic conditions. However, the increase in plasma glucagon with carbohydrate supply – compared to Dh and W (P < 0.05) – remains unexplained.