Voluntary water intake during and following moderate exercise in the cold

Exercising in cold environments results in water losses, yet examination of resultant voluntary water intake has focussed on warm conditions. The purpose of the study was to assess voluntary water intake during and following exercise in a cold compared to a warm environment. Ten healthy males (22±2 years, 67.8±7.0 kg, 1.77±0.06 m, V˙O2peak 60.5±8.9 ml.kg-1.min-1) completed two trials (7-8d). In each trial subjects sat for 30 minutes before cycling at 70% V˙O2peak (162±27W) for 60 minutes in 25.0±0.1°C, 50.8±1.5% relative humidity (RH) (warm) or 0.4±1.0°C, 68.8±7.5% RH (cold). Subjects then sat for 120 minutes at 22.2±1.2°C, 50.5±8.0% RH. Ad libitum drinking was allowed during the exercise and recovery periods. Urine volume, body mass, serum osmolality and sensations of thirst were measured at baseline, post-exercise and after 60 and 120 minutes of the recovery period. Sweat loss was greater in the warm trial (0.96±0.18 l v 0.48±0.15 l) (p<0.0001) but body mass losses over the trials were similar (1.15±0.34% (cold) v 1.03±0.26% (warm)). More water was consumed throughout the duration of the warm trial (0.81±0.42 l v 0.50±0.49 l; p=0.001). Cumulative urine output was greater in the cold trial (0.81±0.46 v 0.54±0.31 l) (p=0.036). Post-exercise serum osmolality was higher compared to baseline in the cold (292±2 v 287±3 mOsm.kg-1, p<0.0001) and warm trials (288±5 v 285±4 mOsm.kg-1; p=0.048). Thirst sensations were similar between trials (p>0.05). Ad libitum water intake adjusted so that similar body mass losses occurred in both trials. In the cold there appeared to a blunted thirst response.