THERMOREGULATORY AND BODY FLUID BALANCE RESPONSES DURING A SWIMMING TRAINING SESSION 938

Previous studies on the thermoregulatory response to swimming have been conducted in artificial or controlled environments. The purpose of this study was to examine the thermoregulatory and body fluid balance (BFB) responses of competitive swimmers during a training session in the natural field conditions of their training habitat. Ten male swimmers (18.4±2.1 yrs, 75.0±5.1 kg, 176.2±0.1 cm, ˙VO₂max=3.8±0.9 L·min^-1, mean ± SD) members of the National Team performed 180 min of swimming (58% ˙VO₂max, mean velocity = 0.84±0.1 m·sec^-1) in a 50m outdoor pool (WBGT=29.8±2.8 °C, and water temp. =26.8±0.3°C). Body mass(BM), rectal (T_rec) and skin temperature, water intake (WI), plasma volume (PV), plasma electrolytes and osmolality (OSMO) were determined before and every 30 min during the training session. Repeated measures ANOVA indicated a decrease in BM of 2.1±0.7 kg (p<0.05), and an increase in T_rec of 0.98 °C (p<0.05). Also the WI (0.2±0.3 kg) did not maintain the BFB (-1.3±0.4 kg). PV decreased 10.4±5.2%. No significant differences were observed in plasma electrolytes and OSMO. Estimated sweat rate and heat storage were 0.3±0.2 kg·h^-1, and 48.2±5.5 W·m², respectively. These results indicate that during this training session the swimmers had a gain in T_rec and loss in BFB. Our data are consistent with the hipothesis that competitive swimmer's body fluid balance is negatively affected during training.