Background: Due to various factors, water balance may vary across seasons. These effects may be particularly prominent in athletes and dependent upon energy expenditure during training.
Methods: Japanese male kendo college athletes participated in this study during their training sessions. The participants were observed for three days each season, i.e., in spring, summer, and winter. The energy expenditure of the participants during training was monitored using the heart rate method. Data regarding the total amount of sweating, rate of sweating, amount of water intake, and rate of water intake were collected for each season and the differences were assessed using analysis of covariance, with energy expenditure as the covariate.
Results: The water balance parameter values observed during a kendo training session in summer were the highest, whereas these values were significantly reduced in winter. Energy expenditure was the highest in spring. The amount of sweating per energy expenditure varied seasonally, reaching as high as 2.14 g/kcal in summer. After adjusting for the influence of energy expenditure, the amount of sweating, amount of water intake, and water intake rate varied significantly by seasons, with the highest values in summer (P<0.001). The sweating rate was high in all the seasons, but the highest rate was observed in summer, followed by spring and then winter. There was a significant difference in the sweating rate in each season (P<0.001). The rehydration rate was 28% in spring, 39% in summer, and 22% in winter.
Conclusions: After adjusting for the influence of energy expenditure, seasonal differences in water balance were observed in Japanese male kendo college athletes during training. These results suggest that water intake is essential after training in any season to maintain the water balance of the body.