Seasonal variations in water balance in elite Japanese university male soccer players during training

BACKGROUND: Water balance, particularly in athletes, can vary seasonally because of various factors and may be influenced by energy expenditure during training. Due to various factors, the water balance may vary from season to season. METHODS: We assessed water balance during training sessions in spring, summer, and winter among elite Japanese university male soccer players. Energy expenditure during training was determined using the heart rate method. An analysis of covariance (ANCOVA) was performed with energy expenditure as a covariate to investigate seasonal variations in sweating amount, sweating rate, water intake volume, and water intake rate across different seasons.RESULTS: During individual soccer training sessions, all parameters related to water balance were significantly higher in summer than in winter (P<0.05). Energy expenditure was significantly higher in winter (P<0.05). The sweating amount per unit of energy expenditure exhibited a significant seasonal difference, with higher mean value of 2.71 g/kcal in summer (P<0.05). When adjusting for energy expenditure, sweating amount and rate were higher in summer, followed by spring and winter, with significant differences between these seasons (P<0.001). The water intake volume and rate also showed significant seasonal differences, with higher values in the summer season (P<0.001). The rehydration rate during training was 42% in spring, 57% in summer, and 52% in winter.CONCLUSIONS: Our study revealed that seasonal variations in water balance among elite Japanese university male soccer players can be effectively analyzed by accounting for energy expenditure. These findings underscore the importance of post-training rehydration in all seasons to ensure optimal body water balance.