Hydration status of rugby union players in hot and humid conditions: a comparative team case study of day and night training sessions

Hydration responses of rugby union players within and between day and night training sessions in hot and humid conditions were monitored. Body mass, fluid ingestion, perceptual thermal stress (TSS) and thirst scores were monitored in ten players (age: 21.94±.4 years; body mass: 97.9±15.5kg; height: 179.5±5.6cm) across both training sessions. Heat index was higher during the day session compared to the night (44ºC vs 34ºC respectively). Significant interaction effects were found for body mass and TSS. Between-group comparisons revealed no significant fluctuations of body mass between sessions. Temporal comparisons showed a significant reduction in body mass across the night session (97.2±15.7; 96.4±15.4 kg), although the mean decrease in body mass did not exceeded >2%. TSS increased significantly across both day (1.2±1.3; 5.2±1.0) and night sessions (1.4±1.0; 3.6±1.6). However, TSS was significantly higher post-training in the day session and players ingested more fluids during the day session (1.4±0.5; 0.9±0.4 L·hr⁻¹). Reduced thermal stress scores may compromise self-mediated hydration practices in rugby players when training at night and lead to greater body mass loss.