May 19, 2017

Melissa J. Baragh, Roderick F.G.J. King, Michael P. Gray, Ben Jones.

Institute of Sport, Physical Activity and Leisure, G05 Carnegie Hall, Headingley Campus, Leeds Beckett University, Leeds, W. Yorkshire, United Kingdom LS6 3QS.

Fluid balance is important for optimal physiological functioning, health, and exercise performance.  Typically, during exercise in temperatures less than 25oC, team-sport athletes have been found to lose between 1 and 1.5% of pre-exercise body mass. The ability to maintain body mass during exercise highlights that team-sport athletes do not produce high fluid losses and (or) are capable of offsetting fluid losses with appropriate fluid intake, avoiding thresholds of 2-4%, which may reduce exercise performance. Interestingly, observations of potential over-drinking have been reported within team-sports, with fluid intake appearing to precede the physiological need to consume fluid. Over-drinking may lead to implications to health and muscle performance, by disturbing electrolyte concentrations, and thus it is important to understand the mediators of fluid intake during such activity to ensure athletes have optimum fluid balance. It has been proposed that over-drinking in high-intensity intermittent activity may be caused by the drive to consume fluid to reduce thermal discomfort, yet, these factors have not been fully investigated in this context to date. Therefore this study aimed to explore the potential physiological and perceptual drivers of fluid intake and thirst sensation during high-intensity intermittent team-sport.

Ten professional male rugby league players participated in a training session consisting of six 6-min small-sided games, interspersed with 2 min rest, where fluid intake was available ad libitum during rest periods. The training session took place in cool environmental conditions. Fluid consumption was measured at each rest period whilst measures of body mass and subjective ratings of thirst sensation, thermal comfort, thermal sensation and mouth dryness were collected immediately before and after the training session. Blood samples were drawn before and after the session, then subsequently analysed for plasma osmolality, serum sodium concentration and plasma volume change, all indicators of hydration. In addition, skin temperature and time motion analysis were recorded throughout the study.

The results showed that during small-sided games, players consumed on average 0.88 ± 0.38 L of fluid and lost 0.17 ± 0.59% of body mass. A decrease in plasma osmolality and an increase in plasma volume were also observed. A large negative relationship was observed between fluid intake and pre-exercise plasma osmolality, suggesting that those who arrived “more hydrated” subsequently drank more throughout the study. This is not consistent with what would normally be expected if osmotic changes were a key driver of fluid intake. Interestingly a weak correlation between fluid intake and thirst was observed, all suggesting that team-sport athletes consumed fluid in excess of homeostatic requirements and beyond thirst sensation. The lack of synergy between plasma osmolality, thirst and fluid intake elucidates that other factors were likely involved in influencing fluid consumption. There was also no association between thermal comfort and other related physiological or perceptual factors on fluid intake. We proposed that over-drinking may be driven by the high frequency of breaks and proximity of fluid during training. Therefore practitioners should look to align drinking opportunities during training with those of match play or competition and consider how much fluid athletes may need by taking into consideration the environmental demands, athlete training status, intensity of the session and their respective arrival hydration status.

This article is a summary of an article published in Applied Physiology, Nutrition & Metabolism. If you intend to cite any information in this article, please consult the original article and cite that source. This summary was written for the Canadian Society for Exercise Physiology and it has been reviewed by the CSEP Knowledge Translation Committee.

Original Article

Melissa J. Bargh, Roderick F.G.J. King, Michael P. Gray, Ben Jones. Why do team-sport athletes drink fluid in excess when exercising in cool conditions? Applied Physiology, Nutrition, and Metabolism, 2017, 42(3): 271-277, 10.1139/apnm-2016-0445