Fluid loss in recreational surfers

Purpose: Surfing is an activity that provides a unique challenge to thermoregulation and hydration. The purpose of this study was to quantify fluid loss in recreational surfers, and to analyze the effects of water temperature, air temperature, exercise intensity, duration, and garment thickness on the total amount of fluid lost during a surf session. Methods: Male (n=255) and female (n=53) recreational surfers were recruited from San Diego, Costa Rica, and Australia to participate in the study. Subjects’ fluid loss during surfing was assessed by comparing the average of three measurements of nude body mass pre- and post-surf session using a portable scale(SECA, CA, USA). Heart rate (HR) was measured throughout the session using a PolarFT1 receiver and T32 transmitter. Environmental conditions and surf characteristics were obtained prior to each subjects’ surf session at their beach location using information directly from the National Oceanic and Atmospheric Administration’s buoys located offshore (Surfline.com). 
Results: Post-surf weight was significantly lower than pre-surf weight with an average of 0.60 ± 0.55kg (0.82% body weight loss) decrease in body weight during a surf session. In multivariable regression, water temperature and surf session duration were associated with fluid loss. For every 5 degree Celsius increase in water temperature, there was a 0.23 kg(SE=0.014; p<0.001) increase in fluid loss and for every 10 minute increase in session duration, there was a 0.06 kg (SE=0.001; p<0.001) increase in fluid loss. Air temperature, HR, and garment thickness were not independently associated with fluid loss. In multivariable regression, water temperature, air temperature, session duration, HR, and garment thickness accounted for 27% of the variability in fluid loss among surfers. 
Conclusion: The findings of this study suggest that prolonged surfing at high environmental temperatures can result in significant body water deficits. Given that there are limited opportunities to rehydrate during the sport, surfers must properly hydrate before surfing to avoid the detrimental effects of dehydration