Hydration

Water regulates body temperature, transports nutrients and cushions joints. Sweating during exercise removes both water and electrolytes, chiefly sodium.

What published research reports

The American College of Sports Medicine position stand on exercise and fluid replacement reports that dehydration beyond about 2% of body weight can degrade aerobic performance and cognitive function, and that sweat rates vary so widely between individuals — roughly 0.5 to 2 litres per hour — that drinking plans should be individualised rather than copied. It recommends beginning exercise well hydrated, drinking to limit losses to under 2% of body weight during exercise, including sodium when sessions run long, and warns that overdrinking plain water can cause exercise-associated hyponatraemia. After exercise, roughly 1.5 L of fluid per kg of body weight lost restores balance quickly.

References

• Sawka MN, et al. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377–390. PubMed