Two thirds of our body weight is water. The critical chemical reactions for providing muscular energy take place in water and water provides an important function in transporting metabolic by-products to the lungs and kidneys and heat to the surface for dissipation.
Fluid Replacement
On hot days large quantities of water are lost in the form of sweat. This can be as much as 4-5 litres over a 2 hour period for an adult. Performance has been shown to deteriorate with water losses of 3 per cent of body weight. This can occur within the first hour of heavy exercise unless replacement is made.
Two glasses of fluid (300-500ml) should be drunk 30 minutes prior to prolonged effort. Regular intake of a glass of fluid (150-250ml) should be taken at 10-15 minute intervals throughout the session on hot days. The performer may not feel thirsty but should be encouraged to drink these amounts. Water breaks should be mandatory during prolonged activities.
While the most important ingredient of the fluid is water the addition of a little sugar (3.5gm per glass) and a little salt (1gm per glass) is desirable in prolonged sessions. Commercial sports drinks are a good premix of the neccessary additives but they may need to be diluted to the athlete's preference.