water replacement

To reduce the risk of dehydration, water should be replaced during vigorous physical exercises lasting more than about 50 minutes. Replacement is particularly important for children and adolescents because their body temperature rises faster than that of adults. The best form of replacement is a cold drink (8-13°C); low in sugars (sugar retards gastric emptying and inhibits the absorption of water); and with a salt concentration less than that of the body fluids. The main purpose of the salts is to speed up the transfer of water through the small intestine into the body. Water lost due to sweating during exercise results in weight loss, and a loss of muscle strength and endurance. As a rough guide, a person should drink two cups of fluid for every pound of weight lost. The rate of replacement should not exceed the maximum absorption rate (about 800 ml per hour). See also thirst.

Replacement of water losses incurred during exercise, or lost from the body through urination, etc. Rehydration is of particular importance to athletes performing repeated bouts of exercise, and to those performing in sports lasting more than 50 min. Without adequate rehydration athletes become dehydrated and their ability to perform is diminished. Water loss during and after exercise is reflected in a loss of body weight. Each 0.5 kg lost, should be replaced with about 500 ml of fluid. Rehydration is best achieved by replacing electrolytes (especially sodium ions), as well as water. Drinking plain water reduces the thirst stimulus and increases urinary output, both of which delay rehydration. Replacement is best accomplished with a cold drink (8-13 °C), slightly hypotonic, and low in sugar (sugars retard gastric emptying). The optimum sugar concentration depends on the individual, but 7% or less is commonly used. Water replacement should not exceed the maximum absorption rate (about 800 ml h⁻¹). See also hyperhydration, thirst mechanism.