ABSTRACT
Heat generated by the muscles during exercise must be dissipated in an attempt to maintain body temperature within a narrow physiological band. It is desirable for those who are engaged in exercise to become hydrated before starting the bout. This can be achieved by drinking fluids with the meal before the exercise, and also ingesting 300-500 ml of fluid immediately before the exercise. The importance of sodium in the drink is to ensure that the fluid ingested is not excreted via urine. It must be remembered that the control of water excretion by the kidney is regulated by the hormone Anti-diuretic Hormone (ADH), secreted from the posterior pituitary gland. Receptors in the posterior pituitary are able to detect changes in plasma volume and the sodium content of blood. If the plasma volume is increased, sodium content of the blood is diluted and so ADH is not released.
