If you plan to race under hot conditions, remember that acclimatization takes about 10 days. Plan to be acclimatized a week in advance. During the week before the event, avoid extra heat stress which may dehydrate and fatigue you for the race. Dehydration or excessive loss of body water reduces the amount of time you can exercise as well as necessitating slowing down. Changes that take place at the cellular level adversely effect muscle contraction.
Sweat is comprised mainly of water and sodium and chloride ions.
These ions are known as electrolytes. Other electrolytes are also present in small amounts. Studies of electrolyte balance during and after exercise have shown increases in the electrolytes in the blood, but these changes are probably due to water loss and muscle use. While the electrolytes are probably not necessary for replacement in runs of marathon length or shorter, they may improve fluid absorption by the body and encourage further drinking by stimulating the bodies thirst mechanism. In runs longer than 90 minutes, the carbohydrate in sports drinks helps spare liver glycogen depletion.