Prehydration

Prehydration is the planned intake of fluids before exercise or competition to ensure the body begins activity in a euhydrated state. It aims to replace water lost overnight or since the last meal and to prepare for expected sweat losses.

Pre-exercise fluid intake guidelines

Starting exercise properly hydrated helps maintain blood volume, regulate body temperature and support performance. Water accounts for 45–75 % of body weight and is lost through breathing, urination and sweating; sweat rates during sport can exceed a litre per hour. To arrive well hydrated, drink about 500 ml of water or an electrolyte drink two to three hours before training, and another 150–250 ml 15–20 minutes beforehand. Plain water is adequate for sessions under an hour, while longer or intense workouts may benefit from a beverage containing sodium and a small amount of carbohydrate to replace electrolytes. Prehydration should not involve excessive drinking, because the kidneys can only excrete roughly one litre per hour.

Prehydration is the planned intake of fluids before exercise or competition to ensure the body begins activity in a euhydrated state. It aims to replace water lost overnight or since the last meal and to prepare for expected sweat losses.

Pre-exercise fluid intake guidelines

Starting exercise properly hydrated helps maintain blood volume, regulate body temperature and support performance. Water accounts for 45–75 % of body weight and is lost through breathing, urination and sweating; sweat rates during sport can exceed a litre per hour. To arrive well hydrated, drink about 500 ml of water or an electrolyte drink two to three hours before training, and another 150–250 ml 15–20 minutes beforehand. Plain water is adequate for sessions under an hour, while longer or intense workouts may benefit from a beverage containing sodium and a small amount of carbohydrate to replace electrolytes. Prehydration should not involve excessive drinking, because the kidneys can only excrete roughly one litre per hour.

Practical examples and tips

Prehydration becomes especially important before endurance events or exercise in heat. Marathon runners and cyclists often monitor morning body weight and urine colour to gauge hydration and adjust their fluid intake accordingly. After an overnight fast, drinking water with breakfast helps avoid starting dehydrated. In hot conditions or at altitude, a modest increase in pre-exercise fluid may be needed. Athletes should plan fluid intake ahead of time and avoid last-minute chugging.

Prehydration means going into a workout or competition already hydrated. By planning fluid intake and matching it to expected sweat losses, athletes can preserve performance and avoid the rapid onset of dehydration once exercise begins.

Related Terms: Hydration, Euhydration, Hypohydration, Hyperhydration, Rehydration