Part 2: Water: Output

Water loss from the body occurs in 4 ways:

1.Urine:

The kidney is obligated to rid metabolic byproducts such as urea, an end product of protein metab olism. Large quantity of protein used for energy accelerates dehydration during exercise.

2.Skin:

Each day a person under normal temperature lose 500 to 700 ml of sweat. During prolonged exercise an athlete can lose up to 12L of sweat in hot conditions (at the rate of 1L per hour).

3.Vapor:

Water loss via small droplets in exhaled air accounts for 200-300ml per day.

4.Faeces:

Water loss in faces is around 100-200ml daily.

Hyponatremia

There is need to drink before, during and after exercise. In many circumstances people are recommended to drink plain, hypotonic water. However, excessive fluid intake can produce hyponatremia or water intoxication. A sustained low plasma sodium concentration creates an osmotic imbalance across the blood-brain barrier that causes rapid water influx to the brain. This can result in confusion, malaise, headache, cramping, seizures etc.

To reduce overhydration and hyponatremia risk in prolonged exercise you can do the following:

1. Drink 400-600 ml of fluid 2 to 3 hours before exercise.
2. Drink 150 to 300 ml about 30 minutes before exercise.
3. Drink no more than 1L per hour of plain water spread over 15 minutes interval during or after exercise.
4. Add a small amount of sodium to the ingested liquid.

This information is more for endurance athletes.