It’s getting to the time of year when the weather starts to get that much hotter. Exercising in the heat can have a dramatic effect on the body’s natural fluid balance. In normal resting conditions the water content of the body remains relatively stable within an individual over time. Although water output may frequently exceed water intake, this imbalance is quickly adjusted with appropriate fluid intake to restore the body’s fluid level balance.

Water Intake

• Water From Liquids

The average individual will consume 1200ml of water each day. During exercise and when the weather is hotter, water intake can increase by five to six times above normal levels. If extra water is not taken in, we may end up in as bad a state as one individual, who reportedly lost 13.6kg of water weight during a 2 day, 17 hour, 55-mile run across Death Valley California. He was experienced and managed to replace much of this while running reducing his overall fluid loss.

• Water in Foods

Most foods especially fruit and vegetables contain large quantities of water. Foods such as lettuce, pickles, green beans and broccoli contain a high water content, whereas the water contained in butter, oils, chocolate, biscuits and cakes is relatively low.

• Metabolic Water

When food is broken down in the stomach to give us energy, water is created as a by-product; the body can then use this water. A staggering 25% of the daily water requirements for a sedentary individual is provided in this way.

Water Output

• Urine

The kidneys expel approximately 1000 to 1500 ml of water per day. This water transports waste products out of the body. A high protein diet has been found to increase dehydration during exercise due to waste products, which are created by protein breakdown.

• Through The Skin

Water is lost through the skin in the form of sweat produced by glands located beneath the skin. This provides a refrigeration mechanism to cool the body. At rest an individual may secrete 500 to 700 ml of water per day. During exercise on a hot day, this may rise as high as 8 to 12 litres.

• Water Vapour

An average individual looses 250 to 350 ml of water, per day, through small water droplets in exhaled air. During exercise an individual may loose as much as 2 to 5ml of water from the respiratory passages which lead from the lungs each minute.

Water Requirements During Exercise.

The most serious consequence of profuse sweating is the loss of body water. The amount of water lost through sweating depends on the severity of exercise as well as the environmental temperature and relative humidity. The term relative humidity refers to the water content of the air and can have a great bearing on the efficiency of the sweating mechanism in controlling body temperature.

During conditions of 100% humidity the air is completely saturated with water vapour. As a result evaporation of fluid from the skin to the air is impossible and this important avenue is closed for body cooling, resulting in the body core temperature overheating. On a dry day however the air can hold a considerable amount of moisture and there is rapid evaporation of fluid from the skin, resulting in efficient sweating and a cool body core.

Aware Of Your Body

It is important when maintaining fluid balance to be aware not only of your body but also the conditions in which you are working out. There are also many factors which dictate what we should drink. This depends to a large extent on the bodies most pressing needs at that time. These issues will be examined in greater depth next month.