You can survive for weeks without food, but you would be lucky to survive more than a few days without water. Your body is 60% water; if for any reason this percentage drops significantly, you are in danger of dehydration. Your body rids itself of heat by increasing blood circulation to your skin, so that you sweat. As sweat evaporates, you cool down; this is an important survival mechanism. However, in the process of cooling down, you are also losing fluids.

The amount of fluid you lose through sweat depends on how hard you exercise, your body surface area and the temperature and humidity of the environment. It is not unusual for an exercising athlete to lose 1 liter (1.75 pints) of fluid in 1 hour, and athletes playing sport in warm conditions have been known to lose up to 4 liters (7 pints) during a single sporting event. This rate of fluid loss will have an adverse effect on performance and is extremely dangerous because it causes dehydration. The effects of dehydration are fatigue, lower blood pressure, lowered performance, increased body temperature, reduced urine output, increased pulse rate and circulatory collapse.

The Signs of Dehydration

There are several stages in the development of dehydration, and each stage shows itself through distinct physical reactions. If you are dehydrating, your knowledge of the symptoms should give you an early alert:

Stage 1: You begin to lose concentration and performance drops.

Stage 2: Your muscles begin to cramp, particularly the large muscles of the thighs and buttocks.

Stage 3: You begin to show symptoms of heat distress and exhaustion, these include nausea, vomiting, dizziness and fainting.

By this stage, you should stop whatever exercise you are doing and, if necessary, withdraw from the event or training to tend to your fluid balance.

Up until and including Stage 3, your heat regulation mechanisms are still coping. Beyond this, you suffer heat stroke and your body is out of control. Heat stroke is a medical emergency and requires urgent hospitalization.