Health & Exercise: Fluid loss & hydration

With a strong and physically fit athlete susceptible to losing up to three litres of water during an hour of intense exercise in the heat, it shouldn't come as a shock to learn that fluid replacement before, during and after physical activity - particularly when performed in a warmer climate - is vital to health, survival and the prevention of dehydration - a potentially life threatening condition that can develop when as little as 2% of the body's water has been lost. But did you know that the amount of fluid lost via perspiration alone can affect the human body on both a physical and psychological scale? Here are just a selection of factors that can contribute to exercise induced water loss via sweating:

• Exercise type and intensity - aerobic endurance based exercise such as cycling and running and anaerobic strength based exercise such as weight lifting and circuit training of a moderately hard intensity over a one hour period, can increase water loss via perspiration by 0.5 - 1 litre. Therefore, those participating in vigorous physical activity are at an increased risk of dehydration, should they fail to rehydrate their bodies via an adequate supply of fluid.

• Body size - dependant on the size of your body, the water lost via perspiration will vary. For example, the larger your body, the more fluid you will lose through perspiration as there is a larger surface area for sweat to evaporate - the more you sweat, the more water you will lose and need to replace.

• Gender - although women have a tendency to sweat less than men, this is not always the case - particularly if you suffer from hyperhidrosis, have a faster metabolism or struggle to naturally cool down during warmer temperatures. Always listen to your body and take additional precautions to cool down i.e. sponging with cold water, if your reduced sweat rate makes it difficult to control body heat during physical activity.

• Exercise duration - the longer you exercise, the more water you will lose via breathing and perspiration. In fact, up to 3% of body weight can be lost through exercise induced perspiration alone, and this has the potential to result in the participant requiring 5-6 times more fluid than normal in extreme conditions - the longer you exercise, the higher your need for fluid replacement. Always incorporate regular water breaks into your workout every 30 minutes when performing relatively strenuous exercise, and every 10 minutes when participating in an extremely athletic workout.

• Climate - the warmer the climate, the higher the risk of perspiration and water loss - the 0.5 - 1 litre water loss during one hour of moderate intensity exercise will increase in a hotter climate. Always ensure that adequate hydration levels are maintained during warmer months by increasing your daily fluid intake, particularly when exercising at any level.

Remember that water is not only essential for survival, but a crucial component in every exercise regime. Failing to ensure that your body remains hydrated - particularly before, during and after physical activity - can have a detrimental impact on life, health, the brain, muscles and blood - the three body components with the highest water content - and physical and psychological performance.