Fluid Intake for Muscle and Fitness

Whenever you exercise you lose fluid, not only through sweating but also as water vapour in the air that you breathe out. Your body's fluid losses can be very high and, if the fluid is not replaced quickly, dehydration will follow. This will have an adverse effect on your physical performance and health. Exercise will be much harder and you will suffer fatigue sooner.

When your muscles start exercising they produce extra heat, in fact about 75% of the energy you put into exercise is converted into heat, and is then lost. This is why exercise makes you feel warmer. Extra heat has to be dissipated to keep your inner body temperature within safe limits approx. 37-38 degrees.

The amount of sweat that you produce and therefore, the amount of fluid that you lose depends on how hard you are exercising, how long you are exercising for, the temperature and humidity of your surroundings and individual body chemistry.. The harder and longer you exercise and the hotter and more humid the environment, the more fluid you will lose. During 1 hour's exercise an average person could expect to lose around 1 litre of fluid. During more strenuous exercise in warm or humid conditions you could be losing as much as 2 litres an hour.

You can estimate your sweat loss, and therefore how much fluid you should drink by weighing yourself before and after exercise. Every 1kg decrease in weight represents a loss of approx. 1 litre of fluid.

An excessive lose of fluid (dehydration) impairs performance and has an adverse effect on health. As blood volume decreases and body temperature rises, it places extra strain on the heart, lungs and circulatory system, which means the heart has to work harder to pump blood round your body. A loss of just 2% in your weight will affect your ability to exercise and your maximal aerobic capacity will fall by 10-20%. If you lose 4% you may experience nausea, vomiting and diarrhoea.

You cannot prevent your body from losing fluid, after all, this is a natural and desirable way to regulate body temperature. On the other hand you can prevent your body from being dehydrated by offsetting fluid losses as far as possible.

Your main priority is to ensure you are well hydrated before exercise so you should choose a drink that delivers fluid relatively fast. Water is fine, however you may benefit further from a sports drink because is also provides carbohydrates, consuming approx. 1g carbs/ kg body weight 1 hour before exercise can help to improve endurance. Therefore a sports drink would help ensure full hydration as well as providing pre-exercise carbohydrates. Alternatively, water together with solid food would do an equally good job.

Always start exercise well hydrated. Drink 500ml of fluid 2 hours before exercise. During exercise start drinking early and at regular intervals, aim for 125-250ml every 10-20 mins. Aim to replace at least 80% of sweat loss during exercise. After exercise replace by 150% and body weight deficit.