Now that the weather is warmer I thought we should look at hydration for those whose fitness regime takes them outdoors. We are encouraged to drink about 2 litres per day. (8 cups) However, if you are exercising for just an hour in hotter conditions you may even need to double this. The rate at which one sweats varies from person to person and also depends upon how hot or humid the environment, what one wears (non wicking and dark colours increase the rate of sweat) and how intense the exercise. Neither can we rely on how thirsty we are – exercise may actually suppress thirst.
So, what is the best check for mild dehydration: weight loss, headaches, dark urine, skin test (if you pull up the skin on top of your hand and it doesn’t bounce back this is a sign of dehydration). If you suffer from any of these take another glass of water. Drinking little and often is the best way to keep hydrated.
Dehydration impairs both physical and mental performance. A 2% drop in body weight (just 1kg for a person weighing 50kg) has been shown to increase perceived effort. Actual performance may drop by 10 to 20%. Therefore, it is important to drink plenty.
Is there a danger of over hydration? There is a rare condition known as hyponatraemia. This is where the level of sodium in the blood is too low for the muscles (including the heart) to function effectively. This can lead to a coma and even death. However, it is difficult to ingest the large quantities of water required to make you hyponatraemic – it has been observed in events lasting eight hours or more where a slow runner might stop and guzzle loads of water at every drinks station.
We are far more likely to suffer from mild dehydration than over hydration – probably jumping on and off the scales before and after exercising in the heat would be a good way of becoming familiar with the amount of fluid loss you are experiencing. This weight loss must be replaced through thorough re hydration for good health.