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Salt, Electrolytes and Carbohydrates

As well as remaining hydrated another concern about running in the heat is salt loss. What should we be doing about it? Do we need to take salt tablets and if so how many?

Sodium concentration in the body is very critical. It has to be maintained within a narrow band. Too much is not good for the heart. Too little is potentially fatal. In fact the level is far too critical to be left to the individual person to remember to “top up” with salt.

Salt is lost from the body in two ways, in the urine and through sweat. The amount of salt lost through urine is carefully controlled by the kidneys to maintain the correct concentration in the body. In a modern diet we take on board more salt than we need. The kidneys maintain the balance by releasing the excess from the body through the urine.

We also lose salt when we sweat.  The hotter the climate and the more exercise we do then the more we sweat and hence the more salt we lose. For many years it was believed that salt tablets were needed in hotter climates to make up for the salt lost through sweat. However more recent research has proved this to be unnecessary.

The salt concentration in sweat is in fact lower than the concentration in the body. So the loss of body fluid actually results in an increase in salt concentration in the body. This has been measured in athletes after prolonged exercise.  Also, as reported in the previous article in this series, the norm is for runners to lose 4% to 7% of body mass due to sweat during an endurance run. Hence the concentration of salt in the body will only fall when the runner has re-hydrated to normal level. Even this drop in salt concentration is far from critical. In fact the only danger is if the runner over hydrates, and takes in more fluid than what has been lost through sweat. This can lead to a condition of hyponatremia. The salt concentration becomes dangerously low.

Studies have further shown that the concentration of salt in sweat reduces for people doing regular exercise or frequently sweating due to living in a hot climate. The mechanism in the body takes about 5 days to adjust for a person moving from a cool climate such as the UK to a hot climate. Initially a person will feel ill and lethargic, but will recover to normal after a few days.

We are all familiar with the white marks on our running kit if we have sweat a lot. This is caused by salt in the sweat. If it is pronounced then this is an indication that the level of salt in the body is probably OK.

So the bottom line is that there is no need for any salt supplement when running in the heat. Just let the body adapt to the conditions.

This also means that drinks which contain electrolytes give very little benefit. In fact the concentration of electrolytes in energy drinks is so low that if taken in large quantities the concentration of salt in the body is diluted.

Carbohydrates are beneficial if the endurance event is long, at least 30km. However, some improvement in performance has been detected in runners after taking on carbohydrates before it is possible for the carbohydrates to have had any really benefit. It is thought that this because the brain has detected, through taste, that additional nourishment has been consumed and tells the body that it’s okay to work harder, more energy is on the way.
Muscle Cramp
Many of you may be familiar with getting muscle cramp after a long run in hot conditions or at the end on an interval training session on a hot day. Like me you have probably thought that this is due to salt or fluid loss. Yet no matter how much you drink (water or electrolytes) it doesn’t seem to have any effect. The cramp is associated with muscle fatigue which is more pronounced by either running long distances in hot conditions or by speed training in hot conditions. I used to suffer a lot from cramp after runs. I would get cramp regularly in bed at night. However, since I went through a regime of training long distances at slow pace the incidence of cramp has almost disappeared. As I said in the previous report I am now taking less fluid and energy gels than I used to take during a distance race or training run.

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