15 April, 2013 | Written by Recuperat-ion Recuperat-ion


 Close relationship between the loss of water and
sodium during physical exercise
During training or a competition at high temperatures, as will soon be
the case in our latitudes, the athlete’s body mainly suffers two types of
losses: water and sodium. And
the higher the temperature, the faster these losses take place.
The loss of water is the effect of breathing, but especially that of
sweating. The loss of sodium is the effect of sweating. Taken together, water
losses can be as high as 0.5-0.8 litres per hour of continued exercise and
those of sodium 200-300 mg per hour. Sodium loses are proportional to water
The hormonal changes brought about by exercise enable
the body to increase the retention of the water consumed during the activity
The human body contains between 35 and 45 litres of water. Perhaps you
think this reserve is abundant. Well it is not, it is extremely fragile for our
75,000 million cells, each of which retains various billionths of a millilitre of
water, necessary for it to survive… As a result, each millilitre of water lost by the body
must be quickly replaced to prevent any cascade in the alteration of cell
functions (that may lead to cell death).
The consumption of between 0.5 and 0.8 litres of liquid per hour of
activity under normal conditions of exercise is an imperative that today is
accepted without discussion. On the other hand, because of the hormonal changes
brought about by exercise, we know that the body better retains water consumed
during the activity, especially due to increased plasma volume (that is, the
liquid part of the blood).
Water doesn’t provides the sodium lost during intensive exercise, and could lead to hyponatraema
This is why it is counterproductive, and may even be dangerous, to exceed these levels during a very long period of activity (except in very special conditions).
Is it enough to consume pure water during exercise, in
any circumstances?
Regular consumption of pure water provides satisfactory replacement of
this liquid in our body and prevents the water reserves from diminishing while we
are performing exercise. But in this case, what about the losses of sodium?
Although our sweat glands have the amazing capacity to reabsorb part of the
sodium lost in sweat, this is not enough to compensate for the massive loss of
such a precious mineral.
Natraemia measures the sodium concentration in our plasma (remember,
plasma is the liquid part of the blood). Normal natraemia values range between
3.1 g and 3.3 g per litre of plasma. If we only compensate for the loss of water, the plasma volume remains
stable, but the concentration of sodium diminishes mechanically
(remember that sodium is lost at a rate of 0.2-0.3 g per hour of exercise).
This means that our body slowly reaches a state known as “hyponatraemia”. This
begins to occur when the sodium concentration drops below 3.1 g/litre of

The consequences of hyponatraemia
Although in principle, it has no important consequences, the state of hyponatraemia
may increase if, in spite of continuing the exercise over several hours of
activity, the sodium is not replaced by means of a drink (and other forms of
supply). Even more so when, as we have seen, there is the risk that the water
consumed during the exercise is better retained by the body, thus increasing
the dissolution of sodium.
The first real indications of
hyponatraemia are nausea, vomiting, fatigue, headache, confusion, coordination
disorders, etc., combined with breakdown of
the electrolytic balance (balance between minerals) and its effects on the
distribution of water between the different compartments of the body. Serious
consequences appear after a prolonged situation of intracranial hypertension
that favours the formation of a cerebral edema, convulsive crises (epileptic
seizures), consciousness disorders, etc., with the possibility of leading to
What measures can prevent hyponatraemia?
The preventative measures are simple and easy to put into practice.
1)      Avoid all irrational consumption of water that is not
related to losses (more than one litre of water per hour, unless conditions
justify it).
2)      Preferably consume electrolytes drinks enriched with sodium or,
if they are not available, solid foods capable of satisfying this need (rich in
sodium or salt*).
*remember that 1 g of salt (sodium chloride) contains 600 mg of chloride
and 400 mg of sodium
Solids or liquids to prevent hyponatraemia?
The solutions for combating hyponatraemia during very prolonged exercise
are classified as follows:
1) Solids – energy bars, biscuits, salty food (sausages, bread, cheese,
2) Semi-liquids – energy gels, etc.
3) Liquids – beverages, vegetable broths
4) Salt tablets
Not all these solutions have the same value. We can eliminate salt
tablets, very controversial, as they are considered to produce an “osmotic
shock” in the body. Osmotic shock is the result of the violent and sudden
confrontation between two mediums of highly different concentrations (the image
of water and fire), in this case the salt tablet (high concentration of sodium,
but very little water) and the internal medium (very low concentration of
sodium compared to the tablet, but very rich in water). Osmotic shock may
increase dehydration and favour diarrhoea.
As for solids, their contribution runs the risk of being random and, in
any case, very dependent on the condition of our digestive system after several
hours of exercise. Effectively, in very long lasting competitions, it is not
unusual to suffer from highly debilitating digestive disorders (nausea,
vomiting, exercise anorexia, etc.). These disorders complicate the consumption
of solid foods and so diminish their capacity to provide sodium.
Regarding semi-liquids, their acceptance by the body after several hours
of exercise is also challenged. This is why it would be rash to base the whole
food strategy (especially the supply of sodium) on this single type of food.
Therefore only liquids
remain, the food source most tolerated during strenuous exercise, and which
stand alone because they enable ensuring and better guaranteeing the
satisfaction of sodium necessities, regularly, hour by hour, throughout
the exercise.
What are the exact recommendations regarding
After two hours of continued exercise, a sports drink should provide
about 500 mg of sodium per hour. The ideal volume of the beverage after two
hours of exercise is 500 ml per hour, so as not to exceed losses due to

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