Normally the daily output of water is about 2.3 liters & we should ingest fluid more than 2.1 liters per day (700ml, approx. 2.8glasses of water, as water in cooking; & more than 1.4 liters as the fluid by mouth as water & beverages, approx.> 5.6glasses of water). In prolonged & heavy exercise, the daily output of water increases more than 2.87 times, & therefore the fluid ingested should be more than 3.05 times the normal value (more than 5.7 liters of fluid by mouth as water & beverages, approx. > 22.8glasses of water).
During heavy exercise or in very hot weather, water loss in sweat may increase to 1-2 liters per hour or almost 50 times normal value per day. Similarly, in prolonged & heavy exercise, insensible water lost through lungs increases almost 2 times that of the normal value per day. All of this will rapidly deplete the body fluids unless adequately taken.
More than 70% of body weight (some say-60% of body weight is total body water) is because of the water it has. Loss of water upto 10% of the total body water, makes a person feel extremely tired & fatigued. A more than 20% loss may result in death. As much as 2.268 to 4.538kg weight loss has been recorded in athletes in a period of one hour during endurance athletic events under hot & humid conditions.
This mainly results from loss of sweat. Loss of enough sweat to decrease body weight only 3% can significantly diminish a person’s performance, & a 5 to 10% rapid decrease in weight can often lead to serious muscle cramps, nausea etc. Hence it is essential to replace fluids as it is lost.
Sweat contains large amount of sodium chloride, some urea & lactic acid. So, considerable amount of salt is lost through sweating. The sweat glands, however, become acclimatized when an athlete becomes acclimatized to the heat by progressive increase in athletic exposure over a period of 1 to 2 weeks rather than performing maximal athletic feats on the first day (acclimatization to heat: the various physiological readjustments & compensatory mechanisms in the body that reduces the bad effects of prolonged heat exposure).
This acclimatization of sweat glands results mainly due to increase secretion of aldosterone by the adrenal cortex. The aldosterone increases the reabsorption of sodium chloride from the sweat & urine, & loss of potassium through sweat & urine.
This leads to an important conclusion-(a) Salt supplementation should be there for all athletes performing exercise on hot & humid days, but once the athletes are acclimatized, only rarely do the salt supplementation need to be considered during the sporting events. Hence there may at many a times be over dose of this salt supplementation which is equally harmful. (b) Some of the supplemental fluids of athletics should also contain proportioned amounts of potassium along with sodium, usually in the form of fruits juices & coconut water etc.
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