Answer
Ordinarily, thirst is a reliable indicator of when we are deyhadrated and need to take fluids to rehydrate. This is so even for athletes . Research has shown that if one drinks water when one is thirsty and does not overload with water or other fluids the risk of suffering from dehydration are very low. However people like marathon runners who participate in extreme extreme sports for long periods run great risks of losing too much water and salts through perspiration and that this risk is greater in high temperatures and for women athletes. In all sports and more so in extreme sports athletes are encouraged by coaches and health authorities to rehydrate adequate to avoid the inimical effects of dehydration It is of course good advice to drink enough fluids to keep hydrated but there is evidence that may atheletes are over hydrating and exposing there bodis to the inimical effects of water intoxication or hyponatremia.
Work Step by Step
A marathon runner definitely needs to replace the fluid he loses by sweating. This is generally accepted. It is also generally accepted that pure water is good for rehydration and that sports drinks like Gatorade and Powerade are not necessary, except for extreme sweaters who also lose a lot of salt during exercise and races. However, the consequences of hyponatremia can be health and life threatening and in some cases are fatal. The dangers arise because extreme sweating disrupts cellular homeostasis in the following way; Normal extracellular fluid has a sodium concentration of about 135-145mML. . When water is lost by sweating, the water concentration in the blood decreases and its sodium (Na+) concentration rises , relatively. Naturally, water flows from ISF and from cytosol to dilute the increased sodium concentration in the ECF. If enough water is lost from the cytosol the cell shrinks and in time will be damaged, if rehydration is not done and isonicity restored. This is where rehydration comes in. At this point its is necessary to imbibe enough water to restore the balance of water and sodium concetrations between the cytosol and the extracellular compartments. Nevertheless, if more water is taken in than can be efficiently and easily lost by sweating or urination the phenomenon of water intoxication develops . In this case there isso much water in the ECF that the cytosol by comparison is hypotonic. As a result water passes by osmosis from ECF to cytosol and continues to dilute it . As the cytosol becomes more diluted the cell swells and if this continues the cell will burst and die. . The diluted cytosol has a lower sodium concentration compared to its physiological state and that iswhy this condition is also called hyponatremia. The symptoms of hyponatremia appear as the Na+ concentration of the ECF falls below 130 mM/L. At 120 mML the nervous system is seriously affected, and brain edema may develop. Some of the early symptoms of hyponatremia are bloating, nausea, vomiting, headache and confusion. Later, lethargy, respiratory distress, seizure, and confusion may develop; unfortunately coma and death sometimes occur if the condition is not professionally treated.
Many drinks like Powerade, Gatorade, All Sports,.Xendurance andVitalyte have been advertised as better than water for rehydration of athletes and treatment of hyponatremia. Many health authorities say hat these drinks are not much better than pure water, except for those athletes who excrete unusual amounts of sodium in their sweat. These sports drinks add varying amounts of potassium, sodium, magnesium and glucose to their aqueous preparations. But it is the general consensus that if adequate amounts of water are taken at the right times, these fancy sorts drinks are unnecessary:
a. Drink 400-800 mls of water per hour during exercise
b. Drink 200-300 mls of water/fluids every 10 minutes of race or exercise period
