Sodium is in extracellular fluids and tissues in humans. These fluids, such as blood plasma and extracellular fluids carry out transport functions for nutrients. Sodium is also in seawater as sodium chloride and completely unrefined, the natural minerals still remain.
Sodium is necessary for regulation of blood and body fluids, heart activity, and certain metabolic functions such as; regulation of blood volume and blood pressure, aids in the transmission of nerve impulses and used to help regulate the acid/base balance in the body.
Like fluid requirements, daily sodium needs can also vary greatly among athletes. Some athletes have a greater sodium need because they lose more sodium in sweat. The sodium needs amount that is recommended during exercise is dependent on the amount of sweat produced.
During endurance events such as road cycling, adventure racing and triathlons, inadequate repletion of sodium can lead to a dangerous condition known as hyponatremia. However athletes sweat is saltier in the earlier stages of training and heat adaptation than after an athlete is fit and fully adapted to exercise in the heat.
Hyponatremia, a low concentration of sodium in the blood, is more common in ultra-endurance athletes. Ironman Triathlon athletes routinely finish with lower blood sodium concentrations and ultra distance running events that take place in hot, humid conditions, and have athletes competing at high intensity are prone for hyponatremia to develop as well.
In hypernatremia, sodium in the blood is too high. The body contains too little water relative to the amount of sodium. The sodium level in the blood becomes abnormally high when water loss exceeds sodium loss, as occurs with dehydration. In most people, hypernatremia results from dehydration.
Hypernatremia occurs when athletes drink too little water and in those who have diarrhea, vomiting, fever, excessive sweating (particularly during hot weather), or abnormal kidney function.
Achieveing hydration and sodium balance:
Sweat evaporation provides the primary cooling mechanism for the body, and for this reason athletes are encouraged to drink fluids to ensure continued fluid availability for evaporation and circulatory flow to the tissues.
Endurnace runners, cyclists, triathletes and adventure racers could be in danger of heat illness if they race too quickly in hot/humid conditions and may collapse at the end of their event. This is due to return circulation to the heart upon stopping immediately.
The athletes that are moving at a much slower pace have lower heat accumulation and drinking is much easier to manage. They are often urged to drink "as much as tolerable," ostensibly to prevent dehydration from their hours out on the race course. Excessive drinking among these participants can lead to hyponatremia severe enough to cause fatalities. A more reasonable approach is to urge these participants not to drink as much as possible but to drink to the dictates of thirst and no more than 400-800 mL (20fl oz.)/hour.
Recently, there have been more frequent cases of hyponatremia among individuals who tend to over-ingest water during exercise lasting more than four hours, and inclusion of sodium chloride in the fluid replacement beverage is often suggested as a potential means of reducing risk of hyponatremia.
Replacement of fluid deficits after exercise and heat exposure is another area that has received considerable attention. Studies in this area suggest that if water is consumed, the volume ingested needs to exceed the fluid deficit by approximately 150% to compensate for the urinary losses that will occur with water ingestion leading to more rapid recovery of the fluid balance after exercise and thermal-induced dehydration.
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