Potassium

While sodium is our principle extracellular cation (positively charged ion), potassium is our principal intracellular cation.
The normal functioning of the human body depends on an intricate balance of potassium and sodium concentrations. Potassium plays a critical role in nerve impulse transmission, maintaining cellular fluid volume and pH, muscle contraction, heart function and tissue growth and repair. Additionally, potassium helps our body hold onto calcium, while excessive sodium leads to both potassium and calcium loss (Rhoades and Pflanzer, 1996; Schauss, 1998).
Potassium is not as readily lost in sweat, partially because the composition of sweat is more similar to extracellular fluids, and potassium is primarily found intracellularly.
However, prolonged sweating in hot environments does lead to potassium loss through sweat, which may have significant consequences. The Committee on Military Nutrition Research, Food and Nutrition Board published a book called Fluid Replacement and Heat Stress. The chapter entitled “Potassium Deficiency as the Result of Training in Hot Weather” came to the conclusion that potassium loss in extreme training conditions may adversely effect blood flow, muscle function and energy storage, impairing both endurance and performance.

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Sodium and chloride

Usually a package deal, sodium and chloride are the major extracellular electrolytes in the human body, sodium providing the positive charge and chloride the negative charge. In addition to providing balance to one another, these ions are essential for maintaining blood volume and pH (Schauss, 1998). 

Sodium and chloride also happen to be the main electrolytes lost in sweat, especially during prolonged exertion in warm and hot environments. Though the average American consumes substantially more than enough sodium chloride, there are some individuals and situations in which these electrolytes should be supplemented. 

Those who experience higher than average sweating, either through recreational activities such as long-distance running, professional athletics, or mining, construction work, and the armed forces, need to replace both their fluids and their electrolytes (especially sodium and chloride) to maintain a healthy balance.

Drinking water alone can sometimes be counter-productive, as it will decrease the osmolality (concentration of ions) of the extracellular fluid, signaling the kidney to let go of even more fluid to find a balance. This “diluted blood” also tends to shut off the thirst mechanism. 

Because strenuous exercise actually requires fluid replacement to be slightly above fluid loss, thirst is a key way to assure that individuals will replace an adequate amount of fluid. 

Eating solid food is an effective way of replacing sodium and chloride, however there are many instances when this would be impossible or impractical. 

Therefore, adding sodium and chloride to the water of individuals who regularly sweat will not only replace the loss of these essential electrolytes, but will also help maintain proper blood osmolality, assuring thirst and kidney mechanisms to maintain adequate blood volume and hydration (Maughan and Shirreffs, 1997).

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