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==Sodium Loss and Sweat Rate==

The concentration of sodium in sweat depends on the sweat rate. This is believed to be because the sweat is released with a high sodium concentration, then the sodium is reabsorbed before it reaches the surface. The faster the sweating, the less chance for reabsorption.

We can convert from per-area sweat rates to whole body sweat rates by using a [http://www.halls.md/body-surface-area/bsa.htm Body Surface Area Calculator]. For example, a 135 pound, 70 inch high person has a skin surface area of 1.74 m², which is 17,400 cm². Therefore 1 mg/cm²/min is 17,400 mg/min, or 17.4 g/min or 1,044 g/hour, or 1 liter/hour.

==Sodium Loss and Fitness==

While some sources suggest that increased fitness reduces the sodium concentration in sweat research<ref name="training"/> shows this is not the case. For both trained and untrained individuals sodium concentration depends mainly on sweat rate. In fact, for a given relative intensity (% of [[VO2max|V̇O₂max]]) trained individuals will be performing a greater absolute work rate and therefore have a greater sweat rate and sodium concentration.

==Sodium Loss and Heat Acclimation==

A study<ref name="sweatheat"/> shows that the sodium concentration of sweat is reduced by heat acclimation training. The study used three bouts of 30 min. of exercise in environmental chamber with 10 min. of rest between each bout.

==Sodium Loss and Skin Temperature==

A study<ref name="skintemp"/> of sweating great sodium concentration for different temperatures has shown that sodium reabsorption is greater at high temperatures. Unfortunately the units used in this study are not comparable with other studies. The mechanism behind this is unclear, but the implication is that the sodium concentration of sweat in cooler weather may be higher than expected from the above studies.

=Sodium Retention=

<ref name="sweatheat">Sodium ion concentration vs. sweat rate relationship in humans http://jap.physiology.org/content/103/3/990.full</ref>

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