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The Science Of Hydration

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==Sodium Loss Table==
Note: the table below is taken from published literature, but is not supported by the latest research on will be updated in the near future.
{| {{table}}
| align="center" style="background:#f0f0f0;"|'''Source'''
|Low Sweat of un-acclimated, unfit||80||1.8||0.9||2.2
|Sweat of un-acclimated, fit||60||1.4||0.7||1.7
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.
[[File:Sweat Rate Sodium Concentration.jpg|none|thumb|300px|Sweat rate and sodium concentration<ref name="sweatrate"/>.]]
==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|V̇O<sub>2</sub>max]]) trained individuals will be performing a greater absolute work rate and therefore have a greater sweat rate and sodium concentration.[[File:Sodium in sweat trained and untrained.jpg|none|thumb|300px|Sweat sodium concentration against sweating great, showing for three different work intensities and for trained and untrained individuals.]]=Sodium Source TableRetention=The human body is very good at maintaining its sodium balance under most conditions. The higher your sodium intake the higher the sodium losses in sweat and urine. There is evidence<ref name="1946"/> that under moderate sweat rates and a restricted sodium diet that the sodium concentration of sweat can drop to extremely low levels. However, I have found no evidence to suggest the sodium retention is effective but significant switching rates.=Sodium Intake=
Below are some sample sources of Sodium, with the concentrations defined.
{| {{table}}
See also [[Comparison of Gels]].
==ExamplesExample Sodium Losses==
Here are some hypothetical examples
* For the next run, Charlie changes his drink to add 1/4 teaspoon of extra salt to his Gatorade. He sweats and drinks the same amounts as the previous run. This time, his drink provides him with 4.7 grams of salt, or 3/4 teaspoon of salt.
=Sodium Loss Sweat Rates While Running= 
Sweat rates in male runners have been measured in the range from 0.75-2.23 in winter to 0.99-2.55 in the summer (Liters per hour)<ref name="acsm"/>. At the low end, we can imagine a fit runner finishing a 3-hour marathon in winter and sweating only 2.25 Liters. Assuming they are also heat acclimated, they would only lose 2 grams of sodium, which is 5 grams of salt, less than a teaspoon. On the other end of the scale, a fit, but unacclimatized runner completing a 5 hour marathon in summer would sweat out nearly 13 Liters, 18 grams of sodium, which is 45 grams of salt or more than 7 teaspoons.
<ref name="training">SpringerLink - European Journal of Applied Physiology, Volume 111, Number 11</ref>
<ref name="1946">Relationship between salt intake and sweat salt concentration under conditions of hard work in humid heat</ref>

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