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=Effects of dehydration=
While it's commonly believed that even small levels of dehydration impacts performance, the research indicates that real world performance is not impacted by dehydration up to 4% of body weight<ref name="Goulet2012"/><ref name="Goulet2011"/>. Greater levels of dehydration will impact performance<ref name="González-Alonso-1995"/>. While authorities have recommended aggressive drinking<ref name="Convertino-1996"/>, these guidelines are now recognized as erroneous<ref name="WallWatson2013"/>, though they are still promoted by the beverage industry<ref name="beverageWWW"/>.
=Glycogen Depletion, Dehydration and Body Weight =A common method of calculating dehydration is simply from body weight. While it's true that an athlete's weight loss during exercise will be predominantly from water, this is not the same as dehydration, nor does it necessarily imply this weight needs to be restored quickly though drinking. This is because a carbohydrate ([[Glycogen]]) is stored with water, in the ratio of about 1g [[Glycogen]] to 2.5g 3-4g water<ref name="OlssonSaltin1970"/><ref name="Nilsson-1973"/>. This means that 2000 calories of [[Glycogen]] depletion that are likely to occur in marathon distance runs would result in about 4lb/2Kg [[Weight Loss]] with no reduction in hydration (2000Kcal/4=500g [[Glycogen]] + 1250g 1500g to 2000g water = 1750g2000g to 2500g). To restore the weight lost in endurance exercise the Glycogen reserves must also be restored, something that may take days. Even moving from a high carbohydrate to high fat diet can see 6lb [[Weight Loss]] from [[Glycogen]] depletion.
=Sodium Intake and Rehydration=
Several studies have shown that drinks containing sodium provide better rehydration by reducing urine output.
==Sodium Loss Table==
The table below is based on the research showing that sweat sodium concentration increases with sweat rate. The table below is for a runner who is 174cm/70inches high and weighs 60Kg/132lbs, but you can create a customized chart at [[Sodium Loss]]. To check your sweat rate, simply weigh yourself before and after a run. Dropping 1 Kg or 2.2 pounds equates to 1 liter of sweating. (Obviously you need to adjust for any fluid intake and avoid urination.)
{| class="wikitable" style="margin-left: auto; margin-right: auto; border: none;"
!
!
=Sodium Intake=
Below are some sample sources of Sodium, with the concentrations defined.
{| class="wikitable" style="margin-left: auto; margin-right: auto; border: none;"
! Source
! Sodium - mmol per liter
=Symptoms of Dehydration=
These symptoms are for the general public<ref name="CLINC"/>, and there is evidence<ref name="SYMPT"/> that they may not apply to athletes suffering from dehydration.
{| class="wikitable" style="margin-left: auto; margin-right: auto; border: none;"
! symptom
! mild dehydration (3-5% body weight)
<ref name="Maughan-1995">RJ. Maughan, JB. Leiper, Sodium intake and post-exercise rehydration in man., Eur J Appl Physiol Occup Physiol, volume 71, issue 4, pages 311-9, 1995, PMID [http://www.ncbi.nlm.nih.gov/pubmed/8549573 8549573]</ref>
<ref name="Nose-1988">H. Nose, GW. Mack, XR. Shi, ER. Nadel, Role of osmolality and plasma volume during rehydration in humans., J Appl Physiol (1985), volume 65, issue 1, pages 325-31, Jul 1988, PMID [http://www.ncbi.nlm.nih.gov/pubmed/3403476 3403476]</ref>
<ref name="OlssonSaltin1970">Karl-Erik Olsson, Bengt Saltin, Variation in Total Body Water with Muscle Glycogen Changes in Man, Acta Physiologica Scandinavica, volume 80, issue 1, 1970, pages 11–18, ISSN [http://www.worldcat.org/issn/00016772 00016772], doi [http://dx.doi.org/10.1111/j.1748-1716.1970.tb04764.x 10.1111/j.1748-1716.1970.tb04764.x]</ref>
</references>
