The problems with the serum electrolyte depletion theory
First of all, there is a key conceptual problem here, and that is that when you sweat, you don’t actually reduce electrolyte concentration. That is, there are certainly electrolytes in the sweat, but the concentration of these electrolytes is so low, that sweating is likely to make you HYPERTONIC, not hypotonic. We looked at this in our posts on fluid – when you sweat, you lose more water than electrolytes, because the sweat is HYPOTONIC. Therefore, sweating cannot lead to a fall in electrolyte concentration.
What transpired was that Gatorade (and the rest of the ‘industry’, it must be said) developed the theory of “salty sweaters”, which is the term they gave to people who they said have abnormally high salt levels in their sweat. Small problem – no one actually knows what a salty sweater is. How much salt does there need to be in the sweat before you are placed in this group? No one knows. Recently, Professor Martin Schwellnus, widely published in this area, posed this question to scientists at the Gatorade Sports Science Institute at a conference on cramping – he received no answer.
The truth is, even the saltiest sweaters around still have hypotonic sweat, and so the more they sweat, the more they will cause their electrolyte levels to rise, not to decrease. This is a very obvious problem that is overlooked by the electrolyte replacement advocates.
from here;http://www.sportsscientists.com/2007/11/muscle-cramps-part-1-theories-and.html