An electrolyte replacement drink, powder, effervescent tablet or gel aims to replace the missing electrolytes, nutrients, or minerals that are eliminated through perspiration and muscle metabolism during intense exercise.
This is essential to prevent exercise associated hyponatremia (low blood sodium) or other deficiencies.
There are many brands available on the market so no doubt there will be some confusion there!
So what to look for:
Bergeron M. 2007 'Exertional heat cramps: Recovery and return to play.' J Sport Rehabil ; 16:190-196.
Sawka M, Burke L, Eichner R, Maughan R, Montain S, Stachenfeld N. 2007 'Exercise and Fluid Replacement.' Position Stand. Med Sci Sports Exerc ; 39:377-390.
Schwellnus MP. 2009'Cause of exercise associated muscle cramps (EAMC) — altered neuromuscular control, dehydration or electrolyte depletion?' B J Sports Med ; 43:401-408.
Walker, AF, Marakis, G, Christie, S & Byng, M 2003, ‘Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study’, Magnesium Research, vol. 16, no. 3, pp. 183-91.