M F Bergeron

Electrolytes are negatively (anions) or positively (cations) charged substances that, when in solution, conduct an electric current. Major physiological electrolytes include Na⁺, K⁺, Cl⁻ and HCO₃⁻, while other electrolytes such as Ca²⁺, Mg²⁺ and trace elements are also found in the body in significant amounts. Na⁺, K⁺, Cl⁻ and HCO₃⁻ are primarily responsible for normal water distribution and homeostasis throughout the body via their effect on osmotic pressure. These major electrolytes also play an essential role in regulating heart and muscle function, maintaining pH and a number of other important biochemical reactions.

An athlete's demand for electrolytes increases with exercise and heat stress, as extensive sweating can mean both large water and electrolyte losses in addition to related changes in extra- and intracellular water distribution. Dehydration and an increase in plasma osmolality, which is primarily driven by Na⁺, will also stimulate osmoreceptors prompting an athlete to drink to maintain further or defend plasma volume.1 The primary electrolytes in sweat are Na⁺ (20–70 mmol/l) and Cl⁻, with comparatively much lower levels of K⁺ (∼5 mmol/l) and even less Ca²⁺ (∼1 mmol/l) and Mg²⁺ (∼0.8 mmol/l).2 As the sweating rate increases, the concentration of Na⁺ in sweat increases correspondingly, even with the lower sweat Na⁺ concentrations observed after heat acclimation.3 With Na⁺ being the major cation of …