A Tale of Five Electrolytes

by Jeff Rocco MD

If you are reading this you are probably an endurance athlete looking to improve your training and performance. You may recall from high school science class that electrolytes are dissolved mineral salts contained in our body fluid–both inside and outside our cells. It is not our focus here to review in depth all of the cellular biology related to electrolyte homeostasis. The enlightened athlete needs to know where electrolytes go when they are lost, what the symptoms are when electrolytes are deficient, and how to maintain electrolyte levels to achieve optimum performance. The five key electrolytes for endurance athletes are Sodium (Na+), Potassium (K+), Chloride (Cl-), Calcium (Ca++), and Magnesium (Mg++)

In our bodies, hydration is linked intimately with electrolyte concentrations. For athletes, electrolyte losses occur primarily through sweating. Early experience with endurance athletes recognized dehydration as a significant problem. Fluid losses as little as 1-2% of body weight can cause a drop in performance, while losses exceeding 4% of body weight can cause critical failure. Realizing this, athletes drank. Things got worse for those athletes when they drank primarily or exclusively water. Consuming water without electrolytes replaces fluid losses, but dilutes electrolytes. In Ironman medical tents, electrolyte deficiencies are now found more commonly than dehydration. Hydration before and during longer events should contain electrolytes.

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