Muscle Cramps during Exercise - Is It Fatigue or Electrolyte Deficit?

BERGERON, M. F. Muscle cramps during exercise - is it fatigue or electrolyte deficit? Curr. Sports Med. Rep., Vol. 7, No. 4, pp. S50-S55, 2008. Skeletal muscle cramps during exercise are a common affliction, even in highly fit athletes. And as empirical evidence grows, it is becoming increasingly clear that there are two distinct and dissimilar general categories of exercise-associated muscle cramps. Skeletal muscle overload and fatigue can prompt muscle cramping locally in the overworked muscle fibers, and these cramps can be treated effectively with passive stretching and massage or by modifying the exercise intensity and load. In contrast, extensive sweating and a consequent significant whole-body exchangeable sodium deficit caused by insufficient dietary sodium intake to offset sweat sodium losses can lead to a contracted interstitial fluid compartment and more widespread skeletal muscle cramping, even when there is minimal or no muscle overload and fatigue. Signs of hyperexcitable neuromuscular junctions may appear first as fasciculations during breaks in activity, which eventually progress to more severe and debilitating muscle spasms. Notably, affected athletes often present with normal or somewhat elevated serum electrolyte levels, even if they are "salty sweaters," because of hypotonic sweat loss and a fall in intravascular volume. However, recovery and maintenance of water and sodium balance with oral or intravenous salt solutions is the proven effective strategy for resolving and averting exercise-associated muscle cramps that are prompted by extensive sweating and a sodium deficit.