Key result
Salt and fluid replacement matching sweat losses prevents exertional heat cramps driven by sodium deficits.
Why the study?
Exertional heat cramps are distinct from muscle overload cramps and are caused by sweat-induced sodium deficit leading to motor neuron hyper-excitability, requiring targeted recovery strategies.
Exertional heat cramps are prompted by sweat-induced sodium deficit and can be prevented or treated by adequate salt and fluid replacement.
May support sodium-matched rehydration for exertional heat cramps; leaves open validation in prospective trials.
In contrast to muscle cramps that are brought on by muscle overload or fatigue, exertional heat cramps seem to be prompted by extensive sweating and a significant sweat-induced whole-body sodium deficit. As a result of a consequent contracted interstitial compartment, axon terminals of selected motor neurons can become hyper-excitable and spontaneously discharge. Barely detectable muscle fasciculations or "twitches" in the affected muscles can rapidly progress to debilitating muscle cramps in just 20 to 30 minutes. To aid recovery, salt (NaCl) and water lost from sweating should be sufficiently replaced so as to restore the extracellular volume and interstitial fluid spaces. Sweat sodium, chloride, and fluid losses incurred during training and competition need to be closely matched by daily salt and fluid intake, in order to prevent an excessive sodium deficit, maintain sufficient fluid balance, and avoid exertional heat cramps.
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Michael F. Bergeron (2007) conducted a review in Exertional heat cramps. Salt and fluid replacement was evaluated. Salt and fluid replacement matching sweat losses is recommended to prevent and recover from exertional heat cramps caused by significant sweat-induced whole-body sodium deficits.
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