Cramping

Etiology

There are many theories as to the cause of EAMC, but none has been universally accepted. Some of the more common theories include electrolyte depletion, dehydration, and muscle fatigue. Because electrolytes, such as sodium, potassium, and magnesium, play vital roles in the physiology of muscle contraction, depletion of any of these elements through increased sweating or urination could inhibit proper contraction of the muscle. Dehydration could also play an important role in skeletal muscle cramping, because water has many important functions in muscle physiology and is an important method of thermoregulation in the body. A third hypothesis for the etiology of EAMC is muscle fatigue, which leads to altered neuromuscular control. The increased excitation of muscle spindles and the reduced inhibitory response of Golgi tendon organ activity could lead to abnormal neuromuscular excitability, which could cause the muscle to cramp. Muscle fatigue could also be caused simply by exercising at a level of higher intensity or duration than is standard for the athlete. There is literature to support all three of these hypotheses.

From a historical perspective, stokers on ships mixed seawater with drinking water to fend off cramps. Heat cramping and exhaustion were reduced when a saline drink was given to industrial stokers and coal miners in England. It has also been shown that the sweat sodium levels of athletes who cramp are significantly higher than in those who do not cramp. The exact mechanism for cramping from sodium loss is not clear. What is known is that sodium loss reduces extracellular fluid space and may alter ion channels to make neuromuscular [Page 330]junctions or muscle units hyperexcitable, causing involuntary and sustained contractions, or EAMC.

It is also important to recognize that skeletal muscle cramps can be associated with numerous congenital and acquired conditions, including hereditary disorders of carbohydrate and lipid metabolism, neuromuscular and endocrine diseases, medicines, and toxins. There are several risk factors that may be associated with the development of EAMC. However, the most important intrinsic risk factors for EAMC are a previous history of EAMC, current hydration status and electrolytic balance, and performing exercise at a higher intensity or for a longer duration than normal training. Participating in hot and humid environmental conditions is the most important extrinsic risk factor.

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