/ by David "Jake" Jacobs, MA, ATC
Athletic trainers know exercise-associated muscle cramps (EAMC) are one of the most common problems athletes experience when their sports seasons begin. For an athlete who’s never had EAMC, it can be scary and painful.
So what causes EAMC? There are a couple theories.
One theory is dehydration and electrolyte loss. The loss of potassium is thought to be one trigger, but only a low concentration of potassium is lost in sweat. The amount of potassium lost in even a large volume of sweat represents a small amount of potassium contained in the body. Meanwhile, a single two-hour training session can result in losing approximately 20 percent of the body’s sodium through sweat.
EAMC are sometimes called “heat cramps” because cramps occur when an athlete is exercising in hot and humid weather, but muscle cramps can also occur in athletes training in cold weather.
Some studies report little change in muscle tissue whether the body is hydrated or dehydrated. Another study reported that electrolyte concentrations are often within normal limits or do not differ in athletes with or without EAMC. Dehydration also does not explain why these cramps can be relieved by stretching when fluids are not consumed. In 2007, the American College of Sports Medicine stated that no strong evidence supports dehydration as the cause of EAMC.
There is also the neuromuscular control theory, which includes but is not limited by these factors: poor conditioning, fatigue and muscle injury. These studies were done on subjects who were dehydrated three to five percent with four to 10 grams of sodium loss, and muscle cramping did not occur. These studies leave more questions than answers about the cause of exercise-associated muscle cramps, especially why some subjects who perform the same exercise under the same conditions cramp while others do not.
No matter the cause of EAMC, there are a few ways these muscle problems can be treated.
Rehydration beverages or beverage additives can be beneficial, and some athletic trainers will suggest pickle juice, mustard, etc., to help relieve EAMC.
Researchers have hypothesized that because ingestion of a substance can relieve the cramp there must be a “mouth to brain to muscle” mechanism. This is the activation of Transient Receptor Potential (TRP), which are ion channels in the sensory nerves in the back of the mouth and the upper intestinal tract. This could reduce the activity of the motor nerves that activate the cramp. These cell groups extend throughout the brain and spinal cord; the activation of these nerves in the spinal cord may prevent cramps by reducing the persistent inward electrical currents (PIC) and restoring normal muscle activity.
Studies have shown that TRP activation may be beneficial to athletes and may help with neuromuscular problems. Studies have shown improvement in work capacity in cyclists with stimulation of the nerves in the back of the mouth.
Because there is no clear cause of exercise-associated muscle cramps, it seems to be a number of factors, especially dehydration, poor conditioning, neuromuscular problems, nutrition and electrolyte imbalance, along with the environment. Dehydration and electrolyte imbalances do play a role in EAMC in some athletes.
The best treatment is prevention if possible. Competitive athletes may benefit from having a hydration and nutrition plan based on replacing sweat losses during activity.
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