What Causes Painful Muscle Cramps During Exercise?

istock_000018120829xsmallYou’ve just finished a tough workout at the gym, and you feel a sharp pain in your calf. Ouch! Muscle cramps are intensely painful, and they’re a relatively common problem among people who exercise. Almost 40% of marathon runners get them, and more than half of all cyclists have one at some point. Despite how frequently athletes experience a cramping muscle, there still isn’t a lot of consensus as to why they occur, but there are some things you can do to reduce your risk of being sidelined by a painful one at the gym.

What Causes Them?

One factor that may contribute to muscle cramps in some people is dehydration and electrolyte imbalance related to sweating. Loss of electrolytes and water is one theory behind why muscle cramps happen. A variety of minerals known as electrolytes regulate muscle function including calcium, sodium, potassium, and magnesium. When you work out and sweat, you lose primarily water, but during longer workouts, you also lose sodium and smaller amounts of calcium, potassium, magnesium, chloride, and phosphate. This can cause an imbalance that causes muscles to be more prone to cramping.

If electrolyte imbalances and dehydration are the main cause of muscle cramps, preventing them should be as simple as staying well hydrated with electrolyte-rich sports drinks and adding more calcium and magnesium-rich foods to your diet. Although this sounds plausible, muscle cramps aren’t strongly correlated with the amount of sweat lost or degree of dehydration. Well-hydrated athletes still get them when they drink sports drinks and aren’t sweating a great deal. Plus, research has failed to find a difference in electrolyte levels between athletes that cramp and those that don’t.

That’s why another theory for muscle cramps is gaining favor. It’s called the altered neuromuscular control hypothesis. It basically means that neural control of the muscle is out of balance, and nerves that signal the muscle to contract are over-stimulating them without giving them a chance to relax. This imbalance may be triggered by overuse and muscle fatigue. If this is the case, muscle cramps are a product of tired muscles. This theory is supported by the fact that stretching the muscle helps to relieve muscle cramping by sending nerve signals that block contraction of the muscle.

It’s possible that both factors play a role in muscle cramping. When you experience a muscle cramp in warm weather, it could be a combination of a mild electrolyte imbalance and muscle fatigue that causes that familiar “sharp as a knife” pain that rips through a muscle and sends you limping to the sidelines.

How to Deal with Muscle Cramps

If you experience a painful muscle cramp, stop what you’re doing, and gently stretch the cramped muscle and hold the stretch until the pain stops. What about prevention? There’s no sure-fire way to ensure you’ll never have another one, but staying well-hydrated and replacing electrolytes lost through sweat may help. Sip water before, during and after a run, and if you’ll be exercising for longer than an hour, drink a sports drink instead.

If the neuromuscular control theory holds true, improving your fitness level without overtraining can make muscles more fatigue resistant and reduce their tendency to cramp. Doing an adequate warm-up before a workout and stretching afterward may also help. If you take medications, ask your doctor if they may be contributing. Some blood pressure medications and diuretics lower potassium and calcium levels and can trigger muscle cramps.

The Bottom Line?

Muscle cramps are painful and not something you want to experience often. There’s no sure way to prevent them, but good hydration with an electrolyte-containing sports drink and warming up before exercise followed by stretching afterward may help. Take these measures every time you exercise to reduce the risk of painful muscle cramps.



Br. J. Sport Med. 2009. Jun; 43(6): 401-8.
Sports Med. 37 (4-5): 368-370, 2007.
The New York Times. “A Long-Running Mystery: The Common Cramp”


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