Ouch! Muscle cramps hurt, and, unfortunately, they’re all too common. One minute you’re exercising, the next you’re hugging the ground with your hand on your calf, furiously massaging it to ease the tightness that gripped your leg. While the acute pain usually subsides after several minutes, some soreness can persist for several days after a muscle cramp. What causes exercise-induced muscle cramps and what can you do to avoid them?
What Causes Exercise-Induced Muscle Cramps?
No one knows why exercise-related muscle cramps happen, but there are some theories. One is that cramping is a protective mechanism triggered when a muscle becomes overly fatigued. As a muscle tires out, the activity of muscle spindles, a type of proprioceptor, increases while the firing of Golgi tendon organs, another type of proprioceptor located where muscles attach to tendons, decreases. Muscle spindles sense changes in muscle length while Golgi tendon organs monitor changes in muscle tension.
Muscle spindles and Golgi tendon organs provide information to the brain about a muscle’s length and tension, so adjustments can be made, when necessary, to prevent injury. When a muscle lengthens too much, muscle spindles increase their firing rate. This sends signals back to the alpha motor neuron, telling the muscle to contract and shorten. When muscle tension increases too much, Golgi tendon organs tell the alpha motor neuron NOT to fire and contract the muscle. So, muscle spindles and Golgi tendon organs work together to protect a muscle from being stretched or shortened too much. Proprioceptors also sense where your body is in space and help you stay balanced.
What does this have to do with muscle cramps? The theory: As fatigue sets, muscle spindles fire while Golgi tendon organs stop firing. The net effect is muscle contraction. In the case of a muscle cramp, the contraction is a violent one, leading to tightness and pain. Most muscle cramps usually involve the hamstring muscles in the thigh or muscles in the calf and last from a few seconds up to several minutes.
Electrolyte Imbalances
The second theory as to why muscles cramp up during exercise is the loss of electrolytes. You would expect exercise-induced muscle cramps to be more common in the summer or when exercising in a hot environment when you sweat more and, potentially, lose electrolytes like sodium, potassium, chloride, magnesium, and calcium. Electrolytes not only help maintain fluid balance, but they also influence nerve conduction and muscle contractility. This theory sounds good, but it does have some flaws. For one, when you sweat, you lose electrolytes, but the quantity of electrolytes lost is small relative to water. So, unless you’re running a marathon or doing HIIT training for an hour in a hot environment, you probably won’t experience a significant drop in electrolytes. Plus, if an electrolyte imbalance is the cause of exercise-induced cramps, why don’t people experience cramps in multiple muscles at once?
Another argument against the sweating/electrolyte imbalance theory is a study showing marathon runners develop muscle cramps even when running in 50 degrees Fahrenheit temperatures. In addition, studies among marathon and triathlon runners show those who experience muscle cramps have similar electrolyte and hydration levels as those who don’t.
Not to say electrolyte loss doesn’t contribute to cramping in some cases. A percentage of athletes are “salty sweaters,” meaning they lose more sodium through sweat than the average person. It’s possible that sodium imbalances explain some exercise-induced muscle cramps, but, based on current evidence, the fatigue theory likely explains the majority of exercise-related muscle cramps.
Risk Factors for Exercise-Induced Muscle Cramps
Now that you know muscle fatigue is the most likely the major contributor to muscle cramping, you’d expect muscle cramps to be more common during or after periods of long or intense exercise because of the fatigue factor. This seems to be the case. Muscle cramps are also more common in poorly trained people who haven’t developed a baseline level of physical fitness. Based on this, one way to reduce the risk of muscle cramps is to gradually advance your training rather than try to do too much too soon.
You’re also at higher risk for muscle cramps if you don’t warm up or do light stretching before beginning a workout. According to some researchers, calf and thigh muscle cramps are more common than in the past because people have fewer opportunities to squat in their daily lives, and squatting stretches the thigh and calf muscles.
Taking some medications also increases the risk of painful muscle cramp.s A number of medications can have this effect. Among the most common is estrogen replacement therapy, raloxifene (used for osteoporosis treatment), and non-steroidal anti-inflammatory medications.
Though there’s no strong evidence that muscle cramps are related to dehydration or an electrolyte imbalance, it’s still important to hydrate well and drink an electrolyte-rich drink if you’ll be exercising for more than an hour, especially in a hot environment. It may not prevent muscle cramps, but it will lower your risk for heat exhaustion or heat stroke.
What You Can Do to Prevent Leg Cramps
Warm-up first and then do light stretching before beginning a workout, but avoid ballistic movements. Stretch again once your workout is completed.
If you have leg cramps at night, stretch your calves and thighs before going to bed and again in the morning.
Don’t try to push yourself too hard too soon when you work out.
If you experience a leg cramp in your calf in the middle of the night, point your toes up towards your head while holding your legs straight to stretch the muscle. Gentle massage to the area to increase blood flow may also be helpful.
If you have frequent leg cramps, see your doctor. Leg cramps can sometimes be a sign of peripheral artery disease, peripheral nerve damage or other health problems.
The Bottom Line
Exercise-induced cramps and night cramps are painful but surprisingly common. The most likely explanation for why they happen is muscle fatigue and a mismatch in input to the muscle telling it to contract. There’s no sure way to prevent them but following these guidelines should help.
References:
SportsMD. Com. “Treating and Preventing Muscle Cramps During Exercise”
The Science of Sport. “Muscle Cramps: Parts 1 through 5)
Med Sci Sports Exerc. 2005;37(7):1081-1085.
Sports Health. 2010 Jul; 2(4): 279-283. doi: 10.1177/1941738109357299.
Br J Sports Med. 2011;45(8):650-656. doi:10.1136/bjsm.2010.078535.
American Family Practice. “Nocturnal Leg Cramps”
Sports Med. 1996 Jun;21(6):409-20.
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