What Really Causes Muscle Cramps

What Really Causes Muscle Cramps

Exercise-associated muscle cramps (EAMC) is quite common and can be very painful. Unfortunately, the underlying cause is often unknown. There are a number of secondary causes we’re aware of, including structural disorders, neurological disorders, metabolic disorders, and some medications, but cramps from these causes are less common. 

If you were to ask the average person about the cause of a muscle cramp, you might hear something like, “You have low potassium. Just eat a banana.” Although electrolytes may play a role, potassium is not the smoking gun. Hopefully, after this discussion, you will have a better understanding of what a muscle cramp actually is and have a game plan for relief if you’re unlucky enough to have one.

Who Does EAMC Affect?

In the general population, it is estimated that nearly 50% of people over the age of 50 experience muscle cramping regularly, and that number increases with age. Muscle cramps affect both men and women equally. In kids, they occur in about 7% of adolescents with a peak occurrence between 16-18 years old. In ultra-distance athletes, like those competing in Iron Man competitions, and the general athletic population, muscle cramps account for 6-25% of the most common medical complaints during competition.

Physiology of EAMC

An EAMC has been described as a sudden, painful, involuntary contraction of skeletal muscle, occurring during exercise or after, and is often noted as a visible knot or bulge in the muscle belly, lasting for seconds to minutes.  The most common areas affected are the gastrocnemius (calf), the quadriceps (thigh), and the hamstring (back of thigh), but any skeletal muscle is susceptible.  Cramps in the rectus abdominis (abs), gluteus maximus (buttock), hands, or feet are also quite common.  

A muscle cramp causes electrophysiologic changes, including increased frequency of muscle action potentials (contractions), increased neuron activity (nervous system excitement), and the depletion of muscle ATP (energy source for muscle contraction). These reactions cause an accumulation of calcium, which prevents the muscle from relaxing – prolonging the cramp.  During a muscle cramp, there is repetitive firing of motor unit action potentials at a much higher rate than normal and there is a gradual increase of motor units recruited.  What this boils down to is the muscle cells firing more often and faster than they should, and a subsequent build-up of by-products from the contraction, blocking the release of the muscle.

Why do EAMC Occur?

Due to the physiological reactions explained above, the most likely answer is not low potassium. There have been countless studies which prove that people who have muscle cramps have normal serum levels of potassium. In fact, a number of recent studies with ultra-distance athletes show no association with decreased serum electrolyte concentrations of sodium or potassium and EAMC.  That being said, if a person does have electrolyte imbalances beyond the normal reference range, for example a potassium level greater than 5.1mEq/L or less than 3.4mEq/L, there is absolutely evidence of muscle contraction abnormalities. However, people who have those lab abnormalities often experience other significant symptoms well before muscle cramping.

In actuality, studies have shown the most likely cause of EAMC is muscle fatigue or overuse, based on the altered neuromuscular control theory.  Without delving too deeply into neurophysiology, this means a muscle is overloaded or fatigued, causing an imbalance of the excitatory drive from the muscle cells to the inhibitory drive of the Golgi Tendon Organ (GTO). The GTO acts like the brake pedal in your car to stop muscle contraction, which is what saves you from tearing tendons under heavy loads.  The result of an inhibited GTO is an increased excitatory drive to the motor neurons producing prolonged muscle contraction. 

Cramps also occur most often when the muscle is contracted in a shortened position, which also depresses the signal to the GTO. For instance, when you lie down in bed and your feet relax the calf muscle shortens, this disengages the GTO, and the over-excited nervous system locks the muscle up. The result? Feeling like there is a vice grip squeezing your leg!

Known Risk Factors That Can Be Adjusted to Reduce EAMC:

  • Exercise intensity and duration (most significant)
  • Having a previous or current injury
  • Participant fitness level
  • Pre-exercise fatigue
  • Acclimatization to exercise demand
  • Weak muscle under high demand causing stronger antagonistic muscles to over-compensate

Knowing these factors, you can take precautionary steps to reduce your risk of EAMC. Firstly, it’s imperative to develop a workout program that gradually increases in intensity to allow the muscles to acclimate to the demands you’re placing on them. When you reach that level of acclimation, you can then increase the demand to increase performance.

Make sure that your physical fitness level matches the activity, sports, or training regime you have decided to participate in. If you have muscle imbalance, focus on making weak things strong. For example, if you are a runner and have weak gluteus muscles, your hamstrings may pick up some of the slack. In doing so, the hamstring will then be overly fatigued and at risk for cramps. If you followed along with Kris Gethin during his Man of Iron trainer, you would have noticed he trained his core much more frequently. Not because he needed a better six pack, but because his core fatigued on his long runs, so his back and legs suffered. Equalizing the load with a strong core keeps him balanced.

Finally, if you’re injured, take the time to go see your doctor and build a proper recovery program. In this case, focus on gradually increasing the work load on the injured muscle group to allow it time to acclimate – just like you did with a healthy muscle.


While the cause and physiology of an exercise associated muscle cramp may be complex and confusing, the treatment is actually straightforward and simple: stretching!  Cramps generally occur in a muscle that is spanning two joints and acutely stretching the shortened muscle relieves the cramp.

Stretching before or after exercise doesn’t seem to help decrease EAMC, but stretching when the muscle is actively cramping relieves the pain by activating the GTO. This results in a reflex inhibition to the alpha motor neuron, causing relaxation of the muscle.  So, the next time you’re in bed and your calf muscle starts cramping, get up and stretch it ASAP. That is, if you’re able to get out of bed! There are a dozen crazy things that have actually been studied in correlation to EAMC relief, such as pickle juice consumption, hyperventilation, and salt tablets. The sad truth of the matter is, there is no evidence that suggests these techniques reduce or relieve cramping.

Remember, there are secondary causes of muscle cramps that are serious and should be evaluated by your physician. If you’re having cramps that are not relieved by stretching or are occurring during times when you are not exercising, that’s a warning sign you should not overlook. In general, muscle cramps are benign, and the best way to treat them is acute stretching of the affected muscle. To best defend against this annoying and painful problem, gradually increase your exercise intensity to the point your body is acclimatized to the demands of your sport or workout. Then, monitor fatigue level and draw a line in the sand when enough is enough.

A great example of this strategy is our own Kris Gethin, a bodybuilder now competing in Iron distance triathlon. Kris didn’t just start running, swimming, and biking those insane distances on day one of his training, he gradually pushed his limits every day and allowed his body to respond and improve. It’s important to have the right coach or trainer, who understands the limits of the human body and how to push them safely.  

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