What causes leg cramps and how can I prevent them?

Stan Megraw
23 January 2012

Image © RyanKing999, iStockphoto.com

This article was reviewed and updated by the CurioCity team in November 2017.

Leg cramps... they can happen anywhere, anytime and often when you least expect it.

You may be sitting at your desk, chilling out in front of the TV, or even sleeping. Then, all of a sudden, you feel a muscle start to tighten up. The more it contracts, the worse the pain gets. Finally, when it seems you can't take it any longer, the muscle relaxes. You’re  left with a lingering soreness to remind you of the experience.

What’s going on?

To understand, you need to know a little about how muscles work.

Did you know? The term "muscle" comes from the Latin word for mouse - "mus". This is because the shape and movement of some muscles (like biceps, for example) were thought to resemble mice.

How Muscles Work

People most often get cramps in the calf, thigh or the arch of the foot. These regions are all controlled by skeletal muscles (muscles attached to bones). What's interesting about skeletal muscles is that they are voluntary muscles. This means that you can make them move just by thinking about them.

Did you know? Involuntary muscles, like your smooth muscle in your gut or your cardiac muscle in your heart, work without you thinking about them. After all, it would be pretty difficult to remember to tell  your heart to keep pumping all day long!

This interaction between your brain and your muscles is called motor control. Let's look at this in a little more detail.

Within each muscle are many hundreds or thousands of muscle fibres. Each muscle fibre is connected to neurons (nerve cells) that originate in the spinal cord (central nervous system).

Did you know? Humans have about 100 billion neurons. A grasshopper has around 16,000.

The neurons receive chemical messages from the brain's motor cortex. An electrical "pulse" is then created, and molecules called neurotransmitters are sent from the neurons into the muscle. These molecules cause the muscle fibres to release calcium ions and, through a series of complex biochemical reactions, the muscle contracts. When the calcium is reabsorbed back into the muscle fibre, the muscle relaxes again.

Now let's turn to why we get muscle cramps.

Muscle Cramps

Unlike a normal contraction of your muscles, a cramp is an involuntary (and painful) shortening of your muscle. What medical researchers have found is that muscle cramps are caused by overactive motor neurons. In other words, neurotransmitters are sent into the muscle much faster than the rate at which the calcium ions can be re-absorbed. As long as the calcium is present, the muscle cannot relax.

How muscles contract: An action potential arrives at neuromuscular junction. ACh is released, binds to receptors, and opens sodium ion channels, leading to an action potential in sarcolemma. Action potential travels along the T-tubules.Thick and thin filament interaction leads to muscle contraction. Muscle shortens and produces tension.
Source: Image © OpenStax, Wikimedia Commons

What causes this "hyperactivity"? No one knows for sure. But it seems that it all starts in the motor cortex of your brain. Also, you may be more susceptible to cramps if the muscle is already in a shortened state. For example, if you're sleeping and the bed sheets force your toes away from your shin, a cramp could develop in your calf.

So what to do?

Cramp management

Fortunately, leg cramps are temporary. The easiest way to help relieve the pain is by stretching the muscle. Here are some suggestions for when you get a cramp in your right leg. Reverse the instructions if you get a cramp in your left leg.

* Front of the thigh — While sitting, put your left ankle under your right ankle. Force down on your right ankle and push upward with your left ankle.

* Back of the thigh — Put your right ankle under your left ankle. Push up with your right ankle and down with your left ankle.

* Foot or calf — While sitting, stretch your right leg out. Use a towel as a sling and pull your right toes towards your body.

As for preventing cramps, there are no dependable remedies. Regular stretching exercises (like the ones above) could help. Also, if you get cramps at night you could try keeping the sheets at the foot of your bed loose.

Did You Know? There's an urban myth that says a bar of soap between the sheets at night will not only stop leg cramps, but cure them from coming back again.

In closing...

Although painful, leg cramps are quite common and rarely a sign of a health problem. But if they happen frequently and are disrupting your life, or if you see signs that the muscle is shrinking, then you should consult your family doctor for medical advice.

Learn More!

Muscle Cramps (2017)

What causes cramps? (2015)
Life Noggin

Muscle Cells (2015)
Crash Course

Muscle Basics: What Athletes need to know about the Muscular System (2015)

Stan Megraw

Stan is a writer/researcher, a PhD graduate of McGill University and was a member of the CurioCity team for several years. As a kid he dreamed of playing hockey in the NHL then becoming an astronaut with NASA. Instead, he ended up as an environmental research scientist. In his spare time Stan enjoys working on DIY projects, cooking and exploring his Irish roots.

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