Leg cramps happen when a muscle involuntarily contracts and won’t relax. The most common cause is a signaling problem in the nervous system, not a muscle problem itself. Your nerves send too many “contract” signals and not enough “relax” signals, locking the muscle in a painful spasm that can last from a few seconds to several minutes. Up to 60% of adults experience leg cramps, most often at night, and they become more frequent with age.
What Happens Inside the Muscle
Your muscles are constantly receiving two types of nerve signals: excitatory ones that tell the muscle to contract and inhibitory ones that tell it to ease off. These signals normally stay balanced. But when something disrupts that balance, the excitatory signals overwhelm the inhibitory ones, and the muscle fires uncontrollably. This is the neuromuscular theory of cramping, and it’s the explanation best supported by current research.
The disruption most often starts in the spinal cord, where nerve messages to and from the muscle are processed. Fatigue appears to be a key trigger. When a muscle is tired, the sensors that normally tell it to relax (located in the tendons) become less active, while the sensors that promote contraction (inside the muscle itself) ramp up. The result is a muscle that can’t fully let go. This is why stretching works as an immediate treatment: pulling on the tendon reactivates those “relax” signals and breaks the cramp.
Why Cramps Strike at Night
Nocturnal leg cramps, the kind that jolt you awake with a rock-hard calf, are the most common form. They tend to hit when you’ve been still for a while. During sleep, your foot often points downward, which shortens the calf muscle and may make it more vulnerable to spontaneous contraction. Roughly 20% of people who get nighttime cramps have them frequently enough to seek medical help.
Several factors raise your risk of nighttime cramps specifically:
- Age. Tendons naturally shorten as you get older, which changes how muscles operate at rest. Cramps become increasingly common after middle age.
- Pregnancy. About 40% of pregnant women experience leg cramps, likely from the added weight straining leg muscles. Lower calcium and magnesium levels during pregnancy may also play a role.
- Sex. Women are slightly more prone to leg cramps than men.
- Prolonged sitting or standing. Keeping muscles in one position for hours can set the stage for cramping later.
The Dehydration and Electrolyte Question
You’ve probably heard that leg cramps mean you’re dehydrated or low on potassium. The reality is more complicated. Sodium, potassium, magnesium, and calcium all play roles in nerve and muscle function, and significant imbalances in any of them can cause cramps, spasms, or weakness. If you’re losing a lot of fluid through sweat, illness, or not drinking enough, an electrolyte shift is plausible.
But for exercise-related cramps specifically, the evidence is surprisingly weak. Four prospective studies published in the British Journal of Sports Medicine measured electrolyte levels in athletes during acute cramping episodes and found no significant difference between crampers and non-crampers. The athletes who cramped were also no more dehydrated than those who didn’t. Another telling detail: if dehydration or electrolyte loss were the cause, cramps would affect muscles throughout the body, since those are systemic problems. Instead, exercise cramps almost always hit the specific muscles being worked hardest, pointing to fatigue as the real driver.
That said, staying hydrated and eating a balanced diet still matter for overall muscle function. Severe electrolyte imbalances from medical conditions, medications, or prolonged illness absolutely can cause cramping. The point is that the average leg cramp after a run or in the middle of the night probably isn’t caused by low potassium.
Medications That Cause Leg Cramps
Certain medications are known to trigger or worsen leg cramps. Cholesterol-lowering statins are among the most commonly reported culprits. Muscle pain, soreness, and cramping affect roughly 5% of people taking statins, though the number who report symptoms is often higher (some of this appears to be driven by expectation after reading about the side effect). Diuretics, which are prescribed for blood pressure and fluid retention, can also cause cramps by shifting your body’s electrolyte balance. Bronchodilators used for asthma and COPD have leg cramps listed as a known side effect as well.
If you started a new medication and noticed cramps appearing or getting worse, that timing is worth paying attention to. There are often alternative medications that don’t carry the same side effect.
When Leg Cramps Signal Something Else
Most leg cramps are harmless, if painful. But some leg pain that feels like cramping has a different and more serious cause.
Peripheral artery disease (PAD) causes cramping pain in the calves, thighs, or hips during walking or climbing stairs. The pain comes from narrowed arteries that can’t deliver enough blood to working leg muscles. The key difference from ordinary cramps: PAD pain reliably starts with activity and stops with rest, and it tends to follow the same pattern every time. In severe cases, it can also wake you from sleep or occur while lying down.
Deep vein thrombosis (DVT), a blood clot in a deep leg vein, can also feel like a cramp. It typically starts as pain or soreness in the calf, but it comes with other signs that a regular cramp doesn’t: persistent swelling in one leg, skin that looks red or purple, and a feeling of warmth in the affected area. DVT can occur without obvious symptoms, but if you have calf pain combined with swelling or skin color changes, that combination warrants urgent evaluation because clots can travel to the lungs.
Reducing Cramp Frequency
Stretching is the most studied non-drug approach for preventing leg cramps, though the evidence is modest. A Cochrane review found that combining daily calf and hamstring stretches for six weeks may reduce the severity of nighttime cramps in people over 55, though it didn’t clearly reduce how often cramps occurred. Calf stretching alone for 12 weeks showed little difference compared to a placebo routine. The benefits seem to come from keeping the calf and hamstring muscles lengthened, which may counteract the tendon shortening that happens with age.
For immediate relief during a cramp, stretching the affected muscle is the most effective response. For a calf cramp, pulling your toes toward your shin (either by hand or by standing and pressing your heel into the floor) forces the tendon to activate the inhibitory nerve signals that shut down the spasm. Walking around for a few minutes afterward helps the muscle fully relax.
Beyond stretching, practical steps that may help include staying physically active without overexerting specific muscle groups, keeping hydrated throughout the day, and adjusting your sleeping position so your feet aren’t pointed downward for long periods. Some people find that sleeping with a pillow propping the feet up or using a footboard to keep blankets off the toes reduces nighttime episodes. During pregnancy, getting adequate calcium (1,000 milligrams daily) and possibly supplementing with magnesium may help, though the research on magnesium remains mixed.