Heat Cramps

First aid for heat cramps

1. Stop the activity and sit or lie down in a cool, shaded or air-conditioned place.
2. Stretch and gently massage the cramping muscle. For a calf cramp, straighten the knee and pull the toes toward you.
3. Drink fluids containing salt, such as a sports drink or oral rehydration solution. Water alone is less effective when salt losses are large. A simple option is a quarter to a half teaspoon of table salt in 1 quart (1 liter) of water.
4. Cool down: loosen clothing and use wet cloths or a fan.
5. Rest for a few hours before returning to hard activity, even after the cramp stops. Pushing on can lead to heat exhaustion.

Do not take salt tablets on their own. They can upset the stomach and raise sodium too quickly. Get help if cramps last more than an hour or other symptoms appear.

Symptoms

• Sudden, sharp, involuntary muscle spasms, often with visible twitching or knots under the skin
• Usually in the muscles doing the work: calves, thighs, hamstrings, abdomen, arms or hands
• Heavy sweating beforehand
• Spasms that come in waves lasting seconds to a few minutes
• Cramps that sometimes start hours after the work has finished, for example in the evening or night

Body temperature is normal, and the person is alert and thinking clearly. Any confusion means a more serious heat illness.

Causes and risk factors

The exact cause is debated. Two mechanisms likely combine:

• Salt and fluid loss: heavy sweating can lose more than 2 to 4 grams of sodium an hour. Replacing it with plain water dilutes blood sodium.
• Muscle fatigue: tired muscles have overactive nerve signals that trigger cramps, which is why cramps happen in the working muscles.

Risk factors include:

• Work or exercise in high heat and humidity
• "Salty sweaters" who see white salt streaks on clothes or skin
• Not being acclimatized: the first 1 to 2 weeks of hot weather or a new hot job
• Drinking large amounts of plain water without salt
• Long events such as marathons, triathlons, football two-a-days and shift work outdoors
• Diuretics and some other medicines, and alcohol the night before

Heat cramps vs other heat illnesses

Heat cramps can occur alongside or just before heat exhaustion, which can progress to life-threatening heat stroke.

When cramps may be something else

Ordinary exercise cramps and night leg cramps happen without heat. See a doctor if cramps happen at rest, without exertion, or come with weakness, numbness or swelling. Possible causes include low potassium, calcium or magnesium, thyroid problems, nerve compression, poor circulation and medicine side effects. Severe muscle pain with dark urine after hard exercise suggests rhabdomyolysis, which needs urgent treatment.

How they are diagnosed

Heat cramps are diagnosed from the situation and symptoms. No tests are needed for typical, short-lived cramps. If cramps are severe, prolonged or accompanied by other symptoms, a doctor may check blood electrolytes, kidney function and creatine kinase (a marker of muscle damage), and take a core temperature.

Prevention

• Acclimatize: build up the intensity and length of work or training in the heat gradually over 7 to 14 days.
• Drink before, during and after activity. For sessions over an hour, use drinks that contain sodium.
• Add salt to meals in hot weather if you sweat heavily, unless your doctor has told you to limit salt.
• Avoid overdrinking plain water, which can cause dangerously low sodium (hyponatremia).
• Weigh yourself before and after long sessions. Each pound lost is about 16 oz (about 500 ml) of fluid to replace.
• Schedule hard work for cooler times of day, take shaded rest breaks, and wear light, loose clothing.
• Improve conditioning, since fatigued muscles cramp more easily.

Frequently asked questions

What causes heat cramps?

Heat cramps are caused by heavy sweating during hard exertion in the heat, which drains salt and fluid from the body, combined with muscle fatigue. Drinking only plain water while losing a lot of salt makes them more likely.

How long do heat cramps last?

Individual spasms usually last seconds to a few minutes and settle within about an hour of rest, cooling and a salty drink. Cramps lasting more than an hour, or coming with dizziness, nausea or confusion, need medical attention.

What is the fastest way to stop heat cramps?

Stop exercising, move to a cool place, gently stretch and massage the cramping muscle, and drink a sports drink or lightly salted water. Most cramps ease within minutes. Rest for a few hours before resuming hard activity.

Are heat cramps a sign of heat exhaustion?

They can be an early warning. Heat cramps by themselves are mild, but they show your body is losing salt and fluid. If you also feel weak, dizzy, nauseous or have a headache, treat it as heat exhaustion: cool down, drink and seek help if not better within an hour.

Should I drink water or a sports drink for heat cramps?

A drink that contains salt works better than plain water because heat cramps involve sodium loss. Sports drinks, oral rehydration solutions or water with a little added salt are good choices.