Injury: Heat Cramps

Definition

Heat cramps are the mildest of the three forms of heat illness that can develop when the body is exposed to heat. They are defined as brief, involuntary painful muscle spasms in the legs or other parts of the body involved in work or exercise outdoors in hot weather.

Description

Heat cramps are painful but brief muscle cramps that occur during exercise or work in a hot environment. The muscles may twitch or jerk involuntarily. The cramping sensations may also be delayed and occur a few hours after the work or exercise.

Demographics

Heat cramps can affect people of all ages who are not used to hot weather, are not drinking enough fluid, sweat heavily, or have not been properly conditioned (improved their level of physical fitness). The cramps are most likely to affect the parts of the body involved in heavy work, such as the calves, thighs, shoulders, and upper arms.

Causes and Symptoms

Heat cramps result when a person sweats heavily during work or exercise in hot weather. Sweating is the body's way of regulating its internal temperature to get rid of heat. As sweat evaporates, it cools the body. In addition to losing water through sweating, however, the body also loses electrolytes, which are minerals that are necessary for the body to function properly. When the levels of sodium and other electrolytes in the blood fall too low, the painful sensations of heat cramps occur.

Conditioning (improved physical fitness) reduces the risk of heat cramps by increasing blood volume; causing people to sweat more quickly, which helps the body get rid of heat; and making the sweat more dilute, so that fewer electrolytes are lost from the body in the sweat.

Diagnosis

Diagnosis of heat cramps is usually based on their characteristics: the cramps are painful; they are involuntary; they come and go; they are brief; and they usually go away on their own. There are no blood tests or other diagnostic studies that can detect heat cramps.

Treatment

Heat cramps are not usually considered a serious health problem even though the muscle cramps may be temporarily painful. They can be treated at home by stopping exercise or work; resting for a few minutes; and drinking fluids mixed with salt to replace the fluids and electrolytes lost through perspiration. People can have either a sports drink like

Gatorade or clear fruit juice, or mix their own salt solution by adding one-fourth to one-half teaspoon of table salt to a quart of water. Salt tablets should not be taken because they upset the stomach.

To ease the cramping sensations, a person can practice gentle stretching or range-of-motion exercises to relax the muscles, or gently massage the affected parts of the body.

A doctor should be consulted when:

• The muscle cramps last longer than an hour.
• The affected person cannot drink the needed fluids because of nausea and vomiting.
• The person has more serious symptoms of heat-related illness, including dizziness, headache, shortness of breath, extreme tiredness, and a temperature higher than 104°F (40°C).

The doctor may administer intravenous fluids and check the affected person for signs of heat exhaustion or heat stroke.

Prognosis

Heat cramps usually go away by themselves once the person has cooled off and replaced fluids lost through sweating.

Prevention

Preventing heat cramps is largely a matter of taking time to adjust to hot weather or visiting a hot climate and dressing sensibly for local weather conditions:

• Most people in temperate climates need time to acclimate, or adjust to seasonal temperature changes. People should work up gradually to outdoor activities during the first few warm days of summer rather than overdoing it. The same is true of visiting a country with a tropical or hot climate. It is best to keep one's activity level moderate for a few days rather than crowding in too many activities. It can take people between seven and fourteen days to adjust to a hot climate. Marathon runners generally take two weeks to acclimate to training in the heat.
• Wear loose-fitting and light-colored clothing; choose fabrics that absorb sweat, such as cotton; wear a hat outdoors.
• Drink some fluids before exercising or working outside in hot weather. The American College of Sports Medicine recommends drinking about 20 ounces (0.6 liter) of water or a sports drink two to three hours prior to exercise, and 10 ounces (0.3 liter) of water or a sports drink ten to twenty minutes before exercise. It is important to not use thirst as a guide to fluid intake; a person can become dehydrated before feeling thirsty enough to want a drink.
• Use sunscreen generously, as sunburn lowers the body's ability to get rid of excess heat.
• Avoid caffeinated beverages and alcohol; they cause the body to lose additional fluid through the urine.
• Exercise during the early morning or late evening, when the temperature is cooler and the humidity lower.
• Consult a heat stress index like the one printed in the American Council on Exercise fact sheet listed below to help decide whether it is safe to exercise outdoors. There are times when the heat and humidity are so high that exercise should be avoided. Heat cramps are likely to occur when the heat stress index (the apparent temperature) is between 90–105°F (32–40.5°C).

The Future

Heat cramps are a common consequence of exercising or working outdoors without proper conditioning or precautions. They are not dangerous by themselves, however. They can be prevented by dressing appropriately for hot weather, drinking enough fluids, and consulting the local heat index before outdoor activity.

SEE ALSO Heat exhaustion; Heat stroke

WORDS TO KNOW

Acclimation: The process of adjusting to seasonal climate changes or to a new climate.

Conditioning: The process of becoming physically fit through a program of diet, exercise, and rest.

Electrolytes: Minerals that are essential for proper body functioning. They include potassium, sodium, calcium, and magnesium.

Heat illness: A general term for heat-related disorders, ranging from heat cramps (the mildest) to heat stroke (the most serious).

Involuntary: Not under the control of the will.

For more information

BOOKS

Dvorchak, George. The Pocket First-Aid Field Guide: Treatment and Prevention of Outdoor Emergencies. Accokeek, MD: Stoeger Publishing Company, 2007.

Isaac, Jeff. Outward Bound Wilderness First-Aid Handbook, revised and updated. Guilford, CT: Falcon Guides, 2008.

PERIODICALS

Comeau, Matthew. “A Hot Issue for Summer Exercisers.” American College of Sports Medicine Fitness Page, Summer 2001, p. 4. Available online in PDF format at http://www.acsm.org/AM/Template.cfm?Section=Search&section=20015&template=/CM/ContentDisplay.cfm&ContentFileID=22 (accessed May 2, 2008).

WEB SITES

American Council on Exercise (ACE). Fit Facts: Beat the Heat before It Beats You. Available in PDF format at http://www.acefitness.org/fitfacts/pdfs/fit-facts/itemid_35.pdf (accessed May 2, 2008). This is a one-page fact sheet on heat stress that contains a useful temperature/humidity index to evaluate the risk of heat cramps.

Nemours Foundation. Heat Illness. http://www.kidshealth.org/parent/fitness/problems/heat.html (updated March 2007; accessed May 2, 2008).