Heat Cramps

  • Medical Author:
    Benjamin Wedro, MD, FACEP, FAAEM

    Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.

  • Medical Editor: William C. Shiel Jr., MD, FACP, FACR
    William C. Shiel Jr., MD, FACP, FACR

    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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Heat cramps facts

  • Heat cramps are intermittent, involuntary spasms of larger muscles that occur in an individual who is physically active in hot weather.
  • Heat cramps, heat exhaustion, and heat stroke are collectively known as heat-related illness. Heat cramps are the least serious of the three, but still may be very painful and alarming.
  • Heat cramps usually affect the major muscles that are being stressed in a hot environment.
  • Individuals at risk for heat cramps include those who work, exercise, or are active in a hot environment.
  • Individuals with impaired temperature control mechanisms, such as infants, young children, and the elderly, are also at a greater risk of heat cramps.
  • Heat cramps are the earliest symptoms of a heat-related illness.
  • Symptoms of heat cramps include profuse sweating with involuntary spasms of the large muscles in the body.
  • Heat cramps also may be a symptom of heat exhaustion.
  • The diagnosis of heat cramps is usually made by reviewing the patient history and identifying the muscle groups that are involuntarily in spasm.
  • Treatment of heat cramps include rest, cooling the body, hydration, and stretching the muscles that are cramping.
  • Heat cramps can be prevented by avoiding exercise or work during the heat of the day, drinking plenty of fluids, and resting in cool or shaded areas when possible.

What are heat cramps?

Heat cramps are the intermittent, involuntary spasm of muscles that occur in an individual who is physically active (for example, working or exercising) in hot or humid weather. They are often associated with dehydration. Heat cramps usually affect the major muscles that are being stressed in the hot environment. Most often these are the thigh and leg (quadriceps, hamstrings, gastrocnemius), the core muscles (abdominal wall and back) and the arm muscles (biceps, triceps).

Heat cramps can also occur after the activity has been completed. For example, construction workers or roofers can develop cramps a few hours after their work shift is over.

Heat-Related Illness Symptoms

Symptoms of heat-related illness or hyperthermia vary according to the specific type of illness.

  • Heat stroke is the most severe form of hyperthermia.
  • Heat exhaustion is a less severe form of hyperthermia, with symptoms like weakness, nausea, vomiting, headache, muscle cramps, and profuse sweating.
  • Heat cramps symptoms include involuntary spasms of large muscle groups
  • Heat syncope symptoms include fainting or lightheadedness.
  • Heat rash symptoms are red bumps on the skin with a feeling of "itchy" or "prickly" feeling of the skin.

Who is at risk for heat cramps?

While heat cramps tend to affect those who are active in a hot environment, it should be noted that heat cramps are one of the symptoms associated with heat exhaustion as part of the spectrum of heat-related illness. Those individuals who have impaired temperature control mechanisms are at higher risk for developing heat-related illness. The body's most effective way of cooling itself is through sweat, and then the sweat evaporates into the environment. Those at most risk for heat cramps include:

  • Infants and young children because they depend upon others to avoid the heat, dress them appropriately (avoid swaddling an infant since it prevents air movement over the skin to promote sweat evaporation) and provide enough fluid to drink
  • The elderly because they may have underlying medical conditions, including heart and lung disease, and they can easily become dehydrated
  • People who live by themselves or who cannot afford air conditioning are at higher risk for heat related illness
  • A variety of medications can impair the body's sweat and heat regulation. Examples of drugs include medication prescribed for psychiatric conditions, including antipsychotic medications and tranquilizers. Over-the-counter cold medications and antihistamines also impair the body's temperature control mechanism.
  • Alcohol consumption

What causes heat cramps?

While it was thought that dehydration and electrolyte imbalance was the cause of muscle cramping, there are alternative theories as to why muscles cramp when the body is exposed to heat.

Since heat cramps begin after significant exercise in a hot environment where the affected individual begins sweating profusely, the theory was that muscles were depleted of water and sodium affecting their ability to contract and relax. Some new research suggests that as the muscles tire from excess activity and work, the ability for the muscle to regulate its own contraction is lost and this is called altered neuromuscular control. Regardless of the cause, the diagnosis and treatment for heat cramps remain the same.

What are the signs and symptoms of heat cramps?

Heat cramps are the earliest symptoms of the spectrum of heat-related illness.

  • There is usually significant sweating with involuntary spasm of the large muscles in the body.
  • The muscles that cramp are usually those that have been stressed.
  • Runners and football players tend to get leg muscle cramps, but people who lift objects as part of their job can get cramps in the muscles of the arms or the core trunk muscles like the abdominal muscles (rectus abdominus).
  • Heat cramps usually begin after significant activity has occurred, but they also can occur hours after the activity has been completed.

Do individuals with heat cramps tend only to have muscle cramps? If an individual has other signs or symptoms such as lightheadedness, weakness, nausea and vomiting, and headache he or she may be suffering from heat exhaustion. Affected individuals who have stopped sweating or who develop a fever and become confused may be developing heat stroke, which is a true medical emergency.

When should an individual seek medical care for heat cramps?

Heat cramps can usually be treated when and where they occur. The affected individual should stop all activity and find a cool place to rest. The muscle cramps and spasms can be overcome by gently stretching the cramped muscle(s). Individuals can often replace their fluid loss by drinking a combination of water, sports drinks, or other electrolyte replacement solutions.

If the cramps cannot be controlled, the affected individual should seek medical care. There is no specific condition that differentiates heat cramps from heat exhaustion. The symptoms of these conditions form a spectrum from mild to moderate heat-related illness and symptoms can overlap. Severe heat cramps may actually be heat exhaustion. This is especially true if the person has nausea or vomiting and cannot replace the fluid loss, if they have significant fatigue and weakness, or of they have profuse sweating that does not stop when placed in a cooler environment.

Heat stroke is a true medical emergency and can be deadly. The body's ability to cool itself no longer functions, and as the temperature spikes, sometimes greater than 106 F (41 C), confusion and coma can occur. Emergency medical services should be activated (call 911) immediately if an individual is thought to have heat stroke. While waiting for help to arrive, the person should be moved to a cool place, clothes should be removed to help air circulate over the body, and cool water should be sprayed or sponged onto the body to attempt to cool it.

Prevention is the key to avoiding heat cramps, or other heat-related illness. A person who has had heat cramps is more prone to developing them again. Some professions are at higher risk for heat cramps, for example, construction workers and roofers are potentially exposed not only to the heat from the sun but also from the radiant heat from the hot shingles and liners on the roof. It may be helpful to acclimate to the hot environment over a period of days to allow the body and its muscles to adapt to its water and electrolyte needs.

How are heat cramps diagnosed?

The diagnosis of heat cramps is usually made after taking the patient's history. It is important to know about the environment where the person affected by heat cramps was working, exercising, etc..

  • How hot was it?
  • How humid was it?
  • Was there adequate air circulation?
  • What activity was being performed and for how long?
  • When did the cramps start? What muscles were involved?
  • Was there associated sweating?
  • Had the affected individual been acclimated to the hot environment?
  • Was the person drinking enough water? One sign of heat cramps or a heat-related illness may be the color of urine. When the body becomes dehydrated, the kidneys conserve water and the result is concentrated, strong smelling, darker, yellow urine. If there is adequate water in the body the urine tends to be clear.

Often the physical examination will be relatively normal. The cramped muscles may be sore to touch and if there hasn't been adequate fluid replacement, the muscle may cramp again when taken through its normal range of motion. The physical exam may find signs of dehydration such as a dry mouth and tongue, lack of sweat in the armpits and groin, and decreased urine output. The vital signs can be a clue (for example, low blood pressure) and rapid heart rate (tachycardia). The affected person's blood pressure may be much lower upon standing compared to lying down (orthostatic hypotension).

What first aid treatments can help heat cramps?

Most first aid treatment for heat cramps can occur before seeking medical care:

  • stop the activity being performed,
  • get to a cooler place,
  • drink plenty of fluids, and
  • gently stretch the muscles that are cramping.

At the health care professional's office or a hospital, medical care focuses on symptom relief.

It makes it difficult to replace body fluids if the patient has nausea or vomiting, so intravenous fluids may be administered. Anti-nausea medications like promethazine (Phenergan), prochlorperazine (Compazine), droperidol (Inapsine), or ondansetron (Zofran) may be used to control those symptoms.

Painful muscles may be treated with over-the-counter anti-inflammatory medications, such as ibuprofen (Advil, Motrin, Nuprin, and others) or naproxen (Aleve, Anaprox, Naprosyn, Naprelan). Though it is a non-prescription medication, it is important to remember that there may side effects or interactions with prescription medications. When you are not certain which medication to consider, consult your health care professional or pharmacist as a helpful information resource.

What are the complications of heat cramps?

There are few long-term consequences of heat cramps, however, once a person experiences heat cramps, they may be at risk for future episodes.

How can heat cramps be prevented?

Prevention is the best treatment for heat cramps. If possible, try to avoid working or exercising in the heat of the day, but if it is required, acclimating to the hot weather is important. Drink plenty of fluids and if the activity lasts a prolonged period of time, consider using sports or balanced electrolyte drinks. This is especially true if significant sweating occurs and electrolytes are lost through sweat. Try to rest in cool or shaded areas whenever possible.

What is the prognosis for heat cramps?

Heat cramps resolve with relatively simple treatments including rest, hydration and stretching. It is important to remember that heat cramps are the initial presentation of heat related illness and may progress to the more serious conditions of heat exhaustion or heat stroke.

Medically reviewed by Avrom Simon, MD; Board Certified Preventative Medicine with Subspecialty in Occupational Medicine

REFERENCES:

Kravchenko J, etal. Minimization of Heatwave Mortality and Morbidity.American Journal of Preventive Medicine 2013: 44(3) 274-82

Schwellnus MP. Cause of Exercise Associated Muscle Cramps (EAMC) - altered neuromuscular control, dehydration or electrolyte depletion. Br J Sports Med 2009;43:401-408

Last Editorial Review: 9/2/2016

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Reviewed on 9/2/2016
References
Medically reviewed by Avrom Simon, MD; Board Certified Preventative Medicine with Subspecialty in Occupational Medicine

REFERENCES:

Kravchenko J, etal. Minimization of Heatwave Mortality and Morbidity.American Journal of Preventive Medicine 2013: 44(3) 274-82

Schwellnus MP. Cause of Exercise Associated Muscle Cramps (EAMC) - altered neuromuscular control, dehydration or electrolyte depletion. Br J Sports Med 2009;43:401-408

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