A cramp is a sudden, brief, unintended (involuntary), and usually painful contraction of a muscle or group of muscles. Muscle cramps can be a symptom of nervous system malfunction Introduction to Symptoms of Brain, Spinal Cord, and Nerve Disorders Disorders that affect the brain, spinal cord, and nerves are called neurologic disorders. Neurologic symptoms—symptoms caused by a disorder that affects part or all of the nervous system—can... read more .
Causes of Muscle Cramps
The most common causes of muscle cramps are
Benign leg cramps that occur for no known reason, typically at night
Exercise-associated muscle cramping (cramping during or immediately after exercise)
Muscle cramps (also called charley horses) often occur in healthy people, usually in middle-aged and older people but sometimes in younger people. Cramps tend to occur during or after vigorous exercise but sometimes occur during rest. Some people have painful leg cramps during sleep. Sleep-related leg cramps Sleep-related leg cramps Parasomnias are unusual behaviors that occur just before falling asleep, during sleep, or when waking up. (See also Overview of Sleep.) Various unconscious and largely unremembered behaviors... read more usually affect the calf and foot muscles, causing the foot and toes to curl downward. Although painful, these cramps are usually not serious and are thus called benign leg cramps.
Almost everyone has muscle cramps at some time, but certain conditions increase the risk and/or severity of cramps. They include the following:
Having tight calf muscles, which may be caused by not stretching, inactivity, or sometimes repeated accumulation of fluid (called edema) in the lower leg
Having low levels of electrolytes (such as potassium Hypokalemia (Low Level of Potassium in the Blood) In hypokalemia, the level of potassium in blood is too low. A low potassium level has many causes but usually results from vomiting, diarrhea, adrenal gland disorders, or use of diuretics. A... read more , magnesium Hypomagnesemia (Low Level of Magnesium in the Blood) In hypomagnesemia, the level of magnesium in blood is too low. (See also Overview of Electrolytes and Overview of Magnesium's Role in the Body.) Magnesium is one of the body's electrolytes... read more , or calcium Hypocalcemia (Low Level of Calcium in the Blood) In hypocalcemia, the calcium level in blood is too low. A low calcium level may result from a problem with the parathyroid glands, as well as from diet, kidney disorders, or certain drugs. As... read more ) in the blood
Having a nerve disorder or an underactive thyroid gland (hypothyroidism Hypothyroidism Hypothyroidism is underactivity of the thyroid gland that leads to inadequate production of thyroid hormones and a slowing of vital body functions. Facial expressions become dull, the voice... read more
)Taking certain drugs
Low electrolyte levels may result from use of some diuretics, alcoholism, certain hormonal (endocrine) disorders, vitamin D deficiency Vitamin D Deficiency Vitamin D deficiency is most commonly caused by a lack of exposure to sunlight. Some disorders can also cause the deficiency. The most common cause is lack of exposure to sunlight, usually when... read more , or conditions that cause loss of fluids (and thus electrolytes). Electrolyte levels may become low late in pregnancy.
Cramps can occur shortly after dialysis Dialysis Dialysis is an artificial process for removing waste products and excess fluids from the body, a process that is needed when the kidneys are not functioning properly. There are a number of reasons... read more 
, possibly because dialysis removes too much fluid from the body, removes the fluid too quickly, and/or lowers electrolyte levels.
Disorders that cause similar symptoms
Some disorders cause symptoms that resemble muscle cramps.
Dystonias Dystonia Dystonia is characterized by long-lasting (sustained) involuntary muscle contractions that may force people into abnormal positions—for example, causing the entire body, the trunk, limbs, or... read more are involuntary muscle contractions, but they usually last longer and occur more often than cramps. Also, they tend to affect other muscles and may affect many other muscles, including any limb muscles as well as those of the back, neck, and voice. In contrast, benign leg cramps and exercise-associated muscle cramping tend to affect the calf muscles.
Tetany is continuous or periodic spasms of muscles throughout the body. These spasms usually last much longer than muscle cramps and are more widespread. The muscles may also twitch.
Illusory muscle cramps occur in some people. These people feel as if they are having cramps but no muscle contraction occurs.
Hardening of the arteries in the legs (peripheral arterial disease) may cause calf pain (claudication Symptoms 
) during physical activity such as walking. This pain is due to inadequate blood flow to muscles, not to muscle contraction as occurs with cramps.
Evaluation of Muscle Cramps
The following information can help people decide whether a doctor's evaluation is needed and help them know what to expect during the evaluation.
Warning signs
In people with muscle cramps, the following symptoms and characteristics are of particular concern:
Cramps in the arms or trunk
Muscle twitching
Alcoholism
Weakness
Cramps that occur after loss of body fluids (dehydration) or use of diuretics
Pain or loss of sensation unless they occur at the same time as the cramping
If people have cramps in the arms or trunk or muscle twitching, the cause is more likely to be a disorder (such as an electrolyte or hormonal disorder) or a drug than benign leg cramps or exercise-related muscle cramps.
When to see a doctor
People with muscle cramps should consult a doctor as soon as possible if they also have alcoholism, sudden weakness or loss of sensation, or severe symptoms or if they have lost body fluids (for example, through vomiting, diarrhea, or excessive sweating). Otherwise, people should call their doctor to discuss how soon the doctor needs to see them.
What the doctor does
Doctors first ask questions about the person's symptoms and medical history Medical History in Neurologic Disorders Before doing a physical examination, doctors interview the person. Doctors ask the person to describe current symptoms, including those related to the nervous system (neurologic symptoms): What... read more and then does a physical examination. What doctors find during the history and physical examination often suggests a cause and the tests that may need to be done.
Doctors ask the person to describe the cramps, including the following:
When they occur
How long they last
How frequent they are
Where they are
Whether any event seems to trigger them
Whether any other symptoms are present
Doctors ask about symptoms that suggest clues to the cause:
Lack of menstrual periods or menstrual irregularities—symptoms that suggest pregnancy-related leg cramps
Vomiting, diarrhea, use of diuretics, excessive exercise, and sweating—symptoms that suggest loss of body fluids or electrolytes
Difficulty tolerating cold, weight gain, and coarse, thick skin—symptoms that may indicate hypothyroidism
Weakness, pain, or loss of sensation—symptoms that suggest a nerve disorder
The person is also asked about use of drugs and alcohol, recent dialysis treatment, and any association between past dialysis treatments and muscle cramps.
The physical examination focuses first on the nervous system (neurologic examination Neurologic Examination When a neurologic disorder is suspected, doctors usually evaluate all of the body systems during the physical examination, but they focus on the nervous system. Examination of the nervous system—the... read more ), including assessment of muscles and reflexes.
Doctors also inspect the skin for signs of the following:
Alcoholism (such as spider veins, red palms, and, in men, changes in the pattern of genital hair)
Hypothyroidism (such as a puffy face and loss of eyebrow hair)
Dehydration (such as less elastic skin)
Testing
No tests are routinely done. Instead, testing is done based on the history and results of the physical examination.
If cramping is widespread, particularly if reflexes are overactive, doctors measure levels of blood sugar and electrolytes (including calcium and magnesium) and do blood tests to check for kidney malfunction (which can cause levels of calcium and magnesium to be abnormal).
If the cramped muscles are also weak, electromyography Electromyography and Nerve Conduction Studies Diagnostic procedures may be needed to confirm a diagnosis suggested by the medical history and neurologic examination. Electroencephalography (EEG) is a simple, painless procedure in which... read more 
may be done. For this test, a small needle is inserted into a muscle to record the electrical activity of the muscle when the muscle is at rest and when it is contracting.
If muscle weakness Weakness Weakness refers to loss of muscle strength. That is, people cannot move a muscle normally despite trying as hard as they can. However, the term is often misused. Many people with normal muscle... read more is widespread and doctors think that it is related to a problem with the nervous system, magnetic resonance imaging Magnetic Resonance Imaging (MRI) In magnetic resonance imaging (MRI), a strong magnetic field and very high frequency radio waves are used to produce highly detailed images. MRI does not use x-rays and is usually very safe... read more 
(MRI) of the brain and spinal cord is done.
Prevention of Muscle Cramps
Preventing cramps is the best approach. The following measures can help:
Not exercising immediately after eating
Gently stretching the muscles before exercising or going to bed
Drinking plenty of fluids (particularly sports beverages that contain potassium) after exercise
Not consuming caffeine (for example, in coffee or chocolate)
Not smoking
Avoiding drugs that are stimulants, such as ephedrine or pseudoephedrine (a decongestant contained in many products that do not require a prescription but are available only behind the pharmacy counter)
Stretching makes muscles and tendons more flexible and less likely to contract involuntarily. The runner's (gastrocnemius) stretch is the best stretch for preventing calf cramps. A person stands with one leg forward and bent at the knee and the other leg behind with the knee straight—a lunge position. The hands can be placed on the wall for balance. Both heels remain on the floor. The knee of the front leg is bent further until a stretch is felt along the back of the other leg. The greater the distance between the two feet and the more the front knee is bent, the greater the stretch. The stretch is held for 30 seconds and repeated 4 or 5 times. Then the set of stretches is repeated on the other side.
Treatment of Muscle Cramps
If a disorder that can cause muscle cramps is identified, it is treated.
If a cramp occurs, stretching the affected muscle often relieves the cramp. For example, for a calf cramp, the person could use a hand to pull the foot and toes upward or could do the runner's stretch. Massage may temporarily relieve some types of cramps.
Most of the drugs prescribed to prevent cramps from recurring (including calcium supplements, magnesium carbonate, and benzodiazepines such as diazepam) have not proved to be effective, and they can have side effects. Quinine is no longer recommended as treatment for muscle cramps because of its side effects, such as abnormal heart rhythms, vomiting, vision problems, ringing in the ears, and headaches. Mexiletine (used to treat abnormal heart rhythms) sometimes helps but also has many side effects, such as nausea, vomiting, tremors (rhythmic shaking of a body part), and seizures.
Key Points
Leg cramps are common.
The most common causes are benign leg cramps and exercise-associated cramping.
Stretching and not consuming caffeine can help prevent muscle cramps.
Drug therapy is not usually recommended to prevent muscle cramps.
