Muscle Cramps - Causes

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What are the types and causes of muscle cramps?

Skeletal muscle cramps can be categorized into four major types. These include "true" cramps, tetany, contractures, and dystonic cramps. Cramps are categorized according to their different causes and the muscle groups they affect.

True cramps

True cramps involve part or all of a single muscle or a group of muscles that generally act together, such as the muscles that flex several adjacent fingers. Most authorities agree that true cramps are caused by hyperexcitability of the nerves that stimulate the muscles. They are overwhelmingly the most common type of skeletal muscle cramps. True cramps can occur in a variety of circumstances as follows.

Injury: Persistent muscle spasm may occur as a protective mechanism following an injury, such as a broken bone. In this instance, the spasm tends to minimize movement and stabilize the area of injury. Injury of the muscle alone may cause the muscle to spasm.

Vigorous activity: True cramps are commonly associated with the vigorous use of muscles and muscle fatigue (in sports or with unaccustomed activities). Such cramps may come during the activity or later, sometimes many hours later. Likewise, muscle fatigue from sitting or lying for an extended period in an awkward position or any repetitive use can cause cramps. Older adults are at risk for cramps when performing vigorous or strenuous physical activities.

Rest cramps: Cramps at rest are very common, especially in older adults, but may be experienced at any age, including childhood. Rest cramps often occur during the night. While not life threatening, night cramps (commonly known as nocturnal cramps) can be painful, disruptive of sleep, and they can recur frequently (that is, many times a night, and/or many nights each week). The actual cause of night cramps is unknown. Sometimes, such cramps are initiated by making a movement that shortens the muscle. An example is pointing the toe down while lying in bed, which shortens the calf muscle, a common site of muscle cramps.

Dehydration: Sports and other vigorous activities can cause excessive fluid loss from perspiration. This kind of dehydration increases the likelihood of true cramps. These cramps are more likely to occur in warm weather and can be an early sign of heat stroke. Chronic volume depletion of body fluids from diuretics (medicine that promote urination) and poor fluid intake may act similarly to predispose to cramps, especially in older people. Sodium depletion has also been associated with cramps. Loss of sodium, the most abundant chemical constituent of body fluids outside the cell, is usually a function of dehydration.

Body fluid shifts: True cramps also may be experienced in other conditions that feature an unusual distribution of body fluids. An example is cirrhosis of the liver, which leads to the accumulation of fluid in the abdominal cavity (ascites). Similarly, cramps are a relatively frequent complication of the rapid body fluid changes that occur during dialysis for kidney failure.

Low blood calcium, magnesium: Low blood levels of either calcium or magnesium directly increase the excitability of both the nerve endings and the muscles they stimulate. This may be a predisposing factor for the spontaneous true cramps experienced by many older adults, as well as for those that are commonly noted during pregnancy. Low levels of calcium and magnesium are common in pregnant women unless these minerals are supplemented in the diet. Cramps are seen in any circumstance that decreases the availability of calcium or magnesium in body fluids, such as taking diuretics, hyperventilation (overbreathing), excessive vomiting, inadequate calcium and/or magnesium in the diet, inadequate calcium absorption due to vitamin D deficiency, poor function of the parathyroid glands (tiny glands in the neck that regulate calcium balance), and other conditions.

Low potassium: Low potassium blood levels occasionally cause muscle cramps, although it is more common for low potassium to be associated with muscle weakness.

Tetany

In tetany, all of the nerve cells in the body are activated, which then stimulate the muscles. This reaction causes spasms or cramps throughout the body. The name tetany is derived from the effect of the tetanus toxin on the nerves. However, the name is now commonly applied to muscle cramping from other conditions, such as low blood levels of calcium and magnesium. Low calcium and low magnesium, which increase the activity of nerve tissue nonspecifically, also can produce tetanic cramps. Often, such cramps are accompanied by evidence of hyperactivity of other nerve functions in addition to muscle stimulation. For instance, low blood calcium not only causes spasm of the muscles of the hands and wrists, but it can also cause a sensation of numbness and tingling around the mouth and other areas.

Sometimes, tetanic cramps are indistinguishable from true cramps. The accompanying changes of sensation or other nerve functions that occurs with tetany may not be apparent because the cramp pain is masking or distracting from it.

Contractures

Contractures result when the muscles are unable to relax for an even more extended period than a common muscle cramp. The constant spasms are caused by a depletion of adenosine triphosphate (ATP), an energy chemical within the cell. This prevents muscle fiber relaxation. The nerves are inactive in this form of muscle spasm.

Contractures can result from inherited (for example, McArdle's disease, which is a defect of the breakdown of glycogen to sugar within the muscle cell) or from acquired conditions (for example, hyperthyroid myopathy, which is a muscle disease that is associated with an overactive thyroid). Cramps of this category are uncommon.

Dystonic cramps

The final category is dystonic cramps, in which muscles that are not needed for the intended movement are stimulated to contract. Muscles that are affected by this type of cramping include those that ordinarily work in the opposite direction of the intended movement, and/or others that exaggerate the movement. Some dystonic cramps usually affect small groups of muscles (eyelids, jaws, neck, larynx, etc.). The hands and arms may be affected during the performance of repetitive activities such as those associated with handwriting (writer's cramp), typing, playing certain musical instruments, and many others. Each of these repetitive activities may also produce true cramps from muscle fatigue. Dystonic cramps are not as common as true cramps.

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See what others are saying

Comment from: Sandy, 45-54 Female (Patient) Published: February 26

I am a 53 year old and I suffer from cramps just about every night. Mainly in my feet, but it also can be in my calves and full legs. I have had no operations, and I am not on any medication and I can"t work it out. I have tried including salt in my diet etc., I do at least 30 minute exercise on the treadmill with a warm up and slow down program so it is not that either.

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Comment from: blue, 45-54 Male (Patient) Published: March 13

I was running on the treadmill one day. I didn't have on proper shoes, the shoes were worn out badly. I wore them and I ran for about as hour. The next day is when I started to have muscle cramps in both legs. The pain is so bad that I can't sleep at night. When I sit down is when I have the pain. Now I put heat pad on it and at night I keep my legs raised up high. I know it will be months before it heals. Make sure you wear proper shoes when you are out running.

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