Voluntary muscles are in a constant state of contraction and relaxation to control locomotion, posture, and deliberate movement. Numerous physiological occurrences act to control these purposeful mechanisms in an ongoing process to facilitate normal everyday human function. When a muscle or group of muscle fibers contract involuntarily it is called a "spasm." If the spasm is forceful and sustained, it becomes a muscle cramp.

Defined as an involuntarily and forcibly contracted muscle that does not relax, a muscle cramp can last anywhere from a few seconds to a quarter of an hour, and may, in a few physiological conditions, last longer. A cramp may recur multiple times before it finally dissipates and normal function is restored. Cramping can vary in severity, as well as in the affected musculature. A cramp can involve a part of a muscle, the entire muscle, or a muscle group.

Cramps are a fairly common physiological phenomenon. In fact, almost every human will experience some form of cramping in their lifetime. Although cramps can occur anywhere, most complaints stem from muscles of the lower extremities with many occurring in the calf.

Skeletal muscle cramps have been classified into four major types according to their different causes and the muscle groups they affect. (1). These include true cramps, tetany, contractures, and dystonic cramps.

True cramps are considered the most common type of skeletal muscle cramp. Most experts agree the primary cause is hyperexcitability of the nerves that stimulate the muscles. True cramps involve part or all of a single muscle or a muscle group that is generally stimulated together for a particular action, such as the hamstring muscle group. True cramps can occur in response to vigorous activity, from muscle spasms following injury, or when muscle fatigue and long duration static position is maintained.

Internal environments can also cause true cramps. Fluid loss from activity or chronic body fluid volume depletion as well as body fluid shifts can predispose the muscle for cramps. The use of diuretic containing products or medications, poor fluid intake, or accumulative dehydration may act similarly to predispose an individual for cramps. Like wise, mineral concentration variations may predispose a person to cramp. Sodium depletion and low blood levels of either calcium or magnesium have been associated with cramps. Loss of sodium, the most abundant chemical constituent of body fluids outside the cell, is usually a function of dehydration, related, in particular to heat syncopy, an excessive mineral loss from sweating. Mineral components acting on the nerve also can cause excitation dysfunction. Low levels of calcium and magnesium directly increase the excitability of both the nerve endings and the muscles they stimulate.

The other classifications of cramps are more specific in nature regarding their purported mechanism for cramping. Although often difficult to distinguish from True cramps, tetany cramps (derived from tetanus) occur when all of the nerve cells in the body are activated, which then stimulate the muscles. The difference between True and tetany cramps is the hyperactivity of other nerve functions occur in addition to muscle stimulation. This reaction causes spasms or cramps throughout the body. It is most commonly associated with low blood levels of calcium and magnesium.

Contracture cramps are another category where the muscle is not able to relax. But rather than the spasms occurring from neural stimulation the constant spasms are caused by a depletion of adenosine triphosphate (ATP). Although the nerves are inactive in this form of muscle spasm the ATP does not allow for relaxation. Contracture cramps are uncommon and usually related to a genetic predisposition rather than external factor.

The last category is dystonic cramps, in which muscles that are not needed for the intended movement are stimulated to contract. In most cases the antagonist is stimulated during an agonistic effort. Essentially in a dystonic cramp the muscles that work opposite to the prime mover contract. Dystonic cramps usually affect small groups of muscles and may occur during repetitive actions requiring dexterity such as writing (writer’s cramp). Dystonic cramps are not as common as "true" cramps.

In addition to the previous mentioned causes of cramping there are numerous medicines can cause cramps. Diuretic medications can induce cramps by depleting body fluid and sodium. AT the same time these fluid depleting drugs can cause the loss of potassium, calcium, and magnesium, identified minerals which can cause cramps. Some name brand drugs known to cause cramps as a side effect include:

Donepezil (Aricept-- used for Alzheimer's disease)

Neostigmine (Prostigmine -- used for myasthenia gravis)

aloxifene (Evista- used to prevent osteoporosis in postmenopausal women)

Tolcapone (Tasmar-- used for Parkinson's disease)

Nifedipine (Procardia and others -- used for angina and high blood pressure, and other conditions)

Terbutaline (Brethine)and Albuterol (Proventil, Ventolin, asthma medications).

Clofibrate (Atromid-S) and lovastatin (Mevacor), for high cholesterol.

Treating muscle cramps is usually associated with renegotiating the imbalance that caused the problem in the first place. Stretching the tissue in immediate response will often stop the cramp if the muscle can be stretched. Adding heat and massaging the affected muscle will also help it to relax. In some cases cold rub will release the contraction. If the cramp is associated with fluid loss -- as is often the case with vigorous physical activity -- fluid and electrolyte (especially sodium and potassium) replacement is essential. Gatorade has already cornered the market on the recommended electrolyte concentration. Due to the acute nature of cramps it is rare for a pharmaceutical intervention to be used. Of course, if cramps are severe, frequent, persistent, respond poorly to simple treatments a person should see their physician. In some cases cramping can be an indicator of the manifestation of a disease. Although it is not common that muscle cramps would result from a medical condition without some other obvious signs that the medical condition is present.

Preventing cramps is relatively easy to do as the primary causes are almost always related to deficiency. For activity related cramping the answer lies in adequate hydration, appropriate consumption of electrolytes, and a reasonable warm-up and cooldown. Intensity acclimation is another consideration as well. Moving from low to high to quickly can cause tonic spasm and cramping.

In the case of low calcium and magnesium either increasing specific foods containing these minerals or supplementation will work. Supplemental calcium and magnesium have each been shown to help prevent cramps, particularly during pregnancy.

Cramps of a dystonic nature can be attenuated by better biomechanics. Persons engaged in repetitive non- vigorous activities should pay careful attention to ergonomic factors such as wrist supports, avoiding high heels, adjusting chair position, activity breaks, and using comfortable positions and equipment while performing the activity. Learning to avoid excessive tension while executing problem activities can help. However, cramps can remain very troublesome for activities that are difficult to modify, such as playing a musical instrument(2).

Cramping that occurs to fatigue and static position or rest or bed cramps can often be prevented by regular stretching exercises, particularly if done before going to bed. Even simple calf stretching repeated two or three times just before going to bed will often be a great help in preventing cramps.

Acute cramping is a common phenomenon that can occur at rest, during mild or everyday activities or in response to vigorous work. Avoiding these annoying and often painful bouts requires a little attention to details. Staying adequately hydrated and eating a well balanced diet can go a long way in preventing cramps. If cramping becomes a common occurrence one should consult a physician as their may be an underlying problem at the root of the cause.