Muscle Cramps – Causes of Muscle Spasms and “Charley Horse”

Muscles are the ‘motors’ of the human body that allow for movement. By contracting and relaxing, muscles move different parts of the body. It is not only the limbs and different segments of the body that move with the muscle action but movement within organs are also facilitated by these muscles. Even the widening and narrowing of passages, like the airways or blood vessels, are made possible by the muscles within their walls.

What is a muscle cramp?

A muscle cramp is sudden and forceful tightening of a muscle that is prolonged. This tightening is due to an involuntary and extreme contraction of the muscle which is also known as a spasm. These spasms may last anywhere from a few seconds to hours and even days. Cramps and spasms are terms used interchangeably but the term cramps is often commonly used to describe painful spasms that persist for longer periods of time.

Charley horse is a common term used to describe a muscle cramps, and specifically cramps of the calf muscles. However, cramps are not isolated to just the calf or the leg. It can occur anywhere in the body and even affect the muscles of the internal organs. This can cause a host of symptoms such as headaches with neck muscle spasm or abdominal cramps with gastrointestinal conditions.

How do muscle cramps occur?

There are three types of muscles in the human body – the smooth muscle, skeletal muscle and cardiac muscle. All types of muscles are made up of vast numbers of fibers. These fibers in turn are made up of many muscle cells with tiny fibrils (myofibrils) within it. The movement of these myofibrils allow for muscles, and therefore for fibers, to shorten (contract) or lengthen (relax).

Muscles are controlled by nerves. Electrical impulses run through the nerves and the nerve endings then release a chemical known as neurotransmitter. This neurotransmitter then travels in the tiny junction between the nerve endings and muscle fibers. Once the neurotransmitter attaches to the muscle cells, it triggers the myofibrils within the muscle cells to shorten which results in muscle contraction.

Tightening and Relaxing of Muscles

There is a limit to which this contraction and relaxation occurs in the course of normal physiology. Muscles can lengthen significantly in which case it may become stretched and strained. Similarly the muscles can shorten excessively with forceful tightening of the fibers. It is this tightening that is referred to as spasm or cramps. It can restrict movement (stiffness), weaken the action of the affected muscle and result in pain.

Causes of Muscle Cramps

Most of the time muscle cramps are due to dietary and lifestyle factors that affect the muscle tone, activity and physiology. It is usually not serious and passes within a short period of time.Rest, ice, compression and elevation (R.I.C.E.) is the approach recommended for self-treatment of acute muscle strain.

However, there are certain diseases involving the muscles, nerves or neurotransmitters responsible for communication between the muscles and nerves that can result in cramps. These diseases have not been covered within this article. Persistent, recurrent and severe muscle cramps need to be investigated by a doctor.

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Strain and Trauma

Any strenuous, excessive or repetitive activity can cause muscle strain which may then lead to cramps. This may also occur with excessive stretching and a blow on the muscles. Strain may occur even without knowing it and the consequences, such as cramps, are only experienced minutes or even hours later. For example, cramps of the leg muscles may only be felt the next day following a long run.

The activity of muscles is largely determined by its physical conditioning. The skeletal muscles, which are under voluntary control and responsible for movement of the body, is conditioned by physical activity. People who are physically active and exercise tend have better conditioned muscles. Therefore physical activity is less likely to cause muscle strain but there is a limit to any person’s degree of muscle conditioning.


Dehydration is another common yet often overlooked cause of muscle cramps. The loss of fluid and electrolytes disrupts normal muscle activity as electrolytes are needed to facilitate muscle contractions and its recovery during the relaxation phase. In severe dehydration, these muscle cramps may occur even at rest but in milder dehydration the cramps may only arise with physical activity, even moderate activity.

Vomiting and diarrhea are the two ways that dehydrate sets in rapidly due to disease but it can also occur with prolonged and excessive sweating. However, even in the absence of severe dehydration with obvious and often serious symptoms, many people may have mild dehydration and not be aware of it. Insufficient water intake and the use of diuretic beverages like alcohol and caffeinated drinks such as coffee may contribute to dehydration.


Muscles, like other cells, tissues and organs in the body, require a constant flow of blood. Oxygen and nutrients are needed by the cells to function normally and carbon dioxide and wastes need to be carried away. This is achieved by a normal and healthy circulation of blood in the target area. Therefore circulatory problems can affect normal muscle functioning and lead to symptoms like muscle cramps.

There are a host of different conditions that may affect the circulatory system. In conditions like peripheral arterial disease (PAD), fatty plaques build up in the artery wall and restrict the flow of blood to the target area. Venous insufficiency (example varicose veins or DVT) refers to vein problems that impair blood from being drained. With anemia, the blood’s oxygen-carrying capacity is lower than normal meaning the muscles receive less oxygen.


Miconutrient deficiencies, particularly of minerals like calcium, sodium, magnesium and potassium, can also affect muscle activity since these minerals are needed for muscle contractions and rcovery during relaxation. These deficiencies may be due to insufficient dietary intake or arise with dehydration. Certain diseases and disorders, such as inflammation of the gastrointestinal tract, may also lead to the absorption and assimilation of minerals.


Certain hormones and substances released during certain times of the menstrual cycle, like during menstruation, may also contribute to muscle cramps. These hormones and substances help facilitate uterine contractions during menstruation in order to push out the sloughed off endometrium. However, if these substances, like prostaglandins, are in high levels and enter the bloodstream, it could affect muscles beyond the uterus.

Read more on menstrual cramps.


Various drugs can affect the muscles in different ways and muscle cramps may be one of the symptoms that arise. This is more likely to be the cause when persistent or repeated muscle cramps arise after starting a new drug or a change in drug dosage. Diuretics for example can lead to dehydration with loss of electrolytes like potassium contributing to muscle cramps. Statins used for lowering cholesterol may cause muscle cramps as a side effect.

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