Muscle cramps

Cramps are painful spasms that mainly affect muscles in the legs and feet. A cramp generally lasts a few minutes and then ends on its own, although massage and stretching can hasten the process, and certain foods may help to prevent its recurrence. Read on to learn more.

The human body is made up of about 600 groups of muscles, which constitute 40 percent of an average person's weight. Each muscle is made up of many thousands of long fibres bound together with connective tissue. The bundled fibres can shrink or lengthen, allowing muscles to contract or relax.

• Glucose. Most of the fuel necessary for muscular activity comes from glucose, the end-product of carbohydrate metabolism, which is stored as glycogen in the liver and muscles.
• Vitamins. The vitamins in the B group are crucial to the process by which energy is derived from carbohydrates, proteins, and fats. In fact, our need for thiamine is directly related to the amount of energy we expend.
• Minerals. We need iron to form hemoglobin, the blood pigment that supplies muscles with oxygen for energy conversion. Also critically important to muscle function are sodium, potassium, and chloride; these minerals are called electrolytes, because their electrically charged particles (ions) relay nerve impulses from the brain to the muscles, instructing them when to contract and relax. Calcium is the trigger for muscle contraction. And to come full circle, potassium is stored in the muscles with glycogen and — like glycogen — it is rapidly depleted whenever the muscles undergo a vigorous workout.

When muscles burn glycogen for energy, ­lactic acid forms as a waste product and remains in the muscle tissue until circulating blood clears it away. During periods of intense exercise, a buildup of lactic acid can cause severe muscle pain and fatigue. The pain, which is similar to muscle cramps, dissipates with rest, which allows the blood to remove the extra ­lactic acid.The correct fluid balance is important in muscle function.

The spasms of true cramps may be caused by an inadequate supply of blood to the muscle, overstretching, or an injury. If the fluid volume is too low, the electrolyte balance is thrown off kilter, the kidneys respond by conserving sodium at a high rate, fluid is retained in the tissues, and there is not enough circulating fluid to flush out waste products and keep the muscle contraction mechanism working smoothly. There should be enough water to keep electrolytes in the proper concentration for relaying impulses from the nerves to the muscles, but not too much water, which dilutes the blood and lowers the electrolyte concentration.

Electrolyte depletion is not often a problem, because these minerals are amply supplied by a properly balanced diet. Although the electrolytes are excreted in sweat, the amounts lost are very small, even with profuse perspiration during vigorous activity. The exception is potassium, which is drawn out of body stores along with glycogen.

Some people are awakened during the night by a jerking of their leg muscles; others suffer an aching, uneasy sensation that doctors call "restless legs syndrome." Certain medications that affect the nervous system may cause these conditions; often, they occur with no apparent cause.

Doctors may detect iron, folate, or magnesium deficiencies and recommend supplements. In some cases, drugs may help; getting out of bed and walking, or frequently changing positions, may give some relief.