Muscle Cramps – OrthoInfo – AAOS

Although the exact cause of muscle cramps is unknown (idiopathic), some researchers believe inadequate stretching and muscle fatigue lead to abnormalities in the mechanisms (bodily processes) that control muscle contraction.

Other factors may also be involved, including:

Poor conditioning
Exercising or working in intense heat
Dehydration
Depletion of salt and minerals (electrolytes)

Inadequate Stretching and Muscle Fatigue

Muscles are bundles of fibers that contract and expand to produce movement. A regular program of stretching lengthens muscle fibers so they can contract and tighten more vigorously when you exercise.

When your body is poorly conditioned, you are more likely to experience muscle fatigue, which can alter spinal neural reflex activity. Overexertion depletes a muscle’s oxygen supply, leading to build-up of waste product and spasm. When a cramp begins, the spinal cord stimulates the muscle to keep contracting.

Heat, Dehydration, and Electrolyte Depletion

Muscle cramps are more likely when you exercise in hot weather because sweat drains your body’s fluids, salt, and minerals (i.e., potassium, magnesium, and calcium). Loss of these nutrients may also cause a muscle to spasm.

Risk Factors

Some people are predisposed to muscle cramps and get them regularly with any physical exertion.

Those at greatest risk for cramps and other ailments related to excess heat include infants and young children, and people over age 65. Other factors that put people at greater risk for muscle cramp include:

Being ill or overweight
Overexerting during work or exercise
Taking certain medications, such as pseudoephedrine (a decongestant) diuretics, and statins (used to treat high cholesterol)

Muscle cramps are very common among endurance athletes, such as marathon runners and triathletes, and older people who perform strenuous physical activities.

Athletes are more likely to get cramps in the preseason when the body is not conditioned and therefore more subject to fatigue. Cramps often develop near the end of intense or prolonged exercise, or 4 to 6 hours later.
Older people are more susceptible to muscle cramps due to normal muscle loss (atrophy) that begins in the mid-40s and accelerates with inactivity. As you age, your muscles cannot work as hard or as quickly as they used to. The body also loses some of its sense of thirst and its ability to sense and respond to changes in temperature.

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