A charley horse is the common name for a muscle spasm, especially in the leg. Muscle spasms can occur in any muscle in the body. When a muscle is in spasm, it contracts without your control and does not relax.

Muscle spasms often occur when a muscle is overused or injured. Working out when you haven't had enough fluids (you're dehydrated) or when you have low levels of minerals such as potassium or calcium can also make you more likely to have muscle spasms.

Some spasms occur because the nerve that connects to a muscle is irritated. The classic example is a herniated disk irritating spinal nerves as they exit the back, causing pain and spasm.

Spasms in the calf often occur while kicking during swimming, and can also occur at night while you're in bed. Upper leg spasms are more common with running or jumping activities. Spasm in the neck (cervical spine) can be a sign of stress.

When a muscle goes into spasm it feels very tight and is sometimes described as a knot. The pain can be severe.

Your health care provider can diagnose muscle spasms by the presence of tight or hard muscles that are very tender to the touch. There are no imaging studies or blood tests that can diagnose this condition. If the spasm is caused by nerve irritation, such as in the back, an MRI may be helpful to find the cause of the irritation.

At the first sign of a muscle spasm, stop your activity and try stretching and massaging the affected muscle. Heat will relax the muscle at first, although ice may be helpful after the first spasm and when the pain has improved. If the muscle is still sore, nonsteroidal anti-inflammatory medications can help with pain. In more severe cases, your health care provider can prescribe antispasm medications.

After you get treated, your health care provider should look for the cause of the spasm so that it doesn't recur. If an irritated nerve is involved, you might need physical therapy or even surgery.

The most common cause of muscle cramps during sports activity is dehydration. Often, drinking water or sports drinks will ease the cramping.

Muscle spasms will get better with rest and time. The outlook is excellent for most people. Proper training techniques should prevent spasms from occurring regularly. If an irritated nerve caused the spasm, you might need more treatment and results can vary.

If you have a muscle spasm with severe pain, contact your health care provider. Even if your spasms are not severe, your health care provider can help you change your exercise program to reduce the risk of spasms in the future.

• Stretch to improve flexibility.
• Change your workouts so that you are exercising within your ability.
• Drink plenty of fluids while exercising and increase your potassium intake (orange juice and bananas are great sources of potassium).