Muscle spasms commonly occur when a muscle is over-used or injured. Working out when dehydrated or with low levels of potassium can also predispose a person to 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 commonly occur while kicking during swimming and can also occur at night while in bed. Upper leg spasms are more common with running or jumping activities. Spasm in the cervical spine (neck) can be a sign of stress.
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