Muscle spasms are sudden, involuntary contractions of a muscle or group of muscles and they are common in conditions such as multiple sclerosis, thyroid disease, cirrhosis of the liver, nerve disorders, spinal cord injury and certain metabolic diseases. The prevalence of muscle spasms in people over the age of 60 is estimated to be around 46%. While most muscle spasms are not serious, they can be painful and interfere with daily activities. In severe cases, they can lead to muscle strains or tears if the force of the spasm exceeds the tensile strength of the underlying connective tissue.