Muscle spasm is a common, involuntary tightening or contraction of a muscle or group of muscles. Muscle spasms typically are not predictable and can be quite painful. Thighs, feet, calves, hands, and arms are common locations for muscle spasms. Muscle spasms are also referred to as muscle cramps. Spasms may last for a few seconds or up to several minutes, and they may recur after they have gone away. The pain can range from mild to severe. The affected muscle may feel hardened to the touch or may appear to have a distorted shape. Twitching is another possible associated symptom. Anyone can be affected by muscle spasms.
Jameson, J. Larry, et al. Harrison's Principles of Internal Medicine, 20th Ed. New York: McGraw-Hill Education, 2018.