Spasms and Cramp – are involuntary contractions of a muscle, usually accompanied by
pain.
Cramps are short-lived, acute contractions, which occur most commonly in the calf muscles; spasms are low-grade, long-lasting conditions.

They are commonly caused by lack of oxygen to a muscle, either through overworking the muscle or because of chronic tension in the muscle that is impeding the blood supply. It can also be due to a lack of calcium or magnesium.