A. There are a variety of causes of muscle spasms, and each cause depends on certain predisposing factors and anatomic areas of involvement.Spasms may occur when a muscle is overused and tired, particularly if it is overstretched or if it has been held in the same position for a prolonged period of time.. There are a variety of causes of muscle spasms, and each cause depends on certain predisposing factors and anatomic areas of involvement.