Heat can reduce muscle spasms, reduce joint stiffness, and make soft tissue more limber.
Heat can be used to help loosen tight muscles and joints during a warm-up period before exercise. For example, you may put moist hot packs on tight leg muscles before running, or on your shoulder before throwing, or on tight neck or back muscles. Use heat for stiff muscles and joints when you are trying to make them more limber. Do not use heat in the first few days after an injury or while your injury has any swelling because heat increases blood flow and can worsen swelling. Moist heat is more effective than dry heat because it penetrates more deeply, which increases the effect on muscles, joints, and soft tissue.