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, 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. 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. Use it for 15 to 20 minutes or longer if recommended by your healthcare provider.
Moist heat from towels soaked in hot water or warmed in a microwave are useful, but the towels usually lose their heat within 5 to 10 minutes. Commercial moist heat packs are more convenient and provide longer therapy. Some commercial heat packs are designed to fit specific parts of your body. Hot tubs or whirlpools are also useful.
Heat creams and ointments are popular but don't provide heat very deeply into muscle tissue. The massaging effect of putting the cream on is helpful. Avoid getting these creams into your eyes or on sensitive skin.
Heat increases the blood flow to an injury and can worsen swelling. Heat packs that are too hot or left in place too long may cause burns.