The application of moist heat to an injured area is often used in conjuntion with other therapies to relax tight muscles and decrease pain or muscle spasms. Hot packs increase blood circulation, which encourages healing. Physical therapists also use hot packs to relax muscles following therapeutic exercise.
It is important not to apply hot packs initially on an injury that is inflammed or swollen. Use cold packs to reduce inflammation first. Once the swelling has abated, apply hot packs to relax the muscles.