Heat opens up blood vessels, which increases blood flow and supplies oxygen and nutrients to reduce pain in joints and relax sore muscles, ligaments, and tendons. The warmth also decreases muscle spasms and can increase range of motion.
Cold slows down blood flow to an injury, thereby reducing pain and swelling. Cold therapy slows circulation, reducing inflammation, muscle spasm, and pain. It should be used if the area is swollen or bruised.