Though it is usually a very simple form of treatment, heat therapy is actually quite ingenious in the way that it relieves pain and muscle stiffness. When applied to sore areas of the body, heat helps to dilate your blood vessels. This encourages blood to rush to the affected area, flushing out toxins and other wastes. This blood also brings oxygen to the site, which helps to repair soft tissue, encourage muscle tone, and relax muscles contractions.
Heat therapy can also lessen the severity of pain symptoms, though it is not completely understood why. It is thought that heat may help to numb the nerve endings inside your body, thereby decreasing your sensations of pain.