What is it about hot water that relieves osteoarthritis pain? What is the mechanism of action and what other therapies have the same properties?

Osteoarthritis. Heat or cold therapy works by stimulating your body's own healing force. For instance, heat dilates the blood vessels, stimulates circulation, and reduces muscle spasms. In addition, heat alters the sensation of pain. You can use either dry heat -- such as heating pads or heat lamps -- or moist heat -- such as warm baths or heated wash cloths. Massage therapy has a similar mechanism of action.