Most back pain is caused by a restriction of the spinal facets (Small spine joints) or sprains of the small inter-vertebral ligaments that cause swelling and inflammation to set in. Swelling puts pressure on the nerves and thus will cause pain
The heat will cause the blood vessels to open up and cause more fluid to leak into the tissues surrounding the area. Heat causes more swelling; this will cause more tissue damage which then will cause more pain.
Ice will cause the opening and closing of blood vessels, it will work like a pump. If you test it at home, you will see your skin will change colours from white to red and will keep on alternating. The pumping effect will get rid of toxins and allows new nutrients into the area to allow the surrounding injured tissue to heal.
Use ice instead of heat because ice CAN’T do any harm, but heat can cause extra tissue damage, thus heat will cause prolonged pain.