Deedee, our PT: Generally, ice is used to decrease inflammation, and heat is used for general relaxation and to mask pain.
During the first 2-7 days following an injury, inflammation is present and a leading cause of pain. Ice can have profound effects on controlling inflammation and relieving pain. Apply ice to the painful area for 20 minutes while you lie or sit in a position of comfort. The area will at first feel cold, then burn, then feel numb. It’s good to let the skin rest from the ice for a couple hours, then apply again. For body parts that are not flat, like knees, I recommend using a bag of frozen peas, or a reusable cold pack found at most drug stores. For flatter areas, like a low back, ice cubes in a bag work very well. Place the bag in a pillow case and apply.
Some people freeze up in response to ice which leads to increased pain. Before giving up on ice completely, I recommend the following: apply the ice right to the painful area, and place a hot pack nearby, or opposite to the ice. For example, if you are applying ice to your neck, place an ice pack either on your chest, or on your back below the ice. The heat may relax you and allow you to tolerate the ice without tightening up.
Heat is used mainly for relaxation. For those with long-term pain, heat may help decrease muscular tightness and add to a greater sense of well-being. Often physical therapists apply heat to a body part prior to joint mobilization or massage in the hopes of relaxing the soft tissues.