When it comes to deciding whether to use ice or heat for an injury, a few factors are important to consider. The first question is usually “is this a new (acute) or old (chronic) injury”. Acute injuries are quick sudden onset injuries that typically do not last long. Chronic injuries are injuries that develop slowly over time. Acute injuries are usually accompanied by sharp pain, swelling, tenderness, redness, and skin that is warm to the touch. Chronic pain on the other hand is usually more associated with dull pain or soreness and stiffness before or during activity.
Ice or similar cold therapy is best to use immediately following an injury typically up to 48 hours. Ice reduces swelling and pain by vasoconstricting blood vessels limiting internal bleeding at the site. It is also helpful in the repetitive or overuse injuries which may be a chronic problem but result in acute injury/irritation after activity. Again this will help to prevent inflammation and further damage to the tissue. It is not recommended however, to ice these types of injuries before activity.
Heat is best used on tissues in injuries that do not result in swelling or inflammation. This would include things like having a sore, stiff, nagging type of muscle problem or joint pain. People with these types of injuries are encouraged to use heat prior to activity to increase blood flow and elasticity of the muscles or ligaments and tendons. Heat should not be applied after exercise as it will cause further swelling and inflammation leading to more of a problem. Also you should never go to bed with a heating pad or hot pack on your body.
Again it is important to note that these are general guidelines and that each case is different. If you have questions about which one to use, you should contact your health care provider for further explanation.