FWIW, from :
http://www.patient.co.uk/health/ice-and-heat-treatment-for-injuries
Ice
With any
sprain, strain or bruise there is some bleeding into the underlying tissues. This may cause swelling and pain and can delay healing. Ice treatment may be used in both the immediate treatment of soft tissue injuries and in later rehabilitation.
During immediate treatment, the aim is to limit the body's response to injury. Ice will:
- Reduce bleeding into the tissues.
- Prevent or reduce swelling (inflammation).
- Reduce muscle pain and spasm.
- Reduce pain by numbing the area and by limiting the effects of swelling.
These effects all help to prevent the area from becoming stiff by reducing excess tissue fluid that gathers as a result of injury and inflammation.
In the later, or rehabilitation, phase of recovery the aim changes to restoring normal function. At this stage the effects of ice can enhance other treatments, such as exercise, by reducing pain and muscle spasm. This then allows better movement. If you are doing exercises as part of your treatment, it can be useful to apply an ice pack before exercise. This is so that after the ice pack is removed the area will still be a little numb. The exercises can also be done with the ice pack in place. This reduces pain and makes movement around the injury more comfortable.
How long should ice be applied for?
Ideally, ice should be applied within 5-10 minutes of injury for 20 to 30 minutes. This can be repeated every 2 to 3 hours or so whilst you are awake for the next 24 to 48 hours.
After the first 48 hours, when bleeding should have stopped, the aim of treatment changes from restricting bleeding and swelling to getting the tissues remobilized with exercise and stretching. Ice helps with pain relief and relaxation of muscle tissue.
Heat
When an injury is older than 48 hours, heat can be applied in the form of a wheat bag, heat pads, deep heat cream, hot water bottles or heat lamps. Heat causes the blood vessels to open wide (dilate). This brings more blood into the area to stimulate healing of damaged tissues. It has a direct soothing effect and helps to relieve pain and spasm. It can also ease stiffness by making the tissues more supple. If heat is applied to the skin it should not be hot; gentle warmth will suffice. If excessive heat is applied there is the risk of burns and scalds. A towel can be placed between the heat source and the skin for protection. The skin must be checked at regular intervals.
Do not use heat on a new injury. This will increase bleeding around the injured area and may make the problem worse. The exception to this is new-onset low back strains. A lot of the pain in this case is caused by muscle spasm rather than tissue damage, so heat is often more helpful than ice.
Ice causes a longer-lasting effect on the circulation than heat, and the painkilling properties of ice are deeper and longer-lasting than heat.
Both heat and ice can be re-applied after an hour if needed.
