No doubt many of you have experienced the comforting effect of applying heat to various parts of your body, particularly in these colder months! But did you know what heat actually does to the various tissues in your body?
What happens when your tissues are heated up?
As the tissues are warmed up (by whichever method you use), the blood supply to those tissues is increased due to an expansion of the blood vessels (called “vasodilation”). This process is controlled by your nervous system. As a result, the following things occur:
- The collagen becomes more extensible, making the muscle/tendon/joint capsule much easier to stretch out.
- The increased blood flow supplies the tissue with more oxygen – an essential energy source for healing damaged tissues.
- The enzyme activity required for tissue repair increases.
- The metabolic waste products (incl. carbon dioxide) are more efficiently removed from the heated tissues.
These 4 things are the biological explanation for the decrease in pain & muscle spasm you get by applying heat to a specific body part.
When should I apply heat?
Despite all those beneficial effects, there are definitely times where the application of heat will do your body more harm than good. If you have just sustained an injury that has caused bleeding & swelling in your tissues (e.g. a muscle contusion, muscle tear or ligament tear) then increasing your blood flow to that area (via the application of heat) will most certainly make that bleeding & swelling worse. Which in turn will take your body longer to recover from. For this reason we always advise our clients not to apply heat within 48 hours of sustaining an injury. There are some people who are “slow blood clotters”, who need to wait even longer after an injury before they can safely apply heat – you should seek assistance from your local physiotherapist if you are in doubt about whether it is safe to apply heat following your injury.
There is also the danger of a burn if heat is applied to tissues with a severe lack of thermal sensitivity (due to previous injury to the nerves) or lack of adequate blood supply.
For most other scenarios, the application of heat is both safe and beneficial.
Different methods of applying heat
There are a number of ways in which heat can be applied:
- Moist heat: Hot shower/bath, Hydrocollator pack
- Dry heat: Wheat bag, Hot water bottle
- Chemical heat: Adhesive heat patches
- Mechanically generated heat: Ultrasound machine, Infrared radiation
Whist there has been historical debate about which method produces the greatest depth of heating, the research doesn’t actually favour one over another. Hence you are just best to utilise whichever method is most practical in your particular circumstances – e.g. Microwaveable Wheat Bags are clean & easy to use if you are at home with access to a microwave, whilst an Adhesive Heat Patch might be better if you need to be moving around whilst you have it on.
So for the most part, using heat as an adjunct to your physiotherapy treatment is a beneficial thing to do. However some care must be taken, so if you are in doubt speak to your local physiotherapist.
Adrian Quinn (B.Physio) - Practice Director @ Back In Motion Camberwell