Cold vs Heat
When it comes to using cold or heat on an injury or to help with pain relief, it can be confusing as to which one you should choose.
Some people will tell you ice is best, others will tell you heat is best, and some will say not to use anything, and let the body do its thing. So what should you do?
Let's start by defining the two therapies a little more...
Defining the two:
Cold therapy is sometimes referred to as 'cryotherapy' ('cryo' referring to the use or production of cold). However, with the introduction of businesses offering sessions in cryotherapy tanks or chambers, this name is not entirely appropriate when referring to the use of various cold items or environments for a therapeutic effect.
Ice (salted, wetted, cubed, crushed), cold packs, cold water immersion, ice bath, cryotherapy chambers/tanks, are all examples of cryotherapy or cold therapy.
Heat therapy can be divided into two different types: moist heat, and dry heat.
Moist heat involves moisture in the heat conduction. This may come in the form of a sauna, spa, moist towel, steam room, or hot bath.
Dry heat does not involve moisture, and arguably does not have as significant an effect in heating the tissues/body. Examples of dry heat include: heat lamp, infrared sauna, hot pack, wheat bag, hot water bottle, or heated blanket.
Comparing and Contrasting the Proposed Mechanisms of Effect
Decreased muscle spasm
Reduction in local blood flow
Reduction in risk of hypoxic injury
- Pain reduction is believed to be caused by a reduction in nerve conduction velocity (the speed a nerve sends an impulse. In this case one that may result in the experience of pain). Cold also stimulates temperature receptors in the skin and provides a 'distracting' stimulus to the brain, which can modulate the production of pain sensation.
- Decreased tissue temperature also appears to decrease spinal reflex loops, which can result in a decrease in associated muscle spasm.
- Reducing tissue temperature significantly enough can have a vasoconstrictive (causes blood vessels to constrict) effect in the locally-cooled tissue. This may reduce the delivery of inflammatory mediators and oedema (fluid retention) in the area.
- By reducing tissue temperature, the locally-cooled tissues have a lower metabolic activity level. This reduces the demand on injured tissue, which may result in less risk of secondary injury.
Increased blood flow and tissue metabolism
Increased tissue elasticity
- Pain reduction may be as a result of stimulation of temperature-related receptors in the tissue, which can (like the use of cold) have a distracting effect on the brain and modulate the experience of pain.
- Heating tissue results in a local vasodilation (dilation of blood vessels) in the heated area, which increases local blood flow. With that increased blood comes increased inflammatory mediators, immune products, and other factors which may increase the healing response.
Increased tissue temperature also increases the local metabolic activity, which has been proposed to possibly lead to a more rapid healing rate.
- Heat increases mobility/pliability of collagen and other fibres that make up connective tissue. This increase in pliability is believed to be a possible reason for heat increasing tissue flexibility.
So Which One Do You Choose?
Acute ankle sprains
Ice has been shown (in multiple studies) to have a greater effect in improving function, and reducing disability associated with the injury if applied in the early stages (first 48 hours).
After the first couple of days ice does not appear to be any better than heat or not using either. There has not been much research investigating whether this is true for most acute joint injuries, though it would likely be a similar case.
Acute back pain
It may come as a surprise, but heat has been shown to have a greater effect on pain and function in acute low back pain.
Heat or ice can be useful in managing pain or stiffness associated with muscular injury. This one comes down to whether you prefer heat or cold.
Nerve injury or Nerve pain
As ice can cause a decrease in nerve conduction velocity in the local area, it would likely be the more effective choice when managing nerve pain (often described as sharp, stabbing, burning, prickling, tingling).
How Should You Apply Them?
The most effective way of cooling the injured or painful tissue is through 'cold water immersion' (sometimes called an ice bath). This isn't always a practical option, and so the most effective of the simpler options is wetted ice in a bag (ice and water).
Wetted ice is more effective than crushed or cubed ice, which is more effective than frozen vegetables, which are more effective than a gel pack or ice brick.
The ice should be applied directly to the skin. Wrapping the ice/gel pack in a cloth or placing a towel underneath will reduce the ability of the ice to draw heat out of the tissues, and will significantly reduce the effect of applying cold therapy.
You can increase the effect further by compressing the ice bag with a compression bandage, or similar.
Apply the ice for a minimum of 10 minutes, but if possible leave for 20+ minutes. This allows the tissues to cool to lower temperatures, which may have a greater effect, and also allows for slower rewarming time (meaning a longer effect).
Remove the ice once the tissue has become numb or if it becomes uncomfortable. Check the area every few minutes to ensure the tissue is not being subjected to 'ice burn'.
Heat is more simple. Heat the hot pack, wheat bag, or hot water (if using a hot water bottle) and apply over the area.
Ensure you test the temperature of the heating object before applying to the skin. As burns are more likely when using heat than ice.
Apply the heat for 10-20 minutes or until the heat source cools.
Further Points and Summary
An important point to mention is that topical ice or heat sources (those applied to the skin such as packs, bags, cloths etc) will only have an effect on the local area where the object is applied, and will only affect the superficial level of tissue. Even ice directly on the skin for 10+ minutes will still only affect the superficial 2-3 centimetres of muscle and fat. So deeper injuries will not be affected in a meaningful way.
Once the ice or heat has been removed the tissues will gradually 'warm' or 'cool' to normal temperatures, respectively. Once this happens, the therapeutic effect will gradually cease, until you re-apply.
None of the research to date gives any strong indication that one option is significantly better than the other, for any kind of injury or pain investigated.
At the end of the day you should choose the one you feel more effective and comfortable for you.