Injuries – When To Apply Heat

When you are hurting, everyone loves a hot water bottle.  Heat is an excellent way to manage pain, however, there are some cases where heat will make things worse and should be avoided at all costs.  This article explains what injuries are best suited to applying heat and how to use it appropriately as a “go-to” in your first aid tool box.

How heat works

The use of heat in injury treatment is also known as thermotherapy.  It isn’t used medically as often as icing, but it is very useful on a day to day basis.   It works via a variety of different interesting mechanisms – some of which are “psychological” and some of which are physiological.

Psychological effects

Warmth from heatThe way you perceive a painful event – is it threatening or helpful? Will it stop? Is it something I can control? – has a massive impact on the way it feels.  If the pain is good – e.g. you just got back from the gym and your muscles feel like you really worked – you are able to ignore it more easily and crack on with life.  You may even celebrate the fact that it is there!  If the pain is bad – you hurt yourself at work and you don’t feel like it is being taken seriously – then it will typically feel worse. You put more focus into it; it enters your thoughts more frequently.  Maybe you change certain behaviors to make allowances for the pain.  All of these are examples of psychological impact on pain – you aren’t “making it up,” your brain is literally choosing to release pain activating or pain reducing chemicals within your body (Butler and Moseley, 2015)!  If you feel like you can do something to either help manage your pain or you are in some way in control of it, you are more likely to trigger the release of the pain reducing chemicals.  Therefore, putting heat on a painful area makes you feel like you are taking positive action, you believe it will have a good effect and you tend to trigger the pain reducing chemicals.

Heat is also a wonderful distraction.  When you have pain, this causes certain nerve pathways (for the academics – this is called your lateral spinothalamic tract!) to start to fire off more quickly and with greater strength.  If you add a positive sensation, like heat, this causes different neurons within the same pathway to fire.  Essentially, the brain has two different types of neurons talking into its “ear” at the same time.  It can’t pay the same amount of attention to the painful sensation, because the good sensation is also taking its attention.  This is known as pain gating (Mendell, 2014).  It’s the same mechanism behind therapies such as massage, heating or cooling gels and even tens machines.  Heat in particular feels good and works well to divert your brain’s attention from negative types of signalling.

Another interesting thought by pain scientist Paul Ingraham: if you think about prehistoric man, heat is also associated with safety – as opposed to cold (hypothermia) which would have been one of man’s biggest dangers.  By utilising heat, you are choosing a therapy your “primitive” brain perceives to be advantageous.  Again, this causes a subconscious reassurance which helps to reduce your stress and therein the release of stress chemicals (Ingham, 2016).

Physiological Effects

Muscle spasmA physiological mechanism is something that has a direct, biomechanical effect on the body.  When you have pain, you start to release stress hormones within the body.  These are typically carried in the bloodstream and lead to inflammation and also vasoconstriction (blood vessels tighten up) which reduces blood flow into the local area (Sigakis, 2015).  Quite a lot of your general aches and pains actually originate from muscles.  In general, this could be due to over-use, strains (a tear in a muscle fibre), cramps, spasms or trigger points (mini-spasms which create tender points within a muscle).  Heat causes the blood vessels to dilate (open up) which promotes fresh blood flow into the muscle.  Blood carries chemicals in it which help to promote healing, so you are improving their access to the muscle, if you like.

Heat also leads to muscle relaxation.  Although no actual research has been undertaken, it stands to reason that heat would help with the muscle stiffness and pain from trigger points.  Although the muscle itself is not overall in spasm, heat will help to reduce overall muscle tone, or reduce the number of muscle fibres being recruited.  Intuitively, heat would therefore also help to relax those mini-spasms as well making the entire muscle relax.

Where heat works best

Muscle painHeat is really good when you are talking about muscular soreness.  An obvious example would be post-exercise, after the gym, wrestling with your two year old or gardening!  Again, this would be true whether you were suffering from muscle cramp and spasm or just general tightness and discomfort from trigger points.

Heat is particularly good for back and neck pain.  These muscles are utilised for almost any movement and typically over-used as people don’t always activate their “core” muscles properly.  Hanson et al (1994) conducted a placebo‐controlled trial that had positive results in reducing back pain via an elastic wrap for the lumbar region (lower back), made of infrared‐reflective material that prevents loss of body heat.  Nash et al (2002) and Mungalani et al (2002) had similar results in

finding regular use (>8 hours/day) of a wrap with similar heat‐retaining properties was associated with >25% decrease in people living with chronic back pain.  Getting hold of kit such as those in the studies may not be practical, but it illustrates nicely application of heat is useful in managing back pain.

Crampy pain such as menstrual discomfort benefits from heat.  Muscle and joint pain from non-inflammatory osteoarthritis (normal wear and tear into the joints) will also be reduced with heat application (Kim et al, 2003).  General widespread pain conditions such as fibromyalgia may also find heat a relieving factor.

When to avoid heat

Back painHeat should definitely be avoided if you have a fresh injury.  If, for instance, you had just sprained your ankle, you will see the area beginning to swell up as a part of the inflammatory response.  Just as heat brings good blood flow into damaged areas, in cases of new injury, by dilating (opening up) the blood vessels, you ma

ke it easier for inflammatory chemicals to infiltrate the area making the overall process worse.  In this case, ice would be a much better choice for you (see my article on when to use ice for further information).

Inflammatory conditions such as rheumatoid arthritis or lupus (SLE) flares should also avoid heat for the same reason.

Heat application Tips

Heat can be applied locally such as via a heating pad or hot water bottle.  This works well, but should be done in moderation for short periods of time.  Sometimes using heat at certain times of the day or night can be helpful.  If, for instance, you were using heat for something like wear and tear arthritis, consider using it first thing in the morning.  This type of arthritis tends to have a predictable pain pattern of being achy the first 30 minutes post waking.  This is, in part, because fluid in the joint that acts like a lubricant to make the joint more slippery becomes viscous overnight (Hills and Thomas, 1998).  Heat will help to relax the muscles and perhaps loosen up this fluid from its “gelled” state so that everything starts moving well again.

Heat can also be more globally applied such as via a hot bath.  However, to get the most benefit out of a hot bath avoid using truly hot water.  Big sensory input such as extreme temperature will activate your sympathetic nervous system (aka your fight or flight response) and your body has to work hard to bring you back into balance.  This “revving up” of your nervous system can make it more difficult to sleep – so if you suffer from insomnia, try a more gently heated bath instead.

If stretching is painful for you generally, doing this after you have been in your warm bath for about 10 minutes can make it much more palatable.  The heat will help your muscles to relax and length out.  However, you need to be careful not to overstretch – if generally you struggle and in the water you are suddenly “Gumby,” you are definitely going too far!  Over-stretching muscles can lead to tears in the fibres and cramp or spasm if it is already irritable.  So approach it with a softly, softly mentality.

Overall, heat has many useful applications.  Its comforting and cheap – well worth considering as a go-to in your first aid toolbox.





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