Hot vs Cold? The Latest Evidence in the Battle for Pain-Relief
So far in our blogs this year we have explained the mechanisms of pain and have also touched on chronic pain. In this blog post we will investigate the effects and the mechanisms of heat vs ice, and when they should be applied.
The following blog is derived from the review article: "Mechanisms and efficacy of heat and cold therapies for musculskeletal injuries" GA Malanga, N Yan and J Stark (2014)
Musculoskeletal injuries associated with pain are a common health condition causing extensive disability in industrialised countries with back pain (neck and lower back) the most common type of pain experienced. Despite the high prevalence of acute musculoskeletal pain around the world it is often under-treated. This can have long-term consequences as under-treatment of acute pain may progress towards chronic pain and disability.
Nonpharmacological treatment of acute musculoskeletal injuries should aim to reduce pain and associated swelling, inflammation and promote healing in order to facilitate a return to normal function and activity. Heat or cold therapies are often used in this context, however there is often confusion about which type (hot or cold) to use, the timing and duration of use, and the mechanism by which each modality works.
Cold or cryotherapy refers to the application of any substance or physical medium to the body that removes heat, decreasing the temperature of the contact area and adjacent tissues. Cold therapy is typically used in the management of acute injury/trauma, chronic pain, muscle spasm, delayed onset muscle soreness (DOMS), inflammation, and swelling. Acute ankle sprains are a typical injury for which cold therapy is used, generally within the context of the RICE (Rest, Ice, Compression, Elevation) principles.
Mechanisms of Cold Therapy
Reduces temperature of skin and muscles.
Activates sympathetic vasoconstriction (narrowing of blood vessels) reflex which
Reduces blood flow to the cooled tissues.
Decreases swelling and slows down delivery of inflammatory mediators.
Induces a local anaesthetic effect (cold-induced neurapraxia) by decreasing the activation threshold of pain receptors and reduces the speed of nerve signals conveying pain.
Reduced muscle temperature also reduces muscle spasm by inhibiting a spinal cord reflex loop.
Recommendations for Cold Therapy Most recommendations for cold therapy in the management of acute musculoskeletal injury are largely anecdotal with only marginal evidence supporting the use of ice and exercise after ankle sprain and post surgery. There was little evidence to suggest that the addition of ice to compression significantly improved swelling and range of motion.
Topical cooling creams may be effective for pain management, although they are ineffective for cooling the skin and surrounding tissue.
A comparative study looked at the differences between an intermittent icing protocol (10 minutes on, 10 minutes off, 10 minutes on every 2 hours) vs continuous protocol (20 minutes on every 2 hours) over the first 72hrs after an acute ankle sprain.
Patients treated with the intermittent icing (10 mins on/10 mins off/ 10 mins on) had significantly less ankle pain on activity compared to those treated with continuous icing (20mins).
There were no significant differences between icing protocols in terms of ankle function, swelling or pain at rest.
Precautions of Cold Therapy If used inappropriately cold therapy can put patients at risk of frostbite, allergic reactions, burns and intolerance/pain.
Cold therapy should be used with caution in patients with hypertension, mental impairment or reduced sensation, and should not be administered to patients with cold hypersensitivity, cold intolerance or Raynaud's disease, or over areas of vascular compromise.
Cold therapy has also been associated with short-term adverse changes to joint position sense, muscle strength and neuromuscular performance which may adversely affect the performance of athletes immediately after cold therapy.
Heat therapy refers to the application of heat to the body resulting in increased tissue temperature. Physiological effects of heat include pain relief, increases in blood flow and metabolism, and increased elasticity of connective tissue.
How Heat Therapy Works
Heat causes activation of receptors (TRPV1) in the brain which are thought to control descending nerve pathways responsible for reducing pain.
Increase in tissue temperature stimulates vasodilation (expansion of blood vessel size).
Increased tissue blood flow promotes healing by increasing supply of nutrients and oxygen to the site of injury.
Local increase in tissue metabolism from warming which further promotes healing.
Heat causes changes in the properties of collagen tissue which may explain the effect of heat therapy in improving range of motion.
Recommendations for Heat Therapy
In a large review on the research in 2006 (Cochrane Databse Review) heat therapy was compared with cold therapies for low back pain. It was found that heat-wrap therapy provided small but significant short-term reductions in pain and disability for patients with acute low back pain.
One study found heat along with exercise therapy significantly improved measures of spinal functional and disability 2 days after the last treatment when compared with either exercise or heat alone, or with no treatment. Pain-relief was also found to be greater with heat AND exercise compared with exercise alone 2 days after the last treatment.
In investigating the effects of continuous heat in preventing DOMS from exercise, it was found that heat applied 4hrs before eccentric exercise significantly reduced pain intensity, disability and intensity and subject-reported deficits in physical function 24hrs post-exercise compared with a stretching group. It was also found that heat applied 18hrs and 32hrs for 8hrs post exercise provided greater pain-relief against DOMS compared to cold packs, although there were no differences shown in physical function or disability between the groups.
Precautions of Heat Therapy
Adverse events reported in trials of superficial heat for low back pain were minor. Precuations should be taken in patients with multiple sclerosis, poor circulation, spinal cord injuries, diabetes mellitus and rheumatoid arthritis, as heat can cause disease progression, burns, skin ulcerations and increased inflammation. Skin should also be protected during heat therapy in heat-sensitive or high-risk patients, especially over regions with decreased sensation.
SUMMARY: COLD VS HEAT
Hot and cold are considered part of standard care for acute musculoskeletal pain. Most recommendations are based on unconfirmed information due to limited evidence in controlled trials. E.g. RICE and PRICE protocols have not been validated in adequately designed research trials. There are low quality trials with current available literature as many trials were subject to bias and potential overestimation of the treatment effects, especially when considering the subjective nature of pain.
Overall due to limitations of the available data it is difficult to make evidence-based recommendations regarding use of heat and cold therapy.
Cold therapy is generally recommended for ankle and other acute joint sprains despite lack of strong supportive evidence, while heat therapy is recommended for reducing pain and increasing function in patients with acute low back pain and in patients with DOMS from eccentric or unfamiliar exercise.
The American College of Rheumatology recommends use of heat for pain and stiffness associated with osteoarthritis (OA) of the hand and in combination with a physiotherapy-supervised exercises for treatment of OA for the hip and knee.
There is need for additional sufficiently-powered high quality trials of cold therapy effects. Heat has been shown to demonstrate therapeutic benefit for both analgesia and promoting healing in certain injuries, and it is the modality of choice for acute low back pain and muscle soreness, but further research is needed to improve our understanding.
Patients can be advised to apply ice during the initial 48 to 72 hours after an acute injury of the musculoskeletal system (eg, sprains, strains), whereas after the first 72 hours there is little evidence for continued benefit.
Overall better education of health care providers and consumers could reduce confusion and optimize the use of these accessible and low-cost therapies in the treatment of musculoskeletal injuries.
Current Available Evidence
Cold therapy = acute injury with inflammation e.g ankle and joint sprains
Heat therapy = musculoskeletal pain and soreness as well as joint pain and stiffness.
Cold or heat may be helpful for acute LBP and muscle soreness but heat is better validated.
Beyond the acute pain, if you need any advice or treatment for an injury don't hesitate to get in touch with us.
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