How does exercise relieve pain?
It is estimated that 1 in 5 Australians live with chronic pain, which is pain that persists longer than the expected healing time (usually 3 months or more). Chronic pain ranges in its severity and frequency and for many people it can be intense, enduring, and have a significant impact on daily function. Many factors, both physical and psychological, contribute to chronic pain and the pain experienced is unique to each individual. Because of this, management approaches tailored to each individual are the most effective.
Numerous therapies are used to manage chronic pain. These range from conservative treatments such as massage and medications to more invasive options such as surgery. The type(s) of treatment will depend on the individual and the amount that physical and psychological factors are thought to contribute to their pain experience.
Another common therapy used to manage chronic pain is exercise. We know that people who exercise regularly are less likely to develop chronic pain and that, for people with chronic pain, taking regular exercise reduces pain and improves function. These benefits of exercise occur largely independent of the type and intensity of exercise performed, meaning that even gentle exercise such as walking can help. When it comes to pain, movement is medicine.
While it’s clear that regular exercise reduces pain, it’s not exactly clear why. This is what our research at NeuRA has started to investigate – the mechanisms of pain relief by exercise. Specifically, our studies have looked at how a single bout of exercise reduces pain in pain-free adults. We took this approach because to better understand how regular exercise reduces chronic pain, we first need to know more about how a single bout of exercise reduces pain.
Using this approach, our research showed that changes in the peripheral nervous system and central nervous system (i.e. the brain and spinal cord) are important. During exercise, the body releases several substances that can influence pain. These include endorphins (one of the ‘feel good hormones’) and endocannabinoids (compounds with similar effects to cannabis). Our results showed that exercise may reduce pain by reducing sensitivity of nociceptors, the body’s pain/danger sensors. We hypothesised that endorphins and endocannabinoids may contribute to this. By reducing sensitivity of nociceptors, the danger signal being sent to the brain is subsequently ‘turned down’, meaning that less pain is perceived.
A separate study of ours showed that changing pain expectations can influence pain responses to exercise as well. In this study, participants received either general education about exercise and pain or more specific education about the pain-relieving effect of a single bout of exercise. We found that participants who received more explicit pain education had a larger increase in their pain threshold (less pain) after exercise. This result implies that changes in pain cognitions are important as well, which is not surprising given the importance of the brain in pain.
Our research has shed some light on how a single bout of exercise reduces pain in healthy adults. We now hope to extend these studies to people with chronic pain to see if the same mechanisms are important. A greater understanding of how exercise influences the biological and cognitive contributors to pain may allow for more effective therapies to be developed; for instance, appropriate combinations of exercise, drug and education or cognitive-behavioural therapies. This would likely provide greater benefits to people with chronic pain for reducing the impact of pain on their life compared to the therapies currently available.
Matthew Jones is an Accredited Exercise Physiologist (AEP) and PhD student at Neuroscience Research Australia and the University of New South Wales. His area of research concerns exercise and pain, specifically the mechanisms by which exercise reduces pain in both healthy individuals and in individuals living with chronic pain.