Many benefits come from regularly exercising, including stronger muscles, lower risk of disease and improved mental health. But a recent study suggests that exercise may have another unexpected benefit: it might make us more tolerant to pain.
The study, published in the journal PLOS One, found people who regularly exercised had a higher pain tolerance compared with those who hardly exercised.
To conduct their study, the researchers used data from 10,732 participants who'd taken part in the Tromsø study - a large study on health and disease that was conducted in Tromsø, Norway. The participants were aged 30 to 87, and just over half were women.
Every participant was assessed twice, eight years apart. During each assessment, they answered questions about their physical activity levels and took part in a cold pressor test. This is a common method used by researchers to induce pain in a laboratory environment. Participants place their hand in 3°C water for as long as they can. The longer they keep their hand in the water, the greater their pain tolerance.
The researchers found that the more active the participants were, the longer they could keep their hand in the water. In fact, those who were categorised as being very active were able to keep their hand in the water for 115.7 seconds on average compared with 99.4 seconds for the least-active participants. The researchers also found that participants who stayed active or became even more active were able to perform better on average during the second test compared with those who remained inactive.
It's worth noting, however, that over the eight years between assessments, everyone became less tolerant of pain on average. This change was roughly the same for everyone - whether people were couch potatoes or avid marathoners. But active participants still had higher pain tolerance compared with inactive people, despite this decrease. It's uncertain why people became less tolerant to pain over time, but it could be because of ageing.
However, we must be cautious when interpreting the findings. Assessing physical activity via self-report is tricky business as participants may be tempted to report they're more physically active than they are in reality. They may also have trouble remembering their physical activities, which can lead to both over- and under-reporting.
The participants were also only asked about their physical activity over the last 12 months, leaving the remaining seven years between assessments unaccounted for in the analyses. This means someone may be classed as sedentary despite having engaged in vigorous physical activity for seven out of the eight years. Such cases may skew the results and lead to a misinterpretation of the outcomes.
Still, this study joins a growing body of research which has shown the benefits of physical activity on pain tolerance.
Exercise and pain
Given these results, it's interesting to speculate how physical activity may affect pain tolerance. While we do have some ideas why this link exists, we're still a long way from knowing the complete picture.
One possible explanation for this link could be due to some of the physiological changes that happen after exercising - such as exercise-induced "hypoalgesia". This essentially refers to a reduction in pain and sensitivity that people report during and following exercise. A good example of this is the runner's high, when the body releases its own opioids, called endorphins. These hormones bind to the same receptors as opioids, producing a similar pain-reducing effect.
Yet endorphins are only part of the magic behind the runner's high. Research suggests the endocannabinoid system has similar effects following exercise. This system is a vast cell-signalling network, comprised largely of endocannabinoids and their receptors. These are neurotransmitters produced by the body that are involved in many processes, including regulating sleep, appetite and mood.
Research also suggests they can help us tolerate pain better. Studies show that exercise can increase levels of endocannabinoids, which may in turn improve our pain tolerance overall.
But pain is not a purely physiological phenomenon. It's an experience, and as such, is subject to our psychology as much as our physiology.
It could be argued that exercise brings with it some level of pain - from stitches and muscle aches to that burning sensation you feel when trying to squeeze out that last rep.
Because of this, exercise has the power to change the way we appraise pain. Exposing ourselves to these unpleasant experiences during a workout can help build resilience - our ability to function in the face of stressful events, such as pain. Physical activity can also build self-efficacy - our belief that we can do certain things despite pain.
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Physical activity also improves our mood, which in turn makes us more resistant to pain. Furthermore, exercise helps us learn how to distract ourselves from pain - such as when we listen to music while running. Regular physical activity can help us overcome fear of pain and movement and allows us to be prepared for the experience of pain. Unsurprisingly, many of these techniques are used as the basis for pain management techniques.
While there are still many questions that future research will need to answer, this research reminds us just how beneficial exercise is to us - even in ways we wouldn't expect. These findings may also add to a growing body of evidence that argues exercise may help manage chronic pain.
Nils Niederstrasser, Senior Lecturer in the Department of Psychology, University of Portsmouth
