Another study has found that people who exercise can tolerate more pain than people who stick to the couch.

Further, the more you exercise, the more you can tolerate pain, up to a point.

It’s not really understood why this is the case. In part, because most of the research doesn’t seem to delve into the why.

The scientists are too busy making their subjects go “ouch”. And not just for the fun of it.

The usual take-away from these studies is that maybe physical activity will make life more bearable for people with chronic pain. And maybe it can.

But it’s a tricky one. The real question becomes: How can we encourage people with chronic pain to get moving … when they’re frightened that moving their bodies will cause them more pain?

Norwegian study

The latest study, from Norway, is persuasive – because of the large number of participants.

Data from nearly 11,000 adults was accessed via the Tromsø Study, a large population survey study that is conducted periodically in Norway.

‘Cold pressor test’ measures pain tolerance.

According to a statement from Open Access publisher PLOS – which published the findings – the researchers used data from two rounds of the Tromsø Study, one conducted from 2007-08 and the other from 2015-16.

This allowed the researchers to get snapshots of the participants’ exercise pain-tolerance levels eight years apart.

Physical activity levels were self-reported (which means they need to be taken with a pinch of salt). Levels of pain tolerance were evaluated via ‘the cold pressor test’.

For this, participants placed their hand in ice-cold water (about 3°C) for as long as possible.

The results

Statistical analysis of the data showed that “participants who reported being physically active in either round of the Tromsø Study had higher pain tolerance than those who reported a sedentary lifestyle in both rounds”.

The higher the total activity levels by a participant, the higher the pain tolerance.

Those who had higher activity in 2015-16 than in 2007-08 had a higher overall level of pain tolerance.

The authors suggest “that boosting physical activity could help to ease or stave off chronic pain”.

What is known

In 2014, Gretchen Reynolds from The New York Times reported on an Australian study involving 12 young and healthy but inactive adults.

Before getting into the study and its findings, Ms Reynolds reported: “For some time, scientists have known that strenuous exercise briefly and acutely dulls pain. As muscles begin to ache during a prolonged workout, scientists have found, the body typically releases natural opiates, such as endorphins, and other substances that can slightly dampen the discomfort.”

Scientists call this dynamic ‘exercise-induced hypoalgesia‘.

It usually begins during the workout “and lingers for perhaps 20 or 30 minutes afterward”.

Ms Reynolds said there were two pressing questions at that time:

• Could exercise alter the body’s response to pain over the long term?
• Are these changes in pain-response triggered when people engage “in moderate, less draining workouts”?

Australian study

These questions were both answered in the affirmative by researchers from the University of New South Wales and Neuroscience Research Australia.

They recruited 12 young and healthy but inactive adults who “expressed interest in exercising”.

Another 12 were also young and inactive, but had no enthusiasm for exercising.

First step: All participants were brought to the lab where their pain threshold and pain tolerance were measure.

Pain threshold and pain tolerance

Your pain threshold is the point at which you start to feel pain, where nagging discomfort pushes through to something more unpleasant and you begin to say “ow”.

The scientists measured pain threshold using a metallic probe. This was slowly dug into the arms of the participants, with increasing pressure. (Read more about pain-pressure threshold testing here.)

Ms Reynolds wrote: “The volunteers were told to say ‘stop’ when that pressure segued from being unpleasant to painful, breaching their pain threshold.”

Pain tolerance is the time you can cope with an aching, burning or freezing sensation – whatever is causing you to say “ow” – before you pull away.

This was measured in a slightly perverse fashion.

The participants had a blood pressure cuff put on their upper arms. This was progressively tightened as the volunteers “gripped and squeezed” a special testing device in their fists.

They were encouraged “to continue squeezing the device for as long as possible”. However long they lasted was taken to represent their baseline pain tolerance.

Exercise, or not

The participants who were keen to start exercising followed a program of moderate stationary cycling for 30 minutes, three times a week, for six weeks.

They became more fit. Their aerobic capacity and cycling workloads increased each week. Of course “some improved more than others”.

The slacker volunteers “continued with their lives as they had before the study began”.

Results

After six weeks, the pain thresholds and pain tolerances of all participants were tested again. The slackers in the control group “showed no changes in their responses to pain”.

Those in the exercise group, however, “displayed substantially greater ability to withstand pain”.

While their pain thresholds hadn’t changed – “they began to feel pain at the same point they had before” – their tolerance had risen. They continued torturing themselves with the blood pressure cuff “much longer than before”.

Those whose fitness had increased the most enjoyed the greatest increase in pain tolerance.

Dr Matthew Jones, a researcher at the University of New South Wales who led the study, said the study “suggests that the participants who exercised had become more stoical and perhaps did not find the pain as threatening after exercise training, even though it still hurt as much”.

This fits with the heroic idea of athletes holding off the agony in pursuit of glory, etc.

Dr Jones, just like the Norwegian scientists, said the findings “could be meaningful for people struggling with chronic pain”.

Chronic pain is the big mystery

Three years later, Dr Jones published another paper – and then published an explainer at Neura.

This study involved healthy participants, but was exploring how expectations might affect people with chronic pain, a condition both mysterious and plain awful.

It also apparently investigated whether a person’s pain threshold could be altered (rather than pain tolerance, which was already shown to be flexible).

Dr Jones wrote: “We tested if we could change a person’s expectations about how exercise might influence their pain and whether this subsequently influenced their pain responses after exercise.”

The researchers did this by measuring pain thresholds before and after exercise in two groups of pain-free adults.

One group were told not to expect any change in their pain after exercise.

A second group were told to expect their pain would reduce after exercise.

The second group were told about exercise-induced hypoalgesia (the short-term reduction in pain that occurs after exercise) to condition them “to expect a reduction in their pain after exercise”.

And it worked.

Good news for people with chronic pain?

Can someone with chronic pain have their expectations changed in this way? Maybe. Depends on the person and their circumstances.

As Dr Jones wrote at the beginning of his Neura article: “In people with chronic pain, the interactions between exercise and pain are complex. On one hand, regular exercise may be one of the most effective treatments because it consistently improves pain, function and quality of life …

“On the other hand, a single session of exercise, such as a brisk 20 minute walk, may actually worsen pain.”

The reasons for these different effects of exercise on pain “are not clear because the mechanisms of how exercise changes pain are not well understood”.

More studies needed. More willing hands to be frozen and prodded.