Pain during exercise trains your mind as well as your muscles

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By the time he reached the 30-kilometre mark of the London Marathon this year, Alexis Mauger was not a pretty sight. His face and chest were smeared with blood from an ill-timed nosebleed, he had a bad blister on his left foot and he was losing a toenail on his right one.

On top of that, there was the pain.

"It was that deep muscle burn associated with intense exercise, which, if you continue to endure it, spreads through the whole body and basically becomes all-encompassing," recalls Mauger, an exercise scientist at the University of Kent in Britain. "I really couldn't imagine running for another hour."

Overcoming pain is often seen as the fundamental challenge in endurance sports. But at last month's Endurance Research Conference, hosted by the University of Kent, a series of new experimental results from Mauger and others offered conflicting views of what role pain plays during exercise and how important it is. The only point of universal agreement: You can't avoid it.

One of the more intriguing studies, presented by Thomas O'Leary and Martyn Morris of Oxford Brookes University, looked at how regular exercise increases pain tolerance. Previous studies have shown that training doesn't change your pain sensitivity (the point at which you say "ouch"), but does increase pain tolerance (how long you're willing to endure a given level of ouch) – a puzzling and poorly understood result.

O'Leary and Morris put volunteers through six weeks of cycling training, involving either continuous bouts at a moderate pace lasting an hour or more, or a set of six high-intensity intervals lasting five minutes each. Both groups got fitter to similar degrees, but the high-intensity (and thus more painful) workouts produced a 45-per-cent improvement in pain tolerance, measured with a tourniquet tightened around the forearm, compared with only 3 per cent in the moderate-intensity group.

That means that getting fitter, on its own, doesn't improve your pain tolerance, Morris says. Instead, repeatedly enduring pain seems to change how you perceive it: You're training your mind as well as your muscles.

However, the unpleasant sensations associated with exercise shouldn't all be lumped together as pain, according to research presented by Walter Staiano of the Danish Institute of Elite Sport and his colleagues at Bangor University and the University of Kent.

Pain is an "unpleasant sensory and emotional experience associated with actual or potential tissue damage," Staiano explained. During prolonged exercise, on the other hand, we're often battling an elevated perception of effort, which is "the conscious sensation of how hard, heavy and strenuous a physical task is." To distinguish between the two, he said, "you have to ask the right questions."

Staiano and his colleagues first tested the pain tolerance of volunteers by having them dunk their hands in ice water for as long as possible. Their rating of pain on a 10-point scale climbed steadily until it reached 10 and they gave up.

But in a test of cycling to exhaustion, their ratings of pain reached an average of only 4.8 before they gave up. Perceived effort, on the other hand, maxed out at 19.6 on a scale in which 20 is the highest possible: It was effort, not pain, that dictated the limits of their endurance.

Meanwhile, Mauger has been using a variety of techniques to alter pain sensation and see how it affects exercise performance. Using a technique called transcranial direct-current stimulation to run a weak current through the brains of volunteers, he was able to reduce their perception of pain during the hand-in-an-ice-bucket challenge.But the same technique didn't alter pain perception during a cycling test, suggesting that exercise pain is processed differently than other types of physical pain.

All of this suggests that simple generalizations about the precise role of pain in endurance will elude us. Instead, we'll continue to learn more about the subtle differences between pain, effort and other exercise-induced sensations, and how each affects different types of exercise – from the searing pain of a sustained sprint to the unrelenting ache that Mauger encountered during his marathon, which he eventually finished in three hours and 22 minutes, having slowed over the last 12 kilometres to make the pain tolerable.

It also suggests, as another researcher proposed after Mauger's talk, that one of the hidden keys to success in endurance sports is a sort of "benign masochism:" Just as some people thrill to the burn of spicy foods, others somehow revel in the pain of pushing their limits.

"All the way around, it was a difficult experience, and I was saying never again," Mauger said of his London Marathon ordeal, "up until the week after, when I applied for next year."