Exercise Helps Lessen Pain, Studies Show

People seem to hurt less after exercise.

Studies involving people who are healthy and those who live with chronic pain find that exercise raises the threshold at which people notice something that hurts.

In one new study, even a single exercise session had an effect. People were slower to notice pain, and to notice it only at a higher level, after they had exercised compared with when they had not.

The process is known as exercise-induced analgesia, said researcher Kelli F. Koltyn, an assistant professor in the University of Florida’s exercise science department. “If the body is exposed to pain, it kicks into gear,” she said.

Koltyn and her colleagues studied 16 people with an average age of 29. All had a finger squeezed for two minutes by a device that delivered what Koltyn described as “a dull aching.”

“The best analogy is to put a finger in a door and apply pressure to that door,” Koltyn said.

Before the pain, participants either sat 30 minutes in a soundproofed room or rode an exercise bike 30 minutes at a moderately intense rate.

The same amount of pressure on the finger was seen as less painful after the exercise than after the quiet time, said the study in the American College of Sports Medicine journal, Medicine and Science in Sports and Exercise.

In addition, the 14 men and two women took twice as long to notice the pain after exercise, the study said.

The study didn’t follow exercisers to find out whether they became continually less sensitive to pain as their bodies became more used to exercise. But Koltyn suspects this might happen.

“When you start out, it may even feel painful, but as people get into better shape, exercise no longer hurts as much,” Koltyn said. Exercisers may be accepting the discomfort of working out but getting in return a reduced sensitivity to real pain, she said.

And, although everyone in the study felt less pain after exercise than after the quiet time, some people still felt pain more than others, Koltyn said.

Even if she might feel less pain after exercise, “I would still feel more pain than Clint Eastwood,” Koltyn said.

The study also did not examine how the body adapts to pain. Another researcher said it may result from an increase in endorphins, the body’s natural painkillers.

“The theoretical view is that exercise results in increased endorphins,” said sport psychologist William P. Morgan of the University of Wisconsin. “If that’s true, then the pain threshold should increase and pain should decrease. And I think that’s what they demonstrate.”

But it would take a different experiment, in which endorphins were blocked in some subjects, to show this, Morgan said.

It’s already known that exercise helps people live with the chronic pain of arthritis, said Teresa J. Brady, director of chronic disease services for Fairview Health System in Minneapolis.

It’s possible that endorphins are at work, but it may also be that exercise strengthens tissue that protects the joints, said researcher Marian Minor, an associate professor of physical therapy at the University of Missouri.

“We have found in rheumatoid and osteoarthritis, exercise is consistently the most effective treatment to manage and reduce pain,” Minor said.

But the prescription must be carefully tailored to the patient, so the force of the workout does not fall on disease-weakened bones or joints, Brady said.

For instance, someone with osteoarthritis of the knees and hips may not be able to run, but could do well with a Nordic ski machine, which would be less jarring on those sensitive areas, Brady said.