Is laughter a kind of exercise? That offbeat question is at the heart of a new study of laughing and pain that emphasizes how unexpectedly entwined our bodies and emotions can be.
For the study, published this year in the biological research journal Proceedings of the Royal Society B, researchers at Oxford University recruited a large group of undergraduate men and women and set out to make them laugh.
Most of us probably think of laughter as a response to something funny as, in effect, an emotion.
But laughter is fundamentally a physical action.
"Laughter involves the repeated, forceful exhalation of breath from the lungs," said Robin Dunbar, a professor of evolutionary psychology at Oxford, who led the study. "The muscles of the diaphragm have to work very hard."
We've all heard the phrase "laugh until it hurts," he pointed out. That pain isn't metaphoric; prolonged laughing can be painful and exhausting.
Rather like a difficult workout.
But does laughter elicit a physiological response similar to that of exercise and, if so, what might that reveal about the nature of exertion? To find out, Dunbar and his colleagues had their volunteers watch, both alone and as part of a group, a series of short videos that were either comic or dryly factual documentaries.
But first, the volunteers submitted to a test of their pain threshold, as determined by how long they could tolerate a tightening blood pressure cuff or a frozen cooling sleeve.
The decision to introduce pain into this otherwise fun-loving study stems from one of the better-established effects of strenuous exercise: that it causes the body to release endorphins, or natural opiates. Endorphins are known "to play a crucial role in the management of pain," the study authors write and, like other opiates, to induce a feeling of euphoric calm and well-being (they are believed to play a role in "runner's high").
It's difficult to study endorphin production directly, however, since much of the action takes place within the working brain and requires a lumbar puncture to monitor. That is not a procedure volunteers willingly undergo, particularly in a study about laughing.
Instead, Dunbar and his colleagues turned to pain thresholds, an indirect but generally accepted marker of endorphin production. If someone's pain threshold rises, he or she is presumed to be awash in the natural analgesics.
And in Dunbar's experiments, pain thresholds did go up after people watched the funny videos, but not after they viewed the documentaries.
The only difference between the two experiences was that in one, people laughed, a physical reaction that the scientists quantified with audio monitors. They could hear their volunteers belly-laughing. The volunteers' abdominal muscles were contracting. Their endorphin levels were increasing in response, and their pain thresholds and general sense of enjoyment were on the rise.
In other words, it was the physical act of laughing, the contracting of muscles and resulting biochemical reactions, that prompted, at least in part, the pleasure of watching the comedy.
Or, as Dunbar and his colleagues write, "the sense of heightened affect in this context probably derives from the way laughter triggers endorphin uptake."
Why the interplay of endorphins and laughing should be of interest to those of us who exercise may not be immediately obvious. But as Dunbar points out, what happens during one type of physical exertion probably happens in others. Laughter is an infectious activity. In this study, people laughed more readily and lustily when they watched the comic videos as a group than when they watched them individually, and their pain thresholds, concomitantly, rose higher after group viewing.
Something similar may happen when people exercise together, Dunbar says.