April 17, 2003 -- Back off, Tarzan. You can swing through the trees while cradling Jane, but that doesn't mean if you both fall it's going to hurt her more than you. Or does it?
Study after study has shown that men have a higher tolerance for pain than women, according to researchers who seem to be making some progress in figuring out why.
"Men and women differ in their pain tolerance," says psychologist Roger Fillingim of the University of Florida, who has spent years trying to learn why. "There's no debate on that."
Pain Measurement Too Subjective
The debate among experts, he says, is over why. Until recently it was thought that Tarzan was just being Tarzan, and men denied their pain to protect their masculine image. A higher tolerance, so the theory went, was just macho stuff.
But a number of studies now indicate that there is much more than the preservation of masculinity at work here. There appear to be fundamental differences in how the two genders deal with pain. And it's not just an academic issue.
"If it were just the fact that women are reporting pain more readily than men, that's not a big deal. But I don't think that's the important stuff," Fillingim says. "The important stuff is that certain factors, whether they be psychological, hormonal, whatever, may influence pain differently in women than in men, and vice versa. If that's the case, then we may need to apply different treatments to women than men in order to reduce their suffering."
The problem, as Fillingim readily admits, is that pain is a very difficult thing to study. You can't put it on the lab bench and look at it through a microscope.
"We're hamstrung by the fact that pain is a subjective experience," he says. "We rely on the person to tell us what they are feeling, and that has all kinds of problems."
Researchers have adopted fairly standardized methods for assessing responses to painful stimuli in an effort to reduce the influence of such things as male stereotyping, but in the end the work still hinges on what the person says. Some scientists are developing techniques that might reduce that by giving injections that will produce uniform levels of pain among a variety of subjects, but that's still in the experimental stage.
So most research projects still depend on the willingness of the person to say honestly when they feel pain, and how much. If the goal of the research is to learn whether males deny pain because that's the manly thing to do, then the researchers have to get a little tricky.
No Pain, No Money
Fillingim, whose pain research is under the school of dentistry for reasons that should be obvious, devised a clever little scheme to see if men are more motivated to deny pain because "they have to maintain their male image."
"Here was our thinking," Fillingim says. Men are motivated to suppress pain, and if women aren't equally motivated, then some reward might boost the pain tolerance among women but not among men because men are already motivated. A little reward might sort of level the playing field.
So 81 folks agreed to stick their hand in a bucket of swirling ice water to see how long they could stand the pain. Some were offered $1 to keep it in the near-freezing water for five minutes, others $20, so the researchers could determine if a higher reward made any difference than the lesser, which amounted to just a nickel for every 15 seconds.
The researchers thought the motivated females would keep their hands in the water longer than they would without the monetary motivation, thus narrowing the gap between Tarzan and Jane because now the females were motivated to stand the pain.
But "we got the complete reversal of what we expected," Fillingim says.
There wasn't any difference for the females. But the men who were offered up to $20 lasted longer than the men who were offered just one lousy buck.
Fillingim says the study suggests that there is much more at work here than the motivation to deny pain.
"The gender-sexual-male macho thing is clearly not the only explanation for sex differences in pain," he says, because even motivated women are not better equipped to deal with pain. "If gender is playing a major role it may not be based on motivation (like the need to protect the male image.) There may be another path."
But, as he admits, maybe he chose the wrong motivation.
"It might be that some other incentive would work better for women," he says.
And of course, no one's saying cheap, cheap, cheap here, but 20 bucks can't buy a heap of motivation these days.
Women’s Pain Varies by Cycle
But at least the project suggests that the motivation to protect the male image is not the only thing at work. That dovetails with other research projects, notably at the University of Michigan, that reveal fundamental biochemical differences in how men and women deal with pain. They found that sex hormones like estrogen play a big part in how we react to pain.
That finding helps explain how women, the so-called weaker sex, can deal with the excruciating pain of childbirth. New non-invasive brain-imaging techniques have allowed these researchers peer inside the brain, examining the chemical processes that occur in the presence of pain.
Estrogen levels among women vary widely during the monthly menstrual cycle, and during pregnancy, and the research shows that estrogen plays a critical role in helping the brain's natural ability to suppress pain.
"When estrogen levels are high, the brain's natural painkiller system responds more potently when a painful experience occurs, releasing chemicals called endorphins or enkephalins that dampen the pain signals received by the brain," the Michigan team reported. "But when estrogen is low, the same system doesn't typically control pain nearly as effectively."
So a woman's ability to withstand pain changes repeatedly over time.
And researchers at the University of California, San Francisco, have found that while women may be less tolerant to the sudden onslaught of acute pain, there is no difference between men and women when it comes to dealing with chronic pain, like cancer. Men and women were found to suffer equally with cancer of the bone.
So, many questions remain. But the "me Tarzan" bit is a little weaker today than it was just a few years ago. We appear to be far more complicated than that, both male and female.
Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.