Pain forces an estimated 36 million U.S. residents to miss work every year and results in roughly 70 million doctor visits. Studies find that exercise is in many cases one of the best remedies for chronic pain. Image

First off, let's set the record straight: Pain is normal. About 75 million U.S. residents endure chronic or recurrent pain. Migraines plague 25 million of us. One in six suffer arthritis.

The global pain industry peddles more than $50 billion in drugs a year. Yet for chronic pain sufferers, over-the-counter pills are typically little help, while morphine and other narcotics can be addictive sedatives.

An overview study published last month in the Journal of General Internal Medicine looked at multiple studies of pain and found "researchers don't yet know how to determine which [treatment] is best for individual patients." From studies of drugs to surgeries and alternative medicines, "We have found that there are huge gaps in our knowledge base," said Dr. Matthew J. Bair, assistant professor of medicine at the Indiana University School of Medicine.

So what is pain and why do so many suffer so long?

Pain is felt when electrical signals are sent from nerve endings to your brain, which in turn can release painkillers called endorphins and generate reactions that range from instant and physical to long-term and emotional. Beyond that, scientific understanding gets painfully fuzzy. Here's what's known:

1. Scientist don't understand pain

When you're in pain, you know it. But if scientists could fully grasp how pain works and why, they might be able to help you more. The American Academy of Pain Medicine defines pain as "an unpleasant sensation and emotional response to that sensation." Some pain is the result of an obvious injury. Other times, it is caused by damaged nerves that are not so easy to pinpoint. "Pain is complex and defies our ability to establish a clear definition," says Kathryn Weiner, director of the American Academy of Pain Management. "Pain is far more than neural transmission and sensory transduction. Pain is a complex mixture of emotions, culture, experience, spirit and sensation."

2. Chronic pain shrinks brains

If you have chronic pain, you know how demoralizing and debilitating it can be, physically and mentally. It can prevent you from doing things and make you irritable for reasons nobody else understands. But that's only half the story. People with chronic backaches have brains as much as 11 percent smaller than those of non-sufferers, scientists reported in 2004. They don't know why. "It is possible it's just the stress of having to live with the condition," said study leader A. Vania Apkarian of Northwestern University. "The neurons become overactive or tired of the activity."

3. Migraines and sex go together

It may not eliminate the phrase "Not tonight, honey ..." but a 2006 study found that migraine sufferers had levels of sexual desire 20 percent higher than those suffering from tension headaches. The finding suggests sexual desire and migraines might be influenced by the same brain chemical, and getting a better handle on the link could lead to better treatments, at least for the pain portion of the equation.

4. Women feel more pain

Any man who has watched a woman having a baby without using drugs would swear that women can tolerate anything. But the truth is, guys, it hurts more than you can imagine. Women have more nerve receptors than men. As an example, women have 34 nerve fibers per square centimeter of facial skin, while men average just 17. And in a 2005 study, women were found to report more pain throughout their lifetimes and, compared to men, they feel pain in more areas of their body and for longer durations.

5. Some animals don't feel our pain

Animal research could offer clues to eventually relieve human suffering. Take the naked mole rat, a hairless and nearly blind subterranean creature. A study this year found it feels neither the pain of acid nor the sting of chili peppers. If researchers can figure out why, they might be on the road to new sorts of painkilling therapies for humans. In 2006, scientists found a pathway for the transmission of chronic pain in rats that they hope will translate into better understanding of human chronic pain. Lobsters feel no pain, even when boiled, scientists said in a 2005 report that is just one more salvo in a long-running debate.

What you can do

Meanwhile, exercise is a useful remedy for many types of chronic pain.

In an Italian study detailed in the May issue of the journal Cephalalgia, office workers did relaxation and posture exercises every two to three hours. Over an eight-month period, they kept diaries, which were then compared to those of a control group that did not change habits. In the end, the group that exercised reported that headaches and neck and shoulder pain decreased by more than 40 per cent, and their use of painkillers was cut in half.

"Physical activity is actually a natural pain reliever for most people suffering from arthritis," concludes another study published in the Arthritis Care and Research journal in April. "Even minor lifestyle changes like taking a 10-minute walk three times a day can reduce the impact of arthritis on a person's daily activities and help to prevent developing more painful arthritis," said Dr. Patience White, chief public health officer of the Arthritis Foundation. "Physical activity can actually reduce pain naturally and decrease dependence on pain medications."