The moment you were born, two balloons inflated inside your chest, began pumping and haven't stopped since. Those sacs of air—a.k.a. your lungs—are responsible for transferring oxygen to your bloodstream and removing waste in the form of carbon dioxide.
Most of the time you're hardly aware of them, but if you're grinding up a long climb, you might notice how hard you're breathing and wonder whether those balloons are any bigger than a couple of grapes. In fact, your lungs are plenty large. "Most of us are born with enough lung capacity to escape a lion," says Norman Edelman, MD, senior medical advisor for the American Lung Association. But if your lungs are compromised, says Edelman, they can slow you down. And many cyclists may unwittingly be doing theirs harm.
Here's what's going on. When you ride at your aerobic peak, you breathe in massive quantities of air—an estimated 150 liters per minute, says David M. Systrom, MD, assistant professor at Harvard Medical School and director of the advanced cardiopulmonary exercise-testing program at Brigham and Women's Hospital in Boston. And with every breath, you suck in microscopic bits of soot, exhaust, dust, aerosols and other pollutants, all of which can cause inflammation.
Ride near heavy traffic or an industrial area, and the problem is exacerbated. Ozone, the main ingredient in smog, is a lung irritant that can give you "what amounts to a sunburn in your lungs," says Edelman. Runners who exercise in areas with high ozone levels develop thickened lungs, similar to what happens to smokers, according to the Health Effects Institute, a Boston nonprofit organization that studies the effects of pollution on health.
And scientists who looked at cyclists exposed to ozone while riding reported that their lung function decreased by 22 percent and their endurance by 30 percent. What's more, researchers in Canada discovered that people who are chronically exposed to such pollutants are 20 percent more likely to die from lung cancer than those who breathe clean air—the same odds you'd face if you lived with someone who lights up.