"I'd wager times and distance events will be well under previous Olympics and that will be proof right there," said Dr. William H.B. Howard, a surgeon who is director of the Arnold Palmer Sports Health Center at Union Memorial Hospital.
Howard said that if the air doesn't clear, many athletes might be off their peak times by 1 or 2 percent, a huge difference considering the fractions of seconds that often separate gold medalists from Olympic also-rans.
"You'll hear more horror stories when these people who are trying to compete go out there and have trouble and say, 'I just couldn't do it,' " Howard said.
Those with asthma will be particularly susceptible to Beijing's dirty air, experts say. About 8 percent of the adult population worldwide has asthma, a rate seen in both the general population and among competitive athletes.
When you exercise, you breathe in oxygen and release carbon dioxide, sending oxygen through the lungs to muscles to make them work, said Dr. Aldo Iacono, a pulmonary and critical care specialist who is medical director of lung transplants at the University of Maryland Medical Center. Polluted air inhibits that process, making it harder to breathe, he said.
"You can't get oxygen to the working muscles, so it would certainly affect their exercise performance," he said.
Exposure to air pollution also is believed to prompt a cardiovascular response that increases the risk of potentially fatal heart attacks, experts say.
A 2004 report published in the Journal of the American Medical Association attributed 3,000 cardiac deaths in the U.S. each year to ozone pollution.
"They're breathing air that can not only make them sick, it can put their lives at risk," said Janice Nolen, a spokeswoman for the American Lung Association.
Exercise requires breathing in 10 to 20 times more air than is required when standing still, so competitive athletes are letting more pollutants into their lungs, said Rundell, a former physiologist with the U.S. Olympic Committee.
This means athletes are more likely to be affected by dirty air as microscopic particles from car exhaust and factories lodge in their lungs. Lungs become inflamed and airways tighten.
"I do think it's going to affect performance. It's going to affect the asthmatics as well as the non-asthmatics," Rundell said.
Researchers who exposed cyclists to polluted air found that it had little effect on their performances when initially exposed for six-minute intervals, he said.
