Effects of Beijing's Pollution Are Seen As Hazy by Experts

As the Olympic Games move outdoors in earnest with the start of the track and field and triathlon events, the question in the air is whether the air will make a difference.

Absent a meteorological meltdown that leaves dozens of athletes gagging and wheezing, it will be impossible to know. The effects of air pollution on sport are subtle and generally small, according to medical experts, altering performance by only 3 to 4 percent even under bad conditions.

Furthermore, the five pollutants of interest are only half the equation. Sensitivity to chemicals and particulates in the air differs from person to person, with asthmatics at the greatest risk but people without the condition showing a range of response, as well. Timing also counts; some exposures do not produce a peak effect for a day or longer.

And then there is the simple issue of information. The International Olympic Committee is not releasing its air-quality measurements; the Beijing city government isn't reporting on levels of ozone, the pollutant most likely to make a difference; and data from independent groups is wildly at odds with the official readings.

"There is a direct relationship between air pollution and athletic performance. I can predict this. But I have no clue as to what is going on in Beijing," said Giuseppe Lippi, a physician and sports physiologist at the University of Verona in Italy.

In an article published in April in the International Journal of Sports Medicine, Lippi wrote that some experts believed this Olympics would be affected by air pollution "on an unprecedented scale."

David B. Peden, a University of North Carolina expert on the relationship between pollution, lung function and performance, said he believes that "to get truly unbiased data will probably be very difficult. Even the IOC may have reason to guard their data."

Will there be a decline in performance?

"I think at the levels of competition we are talking about, there may be single-digit effects, and that might be enough to make a difference," Peden said earlier this week.

Pollution matters little to athletes whose events are over quickly, where anaerobic metabolism is important and there isn't prolonged heavy breathing. That isn't true for endurance athletes, who inhale doses of pollutants that far exceed anyone else's.

People at rest breathe about six to 10 liters of air per minute. That increases tenfold during long races; amounts higher than 150 liters per minute have been recorded. At such high volumes, much of the air goes in and out of the mouth, not the nose, which is able to filter out some pollutants.

The substance with the most clear-cut effect is carbon monoxide. It attaches to hemoglobin, the oxygen-carrying protein in the blood, reducing the amount of oxygen delivered to the muscles. A study published in 1995 found that people who run or cycle on city streets can have carbon monoxide levels of up to 5 percent, comparable to smokers.