"About a half an hour into the race, I had a lot of trouble breathing," he says. "I got to a point where I tried to relax and take a deep breath, and then I started getting nauseous."

Only eight of the 50 athletes who began the race finished it, Horgan-Kobelski says.

Beijing's notorious pollution, sure to be in the news as the biennial World Conference on Sport and the Environment starts Thursday in Beijing, is the U.S. Olympic Committee's "No. 1 uncontrollable concern" heading into the Olympics, says USOC chief of sport performance Steve Roush.

Despite the aggressive measures the Chinese have taken and are planning to take to improve air quality during the Olympics, including shutting down nearby coal-burning plants and limiting the number of cars on city roadways, the USOC is "exploring remedies, if it is very bad, on what we can have for our athletes to lessen the impact," Roush says.

•The USOC will give every U.S. Olympian, as well as coaches and support staff, masks to wear when they are outside, whether they are exploring the sites, shopping or training. The masks for training are specially designed to allow for a higher breathing rate, USOC senior sport physiologist Randy Wilber says.

Athletes won't be required to wear the masks, which use carbon filters to block pollutants. But if air quality is bad, they will be strongly encouraged. They won't wear them during competitions.

"The concern is not necessarily during the race — everybody's going to be breathing that — but the training and the prolonged exposure to it, how it would have lingering effects," Roush says.

•The USOC is encouraging every U.S. team to consider acclimating to Beijing's time zone and August conditions (typically 86 degrees with 78% humidity, according to Wilber) at a less-polluted location in Asia, arriving in Beijing just before their competitions to limit their exposure to polluted air.

Although U.S. teams have done final preparations elsewhere in the past, primarily to keep athletes out of the spotlight, "more sports than I've ever seen" are considering it for Beijing, Wilber says.

•The USOC is testing the breathing capability of potential Olympians while they are competing in polluted environments. For instance, Wilber attended a triathlon Olympic test event in Beijing last month to measure U.S. athletes' pulmonary function immediately after the race.

The idea is to pinpoint athletes who might experience asthmatic symptoms or other breathing problems because of poor air quality. Medications to treat those symptoms need to be applied for and cleared through anti-doping measures before the day of Olympic competition.

Despite the USOC's preparations, USOC chief executive officer Jim Scherr says he believes that air quality during the Games "will be conducive to good performance."

The USOC's approach overall is to "hope for the best and prepare for the worst," Wilber says. Athletes and coaches seem to be focusing on the former, trusting that the Chinese government and organizers will have pollution under control next August.

During year-out ceremonies in Beijing in August, IOC president Jacques Rogge said that Olympic endurance events such as the marathon might have to be rescheduled if air quality is poor. Rogge's comments added urgency to a concern that already was high on Olympic organizers' to-do list.

"Because China's government, the municipal government and the organizing committee have attached great importance and have spent so much money to improve the air quality, we have reason to be confident that we will be able to provide good air quality for the athletes," says Sun Weide, deputy director of media and communications for the Beijing Organizing Committee.

Joe Vigil, who coaches U.S. marathoner Deena Kastor, winner of the 2004 bronze, plans to exude confidence as well. "The more you worry about something, the more inhibitions you'll develop," Vigil said. "And if there are inhibitions on that starting line, you're not going to do a good job. So everything you do has got to be positive. Say, 'The pollution is all right. With your training, you're going to overcome it.' "