Air pollution. Heat and humidity. Time zone changes. All have been cited as potential issues at next month's Beijing Olympics. And the fear is that any of them can throw a superior athlete into dissolution, allowing an inferior athlete to win a competition.
But the truth, exercise physiologists say, is not always the same as conventional wisdom. Jet lag may have no effect on performance. Although Beijing's pollution can be a problem, the biggest drag on performance probably will come from the city's heat and humidity.
"Heat and humidity is worse," says Randall Wilber, a senior sport physiologist for the United States Olympic Committee.
Matthew Ely, a researcher at the United States army Research Institute of Environmental Medicine in Natick, Massachusetts, found that elite marathon runners' times can be as much as 4 percent slower when the temperature is between 68 and 77 degrees as compared with the more ideal temperatures of 41 to 50 degrees. Because people respond differently to heat and humidity, an advantage may go to runners who ordinarily would not have been competitive.
"You will fatigue sooner in the heat," said Jose Gonzalez-Alonso, chairman of the department of exercise science at Brunel University in England. Some athletes cannot finish a race. And exercise just feels harder.
Athletes know the drill — spend some time training in hot and humid conditions to get acclimated. Expect to be slower.
Deena Kastor, a United States Olympic marathon runner, said she deliberately overdressed in training runs to prepare for Beijing. Her goal, she said in an e-mail message, "is to create a more hot and humid environment."
Brian Sell, a member of the Olympic marathon team, is spending a couple of weeks with his family in Florida, getting acclimated to severe heat and humidity and discovering how fast he can run in those conditions.
On race day, just before they compete, some endurance athletes are expected to wear a new version of a cooling vest made by Nike, hoping to start the race with their skin and core body temperatures as low as possible. The vest contains pockets of ice water.
While there is no doubt that pre-cooling the body before exercise in the heat can improve performance, the benefits are proportional to the amount of cooling that is achieved, said Samuel Cheuvront, a researcher who studies the effects of heat and humidity at the Army Research Institute.
Nike has not published data on its vests' effects on cooling or performance. Cheuvront said vests typically had only a small cooling effect, so their benefit was also likely to be small. Even a tiny difference may give a competitive edge in the Olympics, of course. But the sort of cooling that can make a marked difference in performance — drastically cooling the entire body by, for example, immersing athletes up to their neck in icy water — is not practical just before a race, Cheuvront said.
Wilber said that pollution could also affect performance, and athletes have told him that pollution is what they fear the most. As with heat and humidity, its effects are most pronounced among endurance athletes, like distance runners and cyclists.
Few could miss seeing the ever-present photos of Beijing shrouded in a gray mist of smog. Many have heard horror stories from athletes who have competed in Beijing.
The mountain biker Jeremy Horgan-Kobelski raced in Beijing last September. The air was thick with smog and he was convulsed with coughing fits. "I had to abandon the race," he said. He was not alone. Only 8 of the 50 cyclists who started the race completed it, an attrition rate that is "just unheard of," Horgan-Kobelski said.
Wilber's data indicated that Beijing's pollution levels, on a bad day, would be 30 to 35 percent higher than the levels in Los Angeles.
While athletes can acclimatize to heat, humidity and time zone changes, they cannot acclimatize to pollution. In fact, the more time they spend in polluted air, the worse. Effects tend to accumulate with time.
"If I was competing in highly polluted air, I would show up on the day of the competition," said Kenneth Rundell, a professor of health science at Marywood University in Scranton, Pennsylvania, who has studied the effects of air pollution on performance.
And that, it turns out, is what many United States athletes will do.
"One of our strategies for dealing with pollution is to avoid it as long as possible by living and training at other sites," Wilber said.
American marathon runners and track and field athletes have a plan in place, said David Martin, chairman of the men's marathon committee and an exercise physiologist at Georgia State University. Ten days to two weeks before these athletes compete, the Olympic committee will fly them to Dalian, a Chinese city north of Beijing on the coast. They will stay in a former government compound there, which is now a hotel with a weight room, a cafeteria and a nine-hole golf course. Nearby is an unused country road that is perfect for distance runners, Martin said.
During their time in Dalian, the athletes will train, getting used to exercising in extreme heat and humidity and getting used to the new time zone.
"We'd been searching for a place like this for a long time," Martin said. "We wanted a place in the same time zone as Beijing, that was easy to get to by plane and that was on the coast where there would be sea breezes to minimize pollution."
Three days before their events, the athletes will take a 50-minute shuttle flight to Beijing and check into the Olympic village or go to Beijing Normal University, which the Olympic Committee has rented for athletes who want to stay there.
As for the effects of long-distance travel through multiple time zones, Wilber said, the athletes should have that under control. They will wear compression garments — usually just support hose available at any drugstore or supermarket — to prevent fluid from pooling in their legs and feet on the flight to Beijing. When they get off the plane, their legs will feel fresh.
The Olympic committee will also look at the athletes' flight schedules and tell them when to sleep and when not to — in general, it is recommended that the athletes stay awake on the flight. When they arrive in Beijing, the athletes are to do some easy exercise, a slow relaxed run, for example, for about half an hour, have a light dinner and go to sleep at about 9 or 9:30 at night.
It is not always easy, Wilber said, but he added, "We appeal to their ability as athletes to be disciplined."
Within 48 hours, Wilber said, the athletes who adhere to these instructions will have adapted to the new time zone.
But the good news with time zone changes is that it may not matter so much whether an athlete is adjusted.
A position paper by the International Federation of Sports Medicine said that most studies cited as showing time zone effects involved small groups of participants doing laboratory tasks measuring things like hand-grip strength. In addition, the group of experts added, the studies tended to be poorly designed.
Some athletes say they do not perform well when they are jet-lagged, but "there is no consistent or compelling scientific evidence" that that is the case, the report said.
Yet, no matter what the science says, athletes may stick to their convictions.
It can be hard to believe that jet lag may have no effect on performance, but Olympic athletes say they at least know how to deal with time zones — they often have to travel across time zones to compete. And some have said that heat and humidity do not scare them.
Wyatt Allen, an Olympic rower who has been training in sweltering Princeton, New Jersey, said, "I think we've got heat and humidity covered."
As for pollution, some athletes say they are clinging to the hope that it may not be so bad. And even if it is, they add, at least everyone will be in the same situation.
"If I have to run a race uphill, so does everyone else," said Chris Liwski, an alternate on the Olympic rowing team.