Competing at high altitudes is no joke for endurance athletes.
Kiel Reijnen, a professional cyclist from Boulder, knows all about it.
"There's a shortness of breath, and it's easy to get dehydrated. Staying hydrated is one of the biggest things people miss," said Reijnen, 28. "You're used to your legs giving out before your lungs; now your lungs give out before your legs."
He's part of the eight-person UnitedHealthcare Pro Cycling Team, which is competing in this week's USA Pro Challenge, a 524-mile, seven-day race that started Monday in Aspen and finishes Sunday in Denver. Cyclists blast through Colorado Springs on Thursday during a 70-mile circuit.
Riders cross the state in seven stages, including a stretch up 11,539-foot Hoosier Pass - the highest point reached in this year's race.
Reijnen considers himself fortunate his family owns a cabin near the tiny town of Westcliffe, where he trains about four weeks before a high altitude race. It's surrounded by the Sangre de Cristo mountain range, which ascends to 14,000 feet - a perfect training ground for an endurance athlete about to test his limits.
"It takes a few days to feel comfortable," he said, "but once you're past that, you can resume training."
According to Timothy Rummel, a pulmonologist at Memorial Hospital, it takes about eight to 12 weeks for a person to totally adapt to altitude. As an unacclimatized rider ascends, several things happen to his body.
"They will hyperventilate more than they should," Rummel said. "They will have more air hunger and they may have sleep disturbance. They can even get classic altitude sickness: That's headaches, irritability, nausea. In serious cases, it can be dangerous. There can be fluid in the lungs or swelling of the brain."
Once the rider begins to acclimatize, his body will make more red blood cells to carry more oxygen, and gradually his lungs and heart will adapt. A 2005 study in the International Journal of Sports Medicine showed increased red blood cell volume after three weeks at altitude.
"They really have to expose themselves to low oxygen environments if they really want to do well," Rummel said.
Tom Southam, an ex-professional cyclist, is now the assistant team manager of Rapha Condor-JLT, a team from the Manchester, England, area. His team of eight riders arrived about a week before Stage One kicked off so they could adjust.
"Everybody reacts differently to altitude," Southam said from Aspen. "It manifests itself as quite headachey and tired. There's a sort of general sense of nausea."
Higher elevation makes riding much more challenging, Southam said. At lower altitudes, a cyclist can slow down and recover quickly, but when there's less oxygen, it takes more time for the body to recover. He can always spot a rider who's affected because he struggles to do what he can normally do.
The Rapha Condor-JLT team felt the altitude almost immediately, Southam said, even as they walked up to the hotel room in Aspen. Before arriving, he and the other coaches went to great lengths to prepare the team.
"We've had riders sleeping out in altitude tents," Southam said. "We seal it off and reduce the amount of oxygen to simulate the amounts of oxygen they'll have here. They train during the day normally and sleep in them at night."
They use a type of training called "sleep high and train low."
"They'll sleep some place high, like Vail, or have a low-oxygen bed they sleep in," said pulmonologist Rummel. "They're breathing 12 to 15 percent oxygen all night instead of 21 percent. They train at low altitude so they can push themselves harder, but sleep at higher altitudes so their body can get used to it."
In the week before the race, the team did only daily gentle 60-90 minute rides, British manager Southam said.
"Everyone seems quite comfortable so far," he said. "There's a lot of sitting around, which can be quite taxing mentally. We've got three masseuses for legs and back issues. They sort of rest and sleep. Most of our riders are young, and this is their first experience of racing at altitude. It's important we do this correctly. We can't afford to be gung ho about it in any way shape or form."
Because Reijnen lives here, both he and Rummel acknowledge he potentially has some advantage over other riders, particularly those from Europe, but it's still important to be mindful.
"You have to be careful if you go into the red," he said. "It's not like at sea level where you can come back out of it. It puts you at a deficit for the rest of the day. You have to pay attention. You have to slow down, but you can only afford to slow down so much before you're in trouble for a different reason. For the most part, we're just pushing through it."