CHULA VISTA, Calif. — The hardest part for Carrie Johnson is not knowing.
The 28-year-old kayaker can handle endless days of training on the water. She can remain calm in a race — the flatwater sprint — that requires two minutes of explosive strength and steely nerves.
But as Johnson prepares for her third consecutive Olympic Games this summer, something else could quash her medal hopes before she so much as reaches the starting line.
"It's frustrating," she said. "And I have no control over it."
Crohn's disease is an autoimmune disorder that afflicts the digestive tract. The symptoms can include pain, fatigue and weight loss, and they can flare up at any time.
With no known cure, Crohn's has forced Johnson to miss competitions and skip training for long stretches of time. As the 2012 London Olympics approach, she must keep it at bay for the next three months.
"You're continually trying to manage it and watch for the warning signs," she said. "That's all you can do."
Not much slowed the San Diego native as a teenager. She competed in gymnastics for more than a decade before discovering kayaking at a junior lifeguard program.
National coaches soon took note of this new paddler, built light and strong, and brought her into developmental camps at the Chula Vista Olympic Training Center. By 17, she was competing internationally.
But then, in 2003, Johnson began to suffer unexplained fatigue and anemia. The symptoms grew serious enough that she had to turn down a spot on the U.S. team headed for the world championships.
After months of medical examinations, a doctor finally diagnosed the problem.
"I had never heard of Crohn's, so that was scary," Johnson said. "It took awhile to really learn about it and get over freaking out."
The Internet offered tales of the disease in its worst forms, but many of the estimated 700,000 Americans affected by this malady experience lesser symptoms.
Diet and medication can go a long way toward managing Crohn's. Barely a year after her initial diagnosis, Johnson was racing in the 500-meter sprint at the 2004 Athens Games, finishing one spot out of the finals.
"She has a really good strength-to-weight ratio," said Stein Jorgensen, a former Olympian who coaches her. "She gets out really well and can usually put some distance between herself and her opponents."
The following seasons brought a number of promising results, including a World Cup win and a sixth-place finish at the world championships. But the disease was still inside her.
After an especially strenuous year in 2008, which included a trip to the Beijing Olympics and working toward a biochemistry degree at UC San Diego, Johnson ended up in the hospital.
"Her immune system got too low," Jorgensen said. "She just went at it too hard."
The setback forced her to sit out the 2009 season. When Johnson returned to the water in 2010, Jorgensen scaled back her workouts and monitored her health more closely. If she began to struggle during practice, the coach backed off.
And because stress can be a contributing factor, Johnson managed her schedule away from sports more carefully.
The funny thing is, all of this might have helped her paddling.
"Having to take time off made me realize how much I wanted to be doing it," she said. "Now, if I'm having a bad practice or a bad day, I have that extra appreciation."
An appreciation that has inspired her to reach out to others with the disease.
The last few years, Johnson has been telling her story through the mainstream media and various web sites in the Crohn's community. One official calls her "an inspiration" and she receives emails from around the country.
"I don't introduce myself as, 'Hi, I'm Carrie and I have Crohn's disease,' " she said. "But talking about it ended up helping me and I think it has helped other people."
Now Johnson is approaching her last major competition before entering veterinary school at UC Davis in the fall. And she has a chance at a big ending.
The Hungarians will arrive in London as favorites in her two events — the 200-meter and 500-meter sprints — as will paddlers from Germany and Australia. But Johnson won two gold medals at the 2011 Pan American Games and has looked strong in recent World Cup races.
"She's been fifth in the world before," Jorgensen said. "If you've been that close, there's always a shot."
The flatwater sprints — specifically the 500 meters — require a mix of speed and endurance. Any racer who goes out too fast or pushes too hard won't last long enough.
"You've got to stay relaxed," Johnson said, "and maintain your technique."
It is a lesson she has learned in more ways than one over the last nine years. Johnson figures she will be ready for the pressure of the Olympic Games.
Besides, once she makes it to the starting line, the hardest part is over.