"We are deeply saddened to learn of Arielle's injury while training this week in preparation for the 2012 Games," USA Cycling president Steve Johnson said in a statement Wednesday. "She is a true competitor and will be sorely missed in London. We wish her a complete and speedy recovery."
USA Cycling said Martin was hurt during routine training Tuesday at the U.S. Olympic Training Center in Chula Vista, Calif., and taken to Mercy Hospital in San Diego.
A post on Martin's Facebook page said that a "mechanical malfunction" caused a crash during the training session witnesses said her chain broke, ESPN reported and that Martin suffered a lacerated liver and collapsed lung. Her injuries were "initially life-threatening," it said, and Martin has been moved into a trauma unit at the hospital after being treated in intensive care.
"She is expected to have a full recovery and is wishing her teammates all the best in London," the post read.
Martin, a graduate of Lone Peak High School and Brigham Young University, had not left for London yet because her competition does not begin until Aug. 8.
Neither she nor her family could be reached for comment.
Her husband, parents, step-father, in-laws and several nieces and nephews all were planning to go watch her race.
Her husband, Mike Verhaaren, is a crew chief for the U.S. Army on a Blackhawk helicopter who'd taken extra work assignments months ago so he could have time off to watch his wife fulfill her dream of competing in the Olympics. He also planned to secretly take along the American flag that he folds inside his body armor while on assignment in dangerous parts of the world, in case Martin needed it to wave during a medal celebration.
The couple wanted to vacation afterwards, Verhaaren said last month, possibly taking a motorcycle tour of the Italian countryside.
Martin was elated to finally make the U.S. Olympic Team in June, posing proudly for photos in her Team USA jersey during a recent trip back home to Utah, and posting photos of her Olympic bikes on her web site.
"It's so incredibly exciting to be this close," she wrote July 23, "and I'm jumping at the bit now that some of my buddies are already over there and posting pictures of the village and venues. Training has been great, spirits are high and I am definitely riding on some Olympic hype!"
Martin believes she "choked" in the build-up to Beijing, crashing in the quarterfinals of the last qualifying event and allowing teammate and good friend Jill Kintner to sneak through by the smallest possible margin to claim the only American starting position.
Kintner went on to win a bronze medal, while Martin devoted her life to reaching London to make amends.
"The work's not over because I'm an Olympian," she said after making the team. "I have every intent of going and winning a medal, and so there's still stuff to do. I can't slack off."
Martin is a former world bronze medalist, and finished fourth at the most recent BMX World Championships in May in Birmingham, England.
Since she wasn't in London yet, Martin had attended a celebration on the day of the Opening Ceremony aboard the USS Midway in San Diego last week. She also had been a guest of the White House with about a dozen other Olympians at an Independence Day celebration in Washington, where she said she got chills listening to the composer John Williams conduct his famous Olympic theme music.
She had spoken of getting the "monkey off her back" from four years ago, and how exhilarating it was to finally make the team.
"It kind of comes in waves, as far as setting in," she said. "The first couple of weeks, it was surreal. You worked for something your whole life, and you've finally attained it - I mean, at least a part of it. I still want to go and medal. But the big goal of being on that team, it was kind of like just waiting to wake up from the dream, because I'd dreamed it so many times, envisioned it so many times."
Brooke Crain will replace Martin at the Olympics, USA Cycling said.