The knee injury that sparked Shawn Johnson's comeback put an end to it, too.

The Olympic gold medalist announced her retirement from competitive gymnastics Sunday, four days before the start of the U.S. championships. She has had repeated setbacks with her left knee, seriously damaged in a January 2010 ski accident, and she feared she was putting her long-term health at risk by continuing with her attempts to make a second Olympic team.

"It just little by little gets worse and worse," Johnson told The Associated Press. "My body is to the point where I need time to rest and retire so I can be healthy for the rest of my life. It's hard to wrap my mind around. Gymnastics has been my entire life, and now it's no more."

The decision did not come easily.

After winning four medals at the 2008 Games -- only Michael Phelps, Natalie Coughlin and Nastia Liukin left Beijing with more -- Johnson took the next two years off. She won "Dancing with the Stars" and, with her bubbly personality and girl-next-door looks, became a bona fide celebrity. She left the door open to a return for a London, but it wasn't until the ski accident that she realized she still wanted to compete. Her first stop after the doctor's office was her gym, where she and coach Liang Chow began plotting out her comeback.

The long layoff would present enough of a challenge, but her knee made it that much more difficult. She had torn the ACL, MCL and meniscus, along with her hamstring, and it never returned to full strength. She made the team for last year's Pan American Games, where she helped the Americans win the team gold. But when she tried to increase her training over the last few months to get ready for London, her knee would not cooperate. She couldn't do the number of repetitions she needed, and there were days she couldn't even work out because the knee would be so swollen.

"That was a hard, hard thing," Chow said of watching Johnson struggle.

Finally, Chow sat Johnson down and said they needed to be realistic. She couldn't put in the training she needed, and she was looking at an entire knee reconstruction if she kept going.

"It's been a really hard decision. How can you tell yourself, 'No, I think it's time to say it's finally done,"' said Johnson, 20. "I'd like to be 30 and have kids and run around with them. It became more about my future life than this future one moment. I'm looking at the bigger picture of things."

But it still hurts.

"It's weird, for the first time in my career I came up short. But I feel like I succeeded as well," said Johnson, who listed making the Pan Am team after the knee injury as one of her proudest accomplishments. "It almost came too easy the first time. It was a humbling experience this time around."