U.S. Gymnast Shawn Johnson Retires

Shawn Johnson at P&G U.S. gymnast Shawn Johnson closed the door on her competitive career. She announced her retirement over the weekend, citing problems with her left knee making it difficult for her to train properly for the 2012 London Games.

"I still have the heart, drive, and desire to compete and help the USA at the London Olympics," Johnson said in a statement issued by USA Gymnastics. Unfortunately, it has become obvious that my left knee is not able to sustain the demands of gymnastics any longer. All I can do now is gracefully retire and thank everyone who has believed in me and my journey."

Johnson, 20, won home gold and silver medals in the 2008 Beijing Games, is a World Artistic Gymnastics champion, and won the mirror ball trophy on season eight of "Dancing with the Stars." She suffered a knee injury in 2010 from a skiing accident, and had been training to earn a spot on Team USA for the 2012 London Games. She details her journey in her autobiography, "Winning Balance," which is set for release on Tuesday, June 5.

"I have had the honor to train and compete with them, and I am excited to join the gymnastics family and fans in cheering them on to victory. I will be there with every ounce of pride and energy to cheer on my girls and Team USA," she said,

Johnson intends to start college in the fall, although she hasn't said where she'll be attending classes.