Five-time Olympic champion Missy Franklin is retiring from swimming at age 23. She cites chronic shoulder pain that has affected her for the last 2½ years.
She announced her plans Wednesday in a letter posted on ESPN.com.
"It took me a long time to say the words, 'I am retiring.' A long, long time. But now I'm ready," Franklin wrote.
Franklin's success and bubbly personality made her a darling of the 2012 London Olympics. At age 17, she became the first woman to win four gold medals in a single Olympics in any sport.
"The first 18 years of my career were as picture perfect as it can get," she wrote. "The equation couldn't have made more sense: you work hard, you have a positive attitude, you show up every day and give your best, and you get faster. That's how it worked for me. I worked harder, I trained harder and I swam faster, year after year after year."
But at the 2016 Rio de Janeiro Games, Franklin failed to make the finals in either of her two individual events and won her only medal, a gold, by swimming the preliminary heat of the 4x200-meter freestyle relay.
Franklin had surgery on both shoulders early last year, but the pain never completely subsided.
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"Technically speaking, my medical diagnosis is severe chronic tendonitis of both the rotator cuff and the bicep tendon," Franklin wrote. "After the failure of my last round of shots, I had only one other option: another surgery, and even that was a long shot."
But Franklin said she decided enough was enough.
When I heard the word "surgery," I immediately broke down because I already knew my answer: no. I've been in too much pain, for too long, to go through another surgery with a longer recovery time and no guarantee it would even help," she wrote.
Franklin's last competitive race was in the 200 free at the U.S. nationals in July. She finished third in the C final.