"With the way my body feels, with the way that I'm able to feel like I'm able to compete now, I don't know that it's good enough," Roddick explained. "I don't know that I've ever been someone who's interested in 'existing' on tour. I have a lot of interests and a lot of other things that excite me. I'm looking forward to those."
He mentioned the youth tennis and learning center that his foundation is building in his hometown of Austin, Texas, and a radio show he appears on.
The latter would seem to be a natural second career for Roddick, known for a sharp, often sarcastic, wit. He's never been shy about showing his emotions on the court — whether tossing a racket or insulting a chair umpire or line judge — or sharing his opinions off it.
Roddick grew up in the spotlight and the world watched him morph from a brash, Gen-X kid with plenty of 'tude to something of an elder statesman in the game.
He has spoken out about tennis players perhaps needing a union to fight for their rights the way athletes in U.S. team sports do, and he emerged as a mentor to younger Americans.
Up-and-coming players such as Sam Querrey and Ryan Harrison have thanked Roddick publicly for his help, whether it's offering advice about dealing with life on tour or inviting them to come train with him in Austin.
"I was a little shocked. I think he kept it a very good secret," the 20-year-old Harrison said about Roddick's retirement.
"Honestly, there were a lot of things he taught me, but probably the most important thing on the tennis front was the consistency of every day — every day, working, being out there, putting in time and effort. It's 100 percent. ... If you're going to do it halfway, there's no point in doing it at all. That's what he taught me," Harrison added. "That's what he's done throughout his career and that's what he's all about."
Constantly confronted with questions about why his generation wasn't as successful as previous groups of American men — like Pete Sampras and Andre Agassi in the 1990s, or John McEnroe and Jimmy Connors before that — Roddick did his best to keep adapting his game to try to keep up with Federer, in particular, as well as Rafael Nadal and Novak Djokovic.
He improved his fitness. He added a better backhand. He worked on his volleys.
Eventually, though, he found it too hard to stay at the level he once reached.
"I don't know that I want to disrespect the game by coasting home," Roddick said. "I had plans to play a smaller schedule next year. But the more I thought about it, I think you've either got to be all in or not. That's more kind of the way I've chosen to do things."
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AP National Writer Eddie Pells contributed to this report.