Michael Phelps is expecting some pain when he returns to training next week, four months after winning a record eight Olympic gold medals in Beijing.
"My shape is non-existent right now," said the 23-year-old swimmer.
"Four months has been the longest time I've been away. I know it will be a lot of pain for the first few months."
Phelps is in Beijing, filming a TV car advert, part of a seven-figure deal his representatives said is "the biggest for a Western celebrity" in China.
The filming took place in the Olympic water polo venue but Phelps made a stop at the Water Cube, where he took his career tally to 14 golds in August.
"There are times where I will wake up and say to myself, 'I don't want to do this anymore', but there are so many goals and times that I want to hit"
His eight golds at a single Games broke the record of fellow American Mark Spitz, set at the 1972 Munich Olympics.
"It was pretty cool, a pretty special feeling. I'm glad to have the opportunity to relive some of he moments that I had four months ago," Phelps said.
"It's been fun but I really want to get back into a normal regime and get some kind of structure back into my life.
"There are times where I will wake up and say to myself, 'I don't want to do this anymore', but there are so many goals and times that I want to hit in events.
"I'm not going to retire until those are accomplished."
Phelps has spoken about the possibility of targeting different events in London in four years time but was cagey about specifics.
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"These four years are going to be much more relaxed than the last four years," said Phelps, whose next big event is the World Championships in Rome in July.
"There will definitely be a lighter programme than what I did in Beijing.
"I think some backstroke is definitely in the mix, hopefully I can master the 100 free.
"I'm going to try a few different events I haven't tried before."
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