The biggest name in track might also be the biggest question mark heading into the world championships this weekend.
Can Usain Bolt continue to dominate the sprints?
The man who swept the 100 and 200 meters at the last two Olympics has battled injuries and has yet to reach top form this season. Bolt is 28 now and, facing reporters on Thursday, talked about growing older in a young man's event.
"In training I've definitely had to sacrifice a lot more," he said. "I can't just train for three months; I have to do it properly now and put a lot more into training."
American sprinter Justin Gatlin will arrive in Beijing with the four fastest times in the 100 this year. Tyson Gay and Asafa Powell have run well, too.
But with a slew of gold medals and world championships on his resume, Bolt has a history of peaking for major competitions.
"Everything is starting to come together," he said. "I'm ready to go."
The world championships get underway on Friday with the men's marathon. The 100-meter heats are scheduled for Saturday, with the final on Sunday.