The rematch is set.
When Wariner finished second to Merritt at last summer's Olympics in Beijing, many critics said Wariner's best days were behind him.
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"I don't really pay attention to what critics say about me," Wariner said. "I'm more focused on what I need to do, where I need to go, how to get better."
Beijing is in the past. The focus is on Berlin, where Wariner, the defending 400-meter champion, has something to prove.
"I want to go in there and run my hardest and show everybody that I'm not over. I'm not done. I've still got a long career," he said.
Wariner burst onto the scene at the 2004 Olympics in Athens, winning gold in the 400 and the men's 400-meter relay.
In Beijing, he took silver behind Merritt and won gold again as part of the U.S. relay team.
But the silver was a major disappointment.
"It really upset me that I didn't run the race I could have," Wariner said.
After the race, Wariner said he had little desire to compete. But his manager, four-time gold medalist Michael Johnson, convinced Wariner to keep going.
Johnson also convinced Wariner to reunite with Clyde Hart, the coach with whom Wariner split before the Beijing Games.
"It was a tough thing to do for me to go back to Coach Hart... We put our differences aside, and we're moving forward," Wariner said.
Wariner's recent times have been fast.
"Physically, I feel a lot better," he said.
He said his mind is also back on track.
"My head is where it needs to be," Wariner said.