An unmotivated Michael Phelps won four gold medals and two silver at the 2012 Summer Olympics in London.

He says his recent stint in rehab has rekindled his motivation.

Team USA considering lifting ban on Michael Phelps from competing in world championships

In officially announcing his intention of qualifying for the 2016 Summer Olympics in Rio de Janeiro, Phelps said his current training has him swimming the fast times he's had since the 2008 Summer Games in Beijing, according to USA TODAY Sports.

"The last couple of months have probably been the hardest couple of months I've ever had to go through," Phelps said, according to USA TODAY Sports. "I take full responsibility for all of my actions. For me, I know I've hurt a lot of people. It's been terrible. For me, being able to move forward to be able to be back in the pool is something I'm very excited about."

Michael Phelps alleged ex-girlfriend makes porn movie about their relationship

Despite reports that the U.S. National Swimming Team had considered rescinding his ban from this summer's world championships in Russia, he leaned that Team USA will uphold its ban.

"It's obviously very challenging and for me to not be able to compete at world championships," Phelps said at a news conference Wednesday, adding that he did not want this to be a distraction for the team, another USA TODAY Sports report indicated. "I will be in full support of everything they do over there, and I wish them all the luck in Kazan."

Phelps is scheduled to compete in the Arena Pro Series event in Mesa, Ariz. He will race in five events, beginning with the 100-meter butterfly today, AZCentral.com is reporting.

"Everyone has the right to believe whatever they want," Phelps said. "I know exactly how I am now and exactly how I feel now and how I wake up every day and go through my life. If somebody doesn't believe the words that are coming out of my mouth, that's not my choice. I know the only person I can control in any situation is myself.

"I would like to show everybody in the world that I am in a different place and I am much better than I ever have been. I understand that's going to take a lot of time for me to be able to prove I am different and I am changed. This week will be the first week that I can start that. Hopefully people can really see me for who I am and they can accept that. If they can't, they can't. It's their choice."