Shot put medalist Adam Nelson, 40, enters U.S. Olympic Team Trials

Double Olympic shot put medalist Adam Nelson has entered the U.S. Olympic Team Trials and will attempt to qualify for his fourth Summer Games in July.

Nelson, who retired in February 2013, said he has been toying with the idea since late last year, when he decided to file paperwork re-enrolling him in the drug testing pool, a required step in any return to elite competition. He will turn 41 in July.

"At that point, it was more of a whim," Nelson, who lives in Athens, Georgia, with his wife and two daughters, told ESPN.com. "Now, it's real."

Nelson's Olympic career was marked by unwanted drama. He won a silver medal at the 2000 Sydney Games and was edged four years later by Ukrainian Yuriy Bilonog.

In 2012, Bilonog was disqualified after a retest of his urine sample showed the presence of oxandrolone metabolite. The medals were reallocated in 2013.

Nelson also won a world championship in 2005. He qualified for the 2008 Olympics but finished outside the top 10 and was injured in the run-up to London 2012.

An outspoken advocate for clean sport and athletes' rights, Nelson has coached, run a gym and worked in sports marketing since he retired.

His throw of 21.48 meters at a meet in Georgia several weeks ago currently ranks him ninth in the nation, according to USA Track and Field.

"Why not?" Nelson said of his decision. "Once I saw what I was capable of doing off really limited training, I said, this is something I can do and have fun with.

"I like to throw the shot put right now. I'm pretty good at it."