WASHINGTON — Olympic gold medalists Michael Phelps and Adam Nelson gave heartfelt pleas for Congress to help with the effort to eliminate doping in sports.

The athletes were witnesses on Tuesday at an Energy and Commerce subcommittee on Oversight and Investigations hearing entitled “Ways to Improve and Strengthen the Anti-Doping System.”

Phelps, the most-medaled Olympic athlete, humbly introduced himself and said he has spent years teaching children that if they believe in themselves, they can do anything.

“Looking back over my career, knowing how difficult it is to get to the highest level of sport, I can’t help but think how will the next generation of athletes know how to do it,” he said.

Nelson originally won silver in the shot put at the 2004 Summer Olympics, but was awarded the gold nine years later after Ukrainian Yuriy Bilonoh tested positive for doping.

He said he picked up his medal at the food court in the Atlanta airport, to which both Phelps and members of the subcommittee laughed.

“There is no small bit of irony in me losing a medal in this fashion,” he said “As an athlete, I rejected the notion that you needed drugs to compete.”

As he told his story, the members of the committee listened in both sadness and shock.

Nelson has been advocating for clean sport since 2012, but “those voices continue to fall on deaf ears,” he said.

“Athletes want action, not words,” he said. “You have to engage the athletes. We will stand with you as a partner if you empower us to do so.”

In his opening statements, Nelson showed his gold medal to the subcommittee and asked members to ”give meaning to my medal.”

“I’d like to take a moment right now to congratulate Mr. Nelson on his Olympic gold medal,” the subcommittee’s chairman Tim Murphy, R-Pa., said and all the congresspeople and audience clapped.

“Having that special moment, I feel he deserves it,” Phelps said later about how Nelson received his medal.

Phelps said that throughout his career he did think that some athletes were using performance-enhancing drugs, and was sometimes correct.

But of his fellow U.S. swimmers, “I don’t think I ever felt that.”

“When I stand up in the U.S., I know we’re all clean,” he said. “Internationally, there has to be something done and like I said, it has to be done now.”

On the push to prevent doping, Phelps said, “This whole process takes a toll but it’s absolutely worth it to keep the sport clean and fair.”

The other witnesses were Travis Tygart, chief executive officer of the United States Anti-Doping Agency, Rob Koehler, deputy director general of the World Anti-Doping Agency, and Richard Budgett, medical and scientific director of the International Olympic Committee.

On Monday night, Phelps was spotted with Republican Sen. John Thune of South Dakota and a large group at The Oval Room. They arrived about 7 p.m. and stayed for about two hours.