Lia Thomas, the University of Pennsylvania’s transgender national champion swimmer, insists in a new interview that “trans women are not a threat to women’s sports.”

Thomas has become the face of a national debate about whether transgender women should be allowed to compete in women’s sports, with critics arguing they hold an unfair biological advantage.

Thomas competed for three seasons on Penn’s men’s team before transitioning and then competing as a woman this past season, when she won the national championship in the 500-meter freestyle and set six records at the Ivy League championships.

“I knew there would be scrutiny against me if I competed as a woman,” Thomas told ABC News’ Juju Chang in an interview that aired Tuesday. “I was prepared for that. But I also don't need anybody's permission to be myself and to do the sport that I love.”

Thomas, 23, dismissed the idea that she had a competitive advantage, saying being happier after transitioning played a significant role in helping her performance. 

“There's a lot of factors that go into a race and how well you do, and the biggest change for me is that I'm happy,” she said. “And sophomore year (when) I had my best times competing with the men, I was miserable. And so having that be lifted is incredibly relieving and allows me to put my all into training and racing. 

“Trans people don't transition for athletics,” the Austin, Texas, native added. “We transition to be happy and authentic and our true selves. Transitioning to get an advantage is not something that ever factors in to our decisions.”

She said she had delayed transitioning because she wasn’t sure if she would be able to continue competing in swimming.

Thomas met the NCAA requirements to compete as a woman this past season by undergoing hormone-suppressant therapy for at least a year before competing and demonstrating a testosterone serum level below 10 nanomoles per liter.

In January, the NCAA updated its transgender athlete guidelines by allowing each sport’s governing body to make the rules — USA Swimming now sets the testosterone serum limit at 5 nanomoles per liter. But the NCAA said it would not change the rules midseason, clearing the way for Thomas to finish her college career.

Thomas says she has lost muscle mass, become weaker and is a slower swimmer since beginning hormone replacement therapy.

But in February, sixteen of her teammates sent a letter to the school and Ivy League officials saying she still biologically “holds an unfair advantage over competition in the women’s category.”

The teammates, however, wrote that they otherwise fully supported Thomas’s transition from a man to woman. 

Asked about the letter, Thomas said: “You can't go halfway and be like, ‘I support trans women and trans people, but only only to a certain point,’ where if you support trans women as women and I've met all the NCAA requirements and then I don't know if you can really say something like that”

According to the Movement Advancement Project, seventeen states have laws banning transgender students from competiting in sports consistent with their gender identity.

Many conservatives have railed against transgender women competing against athletes who were born female. During a rally Saturday night in Wyoming, former President Donald Trump, who has hinted at running for the White House again in 2024, told the crowd: “We will save our kids and we will also keep men the hell out of women’s sports. Is that OK?” 

Thomas has graduated and will attend law school. She also said, “It's been a goal of mine to swim in Olympic trials for a very long time and I would love to see that through.”