GEOFF BENNETT: Back in December, NCAA President Charlie Baker testified that, out of the more than 500,000 total college student athletes, he believed fewer than 10 were transgender.

AMNA NAWAZ: Last month, President Trump signed an executive order to ban transgender athletes from participating in girls and women's sports.

White House correspondent Laura Barron-Lopez has a closer look at the debate around this issue.

LAURA BARRON-LOPEZ: The president's order was part of a series of moves targeting the rights of trans people.

The order directed federal agencies to withhold funding from schools that allow transgender athletes to compete.

The NCAA quickly changed its rules, limiting participation in women's sports to those assigned female at birth.

And, more recently, Secretary of State Marco Rubio told consulates worldwide to deny visas for transgender athletes coming to the U.S. for competitions.

Also, California Democratic Governor Gavin Newsom broke with his party when he said that fairness is an issue, but that it's important for vulnerable communities to be treated with care.

Dr. Bradley Anawalt is an endocrinologist and professor at the University of Washington.

I spoke with him earlier, and he says that tension is at the heart of the debate.

DR. BRADLEY ANAWALT, University of Washington School of Medicine: In sports, we like to have a sense that the playing field is level, that there is fairness in competition.

Another really important value in sports is that we want everybody to have an opportunity to play, particularly when we're talking about young people.

And as a result, with this particular topic, there is apparent conflict between those two values.

LAURA BARRON-LOPEZ: And when signing his executive action banning trans athletes in women's sports, President Trump said this: DONALD TRUMP, President of the United States: We will defend the proud tradition of female athletes, and we will not allow men to beat up, injure and cheat our women and our girls.

From now on, women's sports will be only for women.

LAURA BARRON-LOPEZ: What does the science say about a competitive advantage or lack thereof among transgender girls competing in sports?

DR. BRADLEY ANAWALT: Well, the evidence is incomplete on that particular question.

The best data we have really comes from military recruits, people that have been enlisted in the Army or the Air Force.

A 2023 study, they have an annual test where they undergo a 1.5-mile timed run.

They do as many sit-ups as they can in a minute, as many push-ups as they can in a minute.

They had data from these individuals before they started gender-affirming hormone therapy, and then each year after that, for up to four years.

LAURA BARRON-LOPEZ: Anawalt says, even though the performance of trans women dropped after starting gender-affirming hormones, it took two years for their running times to fall in line with women assigned female at birth.

The sit-up scores of trans women stayed higher until four years after they started hormones, but their push-up scores remained higher the entire time.

DR. BRADLEY ANAWALT: What we don't really know is, what are the effects in elite athletes?

Most of the data is from people that are not elite athletes.

And the other thing that we don't know is, how long and how significant are these changes over time?

LAURA BARRON-LOPEZ: This ban appears to include school-age K-12 children.

What do we know about the competitive differences at those ages?

DR. BRADLEY ANAWALT: Most experts, there's a general consensus that, before the age of puberty for boys and girls, there's not a significant competitive advantage between the two sexes.

There are some data suggesting there may be some subtle differences between boys and girls, but what's unknown is whether that's due to biological factors or if that's just due to societal factors and expectations, boys being encouraged to participate more in sports and given more opportunities to increase their strength, the speed and power.

LAURA BARRON-LOPEZ: Anawalt has advised major athletic associations on hormone use in sports, including among trans athletes.

He says there are many examples of genetic differences that can lead to competitive advantages in sports, heightened basketball, bigger hands and feet in swimming.

He points to a Finnish cross-country skier who had a rare genetic mutation that ramped up his production of red blood cells, significantly increasing his endurance.

He won three Olympic gold medals in the 1960s.

DR. BRADLEY ANAWALT: None of these genetic variations or mutations have created the uproar that we're facing with the current controversy that we have around transgender athletes and participation in sports.

LAURA BARRON-LOPEZ: You have said we're never going to be able to answer the fundamental question about fairness when talking about this issue.

Why exactly do you say that?

DR. BRADLEY ANAWALT: It comes back to this conflict between these two important values that I alluded to, the fairness and then the desire to allow everybody to participate in sports.

And whenever you do that, there are going to be inherent inequalities between people.

And how do we limit those inequalities and yet allow everybody to play?

I really don't think that science is going to give us a perfect answer on this.

We can get better and better evidence and data about the effects of gender-affirming hormone therapy on athletic performance.

But, ultimately, this is going to be a question for the general public to try to balance out those two very important issues.

And it's also going to be an opportunity for us to ask the question, just how important our sports at the very highest level in our society?

This whole debate rages around sports because of how much we venerate sports and, at this point in time, what an economic engine it's become.

LAURA BARRON-LOPEZ: Dr. Bradley Anawalt, we really appreciate your insights on this.

Thank you.

DR. BRADLEY ANAWALT: Thank you for having me.