Joanna Harper is an avid, competitive runner who can still pound out elite-level workouts in her 60s. She’s also the measured, PhD researcher who would take that same data and make a case for inclusion.

She’s taken her share of slings, arrows, and kudos in the current discourse over transgender participation in competitive sports. At times it's a burden, but she focuses on the importance of the issue.

“There are certainly times when I’d like to have a day when I don’t talk about anything to do with gender and sports,” she told Outsports. “I still have a huge passion for the topic. It has become a central thing in my life, and I assume it will be for the next few years.”

Since 2019, Harper has been based at Loughborough University in the U.K. as part of a project using science and research to aid policy making. The university’s latest research, published recently in the British Journal of Sports Medicine, looks at how the protein in our red blood cells that helps oxygen flow to our muscles for aerobic activity is affected by hormone replacement therapy.

On this week’s new episode of the Outsports podcast The Trans Sporter Room, Harper explains the data, but also delves deeper into its meaning.

Loughborough University’s findings show the hemoglobin level in transgender women falls to levels in line with cisgender women in the space of three to four months on average.

“That is a huge change and it affects all endurance sports, and, in fact, any sport where you were being active for more than a few minutes,” Harper said. “The hemoglobin level in your blood is important for taking up and using oxygen in your muscle. It’s perhaps the single most important reason that men outperform women in endurance events, because of the higher hemoglobin level.

“It has been long noted that hemoglobin levels are closely tied to testosterone levels. When transgender women lower their testosterone levels to female levels, which happens almost universally when trans women under undergo medical transition, trans women move from male levels of hemoglobin to female levels of hemoglobin.”

Harper also points out certain caveats within Loughborough University’s research, including the lack of definitive studies on transgender women athletes. Among trans women who are deemed “non-athletic,” Harper notes the data shows they will have greater strength, more lean body mass and muscle cross section area than non-athletic cisgender women, even after starting hormone replacement. Within the research, however, there are links between HRT-related realignments of those parameters and the decrease of hemoglobin and testosterone, and each were definitive over a period extending 12 months or more.

She cautions that all studies on the issue, even her groundbreaking work in 2015 that first compared a small section of trans women distance runners with each other, has to be placed in a larger context surrounding the discussion of sports.

“For those who suggest trans women have advantages: we allow advantages in sport, but what we don’t allow is overwhelming advantages,” she said. “Trans women also have disadvantages in sport. Our larger bodies are being powered by reduced muscle mass and reduced aerobic capacity, and can lead to disadvantages in quickness, recovery and a number of other factors.

“The bottom line is, we can have meaningful competition between trans women and cis women. From my point of the view, the data looks favorable toward trans women being allowed to compete in women’s sports.”

Loughborough University’s research comes as trans rights issues move to the front pages of news sites, newspapers and of legislative dockets. In at least 23 states, bills calling for efforts to ban transgender student-athletes from competition and other measures calling for limiting and even criminalizing gender-affirming health care are on the table.

Mississippi Gov. Tate Reeves, and South Dakota Gov. Kristi Noem are both set to sign bills banning transgender students-athletes. Each bill was modeled on a similar measure that was signed into law last March in Idaho, but remains subject to a temporary injunction after being challenged in federal court.

Three-time Olympic swimming gold medalist Nancy Hogshead-Makar, now a lawyer who specializes in Title IX-related issues, co-founded the Women’s Sports Policy Working Group to seek a “middle way” forward.

There is also the emergence of the Women’s Sports Policy Working Group, a collection of iconic sports figures and administrators led by Olympic gold medalist and Title IX attorney Nancy Hogshead-Makar. The group calls for common ground, but also seeks certain amendments in the Equality Act for the law to “continue to be obligated to provide males and females with equal sporting opportunities on the basis of biological sex.”

Harper is a supporter of the working group and its primary goal, given the political realities in Washington, D.C.

“I think that the recommendations of this group are the best chance that the Equality Act has of passing in the Senate,” Harper told Outsports. “If we can get it past the Senate this year, Biden will sign it into law and it will be the law of the land to protect all LGBTQ people.”

However, Harper is critical of some of WSPWG’s stances. She’s been a consultant to similar efforts among sports governing bodies, including World Rugby’s much-maligned effort last year.

At the time, she derided the effort: “Well, frankly, I think they had their minds made up, before they called the meeting,” Harper said.

The group sparked criticism from trans activists and allies for its all-cisgender inner circle that includes former Olympic swim champion Donna de Varona and tennis legend Martina Navratilova. Both athletes expressed their opposition to the NCAA considering a boycott of Idaho given the state’s anti-transgender measures.

Despite differences of opinion, Harper says she would be happy to collaborate with de Varona and Navratilova.

“It gives me pause that both of these women signed onto the side of the Idaho divide that I bitterly opposed,” she said. “But if they want to support a policy that I agree with, then I am happy to work with them.”

Editor’s Note: A previous headline incorrectly concluded Loughborough University’s research argues transgender women should be allowed to compete in women’s sports, or that they don’t hold physical advantages for a period of time. The headline has been updated to reflect the nuanced nature of the findings.

Also, a previous version wrongly stated that Harper questioned the motives of WSPWG in recruiting de Varona and Navratilova. We apologize for the errors.

Click here to listen to Joanna Harper’s full interview on the new episode of The Trans Sporter Room, available wherever you get your Outsports podcasts.