Critical to understanding how trans athletes are discriminated against is an understanding of how hormone levels differ between men and women.

As she rounds the corner into the last half mile, she notices the crowds on either side of the route are starting to get bigger. She’s trained tremendously hard for this half-marathon. Her pace has been good so far, right in line with her splits from training, and she still has energy left in the tank. She knows she’s in front of all of the other female competitors and could easily kick to the finish line for the win, but instead her pace slackens. She intentionally slows down, knowing what would be waiting for her at the finish line: the doubts, the questions, the publicity — even if it’s just the local paper.

She doesn’t need that in her life right now. She slows down even more.

First one, then a second and third woman pass her. Finally her legs kick back into motion as she matches the pace of the third-place runner, finishing just behind her, just off the podium. With post-race chocolate milk in hand, she looks longingly at the top three finishers chatting with local reporters and race officials, freshly received medals hanging from their necks. “Those things are just not for girls like us,” she thinks to herself.

What would possess a woman, in the best physical shape of her life, to back off a race like that? The truth is that she’s a transgender woman. And the truth is that most of society believes she has an inherent physical advantage over cis women in athletics.

The real truth, however, is that she doesn’t.

People who are opposed to trans women participating in women’s athletics are most concerned about fairness. The fear of men masquerading as women to gain medals and glory has a long history — but one grounded in very few real-world examples. It has, however, resulted in decades of humiliating gender testing policies for female athletes.

People generally have an assumption that trans women have an inherent, permanent athletic advantage for life based on their assigned gender at birth. Oft-cited factors against trans women’s participation in women’s sports include: height, weight, narrower hips (supposedly making it easier to run), smaller breasts (making arm motion more free), wider shoulders, and a larger ribcage (meaning lung capacity is greater). The common trope for trans women is that we’re all tall, narrow-hipped, small-breasted, and masculine-appearing. This simply isn’t true. I happen to be tall (6’1”), but wide-hipped. I also have trans friends who are 5’4” and 130 pounds. Trans women have bodies that are just as varied in size and shape as cis women.

Moreover, what opponents to trans women’s inclusion in female athletics often gloss over is the drastic effect that a standard regimen of Hormone Replacement Therapy (HRT) has on the athletic performance of trans women.

For trans people, the question of whether to begin HRT is a very personal one; not all trans people end up on hormones or transitioning to live as their true selves. When it comes to competitive trans athletes, however, there are various requirements laid out by governing sports bodies concerning HRT treatment and athletes’ eligibility to compete. And such requirements often differ between the sexes. In January, the International Olympic Committee lifted its requirement that trans women undergo gender reassignment surgery before competing, stating that trans women (assigned male at birth) must complete a full year of HRT before being eligible to compete as women, while trans men (assigned female at birth) continue to be free to compete at any point of their choosing. In fact, there is a trans male hockey player, Harrison Browne, who has decided to put off testosterone treatments until his playing career in the National Women’s Hockey League is over.

To understand how HRT affects trans athletes requires a basic understanding of hormones. Estrogen and testosterone are the two primary sex hormones, and both affect the body in very different ways. Testosterone’s biggest advantage is that it more efficiently builds muscle than estrogen does. You hear women complain about how men can lose weight much faster than women can — testosterone is the reason why. More muscle gives a person the ability to burn fat at a higher rate. This is why those whose bodies run on testosterone appear leaner; bodies on testosterone are simply more athletic than bodies on estrogen.

It’s also important to understand just how Hormone Replacement Therapy affects trans women’s bodies. Speaking from personal experience, the loss in strength is jarring. I started HRT in mid-April of this year and before I moved out of my house on June 1st, I struggled to open jars. My per-mile splits dropped from 9:30-minute miles to 11-minute miles seemingly overnight. Now six months into HRT, fat redistribution has made my hips and rear end bigger and I’m growing a chest. This has had the added effect of reorienting my spine to accommodate new weight in new places, meaning my doctor-recorded height has shrunk from 6’2” to 6’1” with more height loss expected. Not every trans woman loses height, but it’s common enough that most of my friends have lost an inch or two from HRT.

Critical to understanding how trans athletes are discriminated against is an understanding of how hormone levels differ between men and women. During the Olympics this year, we heard much talk about Caster Semenya, who is intersex and not transgender, and her naturally high testosterone levels. Even though Semenya isn’t a trans woman, her story provides an apt introduction to how sex hormones affect athletic performance — and how the media can be misleading concerning these effects.

Outlets commonly reported without context that Semenya’s hormone levels were three times higher than an average woman’s and were, in fact, approaching levels of an “average man.” Stunningly, the actual average testosterone levels were simply left out of reports. Cis men generally have T levels that fall between 300 to 1000 nanograms per deciliter (ng/dL), while cis women typically have T levels in the 15 to 70 ng/dL range — even if Semenya had three times the testosterone of a woman with a high amount of testosterone, she still wouldn’t fall within the average range for a man, demonstrating how inaccurate many media reports were.

Further, the difference in performance between men and women in speed-based sports is about 11%. In other words, women’s times will run about 11% slower than men running at a comparable competitive level. It went unreported that Semenya’s 2016 gold medal winning 800m time was actually 13% slower versus the men’s 800m gold medal time. She may have had higher testosterone than her competitors, but she definitely didn’t run like a man.

Standard HRT treatment for trans women includes a testosterone blocker, usually spironolactone, and synthetic estrogen, called estradiol, which is also prescribed to cis women with hormone deficiencies and to alleviate menopause symptoms. Testosterone is by far the more powerful sex hormone, so the testosterone blocker is definitely needed; otherwise the excess estrogen would simply be swallowed by its counterpart. This is why trans women take two forms of medication for HRT while trans men just have the testosterone injections.

The effects that T blockers have on trans women are astounding. Dosing typically starts small and expands over the first nine months to a year, but when the medical regime is in full effect, trans women’s T levels are typically quite lower than cis women’s. The Olympic committee now requires a full year of testing T levels below 10 ng/dL before trans women are allowed to compete as female.

Without the advantage of testosterone on building muscle, trans women are stripped of any advantages they may have had as a result of once having higher testosterone levels. Yet, sadly, the assumption that trans women have said advantages is so pervasive that very little scientific research has been done to look into it. What’s presented as common sense, in fact, has very little factual basis in science for a crowd that likes to preach biological essentialism.

Joanna Harper, a trans distance runner and medical physicist, has been outspoken in her advocacy on behalf of trans athletes. She wrote about her experience of transitioning as an athlete for the Washington Post:

“Within three weeks of starting hormone therapy in August 2004, I was markedly slower. I didn’t feel any different while I was running. But I could no longer match my previous times. By 2005, when I was racing in the women’s category, the difference was astounding. I finished one 10K in 42:01 — almost a full five minutes slower than I’d run the same course two years earlier as a man. Interestingly, when I looked up my times in USA Track & Field’s age-grading tables — used to compare runners of all ages and both sexes — I found that I was just as competitive as a 48-year-old woman as I had been as a 46-year-old man.”

Every athletic trans woman I know shares this same experience, and yet the comments at the end of Joanna’s article show that cis people just can’t get past our assigned birth genders. When Joanna looked into the scientific research behind transitioning athletes, she realized just how thin the research was, so she took matters into her own hands and published her own study.

“I was curious whether my experience was typical. There had never been any studies of transgender athletes, only of transgender women generally. So over the next seven years, I collected almost 200 race times from eight distance runners who were transgender women (including myself as runner №6).

My research, published last month in the Journal of Sporting Cultures and Identities, found that collectively, the eight subjects got much slower after their gender transitions and put up nearly identical age-graded scores as men and as women, meaning they were equally — but no more — competitive in their new gender category. (The outlier was a runner who had raced recreationally as a 19-year-old male and became serious about the sport — doubling her training load and shedding 22 pounds — years later as a female.)”

Once you get past the relationship between muscle and hormones, the bigotry of the anti-trans argument becomes readily apparent. By singling out trans women with larger ribcages for exclusion, are they saying that cis women with large ribcages have the same advantage? If you’re going to ban all trans women because they’re tall and have an advantage, does that mean that Brittney Griner, who is 6’8”, cis, and can dunk, should be banned from basketball? That feels utterly wrong — in the exact same way as excluding trans women on the same basis would be.

The real damage comes from the dominant social view that trans women “are really men playing dress-up.” This belief runs so deep that it even permeates the thoughts of trans athletes. The story I told at the beginning of this essay was fiction, but it is based on multiple real-life stories that I’ve personally heard from competitive trans athletes.

What does this say, then, about the implications toward the concept of fair play? When a woman with no real advantage feels so oppressed that she would throw her own race rather than bear the harassment that may come from winning, what message does that convey? Is it fair that the cis women who were allowed victory can enjoy the rewards from good competition while trans women cannot? Trans women train just as hard for competitive and casual athletics as cis women do, and yet are systematically and socially cast out from reaping the rewards.

Further, policies dictating whether or not and at which point in transition trans women are allowed to compete in competitive athletics varies widely across different sports and between different athletic governing bodies. It’s not difficult to imagine a trans athlete being allowed to play her sport at her liberal high school during the school year and then also being denied the chance to play in AAU or under another non-scholastic governing body. Everybody seems to try to be putting things together as they go along. Olympic rules on gender and hormone testing have been receiving fairly strong pushback in the wake of Semenya’s gold medal winning performance, but their rules seem to achieve a good balance between fairness and ease of policy.

This is a positive first step and should serve as a model for other organizations as they grapple with the politics and controversy surrounding trans women pursuing athletics. If it’s good enough for the Olympics, it’s good enough for everyone else.

It’s time to push back on the assumption that trans female athletes have an unfair advantage. Hormones are messy and can’t always be easily controlled, but the hormone levels of trans women are the most controlled and easily maintained of any single group of women. With consistent T level testing, there’s simply no valid reason to exclude any trans woman from competitive women’s sports.