Sex testing of elite women athletes is flawed and arbitrary

By: Kay McCallum, McMaster University

It is 2021, and we still can’t decide what constitutes a “woman” in sports.

I’m referring, of course, to the three women in track and field – Caster Semenya, Christine Mboma, Beatrice Masilingi – who have been banned from competing in their sport at the 2021 Tokyo Olympics. These women are not trans athletes, but they are victims nonetheless of sex testing in athletics.

The International Association of Athletics Federation (IAAF) tests athletes for their biological sex, to verify that the athletes competing in women’s sports are biologically female. Although the idea is pretty much as old as human populations – we’ve been classifying people as “male” or “female” for most of human history – the methods the IAAF uses to do so have changed as medical science has advanced. First it was examinations of external genitalia; then, in the mid-20th century, when we learned about DNA, they switched to identifying chromosomes.

The concept of the biological sex binary I describe here – two sets of body parts, two types of chromosomes – should be familiar. But it’s also flawed. The current scientific understanding of the sex binary is that sex is not, in fact, a binary. Biological sex is a bit more complicated than an either/or option.

Gynecological exams can’t tell you whether someone is intersex, for example. And women can have XY chromosomes – Maria José Martinez Patiño, a woman who competed in track for Spain, infamously tested negative on a chromosome test at the World University Games in Kobe in 1985. Martinez Patiño has androgen insensitivity syndrome: genetically, she has XY chromosomes; physically, she is female. Despite this, she had her sex certificate – a literal “woman card” issued by the International Olympic Committee – revoked over the failed test, lost her medals and right to compete, and suffered for years both financially and socially in her efforts to be reclassified as female.

But, of course, the IAAF has learned from the mistakes of the past. They know that sex is more complicated than chromosomes or body parts. So their rules on female athlete classification were updated in 2018 to reflect individuals with differences of sex development. Their testing is not based on body parts or chromosomes; it’s based on hormones – specifically, testosterone.

Testosterone is a hormone that’s tied to the development of a number of characteristics of the human body, especially muscle mass, bone density, and strength. For this reason, the steroid has popped up in a number of steroid scandals in sports, including the infamous East German doping scandal in the 60s, and in fearmongering rhetoric about trans women competing against cis women. Needless to say, athletic competitions are very sensitive to the issue of elevated levels of testosterone in athletes.

Now, thankfully, modern tests can differentiate between naturally-occurring testosterone and testosterone from doping. But in regard to sex testing, it’s a little bit more involved than just having or not having it. Everyone has testosterone. Generally, however, men have more than women: in non-athletes, men tend to have testosterone levels from around 8.8 – 30 nmol/L, and women from around 0.4 – 2 nmol/L. Although certain conditions, such as polycystic ovarian syndrome (PCOS), can increase testosterone levels in women outside this range, there is a pretty clear difference here. To be inclusive of these conditions, though, and other conditions that lead to differences in sex development, the IAAF has set the upper limit for testosterone in a woman’s body to 5 nmol/L for her to be considered eligible to compete in women’s sport.

This is the test that Semenya, Mboma, and Masilingi have all failed this year. Why?

You may notice that these ranges are for non-athletes. People like me, who are not in peak physical condition, who aren’t in the upper echelons of strength and speed and physical fitness.

The thing is, we have data on testosterone levels in elite athletes – athletes competing at the national or international level. In 2014, a team of scientists surveyed 693 elite athletes, male and female, across a number of different sports, for their physical conditions and hormone profiles. Unsurprisingly, these elite athletes have different hormone levels and bodies than non-athletes. The elite women in track and field have average testosterone levels of 4.1 ± 4.9 nmol/L, and men 12.1 ± 7.9 nmol/L. If you think about it, this makes sense: runners need strength and endurance, but not to the extent that they’re bulky.

In practice, this means that there is a considerable amount of overlap between the testosterone levels of men and women in track and field – and yet there are still differences between men’s and women’s competitions. Because testosterone isn’t the only factor that determines biological sex or physical ability. The study took into consideration height, weight, BMI, and a number of other hormones that affect human growth and development; despite the overlap in testosterone, these other factors can account for differences in performance between men and women athletes.

But, according to the IAAF, these three women are not considered “woman enough” to compete in women’s sports because of their testosterone test – and the options presented to them are to dope with androgen suppressants, like birth control, or have surgery to reduce their testosterone output – both of which come with medical risks and side effects. Or, they can quit.

Scientists have known for years that sex testing like this is impractical: every time we’ve developed a test for typing sex based on some binary characteristic, we’ve come across further indication that things are more complicated than a simple two-option system. It happened with genitalia. It happened with chromosomes. It even happened with skeletons. And as we try to scientifically define womanhood, we keep failing women in the process. We subject them to incredible scrutiny, invasion, and humiliation of their bodies, and force them to change themselves to be considered eligible to compete, or oust them from competition altogether.

Sports should be a celebration of the incredible physical abilities in athletes, which are both a product of dedicated training and innate physical differences. But we are shaming talented women athletes for being outside an arbitrary designation of womanhood.

They are women. Let them run.

Edited by participants of the 2021 Science Writing Internship program and B.G. Borowiec. Header photo from Flickr.