Do transgender women athletes have an advantage over cisgender women athletes?

Question

There have been numerous articles in media over transgender women competing in women sports, and debating if this is fair with women whose birth sex was female.

I know there are some studies, like Race Times for Transgender Athletes, that show that after lower levels of testosterone follows a loss of muscle mass and bone density, and thus their athletic capacity is diminished.

I'm not sure if this loss of muscle mass and bone density is enough, or if there are other factors that could still provide an advantage. Perhaps the possible advantages vary for each sport.

So, is there evidence about the possible advantages of transgender women athletes over cisgender ones? Lets limit the question to sports where men have clear measurable advantages over women on average.

We should also specify how far into transition we are talking about, as pointed out in the comments. The International Olympic Committee (IOC) current rules are probably the best reference for how far in transition they must be to be allowed to compete in the women's category:

Those who transition from male to female are eligible to compete in the female category under the following conditions:

The athlete has declared that her gender identity is female. The declaration cannot be changed, for sporting purposes, for a minimum of four years.

The athlete must demonstrate that her total testosterone level in serum has been below 10 nmol/L for at least 12 months prior to her first competition (with the requirement for any longer period to be based on a confidential case-by-case evaluation, considering whether or not 12 months is a sufficient length of time to minimize any advantage in women’s competition).

The athlete's total testosterone level in serum must remain below 10 nmol/L throughout the period of desired eligibility to compete in the female category.

Compliance with these conditions may be monitored by testing. In the event of non-compliance, the athlete’s eligibility for female competition will be suspended for 12 months.

@DevSolar Would it really be better to create a question for each sport, those questions nearly identical apart from the specific sport? — Pablo, Commented Feb 25, 2019 at 16:27
@Pablo - Gymnastics? Seriously? Men's and women's gymnastics are rather different. Male gymnastics focuses on body strength, particularly upper body strength, with three events (parallel bars, pommel horse, and rings) that solely rely on upper body strength. Female gymnastics has a reduced emphasis on upper body strength and enhanced emphases on agility, grace, and style. While the latter might well be a gender norm issue, the reduced emphasis on upper body strength arguably is not. — David Hammen, Commented Feb 25, 2019 at 18:24
What type of transgender women? Trans women who haven't done anything to transition probably perform similar to men (and the question of how the best men and women do in sports has already been answered here). The question of whether trans women who have started transitioning is more interesting (although the answer may depend on how far through the process they are). — Laurel, Commented Feb 26, 2019 at 1:32
@Pablo It might help to focus things if you could select a very specific claim and quote it. I mean, this is an interesting issue that we could have a huge discussion about, but since such huge discussions don't really fit the StackExchange model, it'd help to have a specific instance of the broader claim for people to focus their analysis on. The exact claim you select will provide a context that'll provide a basis in which otherwise ambiguous concepts would be more well-defined. — Nat, Commented Feb 26, 2019 at 5:43
@tim a completely and utterly average man is stronger than about 98% of all women. A fairly average kinda-couch-potato man has pretty good chances of still being stronger than a woman who trains extensively.(note bar for female athletes in the linked post) skeptics.stackexchange.com/a/39372/23087 — Murphy, Commented Feb 26, 2019 at 13:42

nonthevisor · Accepted Answer · 2021-03-23 12:07:26Z

Is the Male Performance Advantage Removed by Testosterone Suppression?

According to a "non" peer reviewed study by Hilton & Lundberg "Transgender Women in The Female Category of Sport: Is the Male Performance Advantage Removed by Testosterone Suppression?" from 2020, transgender women still have greater muscular strength and the biological advantage enjoyed by transgender women is only minimally reduced.

Hilton & Lundberg (2020) Preprint

current evidence shows that the biological advantage enjoyed by transgender women is only minimally reduced when testosterone is suppressed. Sports organizations may therefore be compelled to reassess current policies regarding participation of transgender women in the female category of sport.

Wilk et al. (2020)

This view that changes in transgender women were modest, is also shared by Wilk et al. in their 2020 paper "Muscle Strength, Size, and Composition Following 12 Months of Gender-affirming Treatment in Transgender Individuals", published in The Journal of Clinical Endocrinology & Metabolism.

Wilk et al. (2020)

One year of gender-affirming treatment resulted in robust increases in muscle mass and strength in TM, but modest changes in TW.

Rugby

According to a report in the Guardian newspaper the greater muscular strength of the transgender woman is not only an advantage for the transgender female, but also increases the risk of injury to other female rugby players.

Guardian newspaper

Trans women face potential women’s rugby ban over safety concerns

Joanne Harper

Transgender athlete and Scientist Joanne Harper, speaking to "the Washington post" disagrees however, insisting that the hormone therapy works and that transgender women see a decrease in muscle, bone density, as well as a loss of speed, strength and endurance.

Washington post, Browse now

Hormone therapy for trans women typically involves a testosterone-blocking drug plus an estrogen supplement. As their testosterone levels approach female norms, trans women see a decrease in muscle mass, bone density and the proportion of oxygen-carrying red cells in their blood. The estrogen, meanwhile, boosts fat storage, especially around the hips. Together, these changes lead to a loss of speed, strength and endurance — all key components of athleticism.

Jones et al. (2017)

Jones et al. argue that there is no evidence to suggest that transgender women gain any athletic advantage in their 2017 paper "Sport and Transgender People: A Systematic Review of the Literature Relating to Sport Participation and Competitive Sport Policies", published in Sports medicine (Auckland, N.Z.)

Jones et al. (2017)

Currently, there is no direct or consistent research suggesting transgender female individuals (or male individuals) have an athletic advantage at any stage of their transition (e.g. cross-sex hormones, gender-confirming surgery) and, therefore, competitive sport policies that place restrictions on transgender people need to be considered and potentially revised.

Knox et al. (2019)

In their 2019 paper "Transwomen in elite sport: scientific and ethical considerations", published in the Journal of Medical Ethics, Knox et al. conclude that the testosterone maximum of 10 nmol/L is still significantly higher than that of cis-women and that the advantage gained by transgender women is an intolerable unfairness.

The solution to this they say is to do away with mens and womens athletics and instead recategorize events based upon fairness.