Gender-Affirming Therapy, Muscle Mass, and Athletics

    As the number of individuals who publicly identify as transgender or gender-fluid increases in the US and worldwide, there has been greater public discussion about addressing the issues of fairness and equity that these individuals face. One of the most common concerns is how transgender athletes, particularly transgender women (people assigned male at birth who identify as female), should be categorized to avoid any unfair advantage. Numerous studies have demonstrated that cisgender men have a significant advantage over cisgender women when it comes to several athletic measures, including strength (Miller et al., 1993), oxygen uptake/VO2 max (Cureton et al., 1986), and lean muscle mass (Perez-Gomez et al., 2007), which is used to justify separate competitive categories for men and women. 

    Transgender athletes are frequently required to have undergone a minimum amount of hormonal, gender-affirming treatment in an attempt to mitigate any biologic advantage or disadvantage due to androgen or estrogen levels. That said, there have been few empirical studies examining the correlation between these hormone levels and athletic performance. The few studies that do exist often have conflicting results. A 2004 study concluded that after 1 year of hormone therapy, transgender female athletes showed a significant decrease in lean muscle mass, but still had significantly higher levels than transgender males - the authors reported that hormone therapy "reduces but does not reverse" the gap in muscle mass between men and women (Gooren & Bunck, 2004). A 2019 study, meanwhile, found a significant decrease in grip strength in transgender women after 1 year of hormone therapy, but only found significant change in lean body mass in transgender men (Scharff et al., 2019). 

    Given the relative uncertainty of the issue, it is clear that more research is needed before any definitive conclusions can be made on the role of gender-affirming hormone therapy in professional sports. There is strong evidence, however, that any potential for competitive advantage trans athletes might have is often outweighed by the challenges posed by the lack of comfortable and inclusive environments surrounding sports (Jones et al., 2016). Regardless of any advantage or disadvantage trans athletes might have based on their anatomy, sports governing bodies have an ethical duty to address the cultural and societal barriers that discourage trans people from participating in athletics. 

References

Cureton, K., Bishop, P., Hutchinson, P., Newland, H., Vickery, S., & Zwiren, L. (1986). Sex difference in maximal oxygen uptake. European Journal of Applied Physiology and Occupational Physiology, 54(6), 656–660. https://doi.org/10.1007/bf00943356

Gooren, L., & Bunck, M. (2004). Transsexuals and competitive sports. European Journal of Endocrinology, 151(4), 425–429. https://doi.org/10.1530/eje.0.1510425

Jones, B. A., Arcelus, J., Bouman, W. P., & Haycraft, E. (2016). Sport and Transgender People: A Systematic Review of the Literature Relating to Sport Participation and Competitive Sport Policies. Sports Medicine, 47(4), 701–716. https://doi.org/10.1007/s40279-016-0621-y

Miller, A. E. J., MacDougall, J. D., Tarnopolsky, M. A., & Sale, D. G. (1993). Gender differences in strength and muscle fiber characteristics. European Journal of Applied Physiology and Occupational Physiology, 66(3), 254–262. https://doi.org/10.1007/bf00235103

Perez-Gomez, J., Rodriguez, G. V., Ara, I., Olmedillas, H., Chavarren, J., González-Henriquez, J. J., Dorado, C., & Calbet, J. A. L. (2007). Role of muscle mass on sprint performance: gender differences? European Journal of Applied Physiology, 102(6), 685–694. https://doi.org/10.1007/s00421-007-0648-8

Scharff, M., Wiepjes, C. M., Klaver, M., Schreiner, T., T’Sjoen, G., & den Heijer, M. (2019). Change in grip strength in trans people and its association with lean body mass and bone density. Endocrine Connections, 8(7), 1020–1028. https://doi.org/10.1530/ec-19-0196