A very recent article has gone through the latest physiological reports about transgender women trying to reach a consensus that would support their inclusion, or exclusion, in the female category.
Performance in sports is affected by many physiological factors, that vary between disciplines but also between male and female participants: muscle force, power capacity, anthropometry, cardiorespiratory capacity, or metabolism, among others.
Besides the gender distinction into male and female categories many sports also include classes based on weight and/or age. The reason behind these categories is to allow participants to compete in equal terms of fairness, safety and inclusivity.
But what happens with transgender persons, whose biological sex is different than their gender identity? Regarding the transgender women the IOC determined that they could compete in the female category if suppressing their testosterone levels below 10 nmol/L for at least 12 months before competition. Let´s see this with more detail.
Performance differences Male vs. Female
Before puberty there are no significant differences in athletic performance between males and females. At puberty testosterone levels in males increase greatly to reach a concentration 15 times higher than in females. This increase in testosterone induces anatomical changes, such as reduced fat mass, accompanied with increases in muscle mass, force, haemoglobin levels (12% higher) and cardiovascular and respiratory functions.
In elite sports there are only a few sporting disciplines where males do not have performance advantage over females. The performance gap would vary according to the discipline from 11-13% in rowing, swimming or running to a 18% in jumping events, or higher than 20% in sports with important upper body contributions. In comparison men have stronger upper bodies (and longer arms) while women have stronger lower bodies.
Among non-elite individuals, differences were still there, with males presenting 57% greater muscle size or 162% greater power punch than females.
Effects of 1 year of testosterone suppression therapy in transgender females
- Testosterone levels were reduced to 1 nmol/L, well below the limit imposed by IOC (10 nmol/L).
- Thigh muscle area decreased 9%, and an extra 3% after 2 more years of therapy, although muscle size never went down to female levels.
- No changes in bone mineral density or skeletal measurements (bones length and hip width) were reported.
- Haemoglobin levels decreased by 11–14%. Considering that haemoglobin is 12% lower in females than in males, transgender women would suffer a “penalisation” of about 2-5% in their oxygen transport capacity, and therefore in their aerobic capacity when compared with the female population.
- Superior anthropometric, muscle mass and strength parameters achieved by males at puberty remain with testosterone suppression, making impossible to completely close the performance gap between male and females.
- The residual advantage of transgender women raises concerns about the fairness of competition, especially in sports where muscle mass, strength and power determine performance.
- Using the levels of free circulating testosterone as the deciding factor for inclusion may be unsuitable. World Athletics recently lowered the limit levels of circulating testosterone to 5 nmol/L, and 1 year of suppression therapy already had brought them down to 1 nmol/L.
- Sporting regulatory organizations should reassess their policies for inclusion of transgender women, according to the sport and on an individual basis, ensuring inclusivity, competition fairness and safety for all participants, regardless of their sexual identity.
Hilton, E.N., Lundberg, T.R. Transgender Women in the Female Category of Sport: Perspectives on Testosterone Suppression and Performance Advantage. Sports Med (2020).