Even at miniscule doses compared to males, we see the same dose response relationship like we do in males: increases in muscle mass, leg press strength, chest press power, and lower body power.
So, what exactly does more testosterone do to the human body? Well, testosterone has a strong effect on bone density where males exhibit 10% greater bone surface area compared to females (Knox et al. 2019). Greater bone surface area allows more muscle to be supported which is one reason why males are generally bigger and stronger than females on average.
Additionally, males on average are 7-8% taller than females with longer, denser, and stronger bones that allow greater leverage in sports that involve jumping, throwing, and explosive activities (Handelsman et al. 2018). Further, females suffer more lower body stress fractures compared to males due to the difference in bone density.
While many believe that testosterone only improves muscle mass and strength, it also has a large positive impact on aerobic capabilities. Males have a diaphragm that sits lower than females allowing for greater lung capacity. During puberty, increases in testosterone increase the quantity of alveoli (small air sacs) in the lungs which allows more oxygen to travel from the lungs into the bloodstream.
Males also have a larger heart, increasing stroke volume. Females will pump 33% less blood per heartbeat compared to males.
Finally, males display greater haemoglobin concentrations improving the ability to carry oxygen to the working muscles during exercise. All of these attributes are influenced by testosterone (Knox et al. 2019).
With all of these positive impacts related to testosterone, what is the limit for a transgender female to compete?
The current IOC guidelines for transgender female athletes are as follows:
- They have to declare their gender for sporting purposes to be female for at least four years.
- Their testosterone must be under 10 nmol/L for at least 12 months before competing.
The IAAF guidelines have since lowered the required testosterone level to 5 nmol/L which they state is to “ensure a level playing field for athletes” (IAAF Regulations, 2018). If you remember, the average female testosterone is 0-1.7 nmol/L. And levels approaching the lower range for males is enough to significantly enhance performance and body composition in females.
But what about the belief that transgender females are at a disadvantage because they have to supress their hormones?
There is a very strong body of research investigating male-to-female transitions and the effect of hormone therapy on various performance markers. And unfortunately, it seems that reducing testosterone in transgender females doesn’t reverse all of the adaptations males undergo during growth.
After 24 months of hormone therapy, transgender females retain their bone density and, in some cases, may even be preserved over 12 and a half years (Fighera et al. 2019; Hilton & Lundberg, 2020). After 12 months of hormone therapy, no increases in bone fracture rates were found supporting the notion of retaining bone density (Singh-Ospina et al. 2017).
The largest reduction in muscle mass seen in male-to-female transitions is 12% after 3 years of hormone treatment (Gooren & Bunck et al. 2004). When looking at a 1-year timeline, as per the IOC guidelines, we see an approximate 3-5% loss in muscle mass (Klaver et al. 2018).
The fact that males on average have 40% greater muscle mass than females, this suggests that transgender females have large advantages in this department over their female counterparts (Hilton & Lundberg, 2020).
After eight years of hormone therapy, muscle mass is only reduced by 17% placing them in the 90th percentile for women and grip strength is reduced by 25% placing them 25% higher than normal female values. Further, when testosterone is reduced to within normal female range after 12 months of hormone therapy, grip strength is only reduced by approximately 4%.
Let’s take the hot topic and use Hubbard as an example. Her previous records before transitioning in 1998 were a 135 kg snatch and 170 kg clean & jerk, for a total of 300 kg.
21 years later in 2019, she has hit a 131 kg snatch, and 154 kg clean & jerk in competition for a total of 285 kg. That is a 5% decline in performance. When there is a 30% strength difference between males and females in Olympic weightlifting, that doesn’t bring her much closer.
While no research to date has measured the effects of male-to-female transitioning with hormone therapy on endurance performance, the research suggests that transgender females retain most of the lean muscle mass, strength, and bone density even up to and past eight years in some instances.
Even with all these advantages, some transgender females still don’t have a chance of winning elite competition.