Testosterone - The Facts

Women and girls are being pushed out of sports to make way for biological males who “identify as women”. A desire to be inclusive is having unintended negative consequences at all levels of female sport.

A lot of intentional and unintentional muddying of the science of the sexes in relation to athletic ability has taken place in recent years. Those who are pushing for males identifying as women to be allowed to compete in women's sport go to great lengths to downplay proven scientific facts that show unequivocally that male athletes are biologically advantaged in a large number of ways compared to female athletes.

Virtually all elite sports are segregated into male and female competitions. This is to allow females a chance to win and be the best in their field. It also showcases and celebrates the best of what the female body can achieve. Separate sporting competitions are necessary because females have major disadvantages against males who are, on average, taller, stronger, and faster and have greater endurance due to their larger, stronger muscles and bones as well as having more circulating red blood cells. The ‘performance gap’ between male and female athletes is proven beyond doubt based on decades of sporting records and it ranges from 10-30% depending on the sport. References here and here.

Here we outline some of the facts, figures, and research that support what we all already know - male and female bodies are different and this provides males with an advantage in sport and athletics.


The focus the International Olympic Committee has placed on this hormone has inaccurately framed it as the source of all male advantages. While testosterone plays a significant role in the development of the male body and its ongoing performance, it is by no means the only factor that should be taken into account when assessing the different advantages males have over females. Nevertheless, we will go into the science of testosterone to begin as it remains the marker by which most sporting organisations decide the eligibility of male athletes who identify as women to compete in women's sport.

In 2015 the International Olympic Committee (IOC) relaxed the eligibility criteria for male-born transgender people to compete in female sport. The requirement for genital reassignment surgery was removed and eligibility instead determined by reducing Testosterone to 10 nM for at least 12 months. More recently, the International Athletic Association Federation (IAAF) reduced their limit to 5nM T for some track and field events.

The maximum level of testosterone allowed for male-born transgender athletes is set far too high.

It is currently set at 6-12 times higher than the average level observed in females (0.8 nM). Reference here. The current 10 nM limit is actually closer to the pubertal level of T observed in boys (5-10nM). To put this into context, the high school 100m sprint record set by a teenage boy beats that of the fastest ever female. References here and here. 7nM T has been shown to cause a 12-26% increase in muscle strength when administered to women. Reference here. In a recent study of over 700 male elite athletes 25% had T levels below 12.5 nM. A considerable proportion of males would be expected to naturally fall below the 5-10nM limit. Reference here.

An important thing to remember as well, is that reducing testosterone levels today does not remove the advantages of testosterone in the past.

There is currently no evidence that lowering testosterone to normal female levels can fully remove male-competitive advantage.

Life-long advantage of larger bones and body size

Although it is clear that reducing testosterone to female levels does reduce current muscle size and red blood cell levels in males, it does not reverse the impact that testosterone had during puberty. Puberty and early adulthood is when the size and shape of the male body is formed. It is well known that males are larger, have longer limbs, a larger rib cage with larger organs like heart and lungs, bigger hands, their legs are more vertical due to a narrow pelvis, the list goes on. The male body is optimised for physical performance. In contrast, in females there is an evolutionary trade-off between physical performance and the ability to bear children.


“We all know the outcome of the race before it even starts; it’s demoralising"

Selina Soule, US High School runner on racing against transgender athletes

What about females who identify as men? Do they have any physical attributes that would advantage them over men?

"No. They have female in utero development and basic female physiology. It will be difficult for them to be competitive in the elite male division for most sports.

To exemplify this - in the 1970s and 80s there was state-wide doping in East Germany, especially the female athletes. The doping included anabolic androgenic steroids (AAS) at high doses.

Even with these super-physiologic doses coupled with intense training, the female athletes from this country were very successful and even still hold world records in some athletic events. But they did not achieve the distances or weights of the male athletes. Females can not be turned into little males with androgens, and equally males cannot be reformatted to females with estrogens." Professor Alison Heather, Otago University.