A New Zealand physiology professor says transgender athletes have advantages over their female competitors and more research needs to be done by sporting regulators before they should compete against each other.

Otago University professor in physiology Alison Heather has researched transgender changes, particularly in top level sport.

She is adamant international sporting regulation bodies such as the International Olympic Committee (IOC) have rushed a decision to include transgender athletes in male and female categories, as there has not been enough research.

1NEWS Weightlifter Laurel Hubbard represents New Zealand in Melbourne. (File photo)

Heather says the controversial inclusion of Kiwi weightlifter Laurel Hubbard is a good example of the IOC not taking the time to research the science behind a transition.

"It could be seen as an advantage and that is why they have male categories and female categories."

Heather believes there is a potential muscle memory effect for Hubbard, having competed previously as a man.

She said the increased numbers of myonuclei (muscle fibres) could potentially allow Hubbard's muscles to train better than if she had not previously been a male.

"Also, whether hormone therapy has reduced the larger skeletal muscle fibre area of her previous male physique is questionable."

In 2015, the IOC changed their regulations to include trans women in the women's category of events if they remained under the testosterone levels of 10 nanomoles per litre (NMOL/L) a year prior to competing, as well as during competition.

However, a CIS female (a born female) can reach nowhere near the testosterone level of 10 NMOL/L. The average female sits at 2.8 NMOL/L and the average male 23-25 NMOL/L. This means the likes of Hubbard competes at three times the amount of testosterone to other weightlifting females.

"It hasn't been studied, but logical science will tell you someone who has three times more testosterone has the advantage physically. We need to do more research before arguing either way.

"I don't know what the solution is, but right now it is not fair on CIS females competing against transgender women."

Heather said not only can testosterone levels give trans women an advantage over their CIS female competitors, after transitioning a trans woman's muscle mass, lung capacity and muscle memory all remain the same as when they were CIS male. That could give the trans female athlete a possible advantage when competing in activities that involve physical strength.

"The physiological attributes of males that makes them naturally stronger including anatomical and biological features such as size, muscle mass, lung capacity, and heart size would be an advantage."

Heather said higher testosterone levels could give an athlete an advantage for power and speed sports.

"Higher testosterone levels could potentially have performance enhancing effects."

The IOC settled on a maximum level of 10 NMOL/L for trans female athletes - a level Heather deemed as set "without adequate research".



"There has been very little research into elite male to female transgender athletes.

"Whether this normalising of hormone levels (and at 10 NMOL/L it is debatable whether they are normalised enough) removes the vast majority of the advantage of having been male is still an unanswered question."

Heather said there has been only one study of eight non-elite recreational runners who had transitioned from male to female, and their performance times were very similar. She said it was unfair to base restrictions and regulations on one study.

As current regulations sit with the IOC, there is also no restriction around the level of haemoglobin (increased haemoglobin increases the oxygen carrying capacity of the blood). Scientifically testosterone positively influences haemoglobin levels.

"Given the lack of research, there is a real need to study what physical advantages transgender females carry after hormone therapy with consideration required for different sports, trainability and for performance.

"Until then, it is very difficult to conclude that it is a level playing field for CIS women versus trans women."

The IOC based the 10NMOL regulation on the lower level of a CIS male of 10 NMOL/L - the upper range for a female is 3.1 NMOL/L.

At highest level, a CIS female with polycystic ovary syndrome can have up to two times or more higher levels of testosterone, meaning around 6 NMOL/L.

Disorders of sexual development (DSD) women have testosterone levels in the lower male range of around 10 NMOL/L, and this is another controversial point when competing at an international level of sport, says Heather.

In 2015, Indian athlete Dutee Chand challenged the International Athletics Federation (IAAF) in the Court of Arbitration of Sports (CAS).

The CAS ruled there was evidence that high testosterone levels do increase lean body mass, creating a competitive advantage and the IAAF must produce sufficient evidence about the relationship between enhanced testosterone levels and improved athletic performance.

They suspended the 10 NMOLl/L ruling, and DSD women were allowed to compete without hormone therapy to lower testosterone levels.

Earlier this year, British Journal of Sports Medicine scientists Stephane Bermon and Pierre-Yves Garnier found there was statistically significant differences in the performance of higher testosterone female athletes versus lower testosterone athletes at the 2011 and 2013 International Athletics Federation World Championships across five separate events.

However there has been no change on the suspension of the 10 NMOL/L threshold for DSD athletes - but in the meantime, the new regulations for transgender women were set. Meaning trans gender athletes and DSD athletes are at odds also.

AT A GLANCE:

Transgender athletes

- Presently, they are allowed to compete with 3X higher testosterone levels than the high range CIS female.

- Although there is no scientific evidence to support that this provides them with an advantage, it is known that testosterone (androgens) provide an advantage to females.

- Increased endogenous androgens increase explosive performance.

- Exogenous androgens can be used to enhance performance – increased power, strength and training capacity.