By RNZ

Trans women face several disadvantages as athletes and more research is needed before deciding if they should be allowed to compete in female events, a transgender academic says.

World Athletics, football's Fifa and the World Netball Federation are the latest governing bodies considering a ban on transgender women from competing in female events.

World swimming's governing body Fina has barred transgender athletes from participating in women's events if they have undergone male puberty.

And there will be no transgender players in women's international rugby league matches, including this year's World Cup in England, after a similar suspension was announced yesterday by International Rugby League.

Closer to home, all eyes are on the Australia-based National Rugby League (NRL) to see if it follows suit.

Transgender academic and former athlete Joanna Harper said the Fina decision fell short of a total ban because some trans women could meet the criteria but they were "extremely restrictive".

The moves by swimming and rugby league were based on the differences between male and female athletes, "which were very real but trans women on hormone therapy aren't men".

"In most cases after trans women have been on hormone therapy, the advantages, while they are not eliminated, they are mitigated to the point where we can have meaningful competition between trans and cis women [those whose gender matches the sex assigned at birth]," Harper told Morning Report.

The collection of scientific data about physical attributes from transgender athletes was still in its infancy but would be important in deciding on any advantages they might enjoy.

Harper said the data on any advantages trans women maintained over cis women athletes was nowhere near settled, with only one published paper - which was done by Harper seven years ago and she did not conclude they enjoyed an overall advantage.

"Trans women on average will be taller, bigger and stronger even after hormone therapy than cis women. Trans women will also be powering larger frames with reduced muscle mass and reduced aerobic capacity which can lead to disadvantages in things like quickness recovery, endurance."

Trans women also had a tendency to gain weight, which was another negative, and they faced social and psychological pressures which were just as serious any physiological problems.

"How all these things play out is far from settled and the published data is extremely sparse," Harper said.