The controversy that erupted in the wake of New Zealand transgender weightlifter Laurel Hubbard winning gold at the Pacific Games in Samoa this month is reverberating around the world.

Key points: Trans weightlifter Laurel Hubbard won gold at the Pacific Games this month

Trans weightlifter Laurel Hubbard won gold at the Pacific Games this month The win has sparked fresh debate about whether trans woman have an unfair advantage

The win has sparked fresh debate about whether trans woman have an unfair advantage Some groups are calling on trans women to be banned until there's more science on the matter

The outrage that followed Hubbard's gold medal wins in Apia prompted the Games Council to commit to a thorough review of its policies, and groups in New Zealand and the United Kingdom have since called for the International Olympic Committee (IOC) to suspend its rules that allow male-to-female transgender athletes to take part in women's competitions.

Prime Minister Tuilaepa Sailele said Hubbard should never have been allowed to compete at the Pacific Games. ( Facebook: Government of Samoa )

In the United States, a transgender athlete and scientist who advises the IOC is calling for existing testosterone limits to be halved.

But other observers have argued that the idea that testosterone determines speed and strength — and that trans women athletes will always have an advantage — is a myth that needs debunking.

Samoa Prime Minister Tuilaepa Sailele's anger was palpable after Hubbard claimed gold at the Pacific Games over Samoa's Feagaiga Stowers, who took home silver.

"This fa'afafine [a Samoan third gender] or man should have never been allowed by the Pacific Games Council president to lift with the women," Mr Tuilaepa told the Samoa Observer.

"I was shocked when I first heard about it.

"No matter how we look at it, he's a man [sic] and it's shocking this was allowed in the first place."

More science needed, researchers say

Trans female athletes are playing by the rules, but they are often vilified in the sporting arena. ( NAN104/iStockPhoto )

Up to now there has been very little scientific study of the impact that a sex change has on a male athlete's body, and that undermines the IOC rules, according to Daryl Adair, an associate professor in sports management at the University of Technology Sydney.

Laurel Hubbard withdrew from the Commonwealth Games after suffering an injury. ( AAP: Dean Lewins )

"The IOC has made policy without demonstrating a scientific robustness about this," he said.

"Back in 2003, this wasn't open season for transgender athletes. This was only for those who had gone through the whole surgical procedure."

He said it became controversial in 2015, when the IOC changed its policy to allow hormonally transitioned athletes.

A 2015 study from US scientist and transgender athlete Joanna Harper, who advises the IOC, examined the race times of eight transgender women runners.

It found that collectively the athletes had much slower race times after transitioning from male to female, but she concedes that the study is limited and more research is needed.

"I'd be the first to admit that it's a very limited study. Eight subjects, one sport, and it's a sport where size and strength aren't advantageous," she said.

She said there was "certainly very little data on strength athletes" and that men have "approximately 25 per cent greater upper body strength than women".

Dr Harper is poised to release a second study soon, and will publish a book called Sporting Gender at the end of the year, but in the meantime she is one in a panel of experts who has advised the IOC to halve testosterone limits in women's sport from 10 to five nanomoles.

"We had a meeting in June, we didn't reach any agreement," she said.

"Despite the fact that most trans women can be relied upon to keep their hormone levels low, in elite sport you're definitely going to have to set a limit.

"But will trans women still have advantages after that? Of course. All of the muscle mass and strength isn't going to go away."

Calls for a ban on trans women athletes

The issue of trans athletes has ignited heated debate. ( Flickr: Benson Kua )

New Zealand-based organisation Speak Up for Women, which advocates that sport must be categorised by sex, not gender identity, yesterday launched a campaign to "defend women's sport" in the wake of Hubbard's controversial win.

"Kiwis know that males competing in women's sport is blatantly unfair," said spokesperson Ani O'Brien.

"As a nation we pride ourselves on being good sports, and going into the Olympics next year this is not a good look."

Research director for the UK's Fair Play for Women, Dr Nicola Williams, called for all transgender athletes to be banned from women's sport until a new wave of scientific studies have been completed.

"We must suspend the rules now and wait for that data in the next five, six, seven years and then decide," she said.

"In the meantime there have to be other arrangements for transgender people so that they can compete fairly and females can compete fairly.

"Female sport is there to showcase exceptional women. It's not a playground for mediocre males, and it's certainly not a place to validate gender identity."

The group was last year accused of transphobia online after tweets surfaced suggesting trans women carrying a potential foetus would be infected with "1,000 cancers".

Dr Williams denied knowledge of the tweet and said her group rejects transphobia.

She said Hubbard had an unfair advantage that couldn't be negated by the IOC dropping the testosterone limits.

"Any reduction in testosterone, even to zero, wouldn't actually reverse the male performance advantage that someone has when they go through male puberty, because we can't reverse that," she told the ABC.

"So even if the IOC do reduce [the limit] down to five, it's still blatantly unfair."

Dr Williams pointed out women didn't have a weightlifting category until the 2000 Sydney Olympics.

"So within 20 years, women have built their discipline from scratch and it's now being undermined by people that don't have female bodies essentially," she said.

"Those people are now winning and Laurel Hubbard is the evidence."

Dr Ryan Storr, a lecturer in sports development at Western Sydney University, said there had been a rise in anti-trans sentiment and many claims about trans athletes having a natural advantage were unproven or incorrect.

He agreed the area was under-researched, but said until there was evidence to prove trans women had a clear advantage, they should be allowed to compete in the interests of human rights.

Dr Storr, who is also founder of LGBT sport charity Proud 2 Play, said there was a misconception that a man could wake up and self-identify as a woman the next day, saying transition was a long physical and psychological process.

"People don't wake up and want to win medals so they go into women's sport," he said.

He said there wasn't much incentive, as prize money in women's sport is low and going through a gender transition involved discrimination and abuse.

Should Hubbard be allowed to compete in Tokyo?

The Olympic Games have policies and testing in place to ensure a fair playing field. ( Reuters: Issei Kato )

Dr Storr said no trans athlete had ever qualified for the Olympics, and there were policies and testing in place to ensure a fair playing field.

"If you're banning somebody on a lack of evidence, then that's not really in the Olympic spirit around inclusion," he said.

But Dr Harper says the Olympic question is a thorny one.

"She did hold the New Zealand record for 15 years, so she was pretty good, but certainly no threat to being in the top 10 in the world among men," she said.

No trans athlete has ever qualified for the Olympics. ( Wikimedia commons: Department for Culture, Media and Sport )

"She is among the top 10 in the world among women — so is that fair, is that right? It's a difficult thing."

Dr Adair said attitudes might change, and while Hubbard is in the spotlight now, that might diminish after the 2020 Olympics in Tokyo.

He said if she was to compete with the cohort of women weightlifters at the Rio Olympics, she likely wouldn't take home a medal.

There needed to be more clarity from sporting bodies to ensure athletes who had transitioned from male to female weren't demonised, Dr Adair added.

"One of the elements missing from this debate is that transgender athletes are not doing anything wrong — they're playing by the rules," he said.

"Yet those who are competitive … are widely vilified. Angst should be directed at the rule makers.

"It's in the IOC's hands now. Either they come out with robust evidence for their position or they reconsider their policy."