Like it or not, sport is in transition.

The AFL is just the latest of many national and international sporting organisations that have overwhelmingly failed to adjust to a changing world where shades of grey have replaced the previously black and white male-female gender dichotomy.

The AFL's decision not to allow trans woman Hannah Mouncey play in the elite AFLW competition has been debated widely this week — although mostly superficially.

The idea that the "floodgates will open" appears misplaced.

A tertiary educated, former elite athlete, now working as a coach, summed up the thoughts of many.

"I don't think it's fair that anyone with the advantages of once being a male gets to compete against females," said the coach, who chose not to be named.

"I would not want to be beaten by someone like that after all the years of hard work I put in."

It's a widely held view.

It's why Caster Semenya's future as an Olympic and world champion runner is still being debated almost a decade since her debut.

The running career of South Africa's Caster Semenya is still being debated. ( Reuters: Dylan Martinez )

Every day athletes are beaten by others with identifiable difference. And yet those differences are allowed.

It could be physical difference like longer limbs in sports like basketball or swimming; it could be better training facilities enjoyed by developed nations over developing nations; it could be superior mental strength over those who struggle with big occasions.

But "trans" difference sets off alarm bells.

Trans women judged on looks

Mianne Bagger was the world's first known trans golfer playing on the international circuit.

On a special "sport in transition" episode of The Ticket, she says most of what people know about diversity in transitioned women is fed through sensationalistic media.

Mianne Bagger, pictured in 2004, was the world's first known trans golfer playing on the international circuit. ( Reuters: Will Burgess )

"For the majority of diversity and transitioned women, and women in sport in general, they are getting judged first on looks … that they 'look' too masculine," she says.

"Once that happens the world somehow feels entitled in questioning their femininity."

Athletes who "look" different are targeted for testosterone testing.

It has been the basis of the International Olympic Committee's (IOC) gender policy until being suspended in 2015 by the Court of Arbitration for Sport for a lack of scientific evidence.

Dr Ruth McNair is a member of the Victorian Government's LGBTI taskforce and is one of few experts working in the transgender space in Australia.

She, like others, was not consulted by the AFL before it made its decision to exclude Mouncey from this year's draft.

When women transition they take female hormones as well as testosterone blockers.

"Many trans women affirm their gender by using female hormones … so in trans women the testosterone level is usually suppressed well into the female range," Dr McNair says.

"Most transgender women get into that female testosterone range within the first couple of months of using estrogen … it stays in that range for as long as they continue their hormone treatment."

Medical evidence doesn't support AFL's ruling, doctor says

The big question is whether there is some overlapping benefit of having had the advantage of male levels of testosterone in the years leading up to a person's transition.

"The only benefit is the body shape that developed due to testosterone during adolescence," Dr McNair says.

"So trans women have developed their bodies in a masculine frame so they might have a larger bone mass and be taller, but in general that's the only ongoing effect … [due to treatment] their muscle mass and strength is reduced."

Sorry, this video has expired AFL rules trans footballer Hannah Mouncey ineligible for AFLW draft

The AFL, in this week's decision, cited concerns of stamina, strength and physique.

Dr McNair believes the medical evidence does not support that view.

"No, I don't. Obviously with physique, Hannah can't change that, but the strength and stamina will have altered due to her hormonal treatments," she says.

It's a difference Bagger can attest to as she embarked on her professional golf career.

"I did notice [after transition] there was a significant difference," she says.

"I'd go and play the same golf course — and even playing from the same tees — I noticed I had to use a completely different club, so the change is very real and very significant.

"It does take a period of time, I'm not sure of the quantifiable length of time, obviously two years is one that's used a lot at the moment in most policies, but it is a gradual and very real effect on the body."

'The science says yes': All women can compete equally

US-based medical physicist Joanna Harper, a trans woman and competitive runner, has written an academic paper on transitioning and the impact on sports performance.

"When I started to transition in 2004 … within nine months I had started running 12 per cent slower than I had been before and men run 10-12 per cent faster than women — and so in nine months, I had lost all of my male advantage," she says.

"I have spoken with Hannah off and on for over a year now and Hannah is absolutely a large, strong woman and transgender women are on average bigger and stronger, so of course transgender women have athletic advantages, but they also have disadvantages too.

"So the question is, can transgender women and cisgender women [those who identify as their sex assigned at birth' compete against each other in an equitable and meaningful competition?

"The science says 'yes'.

"Specifically with regard to Hannah, she's big … but one of the things is that she has a large skeletal system which hasn't reduced in size, but her muscles have substantially reduced in size and strength.

"So she now has a female-size engine trying to move this big skeletal frame around and that is going to cause her some substantial disadvantages."

Notion men will transition to win 'laughable then and now'

There are concerns male athletes will transition simply to be able to win by competing as a female.

It's an argument Bagger finds laughable.

"When I first started touring, and that was about 15 years ago, I was getting all the same comments that are going around now, that all the men are going to change sex and be playing on the women's tour and they'll be winning all the tournaments and taking all the prize money," she says.

"It was laughable then and it's laughable now, but at least I have a case history … and I never managed to win a tournament."

Mianne Bagger says concerns that men would transition to win by competing as women is "laughable". ( Reuters: David Gray )

Sports lawyer and gender equity and diversity specialist Catherine Ordway believes the AFL may be concerned about the legal repercussions of allowing trans women to play in the AFLW.

"That is the only argument I can imagine the AFL is running through to come up with this decision," she says.

"That they're concerned on the behalf of the other players, that they may be at higher risk of physical injury on the field.

"However, the fact is, Hannah has been playing in the local league in Canberra for the last season and her coach has publicly said that there hasn't been any issues, and from what he's observed there's no reason to think that there would be and the risk would be extremely low, if at all.

"In this particular case I can't understand why the argument would be that the AFL women are not strong enough to cope with playing with or against Hannah and yet it's OK for what is presumably a weaker competition in the local league for Hannah to continue to play.

"That seems to me to be a contradiction that they can't support."

Trans inclusion a modern day dilemma sport must address

So, if it's not about strength and stamina, what is it all about?

"It's clearly about the discomfort people have of transitioned women and diversity in general," Bagger says.

Dr McNair says: "It's about fear of difference and trying to understand the trans community and how they fit in the world and unfortunately we still don't have an equal society."

Ms Ordway adds: "My concern is the AFL has not been transparent here in their reasoning, we don't actually know so we have to fill in the gaps in the vacuum that's been created and we can only assume it's about brand protection.

Catherine Ordway believes the AFL may be concerned about the legal repercussions. ( Twitter: Catherine Ordway )

"I think what we're looking at is some form of homophobia where they're saying, 'this is not the kind of woman that we want promoting our game' and I think that's very sad."

This is a modern day dilemma that sports must confront in order to remain current and relevant.

Kristen Worley is a former cyclist, now educator and diversity development adviser for Canada's Human Diversity in Sport Foundation.

Earlier this year she celebrated a substantial victory in the Human Rights Tribunal of Ontaria, Canada, challenging the International Olympic Committee's (IOC) gender policy.

She has been fighting the system for the right to compete for over a decade.

As a result of her persistence, and other current cases before the Court of Arbitration for sport, the IOC's policies are currently suspended while more scientific research is done.

"I'm very saddened because both sides of this argument [the AFL and Hannah Mouncey] … are very vulnerable … that is my biggest concern," she says.

"What we need to be able to do is to go forward together and have these broader discussions and articulate these issues, because it's not about changing athletes' bodies, it's about looking at how we do sport."

Sport is in a bind. Professing inclusivity, often practising the opposite.

The challenge is to replace the outdated model of deciding "who can play" with one that enables "sport for all".