In recent years, transgender inclusion in professional sport has become hotly-contested. More specifically, the inclusion of trans women in single sex competitions has sparked fierce public debate.
On the one hand, some argue transgender athletes have the right to compete in single sex competitions at the highest level and it is fair to do so.
Others question whether it is fair for trans sports stars to compete against those whose are cisgender (i.e. their gender identity matches the sex they were assigned at birth).
As the public debate continues to rage, ITV News looks at what the current rules are for trans athletes and where the grey areas lie.
What are the current guidelines?
All sporting bodies in the UK must operate within the law. The Equality Act 2010 prohibits various forms of discrimination on the basis of gender identity.
The act states, however, that it is lawful to restrict transgender people from sporting competitions where physical strength, stamina or physique are important factors in deciding who wins. Most sports fall under this category.
Within the law, sports governing bodies in the UK set their own guidelines for the inclusion of transgender athletes. The bodies are greatly influenced, however, by guidance from the International Olympic Committee (IOC).
The IOC's most recent set of recommendations, released in November 2021, concluded there should be no presumption that trans athletes have an automatic advantage over their cisgender counterparts.
It also contradicted a previous IOC guideline, which said trans women should have testosterone levels below 10 nanomoles per litre for a 12-month period prior to competition.
Now, the IOC states sporting bodies should set a criteria based on "what unfair advantage means in their sport".
The UK's sports councils (Sport Wales, Sport England, UK Sport, Sport Scotland and Sport Northern Ireland) also influence British sport.
In a joint report last year, they said sports should consider one of three paths.
These are: prioritising transgender inclusion; prioritising competitive fairness and safety; and establishing new formats of the sport, for example, to include non-contact versions of team games so that all athletes can play.
Why are there grey areas when it comes to gender identity and sport?
The group of British councils acknowledged there is no solution that balances the participation of trans women in female sport while achieving competitive fairness and safety.
They also argued that because sports are incredibly diverse, they cannot recommend a one-size-fits-all approach to transgender participation.
"There may not be a common single competition model which will meet the needs of full transgender inclusion while retaining competitive fairness, particularly in female sport," the report said.
Another factor that complicates matters, is testosterone. The role of the hormone alone in predicting performance in sport is often unclear, as the IOC has acknowledged.
And the UK sports councils have stated that trans women retain stamina, strength and physique when competing in female sport, even if their testosterone levels have been reduced.
Finally, no two transgender athletes are the same.
For example, some trans athletes receive hormonal treatment, some do not. Some have had gender reassignment surgery, others have not.
Which high profile cases of trans athletes in sport have there been?
New Zealand weightlifter Laurel Hubbard made history as the first transgender athlete to compete in the Olympics as she took part in the women's 87kg+ event, but the 43-year-old failed in all three attempts at snatching beyond 120kg in the superheavyweight competition.
US swimmer Lia Thomas won the women’s 500-yard freestyle in the NCAA swimming championship in Atlanta in March.
University of Pennsylvania student Thomas, 22, made history as the first transgender woman to win an NCAA championship. Florida governor Ron DeSantis later declared Emma Weyant the winner of the US national college swimming title - despite the fact she finished runner-up to Thomas.
Mr DeSantis was critical of the National Collegiate Athletic Association (NCAA) for permitting Thomas to compete.
Transgender cyclist Emily Bridges had been due to compete against leading female riders including five-time Olympic champion Dame Laura Kenny at the National Omnium Championships in Derby in April. Bridges, 21, who won the men’s points race at the British Universities’ championships in Glasgow last month, began hormone therapy last year and had been deemed eligible to compete in women’s events. British Cycling’s regulations, which were updated in January this year, require riders to have had testosterone levels below five nanomoles per litre for a 12-month period prior to competition.
But three days before the event, the cycling authority reversed its decision, saying it had been informed by the Union Cycliste Internationale (UCI) that Bridges is not eligible to compete.
"We have been in close discussions with the UCI regarding Emily’s participation this weekend and have also engaged closely with Emily and her family regarding her transition and involvement in elite competitions," British Cycling said in a statement.
"We acknowledge the decision of the UCI with regards to Emily’s participation, however we fully recognise her disappointment with today’s decision."
Guidelines for trans inclusion, like the IOC's, often apply to athletes with differences of sex development (DSD).
Olympic gold medal winner Caster Semenya is one of the most famous athletes with DSD.