The 18-time Grand Slam tennis champion was criticised earlier this year after using the word "cheating" when discussing whether trans women should be allowed to compete in women's sport.

She later apologised but was dropped as an ambassador by LGBT sport body Athlete Ally.

Now the 62-year-old has made a BBC documentary exploring the issue.

For the film, The Trans Women Athlete Dispute with Martina Navratilova, she meets and discusses trans women in sport with a range of athletes, trans women and scientists.

"What I have come to realise, the biggest thing for me, is just the level of difficulty trans people go through cannot be underestimated," she says.

"The fight for equality and recognition is just huge."

She tells Trans Media Watch founder Helen Belcher: "I hurt people with my comments - that bothers me. I campaigned all my life for LGBT rights."

Later she adds: "That being said, still for me the most important thing in sports - and we have to remember trans rights and elite sport are two different things, although of course they are connected - what's the right way to set the rules so that everybody feels like they have a fighting chance?"

As well as hearing the experiences of trans athletes, she explores the science to find out whether trans athletes have a competitive advantage in women's sport.

"It feels to me that it's impossible to come to any real conclusions or write any meaningful rules until more research is done," she says.

"But for now I think we need to include as many transgender athletes as possible within elite sports while keeping as level a playing field as possible."

Sociologist Ellis Cashmore tells Navratilova sport will have to change in the same way other parts of society are adapting to gender fluidity - but admits he has been struggling "to figure an alternative".

"I don't think women's sport will look the same in 10 years' time," he explains.

"I think a great many sports are going to have to come to terms with the fact they are going to have to mix sports - in other words, dissolve the binary completely and just say they're open."

"Society has changed so much. The rules certainly need to evolve," Navratilova agrees.

"If you don't adapt, you've got problems. So we'll keep adapting and try to find a happy way forward."