When the whistle blew at the end of the 2014 Women's Rugby World Cup final, Kat Merchant was overcome with emotion for more reasons than one.

Wing Merchant was struggling with the impact of a number of concussions - a total "probably in the thirties" - from the ages of 16 to 28.

"There is a great photo someone's got of my face, and I look like I've got 20,000 emotions going on," Merchant told BBC Sport.

"I burst out crying because I was like, 'I am never going to play rugby again'. I was never going to put my boots on.

"I was 28, still kind of top of my game, and I knew I was not going to do this again. Although I was really excited that we won, it was bittersweet."

Concussion and its impact has been discussed more in recent years, particularly in rugby and football. However, there is little research into the specific impact on women.

Some suggests women are at higher risk of concussions and can take longer to recover. But the data is sparse - one sports scientist estimates that in 2021 only 6% of sports science literature as a whole used female-only participants.

Slowly, however, things are changing. BBC Sport looks at the impact of concussion on women in sport and what work is being done to understand it.

'Four months of lying in the dark'

Concussion is a traumatic brain injury affecting mental function, meaning it can alter the way someone thinks, feels and remembers. Only about 10% result in losing consciousness.

For Merchant, her last concussion made her feel as though she was on a ferry, moving all the time. She had a fencing response - where the arms go up in the air in an unnatural position, sometimes for several seconds after the impact - and struggled with confusion in the weeks and months after.

"I was very confused about my family being there - I wouldn't put my clothes on because I said they weren't mine," she said.

"Loud noises, I would physically wince. And bright lights I would have this headache.

"I couldn't look at my phone; couldn't read a book. I would just sort of lie there in the dark. It was four months of that, wondering when you're ever going to feel all right again."

One study found men and women are likely to report different symptoms after a concussion - men, for example, are more likely to experience amnesia in the days and weeks after, while women report prolonged headaches, mental fatigue and difficulties with concentration.

Another suggests women could be more at risk depending on what phase of their menstrual cycle they are in.

Governing body World Rugby said in 2023 there had not been enough research on concussion in the women's game.

It has introduced smart mouthguards, which send alerts of high force to the independent matchday doctor, in the women's and men's game. The devices are also worn in training, helping coaches to tailor sessions.

It is not just rugby. A 2021 study found teenage girls who play football are almost twice as much at risk of concussion as teenage boys, with girls more likely to be concussed on contact with the ball or a goalpost.

There will never be a one-size-fits-all for any injury but, as Chelsea manager Emma Hayes has said, women are not small men.

As she put it last August: "Just because your men's team's workload or gym work is organised one way, that absolutely does not mean it should be planned the same for women."

What is being done now?

World Rugby has made a commitment to funding equal men and women's research - if a study is carried out on men, the same study will be carried out on women.

Smart mouthguards are used in professional rugby to monitor in-game head impacts, while scientists behind a ground-breaking saliva test, where a swab is taken to allow researchers to look at markers of how the brain is functioning, have recently extended their study into women's rugby. All the Premiership women's teams are taking part.

Football's governing body Fifa has funded a research project, taking place at the Institute of Sport Exercise and Health in London, to focus on the impact of heading the ball on women's brain health. The study will also look at whether the menstrual cycle affects cognition.

Men's and women's football are played on the same size pitches and with the same size ball, but the existing research does not mitigate for the differences in physiology.

"Female biomechanics are different - for example, female neck strength levels are different," said University College London researcher Dr Flaminia Ronca, who is leading the project.

"The concern we have is that, from other research, we know women seem to have a poor progression and recovery following head injuries.

"We don't really know whether the research that we see in men is transferable to women and whether there might actually be an increased detriment in female football."

West Brom's women team are involved in the project, which includes tests using mouthguards which monitor the impact on a player when they head the ball. The research is aimed to be published in the coming months.

Merchant still deals with some of the impact of the concussions. In her role as a commentator, she will limit her workload the day before to allow her brain to rest.

"If you have a sore quad, you don't sprint," she said. "So if my brain was a bit scrambled or has been, then I give it the time it needs to process."

Merchant also coaches and says she has seen a change in attitude towards dealing with concussion over the past 10 years, with more education bringing about more understanding.

"Concussion is not uncommon - it just wasn't highlighted as much because women weren't professional; we weren't playing as much," she said.

"You can knock your head and not have a concussion, in the same way that you can knock your knee and not injure it.

"But we need to talk about it and understand it more because then we can protect the players and also still have a game of contact rugby."