At the top of a wind-scoured hill outside Edinburgh, Jasmin Paris’s dog, Moss, patiently waits for his owner. He is, I think, wondering what on earth is taking her so long. The answer, I’m afraid, is me.

We are in the Pentland Hills near her home – easy terrain for a skilled fell runner. For me, it’s a painful reminder that road marathons and track races do not help in the hills. I spend my clumsy descents looking at my feet, and each time I look up, Paris is defying gravity – not so much dropping as floating down.

In January, Paris, then 35, made headlines across the globe when she won the Spine Race, one of those almost comically difficult events that sounds less like a run and more like a sadistic punishment: 268 miles, nonstop, along the Pennine Way. Paris took a week off from her PhD in veterinary science to compete, and thrashed every man in the field in the process.

The race is billed as the world’s toughest endurance contest, and with good reason. It’s dark two-thirds of the time. Racers traverse the Peak District, Yorkshire Dales, North Pennines and cross over Hadrian’s Wall to the Cheviots, sleeping only in snatches. Yet Paris’s time of 83 hours, 12 minutes and 23 seconds beat her nearest male rival by nearly 15 hours. And she did it while expressing milk for her baby daughter in aid stations en route – ensuring more than her allotted 15 minutes of fame when she crossed the line. But it’s a fame she clearly finds a little baffling: it’s a fair bet no one has taken up fell running in a bid to become rich or famous.

“That last day of the race, in the Cheviots, was so remote and so, so beautiful,” she tells me. Where we are in the Pentlands feels fairly remote on a windy day, but it is only a bus ride from Edinburgh town centre. “I think I saw one person in about 10 hours. It was one of those mountain days that you remember for ever. I had stopped thinking about the outside world. It’s a simple existence: you put one foot in front of the other and keep going. Emerging from the darkness to what came after – the whole world seemingly wanting to talk to you – was such a stark contrast. But that wasn’t the reason I wanted to do it. It was a challenge, a personal challenge.” The thing is, I think that might be why she won.

***

Sarah Thomas crossing the Channel in 2012. Photograph: Becky Baxter

When it comes to speed, men will always be first across the line. No woman will outsprint Usain Bolt. No woman will hit the side of the pool ahead of Michael Phelps’s world records. Yet a remarkable phenomenon seems to have gathered pace over the past few years: the longer and more brutal the event, the more women seem to be winning outright, or surpassing men’s achievements.

In September this year, the US swimmer Sarah Thomas (already holder of the world record for the longest open-water swim) completed another breathtaking feat of endurance. The Channel Swimming Association records 1,652 solo, observed, unassisted swims (no neoprene wetsuits or flotation devices) of the Channel since 1875. Thirty-four people have swum it there and back without stopping. Four people have swum it three times in a row (two men, two women). But only one – Thomas – has swum it four times. It took her 54 hours and 10 minutes, and though the crossing at its narrowest point is 20 miles, because of the strong tides pushing against her, she actually swam not 80 but close to 130 miles.

This was despite battling nausea and throwing up everything she ate for the first two crossings. A day into her swim, she was almost ready to bail, but her team told her: just keep going. “So that’s what I did,” she said. “I swam until the sun came up and I started to feel better.”

It’s not only Paris and Thomas. Last month Maggie Guteri became the first woman to win the peculiarly sadistic Big Dog Backyard Ultra in Tennessee. The distance is not even set – it’s a case of last man or woman standing. She ran for 60 hours and covered 250 miles. This year, German cyclist Fiona Kolbinger won the Transcontinental race – 2,485 miles across Europe. And in 2018, British fell runner Nicky Spinks set a record for the course in the Lake District known as the Double Bob Graham Round (one circuit of 42 fells, 66 miles and 26,900ft of ascent isn’t enough). Most of these women aren’t even full-time athletes: Paris got up at 4am to fit her Spine Race training in. Spinks is a farmer. Kolbinger is a medical researcher.

So what is going on here? Are we witnessing the beginning of a brave new world, or are these extraordinary women simply outliers?

***

Those looking for a definitive scientific answer may be disappointed. Until about the age of 10, girls and boys are, athletically speaking, the same. Top running speed is the same for boys and girls, as is top swimming speed. Then puberty happens and testosterone changes everything. By 14, boys have bigger hearts, stronger arms, bigger shoulders, longer limbs, greater muscle mass. More power, and more speed, for life.

Thomas swims Lake Champlain, New York, 2017. Photograph: Ken Classen

In 2010, Israeli physicist Ira Hammerman set out to look at records in 82 different sports, ranging from running to speed skating, to see if there was a pattern to the resultant “performance gap”. In every sport, across every distance, a clear difference emerged: women’s speed records are about 9-11% slower than men’s.

However, when it comes to very long endurance events, the data is limited. While ultrarunning is experiencing something of an explosion in popularity, there aren’t that many 200-mile-plus races, and relatively few women are running them.

So is it not possible that after a certain mileage the relative advantages that male hormones bring just, well, run out? The renowned sports scientist Ross Tucker is doubtful. He points out that the success rate among women in ultra-distance races is probably down to the fact that these are niche events – the tiny numbers of ultra-committed female athletes who do compete make any kind of analysis or extrapolation meaningless. However, intriguingly, he does wonder whether a woman’s body composition might prove to be an advantage when it comes to long-distance swimming. “The higher relative body fat percentage is probably enough to offset the differences in strength between men and women, particularly for cold water,” he says. A higher body fat percentage helps in buoyancy, which in turn reduces energy expenditure. It also helps insulate in cold water.

Then there’s the theory that women do so well in ultra races because they are better than men at burning fat for fuel – making them more efficient. But if that were true, Tucker would expect the gap between the sexes to narrow as the reliance on fat gets larger – which doesn’t seem to be the case.

A lot of the male narrative is about pain and suffering and the pain cave and the glory of pain. Oh God, it’s so boring

“In running, from 100 metres to 90 kilometre ultramarathons, the gap between men and women doesn’t change,” he says. “That said, it could be that there is a kind of ‘inflection’ point where suddenly it begins to count. The data is just too thin to know for sure.”

But if women win because of who else does or doesn’t turn up – how did Paris do so by such a margin? After all, when she won the Spine, the second-place finisher was Eoin Keith, a previous winner and the holder of the course record she smashed – hardly an average competitor. The answer may lie less in the body than in the head.

***

Paris doesn’t run for prizes. She – like Thomas, who works for a healthcare company in Colorado – is an amateur, with a full-time job. If every single fell race in the country were called off tomorrow, she’d still be up in those hills every day. She tells me about holidays spent there in her late teens and early 20s with her brother. They’d pack everything they needed to be self-sufficient for a week, go to the remotest hills and hike, eat, sleep, repeat. She hasn’t raced a huge amount since January’s Spine Race, but in the summer she, her husband and a friend completed the Petite Trotte à Léon (PTL). Part of ultrarunning’s biggest event – the Ultra Trail du Mont Blanc (UTMB) – the PTL is not so much a race as an endurance adventure. The 300km route passes through France, Italy and Switzerland, and includes 25,000m of ascent. “It was kind of a holiday,” Paris says, smiling.

I suspect it’s not most people’s idea of a relaxing week. But it reminds me of a conversation I had with the cyclist Emily Chappell, who was the first woman across the line in the 2016 Transcontinental, and has herself been pondering the question of what can lead to women outperforming men.

“I’ve got this bee in my bonnet about the current narrative for cycling – the male narrative,” she says. “A lot of it is about pain and suffering and the pain cave and the glory of pain and seeking out pain. Oh God, it’s so boring. So the working theory I’ve come up with is that people who do endurance sport are often people who have quite comfortable lives, and they are almost looking for pain elsewhere. I know it’s making generalisations, but what if men are looking for the pain they lack in life, and women are looking for the freedom?”

Emily Chappell near Cheddar Gorge in Somerset: ‘In cycling, women are looking for the freedom they lack in life.’ Photograph: Felicity McCabe/The Guardian

It’s a persuasive theory. So many endurance events are marketed with a hefty dash of machismo – “tough” this, “ultimate” that, “warrior” the other. But is this constant reminder of suffering really the best way to approach an ultra event, when managing your head is as – if not more – important than managing your body? If you buy into this narrative that you are here only to suffer and endure, rather than have fun, then maybe those who start relaxed, looking forward to the journey, might have a head start.

Perhaps this sounds a little woolly. But Thomas agrees that, for her, swimming is about freedom, not glory. “This is exactly me!” she says. “I don’t really care about racing and winning – I just like pushing myself. The long open-water swims make me feel free and strong. To look across the Channel and say, ‘I swam that’ is really empowering. I love being alone in a large body of water, knowing I’m relying on myself to make it through.”

Dr Josephine Perry, a sports psychologist and author of Performing Under Pressure, goes a step further. She believes women are better at dealing with pain. “Eighty per cent of women get period pain at some point in their lives and around 10% have conditions like endometriosis, which can severely impact their ability to perform in sport,” she says. “If a large majority of women have developed strong coping mechanisms to deal with this regular pain, then the short-term pain they feel when running a race will fade in comparison.”

Sports psychologists also often talk about “the process, not the outcome” – enjoying, or at least staying in, the moment. Thomas clearly embraces this. “I was always weird during my competitive swimming days. I loved the training more than the racing,” she says. Perry believes this mindset can, perhaps contrary to expectations, create winners. “Something I see regularly with athletes is that when you are expected to do well, it adds a significant pressure,” she explains. “When there are no expectations we relax and can enjoy the process of seeing what is possible, rather than worrying about failing. These women may well see the event as ‘just a race’ in which they can see what is possible, rather than openly and loudly setting out to win it. This can be incredibly beneficial to performance.”

Then there is the question of pride. Even when women do not win outright, they often perform better than men: better, in that a higher proportion of women finish ultra events successfully. And ego – or rather a lack of one – may be a key factor.

Paris tells me about another infamous ultra race she ran in 2015, the Dragon’s Back: five days, 315km and 15,500m of ascent in the Welsh mountains. “One of my role models is Helene Diamantides, one of the pioneers of women’s fell running. She said to us at the start of the race: look around the room. If you are a man, you have a 50% chance of finishing the race. If you’re a woman, you have a 90% chance. But then, there were far fewer women in the room. Because they have less ego, they wouldn’t turn up unless they were well-prepared. Whereas men can be a bit like, how hard can this be?”

Thomas agrees. “I think women do train harder, generally, and are less likely to wing something than the guys are,” she says. “I remember seeing something a few years ago that ran some numbers as related to speed. There are more guys who do longer swims, so there is a wider range of times, more variation. There are fewer women, but we seem to be more consistent.”

It is backed up, too, by data from less extreme events. In marathon running, we know that women are on average better pacers. Not faster overall, just better at running evenly: less likely to go out too hard and “blow up”. And whether it’s 26.2 miles or 262, going out too hard can be the worst mistake you can make.

“In something like the Spine Race, it’s not even just about being able to run a long way,” Paris says. “It’s the fact that you need to look after yourself. You need to eat enough, feed yourself, look after your feet. I think sometimes the men, maybe their egos give them a single-mindedness and focus. But that’s almost a disadvantage, because actually, in an event that long you have to be able to multitask, to think about lots of things, to navigate [to look after yourself].”

So having the biggest heart, and the highest oxygen uptake, might make you quickest over a certain distance but it won’t necessarily help you over days of endurance. Yet as Tucker suggests, if there is one sport in which women do narrow that performance gap it is ultra-endurance swimming. Over distances of 16-36km, women are generally only 1-6% slower. And in two long-distance swims, the Catalina Channel (32k) and the Manhattan Island Marathon Swim (45.9km) – both of which Thomas has completed – the fastest women ever were faster than the best-performing men. As Tucker suggests, perhaps women’s body fat and its more even distribution is an advantage – fat is buoyant so aids flotation.

Most men are in awe of the women they swim with. They seem to accept that we’re just as tough, just as fast

But Thomas is not one to explore the theories. “I haven’t really looked into the science,” she says. “I just try to accept that my body is strong and can handle cold, no matter how much I hate my love handles.”

***

Of course, women beating men is hardly new. In any race, some women will finish faster than some men – there’s even a phrase for it in the athlete’s lexicon: being “chicked”. It is not something all men take well. Even in my own career as a club runner, I’ve encountered a few who are clearly rankled by it, including a man who refused to let me run faster than him on a simple run commute home, to the point where he ended up throwing up under a tree because he’d pushed himself so hard. And I’ve also lost count of the number of races where the second half has been spent overtaking enthusiastic runners who set off too fast – 99% of them male.

Fortunately, hostility is the exception. Thomas points out that swimming has a longer history of equality than most sports. “Gertrude Ederle was the first woman to swim the Channel in the late 1920s, while the first female to run a marathon didn’t come along until the 70s. So women swimmers have a decades-longer tradition of being accepted than runners do.

“I think most men are in awe of the women they swim with,” she adds. “They seem to accept that we’re just as tough, just as fast. That said, there are always exceptions. I have trained with men who think and act like they can beat me and get their feelings hurt when I pass them. I was sharing a lane with some guys a few years ago. When I was passing them, they tried to obstruct me. When I was getting out, two of them yelled at me for not being ‘respectful’ of their workout, never mind them being respectful of my workout.

Jasmin Paris in the hills near her home in Edinburgh: ‘In a long event, you need to be able to multitask.’ Photograph: Felicity McCabe/The Guardian

“And in 2008 or 2009, I outright won a 10k race. I passed the lead guy with about a mile to go and won by a couple of minutes. When we were done, I went up to congratulate him on a good race. He refused to shake my hand.”

Paris has a similar story about a trail runner who wouldn’t let her pass him up a hill, despite clearly ruining his own race by speeding up too much. But she points out that generally fell running is democratic: “Here, you can have an elite runner and an 80-year-old in the same race, and we all have tea and cake together afterwards. There’s genuinely very little ego in this sport.”

Where female winners often do encounter sexism, though, is in the reactions to their achievements. Thomas remarks that she’s constantly asked if she has kids, “with the assumption that if I did, I wouldn’t be doing what I was doing”. Paris says that she avoided looking too much at the comments under the articles about her victory.

We also talk about Emelie Forsberg, a star of the ultrarunning world, with multiple wins to her name. Recently she had a baby with her partner, Kilian Jornet – himself probably the closest thing ultrarunning has to a household name. Forsberg was posting on Instagram about her return to competition in the Courmayeur-Champex-Chamonix (CCC; part of the UTMB race series), which would take her about 12 hours. Paris says she immediately spotted one reply asking: “When you run for 12 hours, who looks after your baby? Don’t you worry about her?”

“She replied with four words: ‘She has a father,’” Paris says. “And I thought yes, that absolutely sums it up. It’s crazy.”

And so, despite these amazing athletes conquering distances most of us would consider an effort in a car, there’s still a considerable way to go. But make no mistake, times are changing in the endurance game. And these women know better than most how to stay in it for the long haul.

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