By the time long-distance runner Jasmin Paris, 35, arrived at the fifth checkpoint of Britain's most brutal ultrarace -- the Montane Spine Race -- she had run about 200 miles over three days, with around two hours of sleep.

She felt wobbly as she prepared her sleeping bag. She had planned to sleep there for three to four hours, but she realized that wasn't going to work. Former Spine Race winner Eugeni Roselló Solé was only two hours behind and Paris didn't want to be at the checkpoint when Solé arrived. He'd latch on and it'd be hard for her to shake him off.

So, she decided to take a 40-minute power nap instead. But she was too cold and tired to fully fall asleep. She just lay there shaking.

Exactly 40 minutes later, she was on her feet. She had eaten some sausage and chickpea casserole at the checkpoint. She had also expressed milk -- her 14-month-old daughter, Rowan, was still breastfeeding and she had been pumping milk at each checkpoint. With the mandatory 3,000 calories of food (nuts, chocolate bars and fruit loaf) that every runner was supposed to carry from each checkpoint, she was off again.

When Paris crossed the finish line, she’d clocked about three hours of sleep in more than three days. Pete Aylward

All runners are tracked via GPS, and Paris' coach, two-time Spine Race finisher Damian Hall, watched her tiny dot move on his laptop. He gasped. She wasn't supposed to leave so soon. The plan was for her to rest for at least another two hours.

Paris had already revised another plan to sleep for three hours at the previous checkpoint. She and Roselló Solé had run together between the third and fourth checkpoints. At the fourth, Paris decided to push on without taking a nap -- because she wanted the lead.

Now, at the fifth checkpoint, Paris had gone rogue. They hadn't prepared for her to run on such little sleep, Hall thought, his brows furrowed as he stared at his laptop.

"You run the entire day looking forward to the time you can relax at the checkpoint -- it's really nice there, there's food and lights and people smiling at you and helping you -- and for you to say, 'I am only going to stay here for 15 minutes and then I am going to leave' is probably the hardest thing to do," Hall said.

Fifty miles later, Paris, a veterinarian and a Ph.D. student in myeloid leukaemia at the University of Edinburgh, became the first woman to win the Spine Race. And she did it in a record-breaking 83 hours and 12 minutes, beating 135 runners -- and smashing the old course record by more than 12 hours.

Roselló Solé didn't finish the race. He'd pushed himself so much in trying to beat Paris that he had to be taken out of the race with just four miles to go. He was clinically exhausted.

In fact, the next finisher was previous course record-holder Eoin Keith, more than 15 hours after Paris.

Paris started running when she was 24. She was studying to become a vet and running kept her motivated. She woke up early in the morning to train and it helped clear her mind and prepare for the day ahead. While she'd always loved long walks and backpacking, she had no substantial running experience.

During the race, Paris expressed breast milk for her daughter, Rowan, at every checkpoint. Pete Aylward

But she hated running on roads, and she hated marathons. She wanted to become a fell runner -- racing over upland country where the incline of the terrain is an important part of the race. She signed up for competitions like the British Fell Running Championships and the Skyrunner World Series and won most of them comfortably, coming to be known as the best female fell runner in the country.

The first time Hall met Paris was at the 2015 Dragon's Back Race -- Britain's second-most-challenging race after Spine -- a 315-kilometer (195-mile) ultra across Wales. Paris and Hall ran the first day of the race together. He saw that she was unlike most long-distance runners. She smiled a lot, she talked to strangers on the path and she looked likable, he remembered thinking.

Parts of the race were on actual mountain tops, where runners tried to walk across while holding on for dear life. At one point, four men, including Hall, were running with Paris. When they got to Crib Goch (also called Red Ridge) a knife-thin ridge, the men slowed down, clearly intimidated.

Hall paused for a moment and looked up. Paris had just disappeared along the top of it, "dancing into the mist."

"Most of us men were hugging the rock like it was our mothers. She didn't bat an eyelid," Hall said.

She finished second in that race, beating Hall and several former winners.

The two formed a friendship after the race, and when Paris decided to run Spine, he was the obvious choice for a coach -- he'd also finished the race two times.

Paris signed up for the Spine Race with one intention: It would help her wake up at 4 a.m. every morning to run. Her daughter was keeping her up at night and she needed that motivation to start her day. She was confident she wasn't going to go through with it. "It looked miserable out there," she remembered thinking while looking at videos of the race from previous years.

Once she began training under Hall's guidance, she started doing 100-mile runs each week. She carried her daughter on her back during some of her long runs to simulate a backpack, and even ran three eight-hour sessions over the course of three days to mirror the real run. That was when she thought to herself, "Now I want to know if I can actually pull this off."

The first night of the race was the hardest. She missed Rowan and her husband, Konrad. It was the first time she had been away from Rowan for more than three days, and every step she took was a reminder that she still had a million of them to go. It was the dead of winter and she felt miserable running in the dark.

And the navigation was a challenge that was tough to prepare for. The runners were all given maps with the route of the race marked, so she had to keep one eye on the map and the other on the road at all times. Early on, she decided she'd never allow herself to get so tired that she'd get lost in the wilderness.

Paris was also starting to feel uncomfortable. She had planned to wean Rowan from breastfeeding before the race, but Rowan's two viral infections had delayed that process, and her daughter was still breastfeeding. So Paris had to pump milk at every checkpoint.

"You know, it was just something I needed to do. Every runner needed to do something -- change socks, change their headgear or whatever, and I needed to express milk. In a race that takes 83 hours, it's just a drop in the ocean, it's really not that big of a deal," she said.

At the first checkpoint it took her about 10 extra minutes to add in pumping, but as the race went on, her exhausted body was producing so little milk that it was only a minute or two.

By the time she got to that fifth and final checkpoint, Paris had taken off. There was nobody even remotely close to catching up with her. Unless something went terribly wrong, she knew she would win. She was now on the Scottish border, and it was a clear winter day with blue skies. She could see clearly for miles. It was just the way she loved it -- running in the wilderness, with nothing but the finish line to get to.

She ran the last 30 miles with that feeling. She was going to win her first Spine Race. She was going to beat some previous winners and some with more Spine Race experience than her entire running career combined.

But even with that euphoric feeling of success, it was hard to actually take the steps. She could feel her brain turning off. She was falling asleep on her feet.

In previous races, runners had won with 5 or 6 hours of sleep. She was going on 3.

She thought of her daughter and husband. She would get to hold them soon. She shook her head, forcing her brain to wake up.

When she felt the finish line on her waist, a lot of things happened all at once. Rowan was thrust into her arms, Konrad was hugging her, people were screaming questions at her. She could see flashes -- photographers, she supposed.

She had a huge blister between her big toe and her second toe and the tendonitis in her knee was acting up. But other than that, she felt fine. She didn't faint at the finish line. She answered reporters' questions and she even had energy to get dinner with her family.

She heard from Great Britain's ultrarunning team the next day. She was selected as part of the team to compete at the Ultra Trial Championships in Portugal in June.

"Until I begin training for that, I am going to focus on Rowan, my Ph.D. program and recovering from this race," she said.

Would she run Spine again?

"I would never say never. But I had the most amazing race and I don't think I could ever top that ever, and it seems to me a little silly to try to do it again -- I have so many other fell races I want to run and win."