The 31-year-old British athlete Phil Sesemann arrived at the Seville marathon in February with a clear aim: to run the 26.2-mile course in less then two hours, eight minutes and 10 seconds. If he recorded that time or went faster, he’d meet the British qualifying standard to compete for Team GB at this summer’s Olympics in Paris; one second slower, he would be watching the race from his sofa at home in Leeds.

Having a plan and executing it are, of course, very different propositions, especially in the marathon, a fabled distance that has been sadistically breaking hearts, minds and bodies for more than two millennia. And the qualifying time was no small achievement: only three British men had ever run faster. Add to this that Sesemann, who has dark hair and the angular handsomeness of Cillian Murphy, is still pretty raw at the event. For much of his 20s, he combined part-time running with being a junior doctor at St James’s hospital in Leeds. He only switched to the marathon in late 2021 and would need to run a huge personal best (PB) to qualify.

In the buildup, Sesemann trained harder than ever before, clocking up well over 100 miles a week. In January, he decamped to Kenya for a month, running at altitude with (or, often, behind) the world’s top distance athletes. Back at home, he pounded canal paths with his two dogs, Kipchoge and Haile – a spaniel-vizsla cross and German short-haired pointer respectively, named after marathon legends – who have modest Instagram celebrity as the “mileage mutts”.

The final pieces of the puzzle were the shoes that Sesemann would wear on race day. Ever since 2016, there has been a technological arms race between the major footwear brands, especially Nike and Adidas. Nike was first out of the blocks with the original “super shoe”, which it called the Zoom Vaporfly 4%. The 4% referred to the estimated typical improvement in efficiency – verified by an independent biomechanist, Rodger Kram from the University of Colorado, commissioned by Nike – that a runner could expect to enjoy wearing the shoes, compared with the best alternative on the market.

Many innovations are described as gamechanging, but the Zoom Vaporflys were precisely that: a 4% boost, in the marathon especially, was not a matter of seconds; it meant several minutes. World records duly tumbled by jaw-dropping margins. Moreover, the new shoes radically turned on its head what we expected athletic footwear to look like. Conventional wisdom had always suggested that the optimal shoes for long-distance running were sleek and minimalist, with a small strip of cushioning; they were called “running flats”. The Nike Vaporfly 4% looked, in contrast, like a moon boot: a large wedge of foam, adapted from aircraft insulation, sat under the foot. Inside the shoe was a spoon-shaped, carbon-fibre plate, which rocked forwards and made runners feel they were being propelled downhill.

But Adidas, which sponsors Sesemann, along with other footwear brands, had caught up fast. For the Seville marathon, he wanted to run in their latest carbon shoes: the Adizero Adios Pro Evo 1. The Evo 1s had only been out a few months but were already causing a stir. They were super-lightweight, just 138g, which was 40% lighter than any racing shoe Adidas had made before. They also had a “first-of-its-kind forefoot rocker” that encouraged forward momentum and improved running efficiency.

And, extraordinarily, the Evo 1s were recommended by Adidas as single use: you wore them for one race and they were spent. The Ethiopian athlete Tigist Assefa used a prototype of the shoes at the Berlin marathon last September and destroyed the women’s world record by more than two minutes. The Evo 1s were, Assefa said, “like nothing I’ve felt before”.

So yes, Sesemann wanted some of that. The only problem was that there was a global shortage of the Evo 1s. They were released to the public, costing £400, and sold out almost immediately; their resale value is usually more than £1,000. Even as an Adidas athlete, running for Olympic qualification, Sesemann couldn’t be guaranteed getting the shoes. Eventually, a few days before Seville, Adidas sent him a pair of size nines. The snag was that Sesemann is a 9.5: for the first time in his career, he decided to race without socks. He gambled that the benefits conferred by the Evo 1s would outweigh the discomfort.

That gamble, as the race progressed, didn’t seem to be paying off. Sesemann was running faster than he ever had but, according to his calculations, he remained resolutely outside the Olympic qualifying time. Moreover, his feet were being shredded by the tight shoes. “They were very bloody, like congealed, clotted blood on the back of my heels,” he says. “Yeah, it wasn’t the prettiest sight.”

Sesemann dug in as the miles ticked on, but it was hard not to feel disheartened. “It was horrendous, to be really honest,” he recalls. “I was checking my splits on my watch the whole way through and I was just thinking: ‘Oh my God, I’m going to miss this by one or two seconds.’ I basically convinced myself that I wasn’t going to do it.”

And yet, something happened. Sesemann powered on; he forgot about the throbbing in his feet. At the finish line, he looked up and saw the magic numbers: two hours, eight minutes and four seconds. Six seconds faster than the qualifying standard; he was going to the Olympics. “You think: ‘I’ve done it, I’ve worked for so long for this,’” says Sesemann. “So yeah, really sweet.”

Since the race, Sesemann has sometimes wondered what made the difference, that most marginal gain of six seconds over more than two hours. Was it the spell in Kenya? The extra training miles? The super shoes? He can’t be sure, but he’s not going to be tossing his Evo 1s in the bin, anyway. “It’s very hard to throw away a £400 pair of shoes,” he says, smiling. “I’ll probably frame the Seville pair just because they’re covered in blood and it makes me look quite hard. And obviously, it was the peak of my career.”

“Blood, sweat and tears,” Sesemann goes on. “So yeah, I won’t be throwing that pair away for sure.”

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Every sport is streamlined over time by technology and new materials. Where these developments overstep a mark is often contentious. Formula One has seen many battles on this front over the years. In the mid-1970s, the Tyrrell team experimented with a six-wheeled car: it won one race, but struggled with consistency and was phased out. In 1978, Brabham engineers used the (perfectly legal) tactic of installing a large fan in the back of the car, which dramatically improved its aerodynamics. The BT46B won its first race by 34 seconds but was promptly withdrawn, and later banned, after complaints from rivals.

But the most direct comparison with carbon running shoes is the Speedo LZR Racer full-body swimsuit that was launched in 2008. At the Beijing Olympics that summer, 98% of all swimming medals were won by athletes in the suit, which significantly reduced skin-friction drag. In a little over a year, 93 world records were broken in the LZR Racer, leading swimming’s governing body Fina to bring in a set of new restrictions in 2010 that essentially outlawed full-body suits.

When the Nike Zoom Vaporfly was first released, similar concerns were raised about “technological doping”. In the men’s marathon at the 2016 Olympics, all three places on the podium were taken by Nike-endorsed athletes wearing an unreleased prototype of the Vaporfly. As the other shoe brands scrabbled to catch up, it became manifestly clear that the playing field in distance running was no longer a level one. Athletes not wearing the Vaporfly were clearly at a disadvantage: in these early days, some desperate top runners who were sponsored by other brands even took to wearing the shoes and taping over the swoosh.

Unlike swimming, the athletics authorities took a more lenient view of the new technology. World Athletics, the governing body of track and field, only stepped in in 2020, stipulating the foam base of the shoes can be no higher than 40mm (the exact height of the Vaporfly, as it happens) and ruling that there could not be more than a single carbon plate. They also initially forbade the use of prototypes – athletes could only race in shoes that had been available to purchase for at least four months – but that judgment was later overturned.

The decision not to restrict carbon shoes had a significant impact on the record books. On both the men’s and women’s side, nine out of the 10 fastest marathons in history have been run by athletes wearing carbon shoes. Comparing the best runners of today with previous generations is now pretty well impossible. “There’s a sizeable constituency of people who think that super shoes have made the world record pretty meaningless,” says Andy Dixon, the editor-in-chief of Runner’s World. “It’s like comparing apples with pears. If the shoe is giving you three or four minutes, then this idea of a world record being a metric for human excellence is definitely skewed. Some people have even suggested that there should be an asterisk by records set with super shoes.”

The only female athlete from the pre-carbon-shoe era to feature in the top 10 marathon times is Britain’s Paula Radcliffe. Her mark – two hours, 15 minutes, 25 seconds – was recorded at the London marathon in 2003; it would remain the world record for 16 years and is still the sixth-fastest time in history.

Does Radcliffe think there should be an asterisk next to the new times? She shakes her head and laughs, “I would love it to still be the world record. And for the shoes maybe to have not come along. But I think the one thing that most athletes want to be able to do is finish their career and say: ‘OK, I achieved what I was capable of doing. I ran as fast as I was capable of doing.’ And I guess in all areas bar the Olympic Games, I can say that I did that with my career. So those times, yeah, do make me proud. Then, in my mind, I know that they were run in the old shoes as well!”

Radcliffe had a front-row seat as carbon shoes were being developed. She was sponsored by Nike throughout her career until she retired in 2015 after a long-term battle with degenerative osteoarthritis in the arch of her foot. The prototype of the Zoom Vaporfly was unveiled the following year. “I know some of the designers at Nike,” she says, “and they told me: ‘We’re designing a shoe that’s going to break your record.’ I was like: ‘Thanks, guys!’”

Ultimately, though, Radcliffe has decided that she was fortunate to compete in the era before super shoes. She was known for her attritional style of racing – her head furiously bobbing, every sinew stretched – so the idea of a labour-saving piece of kit is not really on-brand for her.

“People have asked me a lot of times: what could I run in the shoes?” she says. “And the answer is I don’t know. I think I could have run quicker. But at the same time, I’m glad I had my time when I did because what made me strong and unbeatable through 2002 and 2003 essentially wouldn’t be as big of an advantage in today’s shoes. Because I was very, very good mentally and physically at withstanding the beating up of your body that hits you at 30km, and keeping going. That doesn’t hit runners now.”

* * *

All serious runners can remember the first time they wore carbon shoes in a race. For Rose Harvey, a 31-year-old athlete who now has the sixth-fastest marathon time for British women, it was in 2017. Back then, she was a corporate lawyer in London who mainly used to run to work, dodging commuters. Her goal was to break 80 minutes for the half-marathon and she just couldn’t do it. Eventually, Harvey cracked and dropped £200 on the second iteration of the Nike Vaporfly.

“I was sceptical about them for a long time thinking: ‘Oh, it’s just marketing,’” says Harvey. “Put them on for the race day and yeah, I ran a lot faster. I ran one hour 16 minutes, so just immediately knocked five minutes off my PB. I also got the worst blisters ever. I couldn’t walk the next day, but it was worth it!”

Afterwards, however, Harvey did feel some conflict. “Now everyone just wears them,” she says. “And it’s just become: ‘Why wouldn’t you, if you can run faster?’ But back then I wasn’t doing this professionally, I was literally doing it just to see if I could break 80 minutes, and it did feel a bit like cheating.”

Carbon shoes may have inspired some soul-searching in elite athletics, but Harvey is right: among recreational runners, they are wildly popular. “I don’t think people care [about the world record debate]!” says Dixon. “If you were chasing a PB in a marathon it’s like: ‘Would you choose a hilly course or a flat course?’ You’d choose a flat course. ‘Would you wear a normal shoe or a super shoe?’ There’s no doubt, you’d go for a super shoe because well, that’s an extra two minutes off your time. So these shoes have been massively commercially successful.”

It’s certainly true that there has been a softening in opposition to carbon shoes. When they were first released, they appeared to threaten the integrity of long-distance running. Now, it’s not hard to find advocates who believe the shoes are injecting new excitement into – maybe even becoming the saviour of – events such as the marathon. One of these is Matt Taylor, the founder of upstart running brand Tracksmith, which is looking to do for running what Rapha has done for the cycling market. Like everyone else, Tracksmith will be unveiling its own carbon shoe, the Eliot Racer, this summer.

“Without super shoes, I think the marathon would be declining, declining, declining,” says Taylor. “We had reached the peak. It was like: ‘OK, everyone’s run a marathon. It’s not that impressive any more.’ And then the super shoes came along and now it’s reignited this interest in that distance.”

For Taylor, the shoes will inspire individuals to see if they can go faster or further. “Marathons are two to three hours, right, but people that are running four, five, six, seven hours, that’s where it could get really interesting in terms of chasing where the limits are,” he says. “There’s a ton of potential still on the ultra side.”

Rose Harvey, meanwhile, has gone from being a weekend runner to one of Britain’s top endurance athletes. The journey – a “sliding door moment” – started when she was made redundant from her job as a lawyer at the outset of the Covid pandemic. Running became her lockdown project and she took hefty chunks off her marathon times: from a personal best of nearly three hours, down to two hours, 23 minutes at the Chicago marathon last year. Harvey is now sponsored by Puma and will find out this month if she has been selected for the British Olympic team.

For serious athletes such as Harvey, perhaps the main benefit of carbon-fibre shoes is that they allow you to train more intensively, with a lower risk of injury. (Like many professionals, she does about 70% of her training in non-carbon shoes; super shoes are reserved for the most extreme efforts.) “They obviously do make you go faster, which on race day is a big advantage,” says Harvey. “But in training, the main advantage of carbon shoes is just the recovery. Before, I wouldn’t be able to walk the day after … well, for a week after a marathon. But after Chicago, I was running the next day and your legs don’t feel that beaten up.”

Super shoes are here to stay, and most experts expect to see the records keep tumbling. The foam formulations should become even lighter and bouncier; the carbon plates will offer more spring and responsiveness. On the men’s side, the two-hour marathon, which for so long has been the holy grail of distance running, will probably finally be toppled. Kelvin Kiptum from Kenya, last year’s winner of the London marathon, had already come close, winning the 2023 Chicago marathon in two hours, 35 seconds, a new world record. Kiptum, though, died in a car crash in February, aged 24.

At this year’s London marathon, on Sunday 21 April, super shoes will certainly be on the feet of many runners. Some will be looking to set new personal bests; but most will be happy to cover the course without their bodies surrendering to the pummelling. “It still is that mythical, humbling distance,” says Radcliffe, who will be commentating on the event for the BBC. “But I guess it’s that little bit more tamed, that little bit more accessible now than it was.”

Just a word of advice: if you speak to someone who has completed the marathon, don’t make the mistake of thinking that their super shoes made it easy. “At the end of the day, the shoes do help, but you’ve still got to be able to run at that pace,” says Rose Harvey. “You’ve still got to run the damn thing!”