The story of Gustav Iden’s rule-changing supershoe

Words by Robert Birnbaum.

The long-distance triathlon World Championship in Kona, Hawaii. Just qualifying for this race is a bucket list item for the fastest triathletes. A 2.4-mile (3.9 km) swim, followed by a 112-mile (180.2 km) bicycle ride and a 26.22-mile (42.2 km) marathon run in scorching heat and suffocating humidity. If qualifying is an achievement, finishing is remarkable. Contending for the win on the legendary course takes years of brutal training, an immeasurable amount of grit — and equipment that won’t let you down. 

When Olympic triathlon gold medalist and three-time Kona winner Jan Frodeno set a new Kona course record of 7:51:13 in 2019, it seemed to be one for the ages. Not to be improved on. But in 2022, expectations were re-written, as On triathlete Gustav Iden did the unthinkable. The Norwegian broke the record with room to spare, clocking a final time of 7:40:24 – almost 11 minutes faster than the previous best. 

Gustav swam well, leaving the water with the front group. After the bike leg, he found himself in third place. But it was next, on the run, that he unleashed an effort that would change the Kona race forever. 

As Gustav made his way to the front of the race, he first passed another Olympic Champion, and pre-race favorite, Kristian Blummenfelt. Despite the pair sharing almost everything from sponsors and coaches to training sessions, Gustav seemed to have another gear that day, leaving his fellow Norwegian in his wake. 

With no let up in the pace as he moved through the lava fields, Gustav soon passed frontrunner Sam Laidlow to take a lead that he would not relinquish. As he lifted the famous finish-line banner to take the win, Gustav’s marathon time was clocked at  2:36:15 – another course record.

There’s no doubt that the incredible result was earned through years of relentless training and a level of mental fortitude few can muster. But on this day, Gustav Iden did have another ace up his sleeve. Or rather, on his feet. The shoes that carried him to the win were a special variant of On’s Cloudboom Echo 3 shoe. And this would be the one and only time he would be able to wear them in a race. 

Chatting with Gustav a year on from that famous win, the Iron-distance world champion recalled the story of that special shoe. 

“I signed with On because of the amazing team that was willing to do whatever it takes to make things happen,” Gustav says. “I never paid much attention to other shoe companies. Ever since the first real supershoes launched, I was worried that somebody would come out with the next big innovation. I didn’t want to be tied to only one brand. But I saw the extreme potential for the future [with On], especially with the team.” 

“Gustav only signed with On six weeks before the World Championships in Kona,” Innovation Concept Design Lead at On, Eric Hullegie, recalls. “Until this point, Gustav had been racing in a competitor brand. We would need to provide a faster shoe to convince him to wear On shoes in Kona. It became our task to create the fastest shoe for him before Kona.” 

The team were already in the lab, working on the next-gen Cloudboom Echo 3, a so-called “supershoe” with advanced Helion™ HF foam technology and a carbon plate known as a Speedboard®. Different versions of the shoe had already appeared in elite competition, worn by the likes of 2023 Boston Marathon champion Hellen Obiri. But the team wanted to create something specifically for Gustav or, more accurately, with Gustav. 

“If I’m involved in the process [of developing the design], I know I’m not getting a random shoe. I’m getting a shoe that’s the best for me,” Gustav explains. “Of course, I didn’t think the shoe would just magically appear. But I was willing to do my part, to make the best shoe ever.”

A committed crew of designers, developers and product managers wasted no time in working up the first prototypes. 

“We asked ourselves how we could create additional benefits for Gustav based on the technology of the Cloudboom Echo 3. We visited Gustav at his training camp again and again, showing up with different versions of the shoe. 

To ensure his feedback remained unbiased, the team never told Gustav about the differences between the versions. These efforts were quickly negated by Gustav’s innate ability to analyze his movements and performance – the result of years of extensive his testing and training.

“I spend so much time getting to know my body.” Gustav says. “After all my training, I just have an extremely good understanding of intensity, heart rate, power and so on. I’ve also tested so many running shoes over the years, always analyzing how they felt, what was different about them. So I was usually able to tell quickly what the difference in the shoes was. Different stiffness in the plate, different foam density, different stack height.”

Gustav’s team, which includes renowned coach and sports scientist Olav Aleksander Bu, are known for their meticulous, science-based approach. Gustav’s instincts were quickly validated by their analysis. 

“Along the way, we worked closely with Olav to verify that what he was feeling matched up with the collected data,” Eric says. “When Gustav gave us positive feedback, nine out of ten times, we saw a correlation in the testing results. When we started to see ‘Oh wow, this prototype is actually starting to outperform the competition,’ we doubled down on that version and refined everything further.” 

This was a race against time. It can take years to design, develop and test a new shoe, especially one that needs to handle the rigors of elite endurance racing. Those regular timelines had to be scrapped, the accumulated expertise in the On team was called upon – and more risks needed to be taken, Eric admits. 

“Literally a few weeks before Kona, we had a shoe that we felt was race-ready for Gustav. It was still a shoe that didn’t go through extensive testing and was essentially handmade in the On Lab in Zurich. It was a bit of a risk. But we had made enough versions and were confident in the results of the tests we had conducted. We triple-checked everything. We felt good about the shoe, that it would hold up.” 

Gustav didn’t necessarily see the decision to run in the shoe as a gamble, but a calculated risk. “I have no issue changing my game plan for something better. You always take little risks. Just like I use thinner bike tires because they’re faster. I’m trusting in my karma that everything works out.” 

The design of a race shoe is governed by numerous regulations. One of the limits set by World Athletics relates to the shoe’s stack height – the thickness of the midsole separating the foot from the road. Any shoe that does not fulfill these regulations cannot be used in World Athletics races. However, long-distance triathlons like the Iron-distance World Championships in Kona have their own regulations, leaving more room for innovation that can help set new standards. 

With exactly this mindset, Eric and the team set out to find new boundaries. “In World Athletics races, a shoe’s stack height is limited to 40 millimeters (1.57 inches). We found out that doesn’t apply in long-distance triathlon. So we had much more room to play and go above that stack height. 

“We went through all the legal research to ensure that this shoe would not cause Gustav to be disqualified. It turned out it was kind of a loophole, one it seems that nobody was aware of.” A thicker midsole means more energy-returning foam could be added to Gustav’s shoe. And it made a tangible difference.

“I actually changed my race strategy because of how this shoe felt. It was so fast during downhills and the faster sections of the course. When everything feels smoother, I don’t have to push that hard. I knew nobody could follow me out of Energy Lab [a famous landmark on the Kona course]. I thought if I can cruise until that point, I’m gonna win this race.” 

But it wasn’t all smooth sailing. Gustav’s first runs on the island in his new supershoe didn’t feel immediately game-changing. “I had never been to Kona before. I only realized when I got there that the roads by the ocean are slightly angled. With the high stack height and soft foam, running felt a little crooked at first, but I was able to find enough flat spots on the road to make it work.” 

The result in the race spoke for itself and served as an example of how direct athlete involvement in innovation – which is central to On’s innovation approach – has a significant impact on product design and performance. 

Shortly after Gustav’s record-breaking performance, the long-distance triathlon federation changed the regulations and the loophole was closed. The exact shoe that Gustav wore to take the World title won’t be seen on a starting line again. But the spirit of the design lives on in the Cloudboom Echo 3, which is engineered to perform – and conform – at the elite level. 

“It’s a bit sad [not to be able to compete in the shoe anymore] but it also makes the shoe even more iconic." Gustav says. “It’s fun to push the limits, to see what’s possible. That’s how evolution [in the shoe game] works. Obviously I’m not comfortable with breaking rules, I truly believe in fair sports. But this shoe was well within the regulations. At the end of the day, sport is about having fun, and what’s more fun than creating your own shoe?

“It’s fun to be the reason they have to change the rules. Maybe the run was so good that they had to create a new rule – the Iden Rule,” Gustav jokes before we say our goodbyes and he gets back to training for his next big goal – Paris 24.