Arc Project, the unsanctioned ultramarathon series that exists to show ordinary people the limits they were taught are not the limits they actually have, is staging its most ambitious project yet: a 24-hour treadmill ultramarathon relay in a decommissioned World War II tank factory in North London. The format has never been attempted anywhere in the world.
200 runners will take to 50 treadmills at 10am on Saturday 30 May, competing in teams of four until 10am Sunday. Winning team covers the furthest cumulative distance. Every team must be two women and two men. This is a hard rule of entry, not a target.
Each of the 24 hours is a distinct experience of light, sound and temperature, curated by a London DJ. Organisers describe the arc across the race as simulating the psychological journey of a psychedelic trip, without the illegal stimulus.
Participants are not professional athletes. They are scaffolders, office workers, parents and teachers, most of whom have never attempted anything close to this distance. At 3am, they will be 17 hours in. To take part, participants must complete essay style questions to understand their motivations. Only those that show conviction in their answers are admitted.
Tackling the gender gap in ultra running
The numbers on women in ultra running make difficult reading. Female participation in ultra distances has fallen by roughly 10% since 2020, the steepest decline of any running distance. Men make up 76% of 100-mile fields globally. Arc Project mandates a 50/50 gender split at every event as a hard rule of entry. AP4 is, to its organisers’ knowledge, the most prominent gender-balanced ultramarathon ever staged in the United Kingdom.
AP4 follows AP3, Arc Project’s 600km relay across the entire London Underground network, contested by 150 runners on 29 November 2025, the busiest shopping day of the year. The event generated over 3 million social impressions and received a standalone feature in the Evening Standard.
James Taker, Co-Founder of Arc Project, said: “We built AP4 to be the hardest thing most of these people have ever done, inside a room that looks and feels unlike anything in sport. By 3am, something happens to people. A new version of them starts to surface. That is the part we want the world to see. Finish 24 hours in that room and you cannot go back to thinking small about yourself.”
Sonni Dyson, Co-Founder of Arc Project, said: “Ultra running has a problem when it comes to women, and the industry has spent years talking about it. We decided to try and fix it. Every Arc Project event has a mandatory 50/50 split. That is the baseline, not the achievement.”
Hamish Myers, Co-Founder of Arc Project, said: “We mapped the psychological arc of a psychedelic experience on a graph and overlaid it with what we know happens to the body and mind across an ultramarathon. The curves were closer than we expected. Both follow the same pattern: a controlled descent into discomfort, a moment where everything breaks down, and then something on the other side that most people never reach. We built each hour of AP4 to correspond to a specific point on that arc. The factory is the drug.
