Four laps, flat out, from a standing start. Legs and lungs screaming, lactic acid building.
The kilo, track cycling's one-kilometre time trial, has a punishing reputation.
And yet Jody Cundy has been putting himself through it for decades.
"At the end of it, your legs don't want to pedal. You're fighting everything," he tells BBC Sport. "But when you get it right, it's really cool."
Cundy is king of the kilo. At the Para-cycling Track World Championships, he has been unbeaten in the event since 2006.
If he wins again at this year's edition - which starts on Thursday in Apeldoorn, the Netherlands - it will mark his 20th straight year in the rainbow jersey.
Not bad for someone who has just turned 48 years old.
"It's a fairly dominant run," he said. "There have been some moments where I thought it wasn't going to happen and somehow I've pulled something out of the bag.
"But I am getting older and the competitors are getting younger. It's going to be very hard to keep that unbeaten run.
"As much as I would love to do it, the people I have to race this year...I'm in trouble."
Some of that "trouble" comes from within the Great Britain squad.
Archie Atkinson, 22, was eight years from being born when Cundy won his first Paralympic gold medal - as a swimmer - at Atlanta 1996. Atkinson was just two when Cundy first became world champion as a cyclist, after switching sports.
"One of my first races was against him," said Atkinson. "That felt pretty special.
"This guy was Paralympic champion, world champion and held a world record at the time."
But Atkinson is catching up. Last year he beat Cundy at the National Track Championships, only to be beaten in turn by Cundy at the World Championships a few months later.
"I want to win," Atkinson said. "But if he wins, it's historic. There aren't many people who can win for 20 years."
In addition to his world titles, Cundy is a six-time cycling Paralympic champion - two of those victories coming in the kilo, which he won at the 2008 and 2016 Games.
Such is Cundy's standing in the squad that his team-mates call him "captain".
"It feels like I've earned a bit of respect from being here for so long," he said. "I try to be the person everyone looks up to.
"But I know at some point somebody's going to have to take my place and I'll be walking away from the sport."
When Cundy will walk away is anyone's guess.
He says he doesn't have a plan for his retirement, but he knows that qualifying for the 2028 Paralympic Games in Los Angeles will be difficult.
"If I'm still performing at the very top level and that means that they want to take me, because I can go win in LA, then I shall be there and I'm there to be counted," he said.
"I'm realistic in the fact I'll be 49 when it comes to LA and I'm no spring chicken any more.
"What we do afterwards I really don't know, whether it's in sport in some way, shape or form.
"It's 31 years I've been in elite sport. If I go away and take all of that knowledge away with me, I feel like I'm kind of cheating the system a bit.
"So there's part of me that wants to come back and help - whether it's in a coaching role or a managerial role, or even further up in governing body roles and trying to influence the UCI [cycling's world governing body] and the IPC [International Paralympic Committee] - to make cycling better than what it actually is."
The UCI, Cundy says, has "let the sport down" by the lack of Para-cycling track competitions it hosts outside of the World Championships and Paralympics.
At the upcoming Worlds, Cundy and Atkinson are among a 24-strong Great Britain squad - but it is the first time the team will have raced at a UCI track event since the last edition of the Worlds in Brazil last year.
"When it comes to track cycling we have one race a year, the World Championships, and then every four years we have a [Paralympic] Games. That's really not good enough," he said.
"When I first started we used to have competitions, we used to travel and go race in places. Now you go 12 months without seeing anybody.
"You see a start list and you don't know who half of the names are on it. You don't know whether they're going to be fast, slow, whether they're any good. There's not really any results or rankings to follow."
The UCI did not respond to a request for comment.