Never heard of it?
As the term implies, it is an activity that combines jogging with juggling. The two athletes will run the marathon's full 26.2-mile distance while juggling three beanbags.
And they'll be passing a lot of people.
Warren, originally from West Virginia and now doing laughter research at Harvard, is the current Guinness World Record holder in "fastest marathon while juggling three objects." Warren set the record with a time of 2 hours, 52 minutes, 15 seconds at the Philadelphia Marathon in November 2006.
Kapral, a native of Canada and the senior editor of Captivate Network, first set the world record in 2005 with a time of 3:07. He expected his time to remain a record for a while, but Warren had other ideas.
"I had broken the previous record by 13 minutes, and it was five years old," Kapral said. "I figured I had it locked up for a good while. Then a reporter in Boston called me [two months later] to ask me about someone breaking my record. I said, 'What?' I immediately challenged him to a dual marathon of his choice."
As Kapral put it, Warren "trounced" him in that first meeting. Kapral, however, did briefly reclaim the record, before Warren again took it back.
Both Warren and Kapral say joggling is an extremely difficult thing to do, especially at a marathon distance. But that doesn't necessarily keep spectators from wondering what in the world they're doing on marathon courses.
"The reactions vary from sheer laughter to excitement, and sometimes people are offended," Warren said. "They're barely running a marathon, and they'll say, 'How dare you juggle?' "
Warren said that although joggling isn't something that's for everyone, any person who is juggling many things at once in their life can relate to the activity.
"It's the fundamental metaphor for living in the modern era," Warren said. "You're always on the go. Everything is in the air and you hope you don't drop the ball."
Kapral said he first learned of joggling while he was reading the Guinness Book of World Records with his sister when he was a kid. "I thought it was the funniest thing," he said. Three years ago, after breaking the Guinness World Record for "running a marathon while pushing a baby in a stroller" - he pushed his daughter Annika - he thought seriously about breaking the record that once made him laugh.
Warren had a roommate in college who would get a full-body workout by joggling. He started to consider doing it on his own after he learned how to juggle while working with a children's circus in Afghanistan in 2005. Inspired by kids who were orphans and refugees displaced by violence, Warren said he learned how to juggle to do "something 'circusy' to be a part of the circus."
Warren will run on Saturday to raise money for the Afghan Mobile Mini-Circus for Children. The funds go to teachers' salaries and circus equipment.
"It's my way of doing something," said Warren, who will soon return to Afghanistan to study the healing effects of laughter and work with the circus. "I'm sick of awful news coming out of Afghanistan."
Kapral is also running for a worthy cause. He'll earn money for "A Run For Liane," which supports childhood cancer research at Toronto's Hospital for Sick Children.
Kapral, 34, said this might be his final joggling marathon on Saturday. And worthy causes aside, he's hoping to even the score with Warren, 25.
"It's payback time," Kapral said.
A joggling dual
* Zach Warren, the current Guinness World Record holder in "fastest marathon while juggling three objects," will run against Michal Kapral in the Salt Lake City Marathon on Saturday.
* Kapral set the record for the first time in 2005 by beating the old mark by 13 minutes. Warren broke Kapral's record two months later.
* Warren is originally from West Virginia, and now studies laughter at Harvard. Kapral is from Canada and is the senior editor of Captivate Network.
Salt Lake City
7 a.m., Saturday