British astronaut Tim Peak is becoming the first man to run a marathon in space - nine years after a woman ran one. Here's a look at just how he's going to run 26.2 miles on the International Space Station. (Jenny Starrs/The Washington Post)

On Sunday morning, as 38,000 runners tie on their bibs, lace up their shoes and line up at the starting line of the London Marathon, British astronaut Tim Peake will unstrap himself from his vertical sleeping station, float over to Node-3 of the International Space Station and strap himself onto a treadmill.

And then he’ll run for 26.2 miles as the ISS whizzes around Earth roughly 2.5 times while he’s running. Peake will virtually participate in the race, by monitoring the RunSocial app that allows well-wishers to cheer runners on, and hopes to finish in 3 1/2 to 4 hours.

“I’ve done a few half-marathons and a little bit longer distance than that as well [onboard the ISS]” said Peake during a video press conference on April 20, not mentioning his 1999, on-Earth marathon when he finished in an impressive 3:18:50.

“But I’m sure there will be a few points where I’ll be wishing I did a bit more training,” he said with a grin.

When he would have fit in that extra training is a mystery. Astronauts’ days already include at least two hours of mandatory exercise, because of the threat of bone density and muscle mass loss while in space. Anyone who’s ever run on a treadmill knows it’s not easy to stave off the monotony of its mechanical whirring and your footsteps’ clomping “thump-thumps” for more than a couple miles, but Peake has to deal with the additional difficulty of being harnessed onto the contraption.

“[It] keeps me on the treadmill and it gives me the weight-bearing that I need on my legs,” Peake explains. In the space station’s weightless environment, the harness ends up adding 60 to 80 percent of his body weight back on, Peake’s personal trainer Patrick Jaekel told Wired.

“That means having to run a marathon with your bodyweight lying on your shoulders…It’s very tough and very hard,” Jaekel said. And that also means extra chafing from all the straps.

But Peake, surprisingly, will not be the first person to run a marathon in space, although he will be the first man. NASA astronaut Sunita Williams ran the Boston Marathon from the ISS in April 2007, clocking in at 4:23:10.


NASA astronaut Sunita Williams, Expedition 32 flight engineer, equipped with a bungee harness, exercises on the Combined Operational Load Bearing External Resistance Treadmill (COLBERT) in the Tranquility node of the International Space Station. (NASA)

Williams didn’t just break that record, however. On a later trip to the station, in Sept. 2012, Williams became the second woman ever to assume command of the ISS and then participated in the first space triathlon.

If Peake hits his target time, he’ll end Williams’s reign as intergalactic champion by setting a new space marathon record. But he’s only on the ISS for another two months, with no triathlons on the schedule — meaning she’ll stay enthroned as the cosmos’s unbeaten triathlete champ.

Peake plans to stream his run, which start at 10:00 a.m. in London, 5:00 a.m. EDT.