Peake told the Associated Press that one of the biggest challenges of running a 26.2-mile race on the International Space Station is the harness he wears to keep his feet on the treadmill in weightlessness, which rubs his shoulders and waist.
"It's a great challenge that I set myself, and I'm quite glad this is happening later on in the mission," Peake told the AP.
Peake, who arrived at the ISS in December, told the publication that he wants to finish the marathon in under 4 hours.