The upcoming London Marathon will take place on April 24, 2016. This will not be Peake’s first time participating in the annual event, as he completed the run in three hours and 18 minutes in 1999.
"I don't think I'll be setting any personal bests. I've set myself a goal of anywhere between 3:30 to 4 hours," Peake said as quoted by The Independent.
According to the astronaut, the biggest challenge in running the marathon on board the ISS will be the harness system.
"In microgravity I would float if I didn't strap myself down to the treadmill, so I have to wear a harness system that's a bit similar to a rucksack," Peake explained.
Timothy Peake, of the European Space Agency (ESA), will go to the ISS on December 15.
He is not the first person to run a marathon in space – in 2007, US National Aeronautics and Space Administration (NASA) astronaut Sunita Williams ran the Boston Marathon aboard the International Space Station.