With no hot bath to ease his post-race muscles the astronaut will make do with warm water and wipes, but says he’s feeling good ahead of Sunday’s marathon

You could call it an unfair advantage. As tens of thousands of runners start the London marathon on Sunday, another competitor will take up the race unencumbered by endless queues for portable toilets, moving at 17,500mph high above their heads.

But there is nothing unfair about Tim Peake’s marathon plans. The British astronaut who arrived at the International Space Station four months ago will run the 26.2 mile course on a treadmill in a cramped room that has no windows offering views on the blue-green world below. If he gets too hot, there is no fresh air to cool him, no water he can pour over his head.

The big question for Peake, though, is the one every runner asks as race day comes around: has he done enough training? In the past six weeks, he has managed half a dozen two-hour runs on the station’s treadmill. “I don’t think you can ever do enough training for a marathon,” he said via video link from the space station on Wednesday.

To be in orbit is to fall without landing. And with no body weight to pull him down, Peake must be anchored to the treadmill with bungee cords and carabiners that latch on to the rucksack-like harness he wears when he runs. Answering a question from the Guardian about his training so far, Peake said: “The toughest part has been getting used to harness system. It’s like running with a clumsy rucksack on. You can get chafing around your hips and shoulders.”

This is not Peake’s first London marathon, which this year has the formal title of the Virgin Money London Marathon. He ran in 1999 and finished in 3 hours and 18 minutes. But the race in space is a different beast. Peake may have lost some muscle fitness in his four months in orbit. His legs may have weakened. On the treadmill, depending on the harness settings, he will feel he is carrying about 70% of his true body weight on Earth.

He will also have no live crowds to cheer him on. Instead, he has an iPad and an app called RunSocial. As he runs on the treadmill, the streets of London will slip past, complete with roaring, digitised well-wishers. Running for the Prince’s Trust, he hopes to finish in 3.5 to 4 hours. “Hopefully I’ll get the telly sent up to the space station as well,” he said, referring to Sunday’s televised coverage of the marathon. “That will be a huge boost for me.”

Peake has been supported by trainers on the ground, and on Sunday, other crew on the space station will be on hand to offer encouragement. With velcro straps, he will attach water pouches to the wall near the treadmill. He packed a few energy gels for the trip, for just this occasion. Should he get caught short, as many runners do, he has a near monopoly on the toilet, which is installed right next door to the treadmill.

Back on Earth, European Space Agency (ESA) medical experts and trainers will be monitoring Peake’s physiology and his progress as he pounds out the miles. They know a lot already about the need, both physical and psychological, for exercise in space. But less well understood is how people recover from strenuous physical activity in orbit. “Anecdotally, we’ve heard from crew members that they feel they recover more quickly. When you’re not exercising, you’re completely unloaded, so there’s a good chance for the body to recover,” said Jonathan Scott, the head of ESA’s medical projects and technology team. That said, Peake is likely to feel it on Monday morning. “There may be some unusual aches and pains,” Scott conceded.

Peake is not the first astronaut to run a marathon in space. In 2007, Nasa’s Sunita Williams ran along with the Boston marathon on the space station treadmill. Having qualified by completing a previous marathon in 3 hours 30 mins, she finished on the treadmill after 4 hours 24 minutes. Ahead of Sunday, Peake and Williams talked tips. Breakfast is a key decision, and Peake has his eye on baked beans, sausage and eggs.

Unlike many of Sunday’s runners, Peake cannot run into the arms of his family and friends. But the space station offers perhaps the next best thing: a video conference with his wife Rebecca, and their two sons. A long soak in the bath is out: Peake will make do with warm water and wipes. Life in space, he said, is a little like camping.

Is he ready for the big day? “I’m feeling good,” he said. “They’ve been keeping me in good shape.” But then the marathon was never meant to be easy. “I’m sure there’ll be a few points where I wish I did a bit more training,” he added.