British astronaut Tim Peake ran the London Marathon in space

As if running more than 26 miles here on Earth wasn't a challenge enough.

British astronaut Tim Peake completed the London Marathon on Sunday while strapped to a treadmill in the International Space Station -- floating in orbit about 200 miles above his nearly 40,000 competitors on the ground.

After wishing his fellow runners good luck and kicking off the race in a recorded message, Peake finished the 26.2-mile course in about three hours and 35 minutes, the European Space Agency tweeted.

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In order to simulate the atmosphere of the race on the ground, Peake watched a digital recreation of the route -- complete with a cheering crowd -- on the RunSocial iPad app as he ran.

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Regular exercise is critical for astronauts in the space station to stave off muscle loss, bone density decline and the many other health problems that can come with long periods of weightlessness.

Even so, NASA has found that astronauts lose about 15% of muscle during a spaceflight and 1-2% of bone mass per month in space.  

Zero-gravity running also poses its own set of challenges. Peake had to be tethered to a state-of-the-art space treadmill with bungee cords, and doctors on Earth closely watched his physiological readouts throughout, The Guardian reported.

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But there are also some advantages, Peake told the newspaper. His muscles relax and recover more readily after the race and any injuries like aches or sprains will heal faster.

Peake is actually not the first astronaut to complete a marathon in space. That distinction belongs to American astronaut Sunita Williams, who finished the Boston Marathon on the space station in 2007 and even went on to compete in the first triathlon in space, using specially callibrated strength training equipment to simulate swimming.

Peake did however manage to grab up the record for fastest marathon run in space, according to Guinness.

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