Before Simon Wheatcroft starts running near his home in Doncaster, Great Britain, he finds where the grass begins on his left and takes one step to his right, positioning himself in the center of a ribbon of sidewalk. Like any run, light poles and street signs jut slightly onto the path on occasion.

While a general runner easily passes by, Wheatcroft must always remember where these objects are because he is blind. He can’t see the obstacles in front of him, so he relies on a mental map he created that blends his knowledge of familiar terrain and the mileage audio alerts through the app, RunKeeper.

For example, that sharp dip he knows in the pavement may mean he needs to anticipate an upcoming right turn. When he hears a specific distance on the app, say 1.5 miles, he knows to drift to one side to avoid an obstacle like a fire hydrant. 

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In this manner, Wheatcroft has memorized a regular 3-mile route that, along with a handful of out-and-back offshoots, allows him to run up to 12 miles solo. He hovers around 9-minute per mile pace. Any faster and he says his memory wouldn’t be able to keep up.    

“Running without a guide is freedom,” Wheatcroft, 33, told Runner’s World. “In other ways, my life is relatively controlled in terms of the areas I go to and having to use mobility aids. Running was something I can do by myself.”  

When he was 13, Wheatcroft was diagnosed with a degenerative eye condition called Retinitis Pigmentosa. He gradually began losing his vision, and four years later, he became legally blind. Initially, he refused a mobility aid, but as his eyesight worsened by the age of 28, he started using a long cane. A couple years later, he got a guide dog named Ascot. 

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Around the same time in 2010, Wheatcroft decided he needed to lose weight. He couldn’t afford a gym membership or a treadmill, so he went out to the soccer field behind his house and began running back and forth across the length of the pitch. Eventually, he built up to a mile.

“Running on the soccer pitch wasn’t too difficult,” Wheatcroft said. “The hardest thing about it was getting to it. One day, they planted trees between my house and the pitch. I usually went there without my cane, and I bumped into a tree.” 

Soon the field became boring and had its other challenges like pedestrians with dogs. So he went to an unfinished airstrip nearby where there were no cars. The area allowed him to pick up his pace and learn how to sense the ground underfoot. 

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Once that became easy to navigate, he transitioned to the sidewalk. Instead of a human guide, Wheatcroft spent $6.99 on the mobile app RunKeeper, which provides audio cues for pace and distance run. He realized it could help him better memorize a route because he could pair landmarks with mile markers. 

“At first, I wasn’t sure if it was possible,” Wheatcroft said. “The only mistakes I made with poles and lampposts and traffic lights were the first few times I went running because once you hit them once, you definitely remember where they are.” 

Once he learned a route, Wheatcroft could continue to build his endurance. Because his pace is limited, he focused on distance and began training for marathons and ultramarathons. 

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Wheatcroft retraces his steps on his main route for his long runs, going out and back over and over until he’s reached his intended goal. His longest solo effort to date is 30 miles.

Though he prefers running for the sake of it, Wheatcroft has raced in a handful of marathons and ultramarathons, all with a sighted guide. Last year, he ran the New York City Marathon in 5:13:18, which he completed shortly after running the more than 200-mile distance to the city from RunKeeper’s headquarters in Boston.  

At this point, Wheatcroft’s eyesight is nearly gone. All he sees are big washes of color and his peripheral and central vision is severely compromised. 

Yet he’s running farther than he ever has and is planning to attempt a race solo. Next year, he is signed up to run the Four Deserts Series Sahara Race in Namibia. There, he’ll use GPS coordinates to navigate each mile across the 250 kilometer distance, and he plans to carry a radio to call for help in case he gets lost. 

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“I’m not really competitive,” said Wheatcroft, who now works as a motivational speaker. “I just like to see what’s possible.”

This article originally appeared on RunnersWorld.com.