This man has just 3 days left to break a 2,189 mile speed record spanning hundreds of thousands of feet

Scott Jurek is on the move.

The ultramarathoner - who became well-known outside the running world through Christopher McDougall's excellent book "Born to Run" - has already accomplished feats that boggle the mind, showing the amazing things that can be accomplished by a determined athlete.

As Outside's Kathryn Miles reports, Jurek won the Western States 100-Mile Endurance Run seven consecutive times, from 1999 to 2005. He's won the 153-mile Spartathlon, the Badwater 135-mile ultra, and holds the US all-surface record for most distance covered in a 24-hour run, 165.7 miles.

Now the clock is ticking as Jurek is trying to accomplish what he has called his "masterpiece," an attempt to set a new speed record while running the 2,189 miles of the Appalachian Trail, with 515,000 feet in elevation change.

It's coming down to the wire.

For Jurek to beat Jennifer Pharr Davis's current record (46 days, 11 hours, and 20 minutes), he needs to reach the end point on Maine's Mount Katahdin by 5:15 p.m. on July 12, this Sunday.

On July 8 at around 3 p.m., Jurek posted an Instagram shot from the 2,000 mile marker, meaning 189.2 miles left.

 It hasn't been an easy trip.

The 41-year-old injured his knee just seven days into his run, which he began in Georgia, thinking the run itself would help condition him for the rough and rocky patches of New Hampshire and Maine.

At points, this has slowed his pace to a crawl, yet he's still basically kept to his original plan: 50 miles a day, day after day.

Of course, it's not all running, as evidenced by this river-crossing photo Jurek posted this morning:

 Andrew Thompson, who currently holds the men's record for fastest known trail completion (Pharr Davis beat his time by over 24 hours), told Outside that "If everything goes absolutely right from here on out, Scott will be hiking up Katahdin on Sunday looking at the second hand of his watch."

Thompson helped pace Jurek for a few days in New Hampshire's White Mountains.

Pharr Davis told Runner's World that she supports Jurek's effort too - apparently it's an unwritten rule that if you are going to try to break the record, you call the current record-holder first.

"If he does break it, I will take him out for a vegan dinner," she told Runner's World - Jurek is a noted vegan, and says a plant-based diet helps him perform at an optimal level. "Although if he doesn't break it, maybe we will have to go get barbecue."

Others have shown up to support or snap photos with him along the way, with Jurek's Facebook page full of shots documenting the journey.

 When it's over, Jurek has said that he's close to ready to retire. Until then, he's going to push through.

"There's a joy to discomfort and pain," he tells Outside. "Any time you push through a barrier of discomfort there's an ease and a lightness on the other side."