ATLANTA — (CNN) He stands at the foot of Maine’s Mount Katahdin. He is 3,524 kilometers away from making history.

Forty five days, 22 hours, and 38 minutes later, American ultrarunner Karl Meltzer, with strapping on both knees and a head torch to light the way, arrives at Springer Mountain in Georgia.

He slaps the landmark sign in delight. No wonder — he’s just completed the equivalent of going up the Empire State Building 443 times.

Since August 6, he’s been running an average of 14.8 hours a day, burning 345,122 calories, crossing 14 states, and working through 20 pairs of running shoes.

But all that fades into irrelevance now — 11,000 people are estimated to have completed the Appalachian Trail, but none as fast as Meltzer.

The record-breaking run

The Appalachian Trail runs along the east coast of America and is a favored route for ramblers. It mainly covers a terrain of forest trails and open fields, but also traverses roads, towns and farms, taking in some breathtaking scenery.

The Trail would take hikers about six months to complete in its entirety, but Meltzer’s record took just a quarter of that, though his record attempt has been nearly a decade in the making.

“I’ve been trying to do it for nine years and the Appalachian Trail has been one of my favorite trails ever to run on,” he told CNN. “Now, after trying three times, I finally get the chance to say I’m the king of the AT.”

The previous record of 46 days, eight hours and seven minutes was held by Scott Jurek, a friend, training partner, and rival of Meltzer. Jurek ran his record from south to north, the opposite way to his counterpart.

“It was great to beat Scott Jurek’s record, too,” said Meltzer, “and to have him there at the end to run with me. It was really an honor and inspiration. Now it’s my turn to hand over the baton to someone else.”

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‘A long journey of misery’: Ultrarunners — a rare breed

After one and a half months of four o’clock starts in the morning in order to run 50 miles, Meltzer’s feat was grueling and, in his own words, miserable.

But the 48-year-old is by no means alone in his quest to carry his body over immense distances.

An ultramarathon refers to any race longer than 42.195 km (26.219 miles), the length of a regular marathon. They can take place over a succession of days, or simply involve a single race, usually measuring between 50 and 200 km.

These races are often made worse by punishing conditions overhead and underfoot. The Marathon des Sables (MDS), for example, is a six-day, 251-km race across the Sahara Desert. Not only is the soft sand notoriously difficult to run on, but temperatures also often exceed 120°F (50°C).

It’s not for the fainthearted. Blisters can develop from the smallest grain of sand getting in your shoes, and feet can swell from the heat. There are also more long-term problems: research has suggested that running such extreme distances may cause damage to heart tissue.

The Badwater Ultramarathon vies with the MDS for the title of the world’s toughest footrace. The 135-mile course in California’s Death Valley reaches temperatures similar to those in the Sahara.

Contestants are often seen wearing full body white suits as protection from UV light. It is estimated that 20-40% of runners on the start line fail to reach the finish.

Then there’s the Hardrock Hundred Mile Endurance Run in Colorado that covers 12,000 feet (3,700 m) of elevation 13 times. The quickest time is a mere 22 hours 41 minutes.

Meltzer has won this race five times — more than any other man (Betsy Kalmeyer has the most female wins, also with five.) He’s completed 89 ultramarathons in his career and has won 38 100-mile races — again, more than any other man — having racked up six wins at the Wastach 100 and five at the Squaw Peak 50.

But despite his breathtaking stamina, Meltzer is still human, snacking on candy, and ended each day on the Trail with a cold beer. Record broken, he now intends to catch up on sleep and play some golf.

But of course he’s got a world record for that, too, having played the most holes ever (230) in 12 hours. Maybe not so human after all.

The-CNN-Wire ™ & © 2016 Cable News Network, Inc., a Time Warner Company. All rights reserved. (PHOTO: Karl Meltzer Facebook page)