[What you need to know to start the day: Get New York Today in your inbox.]

The Black Sheep pub in Midtown was crowded as usual on a recent Friday night , but there was a sense of urgency in the air. Regulars periodically put down their beers to go and wish good luck to the bar’s owner, Tom McGrath, 69, who sat wearing a tracksuit and drinking coffee from a mug.

As Mr. McGrath shook their hands, he sometimes paused to massage his legs. “I never like sitting when I’m preparing for a run,” he said. “Got to keep the blood moving.”

Posters around the bar illustrated with shamrocks, Irish flags, and a photograph of Mr. McGrath in jogging shorts indicated the cause of his well-wishers: he was flying to Ireland the next day to participate in a marathon, but it wasn’t going to be any ordinary run.

Mr. McGrath has been a publican in New York for 50 years. He has also been a star of the extreme long distance marathon sport known as ultrarunning, jogging alone for days over hundreds of miles, testing the very limits of human endurance.