A marathon covers 26.2 miles, but the most important distance is “the nine inches above the shoulders,” according to a saying by Joe Vigil, a renowned American coach.

In his widely held view, the head as much as the legs often determines the outcome of the race.

“No elite runner goes into it unprepared for the distance,” said Dakotah Lindwurm, 29, who finished 12th in the women’s marathon at the Paris Olympics and will run the New York City Marathon on Sunday. “I think the limiting factor is often our brain.”

So, what do marathoners — elite and everyday — think about as they run 26.2 miles?

The answer is: remarkably little and, somehow simultaneously, absolutely everything.

Brendan Leonard, 45, a writer and illustrator, described his thoughts as bouncing “from my legs and feet, to the person or people in front of me maybe running just a tiny bit slower and should I pass them or not, to the port-a-potty situation.”

He said he thinks of all the “grand things” he will do when he gets home, such as painting the living room ceiling, taking Spanish lessons or writing the rest of a book.

Indeed, the mind can go in some interesting directions.

Here’s what some 50,000 runners may be thinking when they take to the New York City Marathon on Sunday.