Training for a marathon can be a deeply solitary exercise, generally requiring runners to grind out miles multiple times a week to little fanfare.

But on Sunday, the more than 50,000 people who will pound the pavement for the New York City Marathon will be met on the streets by hundreds of thousands of others for whom the race is a spectator sport.

“On that day, you’ve got a million people cheering for you,” said Michael Capiraso, the president and chief executive of New York Road Runners, which organizes the marathon. “Someone’s going to pick you up along the way.”

Mr. Capiraso, who this year will be running his 28th straight New York City Marathon, said the crowds are crucial to keeping runners in good spirits.