The spectators lined up shoulder to shoulder in Coney Island on Tuesday, many sporting headwear that captured the essence of the day: Nathan’s foam hot dog hats or blue caps provided by an antacid company.

For most of America, the Fourth of July evokes thoughts of fireworks, family and cookouts. But hours before any of those things begin in earnest, many Americans turn their attention to a curious spectacle that has become another holiday tradition: the Nathan’s Famous Hot Dog Eating Contest.

Each year on Independence Day, thousands of spectators, braving the heat and the effects of inexplicable fervor, descend upon an intersection in the Coney Island section of Brooklyn to watch an elite corps of competitive eaters consume as many hot dogs as humanly possible in 10 minutes.

The definition of humanly possible has one meaning for most of the meat-eating world; it has quite another for most of the contestants. That is especially true for the defending champions, Joey Chestnut and Miki Sudo, who were back to defend their titles and possibly expand the notion of what is humanly possible.

Mr. Chestnut holds the men’s world record of 76 hot dogs and buns eaten in 10 minutes in 2021, while Ms. Sudo holds the women’s world record of 48.5 hot dogs in 10 minutes. Both were overwhelming betting favorites to win.

The women’s contest started first, and Ms. Sudo, the last of the participants to be introduced, was described as “the spiral that swirls at the core of the American spirit.”

She prevailed, eating 39.5 hot dogs in 10 minutes, six more than her closest competitor, Mayoi Ebihara.

The men’s event, scheduled for noon, was delayed after rain and lightning hit the area, sending fans scattering for cover.

Mr. Chestnut, who is also known as Jaws, won the men’s contest for the 15th time last year by eating 63 hot dogs. Ms. Sudo won for the eighth time by eating 40 hot dogs.

Legend holds that the Nathan’s competition, which is divided into separate men’s and women’s events, has been held each year since 1916. Legend, however, does not comport with fact: In 2010, one of the original promoters of the contest, Mortimer Matz, admitted that in “Coney Island pitchman style,” they had made it up.

The event actually began in the early 1970s, and its current incarnation is fueled by a supercharged dose of puns and patriotism from George Shea, who oversees the event with his brother, Rich Shea.

Over the years, the Sheas have gently coerced mayors, including Rudolph W. Giuliani, Michael R. Bloomberg and Bill de Blasio, to preside over weigh-in ceremonies that are rich with one-line groaners. (After delivering one such groaner in 2012, Mr. Bloomberg famously remarked aloud, “Who wrote this [expletive]?”)

They have expanded the Coney Island event into a national spectacle of competitive eating run by Major League Eating, a group that describes itself as “the governing body of all stomach-centric sports.” The men’s contest will be carried live on ESPN2; the women’s contest was shown live on the ESPN app.

For those of you who may be curious, scientists (scientists!) have determined that the human body is capable of eating — at most — 83 hot dogs in 10 minutes, according to a study published in 2020 that was based on 39 years’ worth of data from the contest.

According to that paper, the most elite human competitive eaters in the world could go toe-to-toe with a grizzly bear in terms of the amount of food eaten per unit of time.

Bears can eat about eight hot dogs per minute, and Mr. Chestnut can eat about 7.5 hot dogs per minute. But the bears usually tap out around six minutes, while Mr. Chestnut can scarf hot dogs for a solid 10 minutes straight.

“Most of the top eaters use a pretty similar technique: we separate the meat from the bun,” said Mr. Chestnut, in an online video describing his championship technique. “If you’ve got to eat it fast, you have to dip the bun in water.”

He said he began training for the contest each year at the end of April, with a series of practice contests followed by periods of fasting. He also eats outside on hot days.

He has managed to eat more than 80 hot dogs in 10 minutes on five separate occasions while training, he said, but has never been able to duplicate that feat in competition.

“A lot of it is psychological and mental,” he said. “Your body tells you you’re full.”