Like many high school athletes, Bobby, 16, a junior from Long Island, has spent years whipping his body into shape through protein diets and workouts.

Between rounds of Fortnite and homework, Bobby goes online to study bodybuilders like Greg Doucette, a 46-year-old fitness personality who has more than 1.3 million YouTube subscribers. Bobby also hits his local gym as frequently as six days a week.

“Those guys made me realize I wanted to get bodies like them and post stuff like them,” said Bobby, who has fluffy curls of dark hair and the compact frame of a gymnast. (The New York Times is not publishing the surnames of minors or the names of their parents in this article to protect their privacy.)

He makes sure to hit the fridge, too, grazing on protein-packed Kodiak Cakes and muscle-mass-building Oreo shakes. He consumes so much protein that classmates sometimes gawk at him for eating upward of eight chicken-and-rice meals at school.

But Bobby isn’t getting buff so he can stand out during varsity tryouts. His goal is to compete in a different arena: TikTok.

Bobby now posts his own workout TikToks. Shot on his iPhone 11, usually at the gym or in his family’s living room, the videos are devoted to topics like how to get a “gorilla chest,” “Popeye forearms” or “Lil Uzi’s abs.”

Bobby said that he has occasionally fallen behind on his schoolwork because he dedicates so much time to weight lifting and prepping high-protein meals.

“When Bobby first started posting his videos, our family did not even know what he was doing for months, as he was extremely independent and did stuff on his own,” said his father, 49, who is a correctional officer at Rikers Island. “He doesn’t really talk much about what goes into his videos, but I know he takes his time with them to make sure they’re perfect.”

Bobby’s father can, in some ways, relate. “When I was younger, I remember seeing the men’s fashion magazines and seeing the jacked, buff guys on there and wanted to look like them,” he said. “It took me a while to realize that those men’s bodies were most likely unattainable.”

But unlike his father’s experience, as Bobby’s body mass grows, so does his online audience. “Young guys see me as their idol,” said Bobby, who has more than 400,000 followers on TikTok. “They want to be just like me, someone who gained muscle as a teenager.”

Among his disciples is Tanner, 16, a high schooler from Arkansas, who reached out to Bobby on Instagram. “Thank you for inspiring me,” Tanner wrote.

For many boys and young men, muscle worship has become practically a digital rite of passage in today’s beefcake-saturated culture. Examples are everywhere — the hypermasculine video games they play, the mesomorphic superheroes in the movies they watch. The top grossing films of last year were ruled by C.G.I.-enhanced masculine clichés: Spider-Man, Shang Chi, Venom and the entire Marvel universe.

Many doctors and researchers say that the relentless online adulation of muscular male bodies can have a toxic effect on the self-esteem of young men, with the never-ending scroll of six packs and boy-band faces making them feel inadequate and anxious.

And while there has been increased public awareness about how social media can be harmful to teenagers — spurred in part by the leak of internal research from Facebook showing that the company hid the negative effects of Instagram — much of that focus has been on girls.

Recent reports, however, have found that those same online pressures can also cause teenage boys to feel bad about their bodies.

“Girls discuss those pressures more, but it’s completely the same for boys,” said ​​Elliot,17, a mop-haired high school student from Colorado, who began posting workout videos on TikTok two years ago, often with the hashtag #teenbodybuilding. “I feel like I’m trying to be some character just to get more views, rather than the person I want to be.”

A 2019 survey published in the Californian Journal of Health Promotion examined body image in boys. Almost a third of the 149 boys surveyed, aged 11 to 18, were dissatisfied with their body shapes. Athletes were more likely to be dissatisfied than non-athletes and most wanted to “increase muscle,” especially in the chest, arms and abs.

The quest for perfect pecs is so strong that psychiatrists now sometimes refer to it as “bigorexia,” a form of muscle dysmorphia exhibited mostly by men and characterized by excessive weight lifting, a preoccupation with not feeling muscular enough and a strict adherence to eating foods that lower weight and build muscle. The condition can also lead young men to become obsessed with their appearance, checking themselves in the mirror either constantly or not at all.

Bryan Phlamm, 18, a college freshman in Illinois, often posts shirtless videos of himself in the locker room of Charter Fitness, flexing his chiseled hamstrings and pectoral muscles. But once his camera is off, he throws on a hooded sweatshirt to disguise his body while he works out on the gym floor.

“I try not to look at myself,” he said. “I just get discouraged, especially when you look at social media and see these guys who utilize camera angles and lighting to make themselves appear as if they’re three times the size they actually are.”

More Muscles, More Views

“Most studies on the topic of body satisfaction and social media are conducted with a female population in mind, which, of course, is quite understandable,” said Thomas Gültzow, a public health researcher at Maastricht University in the Netherlands. “Almost none of what is out there focuses on men.”

In 2020, Mr. Gültzow and his co-authors published a study that analyzed 1,000 Instagram posts that depicted male bodies. Idealized images of “highly muscular, lean men,” the report found, received more likes and shares than content showing men who are less muscular or have more body fat.

A scroll through the most popular TikTok or YouTube accounts today reveals a landscape dominated by musclemen. Social media stars like the bros from Dude Perfect, the bodybuilder and comedian known as The Black Trunks, and the bad-boy creator Jake Paul all have bulging biceps and rock-hard abs. TikTok hype houses are populated by heartthrobs like Noah Beck, Chase Hudson and Bryce Hall, who strut around shirtless.

Even many gamers, once dismissed as geeks, are sizing up. PewDiePie ignited a Reddit frenzy when he showed off his newly ripped physique during the pandemic. His 20-minute workout diary has been viewed more than 10 million times on YouTube.

Some Hollywood hunks have started reassessment, though. Last month, Channing Tatum pushed back against a shirtless image of himself from “Magic Mike XXL” that was flashed in front of the audience of Kelly Clarkson’s daytime talk show.

“It’s hard to look like that. Even if you do work out, to be that kind of in shape is not natural,” Mr. Tatum said. “That’s not even healthy. You have to starve yourself. I don’t think when you’re that lean, it’s actually healthy.”

Even if there is a long history of celebrating muscled physiques, no form of media has disrupted how young men view their bodies quite like the insatiable voyeurism and staged exhibitionism that fuels platforms like TikTok and Instagram.

“Social media is really where young men experience evaluations of their appearance from others,” said Veya Seekis, a lecturer at the School of Applied Psychology at Griffith University in Queensland, Australia. “The more men view their bodies as objects for public display, the more they fear being negatively evaluated, which so often triggers compulsive exercising and other ‘healthy’ behaviors that can end up having an impact on their well-being.”

For three years, Dr. Seekis has been collecting data on the social-media habits of 303 undergraduate men and 198 high school boys in Australia. She has found, in part, that exposure to images of archetypal masculine physiques was linked to low body esteem in young men and an increased desire to become more muscular.

It’s a fitness feedback loop that has ensnared Johnny Edwin, 22, a linebacker-size scaffolder from British Columbia, Canada. He said that when he was in high school, he would spend hours glued to YouTube channels like that of Chris Jones, a self-described exercise guru known as Beastmode Jones.

“Social media, and the pressure to live up to those guys and have that manly-looking physique, has completely taken over my life,” said Mr. Edwin, who still watches weight lifting videos on YouTube.

Three years ago, Mr. Edwin started uploading his own gym-training content on TikTok under the user name Big Boy Yonny, where he has more than 12,000 followers. “Even though people are saying I look good or whatever, I know I’ll never have a perfect body,” he said. “If I gain any weight now, I’m not going to look as good, which means I’ll lose followers.”

Pressure for a better body can start as early as elementary school.

Rudy, 17, a senior at a Los Angeles high school, said boys as young as 10 have hit him up on Instagram and YouTube seeking advice on what to eat and how to achieve a “Dorito physique,” the broad-shouldered triangular shape desired by many fitness influencers.

“I just tell them, ‘Have your parents buy you chicken breast or lean meat with white rice and vegetables,’” Rudy said.

The schoolboy body talk can be startling. Two parents from Burlington, Vt., gave their 13-year-old son permission to use social media for the first time last summer. “It opened up this whole new world to him of Instagrammers and YouTubers in muscle shirts,” the boy’s mother said.

Over the next several months, their son became fixated on his lack of muscle definition and complained he felt “weak” and not “the right size.” “When you have 10 to 20 boys, all in eighth grade, referring back to that content — content that has become their goal of what a man is and what they want to look like — that’s a powerful stew,” the mother said.

The boy’s father said that his son “doesn’t even have a man’s body yet because he hasn’t gone through puberty, but he already has this incredibly high standard of what he should look like.”

‘I’ve Completely Lost My Social Skills’

Dr. Jason Nagata, a pediatrician who specializes in adolescent medicine at the University of California, San Francisco, believes that the pandemic may have exacerbated some of these unhealthy behaviors.

“The pandemic created a perfect storm for eating disorders with the combination of social isolation, disruption of normal routines and sports seasons, and constantly being in front of cameras through social media or videoconferencing,” Dr. Nagata said. “A lot of boys had their schedules and regular sports activities interrupted during the pandemic, which caused them to become anxious about either losing or gaining weight.”

Dr. Nagata has met with teenage boys who have fainted at the gym — sometimes suffering headaches, temporary blackouts and confusion — because they overexerted themselves lifting weights and had low energy because of a compulsion to count calories (a condition known as orthorexia).

A study published last year in The Journal of Adolescent Health looked at eating disorders among men throughout young adulthood. By age 16 to 25, one-quarter of the 4,489 male participants told researchers they were worried about not having enough muscles. Eleven percent reported using muscle-building products such as creatine or anabolic steroids.

The consumption of over-the-counter supplements has become so pervasive that dry scooping protein powder — consuming it without mixing it in water — became a popular TikTok challenge last year. The stunt was dangerous enough to cause health experts to issue a warning that it could lead to wheezing and breathing troubles. Over-consuming powdered protein can also cause problems with metabolism and gut comfort, according to a Finnish meta-analysis.

The line between getting fit and fanatical is not always clear. “We know there is a ton of pressure on guys, but disordered behaviors that fall specifically on the more muscular end of the spectrum tend to get a pass publicly, since goal-oriented habits around the gym are socially accepted, glamorized even,” said Stuart B. Murray, who directs the eating disorders program at the University of Southern California.

Bigorexia can lead to interpersonal problems too. Many young men who overexercise and follow rigid diets often skip meals with family and friends, and complain of feeling isolated and socially anxious.

“I’ve completely lost my social skills,” said Mr. Edwin, the Canadian TikToker. He frequently misses birthday parties and avoids socializing with friends because he fears “the next day’s workout and how that could affect my muscle growth,” he said, adding, “there are so many memories that I’ve missed because I’ve been at the gym. I basically don’t leave my house besides for groceries, work and the gym.”

Mr. Edwin said that he ignores “texts and calls from everybody” and rarely finds the time to see his family, who lives 15 minutes away by car.

“If there was no social media or internet, I probably wouldn’t even care about my physique, to be honest,” he said.

Bobby, the high schooler with a big TikTok following, has also experienced the downsides of so much working out. His mood at school may depend on how good he thought he looked that morning.

After school, socializing often takes a back seat to the gym, even though he feels a certain malaise when he sees his classmates on Instagram having a social life. When he does attend a party, he sometimes spends the whole night thinking, he said, “I could have been getting an arm pump right now.”

At first, he thought a muscular physique might be a way to make new friends, especially among the girls at school. But most of the attention has come from other boys on TikTok looking to get buff.

“Your only new friends are the weights,” he says in one video.