Charlie is working on two things in lockdown. First, his studies: at 13, he’s the first to admit his focus is patchy. “I don’t do a lot of homework,” he says. “My mum complains about that all the time.” That isn’t to say he hasn’t thought about a career. “I wanted to be a game designer, but now I think the future’s in diseases, in microbiology, so I am also interested in that. A bit.”

His other work requires hours of dedication and is something Charlie has genuine enthusiasm for: working on his body. His daily routine starts with 40 press-ups while his shower is running. He eats five eggs and four pieces of toast for breakfast. His ideal lunch would be grilled fish and rice, but when he is at school he typically has to eat pasta with tuna sauce, since the canteen’s focus is feeding children, not lean body sculpting. “He won’t eat sausages or any processed stuff,” says his mother, Helen. She is married and lives in Liverpool with the couple’s three children, aged five to 13.

Charlie snacks on bananas, strawberries, protein yoghurts and expensive juices with ingredients such as broccoli and barley grass. He hasn’t eaten refined sugar since 2017. “I started to get acne and cut down,” he explains.

“I couldn’t believe it,” his mother says. “He was the Nutella king. Now he’d be gobsmacked if I served him chocolate.” He drinks lots of water.

At 5pm, it’s time for Charlie’s workout, a ritualised activity he does in his bedroom. He wouldn’t be allowed in a gym – the minimum age in most is 16 – but he doesn’t really like the idea anyway, mainly because he wouldn’t know what to do with the equipment.

Instead he has developed his own programme: a rapid-fire routine of push-ups (55 x 3); curls (65 in five minutes); planks (hold for four minutes x 3); biceps curls with dumbbells (150 each side). His exercises are directed at the parts of his body he most wants to transform: his arms and chest. “I don’t really work on my legs, because no one sees them. I don’t wear shorts much.” He prefers a pair of joggers and a sleeveless top to emphasise his biceps and shoulders.

He works until his muscles can’t take any more. “I push myself until I can barely breathe and I’ve got a headache. Then I go downstairs to have some food, and then go back up again.” After he’s finished, Charlie warms down with five minutes of leg raises, then has dinner: four salmon fillets and rice. “I am probably spending an extra £40 a week on him,” Helen says. “I also spend loads on skincare products. Charlie will say, ‘I need charcoal soap – everyone says it’s good for your skin.’ Or, ‘I need ginger shampoo because it’s good for dandruff.’” The recommendations come through Instagram, she says. “When I was 13, my mum just put a bar of soap in the bathroom and that was it.”

Is she spending more than she should? “Yes, it’s expensive, but everything healthy costs more,” Helen says. “My husband says there are worse things he could be doing. Muscles, training and fitness – it’s not the worst vice to have.”

But she does worry Charlie might be damaging his muscles. “Maybe a 13-year-old isn’t supposed to have a 23-year-old’s body. But as a mum you always worry. If you’ve got a child who is overweight and eating loads of chocolate, you worry. I’ve got one who is extremely muscular and lean, and I am still worried. God forbid he gets into steroids. At the moment his body is a temple. He won’t vape. He won’t smoke. He doesn’t want to damage anything.”

Charlie was quite shy as a little boy, according to his mother, and had a slight stutter. Things came to a head when he was nine. “I wouldn’t say I was being bullied, but I was being pushed around by a load of kids, because I was really skinny,” Charlie says. His mother enrolled him in boxing classes, twice a week, after being told “boxing is very good if you get bullied. It channels your energy and controls your emotions.” He did karate twice a week.

And as he got stronger, he felt better. “It made me feel I can handle myself,” Charlie says. He no longer gets pushed around by older boys. The way he sees it, working on his body is paying off. “Yes, I would say I’m popular,” he says.

“He’s started a big trend in his year group,” his mother adds. “The boys want to be fit because he gets a lot of attention from being like this – from girls.” He also gets approval on social media, something that motivates many teenagers. “You have to look good on camera, or people are going to judge you,” he says.

“It’s massively different to when I was young,” Helen says. “We might not have seen our friends after school. You wouldn’t have to look good all the time, whereas they are socialising 24/7, on their phones, Instagram and Snapchat, sending photos. They’ll be posing in front of the mirror. They’re still arguing, fighting, flirting, whatever. We went home and you wouldn’t speak to anybody.”

Is there anything you would like to change about your body, I ask Charlie. “I’d like to wax my back,” he replies. He’d also like bigger muscles. “School is probably cancelled until September, so I’ve got a load of time to work on that.”

***

“The pressure on young men, and boys, to become more muscular has grown,” says Jason Nagata, assistant professor of paediatrics at the University of California, San Francisco, and an expert in body image and eating disorders. In a 2018 study of more than 15,000 US high school students published in the Journal of Adolescent Health, nearly one third of teenage boys aged 13-18 reported trying to gain weight or bulk up. This ambition affects even small children. “There have been studies that show boys internalise a desire to be muscular as young as six,” Nagata says.

This messaging starts with toys. In 2006, sports scientists measured the necks, chests, arms, forearms, thighs and calves of five popular action figures, comparing them with the dimensions of their original designs. They found that Batman, Superman, the Incredible Hulk et al were significantly more muscular than their original counterparts.

The same thing has happened to Hollywood actors. “Is Daniel Craig’s James Bond too buff?” asked one columnist in 2012. While Sean Connery’s Bond was all savoir-faire and sophistication, Craig’s put the emphasis on delts and pecs. The actor’s most recent photoshoot, promoting the now-delayed No Time To Die on the cover of GQ, topless and with jeans unbuttoned, suggests the era of the body-shaming Bond is not over yet. (It was Chris Hemsworth, the actor who plays Thor in the Marvel films, who first inspired Charlie to start working out.)

It’s now not just Premier League footballers who are ripped; it’s their offspring, too. When David Beckham’s middle son, Romeo, 17, posted a picture of himself working out on Instagram last year, all abs and pecs, the photo got more than 185,000 likes. Meanwhile Cruz Beckham, 15, has joined his dad for gym sessions and, recently, a lockdown workout of 50 crunches.

“I wonder how many young lads would be going to the gym if it wasn’t for social media,” says Terry Anderson, owner of CrossFit All Out, a gym in Newton Aycliffe, County Durham. A gym chain manager for 13 years, he opened his own gym in 2014 after spotting a growing demand for CrossFit – a fitness programme that combines weightlifting, running and gymnastics – especially from those too young to join regular gyms. He caters for children as young as three; the half-hour session includes squatting (to understand the correct position for when they come to lift a barbell) and swinging 2kg kettlebells. Anderson says he wants children to learn the joy of physical activity, which is one reason why his gym is mirror-free. “I don’t want kids stood posing in front of mirrors. If you go to normal gyms, it’s lads looking in the mirror at their biceps when they’re doing their curls, and taking selfies on the machines.”

Is three too young to be lifting weights? Anderson argues that the children are “excited” to use the little kettlebells, and that 2kg is not a harmful weight. “We often have a superhero theme,” says Vikki, Terry’s wife. “It’s low-key, very basic, just giving them a little taste. The actual workout is maybe 10 minutes.”

Of course, getting fit can be a good thing when so many children are overweight (almost one in five when they start primary school). But experts worry when the ideal becomes a tyranny. “There is a fine line,” Nagata says. “Some young men become obsessed with their appearance and engage in excessive or compulsive exercise, and body image takes over their lives.”

How did body sculpting go from a niche hobby, practised by bodybuilders in underground gyms, to a physical goal for many young men around the world? And just how worrying is today’s pressure on young boys to get ripped?

***

In the 60s and 70s, we had the likes of David Bowie and Mick Jagger, who reinforced the desirability of a specific type of body: thin, elegant, suggestive of a drug habit. In the 80s, there was a shift; we had Arnold Schwarzenegger in Conan The Barbarian, and Sylvester Stallone in Rambo. The world of advertising was waking up to the marketability of men’s bodies, too. “Advertisements were no longer just the kind of Marlboro Man cowboy, clothed from head to toe. We started to see shirtless ads,” says Roberto Olivardia, clinical psychologist and lecturer in the department of psychiatry at Harvard Medical School, and co-author of The Adonis Complex. Where advertising had long preyed on the insecurities of women, it was, Olivardia says, the turn of men.

The turn of the century marked another shift. David Fincher’s Fight Club was released in 1999, and developed a cult following among men who wanted to replicate Brad Pitt’s “lean and mean” body: muscular but not bulky. The cult is still strong, and Pitt’s Fight Club body remains a topic of conversation on bodybuilding and nutrition forums 20 years after the film’s release. It is a difficult look to achieve, a physique that requires a strict high protein diet and a lot of hard working out.

In today’s world of work, looking toned is seen as a career asset because of the discipline involved. A lean, fit boss is an indicator of a lean, fit business; both Amazon’s Jeff Bezos and Apple’s Tim Cook have made headlines for their “super buff” bodies. “I work with a lot of men who feel this pressure to go to the gym – not to be healthy but to achieve this body image that says, ‘I am in control,’” Olivardia says.

There are, of course, pleasures to be found in self-improvement. William is 15 and lives in Newcastle with his brother, Liam, 16, and his mother, who runs a business. Most days, William wakes at 6am, runs to the park, where he does pull-ups and dips in the workout zone. About 40 minutes later, he’ll run home and get ready for school. After school, he does his homework and then spends an hour working out in the garage, where there is an exercise bike, rowing machine and punchbag.

About three times a week, he’ll do a routine of push-ups, sit-ups and maybe some chest-openers. He works out in his bedroom, where the decor includes a poster of Captain America, a duvet patterned with Marvel comics and a book he got for Christmas, Men’s Health Best: Weight-Free Workout. He has an Apple Watch fitness tracker to record his progress.

William started on his regime when he was 13. “I gave up my iPad for Lent and had loads of free time. I just wanted to get stronger because it’s good for you,” he explains. He’s grown up in a household that values fitness: his mother runs, and his grandfather was a bodybuilder.

William’s mother describes her son as self-disciplined and persistent, someone who likes targets. His friends are into comedy shows, not fitness, but he is a convert because of its psychological benefits. “I am definitely more focused. If I didn’t do any exercise for the whole day, I’d have excess energy and wouldn’t be able to concentrate.” That’s not to say he doesn’t also take pleasure in the physical results. “My legs and chest are definitely more defined than they used to be,” he says. His mother adds that he has “a beautiful, flat tummy”.

“Girls naturally mature into their bodies – they get their boobs and waist and everything – but boys don’t naturally grow muscles,” she continues. “To get the muscle definition they’ve got on Love Island is unattainable, unless you’re eating a really strict diet. But that’s what society has moved towards. What boys see online is what they think they should look like.” The UK’s 2019 Good Childhood Report, a survey of almost 2,400 children, echoed this, finding that one in 12 boys aged 10-15 were unhappy with their appearance, citing the “ripped” male body types shown on Love Island as one factor.

Jack, 16, who lives in London, is clear about why he goes to the gym. “Muscles are attractive to girls,” he says. “Pretty much anyone who is popular has muscles.” He’d been desperate to join his local gym since he was 14, but the rules said he had to wait until his 16th birthday. Pre-lockdown, he would typically go four times a week after school, with a group of seven friends, all boys. They work on a different part of their body each time – chest, arms, legs – hoping for a return on their £23.99 a month investment.

After the first visit, he was so sore, “I couldn’t put my shirt on for school the next day without my mum’s help. My muscles had tensed up.” He was just beginning to see the results, Jack says, when lockdown started. Now he does a few sit-ups and push-ups at home. “Mum has a resistance band and I’ve been trying to use that, but it’s a bit too small. So I feel I’m going back to how I was before.”

Joshua, 18, was typically spending around 18 hours a week in the gym. He started going because he wanted to get bigger for the school rugby team, but now he is twice the size – going from 50kg (7.5st) when he started, aged 15, to 105kg (16.5st) – working out is about more than performance. “I am definitely more confident. I am not the skinny guy. I am the guy who stands out.”

With the gyms closed, he fears going back to square one – “I worry I am falling behind” – so he is improvising with his rucksack. “I fill it with anything heavy, like my school books, and put it on my back when I’m doing push-ups, or hold it for biceps curls.”

Are boys under pressure to look a certain way? “Yes, definitely,” Joshua replies. “I’ve got friends who just train their ‘glamour muscles’, their arms and shoulders, rather than doing a proper workout, and that comes from society: ‘If you want to get this – girls or whatever – you’ve got to look like that.’ Also, the way social media tailors its advertising – I get a lot of ads on Facebook, Instagram and Snapchat for personal trainers and bodybuilders, all with amazing physiques.”

“Eating disorders and body image in boys is very under-recognised,” Nagata tells me. Screening is often based on the premise of thinness, and doesn’t take the “ripped” phenomenon – muscle dysmorphia or “bigorexia” – into account. “We don’t ask about muscle-enhancing behaviours, so I think a lot of these [disorders] are missed.”

Professor David Veale, a London-based consultant psychiatrist in cognitive behaviour therapy, and an expert in body dysmorphic disorder (BDD), says it’s not a problem BDD practitioners see a lot, but that doesn’t mean it’s not there. “In general, it’s below the radar. They don’t tend to be so distressed that they are seeking mental health help. Many cope and get by.”

So nobody knows how many boys might have BDD?

“Absolutely. Mental health services are completely stretched anyway, and compared with other people with severe body image problems, they tend to get away with it. But I am sure they are building up problems for themselves.”

Kitty Wallace of the UK-based Body Dysmorphic Disorder Foundation agrees. “When boys start to show this behaviour, it can be responded to quite positively by people around them, and by social media. But they’ll miss some of the more negative behaviour that goes with it, such as huge anxiety about body image. By the time it starts to affect a boy’s day-to-day life, they are often older and don’t necessarily have people around them who are able to say this isn’t quite right. Then they find it harder to come forward and talk about their mental health.”

Symptoms of muscle dysmorphia include working out compulsively, prioritising exercise over family and friends, and abuse of anabolic steroids, supplements and protein shakes. A 2015 BBC report estimated that 10% of men who use gyms may have muscle dysmorphia. While there are no comparable figures for teenage boys, a 2019 study published in the International Journal of Eating Disorders found that 22% of young men aged 18-24 had disordered eating due to a desire to enhance muscles, while a 2011 study published in the British Journal of Psychiatry found boys accounted for 33% of “other eating disorders” – a catch-all category that includes bigorexia.

But at what point does a healthy interest become a dangerous obsession? What should make a parent worry? “First, how accurate is the person’s body image?” says Olivardia, who treats boys with bigorexia. “When they look in the mirror, are they able to see how they look, or is there a distortion? Are they always dissatisfied with the way they look?” He also points to the amount of time a boy is spending on his body, “and how much time it is taking away from other things that are important and fulfilling in life. He has to do well at school, has to be healthy and has to foster real relationships, not just online likes.”

The patients referred to him have a very narrow sense of identity, he says. “It is defined by their body image. I have some patients who are nearly suicidal because they can’t work out, because they have sustained some kind of injury – often from overexercising. It shouldn’t take on that much importance, that you feel life isn’t worth living because you are going to lose some muscle mass.” Olivardia treats these patients in a similar way to others with eating disorders and OCD: through a combination of education about nutrition and the dangers of overexercising, and cognitive behavioural therapy to address negative thinking patterns.

***

In Liverpool, I ask Charlie what teenage boys worry about most. He says his friend Nathan, who is football-obsessed, would be “distraught” if he didn’t make the school football team. “Others worry about, ‘Oh no, will I lose this game on Call Of Duty?’ I don’t worry about that.” He pauses. “Mum and Dad have no idea about this, but I mainly worry about my great-grandma. She’s really old and we’re really close. My biggest worry is losing her.”

When it comes to working out, it’s the validation Charlie gets from social media that is the biggest draw. Olivardia says he sees this as one of the hardest habits to shake. “As the parent of a 15-year-old [boy] and a 13-year-old [girl], my goal is for neither of them to have social media until they’re at college. I am generally very open-minded, and as a teen I would have absolutely loved social media. But I know it wouldn’t have been good for me.”

How big a problem does he think bigorexia is becoming among young boys? Olivardia says it’s important to keep it in perspective; there are other, worse health crises: “We have a very big problem with obesity in children and teenagers.” Larger numbers of teens are playing video games and not exercising at all. Working out and getting fit, even at a young age, is fine, he says, up to a point. “As long as the conversation is always around health and the joy of physical activity – as opposed to just being strong for strong’s sake, or looking good for looking good’s sake.”

• Some names and identifying details have been changed.

• This article was amended on 11 May 2020 to correct references to “bicep” to biceps.