The beefcake is back with a vengance - but there are fears men could turn to quick fixes in order to emulate celebs

Swinging topless from rings high in the air, Zac Efron strains as his biceps bulge, his shredded shoulders swell and his sculpted six-pack is shown off to the max.

The actor, on the set of Baywatch , is so proud of his buff body he posted his workout pictures to his 11.6 million Twitter followers and 12.1 million Instagram followers.

One caption said: “Blood, sweat and Respect. The first two you give, the last one you earn.”

To get ripped for his role as lifeguard Matt Brody, Zac has done months of training and followed a strict diet. He tweeted: “Nine days of zero carbs and sugar. Only organic grass fed/free range protein and organic leafy greens.”

Read more: Zac Efron looks RIPPED as he goes shirtless

Zac, 28, is one of many stars who have transformed from fit-but-lean to beefcake – and shared the results on social media. Mark Wright , 29, was almost unrecognisable in an Instagram selfie last week. David Charvet, who played Matt Brody in the Baywatch TV series in the 1990s, was nowhere near as big as transformed High School Musical star Zac.

Read more: What happened to Baywatch cast after they traded in red swimsuits?

Experts fear that with the rise of the gym selfie, there is a much darker side to the example these men are setting – warning it could lead to serious psychological issues for guys who feel they need to achieve near-impossible body goals.

Dr James Byron-Daniel, senior lecturer in sports and exercise psychology at the University of the West of England , says: “There is massive pressure on men now because they see so many body images on social media, which we didn’t see 10 years ago.

“The problem comes when young men are not sure how to attain the body ideals they see but just want to get bigger and bigger.

“Constantly comparing themselves to others and not achieving unattainable aims potentially leads to psychological issues such as depression and anxiety.

“It’s a big problem – bigger than we realise because men are less likely to share their worries and seek help. It really is a ticking timebomb.”Celebs work hard on their looks with what trainers estimate to be up to three hours a day in the gym and the right advice to do it healthily. But experts say the man on the street, who doesn’t have the correct advice, is increasingly turning to dangerous quick fixes.

“We’re seeing younger and younger men joining gyms,” says Dr Ruth Lowry, exercise psychologist at the University of Chichester. “We also have a rise in concerns about the obsession with highly muscular celebrity body ideals.

Read more: Orlando Bloom's got muscles: Actor shows off his "gains"

“It can start off being proactive with exercise and healthy eating but can be taken to an extreme with people choosing a calorie-restricted diet and supplementation. All these things in moderation can have a beneficial effect but in a quest for that perfect image, which takes time, dedication and money, they are looking to achieve goals too quickly.

“We’re seeing men just concentrating on pumping iron instead of cardio health. Then there are conversations about other things, such as steroids.

“Becoming exercise dependent also means prioritising time at the gym to the detriment of other aspects of their lives. They can experience disordered eating patterns. And they can develop muscle dysmorphia, a specific type of thinking which means perceiving yourself as much thinner and less muscled than you are.”