Not every celebrity started out looking like a gym regular. Some of today’s fittest famous men were once known for their slim frames before surprising fans with dramatic muscle transformations.
Whether it was for demanding movie roles, intense action scenes, stage performances, or simply personal fitness goals, these stars completely changed their physiques through hard work and consistency.
From actors like Jake Gyllenhaal and John Krasinski to performers like ATEEZ’s San, their glow-ups prove that dedication can completely reshape both body and career.
#1 John Krasinski
John Krasinski’s transformation from the goofy, lovable Jim Halpert in The Office to a full-blown action star surprised a lot of people.
For years, he was known as the “nice guy” type, but everything changed in 2016 when he took on the role of a CIA contractor and former Navy SEAL in 13 Hours: The Secret Soldiers of Benghazi.
To prepare, he completely rebuilt his body, dropping from 26 percent body fat to just 9 percent in a few months.
Krasinski trained twice a day, five days a week, with trainer Jason Walsh. His workouts included heavy squats, deadlifts, sled drags, front squats, Bulgarian split squats, rows, pulls, and lots of metabolic conditioning.
He told Men’s Health, “I gotta be honest: It was brutal at times. We did tons of metabolic work, dragging sleds and all this stuff I’ve seen NFL players do.”
His diet was just as strict, mostly salad, chicken, complex carbs, and a lot of water, while cutting sugar almost completely.
At 35, he called it the best shape of his life, saying, “Physically I had a bad back, bad core strength, bad everything.”
That transformation changed his mindset. He admitted, “I did it for the role, and then I definitely got addicted to it.”
Since then, he has maintained that physique for roles like Jack Ryan, training five days a week with active recovery on weekends.
For years, he was known as the “nice guy” type, but everything changed in 2016 when he took on the role of a CIA contractor and former Navy SEAL in 13 Hours: The Secret Soldiers of Benghazi.
To prepare, he completely rebuilt his body, dropping from 26 percent body fat to just 9 percent in a few months.
Krasinski trained twice a day, five days a week, with trainer Jason Walsh. His workouts included heavy squats, deadlifts, sled drags, front squats, Bulgarian split squats, rows, pulls, and lots of metabolic conditioning.
He told Men’s Health, “I gotta be honest: It was brutal at times. We did tons of metabolic work, dragging sleds and all this stuff I’ve seen NFL players do.”
His diet was just as strict, mostly salad, chicken, complex carbs, and a lot of water, while cutting sugar almost completely.
At 35, he called it the best shape of his life, saying, “Physically I had a bad back, bad core strength, bad everything.”
That transformation changed his mindset. He admitted, “I did it for the role, and then I definitely got addicted to it.”
Since then, he has maintained that physique for roles like Jack Ryan, training five days a week with active recovery on weekends.
Report
50points
#2 Jake Gyllenhaal
Jake Gyllenhaal has gone through some of Hollywood’s most extreme body transformations, from looking dangerously thin in Nightcrawler to becoming a full-blown fighter in Southpaw and later Road House.
For Nightcrawler, he dropped to around 66 kg to play the gaunt and obsessive Lou Bloom. But for Southpaw, he did the complete opposite, packing on nearly 13 kg of muscle to become boxer Billy Hope.
His Southpaw routine was brutal. Gyllenhaal started mornings with 1,000 sit-ups and an eight-mile run before breakfast, followed by one to two hours of boxing and sparring.
Afternoons meant more boxing, cardio, and core work, and evenings ended with weightlifting plus another 1,000 sit-ups.
He also flipped a 250-pound tractor tire and hit it with a sledgehammer for conditioning. Director Antoine Fuqua told him, “To act like a fighter, you have to train like one.”
For 2024’s Road House, Gyllenhaal trained for over a year with Jason Walsh, dropping from 205 pounds to 184 pounds and reaching just 5% body fat.
His workouts mixed heavy compound lifts, sled pushes, squats, bag drills, grappling, fight conditioning, and high-intensity intervals.
Walsh said, “Jake works his a*s off, plain and simple… He earned every bit of it.”
Gyllenhaal himself said fitness became a lifestyle, “I love it. It makes me feel good.”
For Nightcrawler, he dropped to around 66 kg to play the gaunt and obsessive Lou Bloom. But for Southpaw, he did the complete opposite, packing on nearly 13 kg of muscle to become boxer Billy Hope.
His Southpaw routine was brutal. Gyllenhaal started mornings with 1,000 sit-ups and an eight-mile run before breakfast, followed by one to two hours of boxing and sparring.
Afternoons meant more boxing, cardio, and core work, and evenings ended with weightlifting plus another 1,000 sit-ups.
He also flipped a 250-pound tractor tire and hit it with a sledgehammer for conditioning. Director Antoine Fuqua told him, “To act like a fighter, you have to train like one.”
For 2024’s Road House, Gyllenhaal trained for over a year with Jason Walsh, dropping from 205 pounds to 184 pounds and reaching just 5% body fat.
His workouts mixed heavy compound lifts, sled pushes, squats, bag drills, grappling, fight conditioning, and high-intensity intervals.
Walsh said, “Jake works his a*s off, plain and simple… He earned every bit of it.”
Gyllenhaal himself said fitness became a lifestyle, “I love it. It makes me feel good.”
40points
#3 Jay Harrington
Jay Harrington may be 54 now, but his major body transformation began when he prepared for the later seasons of S.W.A.T. in his late 40s.
Playing Sergeant David “Deacon” Kay meant long days in heavy tactical gear, carrying weapons, and filming demanding action scenes.
Before the series even began, the cast went through a police maneuvers bootcamp to understand what real SWAT officers go through.
Harrington admitted to Men’s Journal, “I put on the tactical gear, picked up the primary weapon, and was shocked by the weight of it all.”
As the seasons went on, the physical strain became harder to manage.
“Bodies don’t recover as they do in your 20s and 30s,” he said, especially while filming long hours on set.
In 2021, wanting to feel stronger and move better, he teamed up with trainer Andre Bolourchi at Double Ops in Santa Monica to build muscle without getting too bulky.
Bolourchi designed a push-pull strength program focused on back, biceps, and core, since Harrington was already constantly on his feet while shooting.
He also kept up outdoor cardio by running stairs in Santa Monica, saying, “I enjoy sweating outside as much as I can.”
The results were clear, he added noticeable size, felt stronger, and moved better during action scenes. Fans noticed too, with one surprised comment reading, “wait that’s really him???!”
Playing Sergeant David “Deacon” Kay meant long days in heavy tactical gear, carrying weapons, and filming demanding action scenes.
Before the series even began, the cast went through a police maneuvers bootcamp to understand what real SWAT officers go through.
Harrington admitted to Men’s Journal, “I put on the tactical gear, picked up the primary weapon, and was shocked by the weight of it all.”
As the seasons went on, the physical strain became harder to manage.
“Bodies don’t recover as they do in your 20s and 30s,” he said, especially while filming long hours on set.
In 2021, wanting to feel stronger and move better, he teamed up with trainer Andre Bolourchi at Double Ops in Santa Monica to build muscle without getting too bulky.
Bolourchi designed a push-pull strength program focused on back, biceps, and core, since Harrington was already constantly on his feet while shooting.
He also kept up outdoor cardio by running stairs in Santa Monica, saying, “I enjoy sweating outside as much as I can.”
The results were clear, he added noticeable size, felt stronger, and moved better during action scenes. Fans noticed too, with one surprised comment reading, “wait that’s really him???!”
35points
#4 Sam Heughan
Sam Heughan’s transformation from a lean marathon runner to the broad-shouldered Highland warrior fans know from Outlander is one of the most noticeable glow-ups on television.
Before landing the role of Jamie Fraser, Heughan was around 82–84 kg and focused heavily on long-distance running, even completing marathons.
But once he was cast, he knew he had to look like “someone who could take care of himself,” he told Men’s Fitness.
Since Jamie was written as a soldier, farmer, and fighter, Heughan spent six intense weeks training at a CrossFit gym in London, learning deadlifts, Olympic lifts, and heavy conditioning work.
By the end of that transformation, he had bulked up to around 92–94 kg and significantly increased his strength.
He later shared, “Throughout the year I built up my way to 92-94 kgs and really saw my lifts get a lot stronger.” His personal best deadlift even reached 180 kg.
To support the muscle gain, he admitted he was “eating everything,” while still trying to keep it clean with sweet potatoes, chicken, peanut butter, and protein bars he could sneak onto set inside his kilt sporran.
Over time, Heughan also learned to see food differently. In his memoir, he revealed he once struggled with a “low-level eating disorder” caused by pressure to look a certain way.
He wrote, “It was only when I set out to become more muscular that I began to think of food in terms of nutrition.”
Now 45, he still keeps up strength work, functional carries, running, and hiking, balancing fitness with his love for whisky and cocktails.
Fans definitely noticed the results too, with one writing, “He is a feast for the eyes!”
Before landing the role of Jamie Fraser, Heughan was around 82–84 kg and focused heavily on long-distance running, even completing marathons.
But once he was cast, he knew he had to look like “someone who could take care of himself,” he told Men’s Fitness.
Since Jamie was written as a soldier, farmer, and fighter, Heughan spent six intense weeks training at a CrossFit gym in London, learning deadlifts, Olympic lifts, and heavy conditioning work.
By the end of that transformation, he had bulked up to around 92–94 kg and significantly increased his strength.
He later shared, “Throughout the year I built up my way to 92-94 kgs and really saw my lifts get a lot stronger.” His personal best deadlift even reached 180 kg.
To support the muscle gain, he admitted he was “eating everything,” while still trying to keep it clean with sweet potatoes, chicken, peanut butter, and protein bars he could sneak onto set inside his kilt sporran.
Over time, Heughan also learned to see food differently. In his memoir, he revealed he once struggled with a “low-level eating disorder” caused by pressure to look a certain way.
He wrote, “It was only when I set out to become more muscular that I began to think of food in terms of nutrition.”
Now 45, he still keeps up strength work, functional carries, running, and hiking, balancing fitness with his love for whisky and cocktails.
Fans definitely noticed the results too, with one writing, “He is a feast for the eyes!”
32points
#5 San
ATEEZ’s San has had one of the most talked-about transformations in K-pop, going from a skinny rookie to one of the industry’s most muscular performers.
When ATEEZ debuted in October 2018, San was just 19 and known for his youthful, playful energy, slim frame, and bright smile. Fans loved his cute visuals during the Pirate King and Treasure era, where he had colorful styling and a softer image.
As the group’s performances became more intense, San’s physique began changing too.
By eras like Wave, Wonderland, and especially Fireworks (I’m The One) in 2021, fans noticed how much stronger and more muscular he had become.
His sleeveless stage outfits made his toned arms and sculpted build impossible to miss, while teaser photos showing his abs during the Fireworks comeback sent fans into meltdown.
His transformation became a huge topic online, with even casual fans praising how much effort he clearly put into becoming stronger for performances.
Despite the physical glow-up, fans still pointed out that behind the powerful stage presence, he remains the same shy and cheerful person. “I do love his shyness.”
One fan summed it up perfectly, “Netizens just can’t handle San’s transformation from a skinny rookie to a muscular legend.”
When ATEEZ debuted in October 2018, San was just 19 and known for his youthful, playful energy, slim frame, and bright smile. Fans loved his cute visuals during the Pirate King and Treasure era, where he had colorful styling and a softer image.
As the group’s performances became more intense, San’s physique began changing too.
By eras like Wave, Wonderland, and especially Fireworks (I’m The One) in 2021, fans noticed how much stronger and more muscular he had become.
His sleeveless stage outfits made his toned arms and sculpted build impossible to miss, while teaser photos showing his abs during the Fireworks comeback sent fans into meltdown.
His transformation became a huge topic online, with even casual fans praising how much effort he clearly put into becoming stronger for performances.
Despite the physical glow-up, fans still pointed out that behind the powerful stage presence, he remains the same shy and cheerful person. “I do love his shyness.”
One fan summed it up perfectly, “Netizens just can’t handle San’s transformation from a skinny rookie to a muscular legend.”
Report
30points
#6 Brandon Sklenar
Brandon Sklenar’s transformation for the 1923 season 2 was one of the biggest physical changes of his career, and he made sure it showed on screen.
After season 1 made him a breakout star as Spencer Dutton, Sklenar wanted the next chapter to feel heavier, both emotionally and physically. Since Spencer had spent months shoveling coal and surviving brutal conditions, Brandon felt the character needed to look stronger, tougher, and more intimidating.
He personally called creator Taylor Sheridan months before filming and told him, “I think I’m going to show up and be visibly, way bigger,” via The Wrap.
Taylor simply replied, “Cool.”
Sklenar further explained, “I wanted to feel like an animal, and I wanted to feel scary, and I wanted to look intimidating.” He added that he wanted Spencer to have “a real presence” and to feel like “a force to be reckoned with.”
To make that happen, he spent months training hard in the gym with long, intense sessions.
His trainer, Wesley Wilson, later revealed on his Instagram that they were doing “2+ hour grueling workouts” consistently for months. The diet was just as serious, with Wilson joking they ate “enough elk and salmon to feed a freaking village.”
Shirtless training photos showed a much bulkier and more muscular Sklenar, and fans immediately noticed how ripped he looked.
Sklenar has also admitted that he enjoyed his physical transformation for roles and does it for almost every project, even if it’s subtle.
“I love using my body. I’m really good at it,” he said in an interview with Sydney Sweeney for Interview Magazine, explaining that he grew up fighting and doing construction.
He also performs most of his own stunts and believes using his body helps him fully disappear into a role. That commitment made Spencer Dutton feel even more dangerous in season 2.
As one user justified his transformation, writing, “Brandon Sklenar is the biggest example of twink to hunk pipeline. I would have never recognized him.”
After season 1 made him a breakout star as Spencer Dutton, Sklenar wanted the next chapter to feel heavier, both emotionally and physically. Since Spencer had spent months shoveling coal and surviving brutal conditions, Brandon felt the character needed to look stronger, tougher, and more intimidating.
He personally called creator Taylor Sheridan months before filming and told him, “I think I’m going to show up and be visibly, way bigger,” via The Wrap.
Taylor simply replied, “Cool.”
Sklenar further explained, “I wanted to feel like an animal, and I wanted to feel scary, and I wanted to look intimidating.” He added that he wanted Spencer to have “a real presence” and to feel like “a force to be reckoned with.”
To make that happen, he spent months training hard in the gym with long, intense sessions.
His trainer, Wesley Wilson, later revealed on his Instagram that they were doing “2+ hour grueling workouts” consistently for months. The diet was just as serious, with Wilson joking they ate “enough elk and salmon to feed a freaking village.”
Shirtless training photos showed a much bulkier and more muscular Sklenar, and fans immediately noticed how ripped he looked.
Sklenar has also admitted that he enjoyed his physical transformation for roles and does it for almost every project, even if it’s subtle.
“I love using my body. I’m really good at it,” he said in an interview with Sydney Sweeney for Interview Magazine, explaining that he grew up fighting and doing construction.
He also performs most of his own stunts and believes using his body helps him fully disappear into a role. That commitment made Spencer Dutton feel even more dangerous in season 2.
As one user justified his transformation, writing, “Brandon Sklenar is the biggest example of twink to hunk pipeline. I would have never recognized him.”
Report
28points
#7 Conor Storrie
Connor Storrie’s transformation from a skinny creative kid in West Texas to one of Hollywood’s fastest-rising muscular stars has become a major talking point online.
Before Heated Rivalry made him a breakout name, he grew up with fitness already around him; both of his parents were former bodybuilders, and he also trained in gymnastics and skating as a kid.
Still, his early passion was acting, making YouTube videos under the name “actorboy222” and creating characters long before fame found him.
He later joked that a younger version of himself “was on to something. He got me here.”
For Heated Rivalry, where he plays Russian hockey star Ilya Rozanov, Storrie’s physique became part of the role.
Fans were stunned by his muscular build, especially his now-viral glutes and broad shoulders.
He told Variety, “Working out is just time. Real fitness is four or five times a week, getting to the gym every single week for years.” He also admitted, “Shoulders are big. Shoulders are a big deal.”
When asked directly about his glute routine, he laughed and told Vanity Fair, “I do a lot of dumbbell squats, like elevated dumbbell squats, so I go really deep. That’s kind of it. My parents have big butts.”
The internet couldn’t stop talking about the glow-up, with one user writing, “From non binary drag performer to hunk is crazy.”
Before Heated Rivalry made him a breakout name, he grew up with fitness already around him; both of his parents were former bodybuilders, and he also trained in gymnastics and skating as a kid.
Still, his early passion was acting, making YouTube videos under the name “actorboy222” and creating characters long before fame found him.
He later joked that a younger version of himself “was on to something. He got me here.”
For Heated Rivalry, where he plays Russian hockey star Ilya Rozanov, Storrie’s physique became part of the role.
Fans were stunned by his muscular build, especially his now-viral glutes and broad shoulders.
He told Variety, “Working out is just time. Real fitness is four or five times a week, getting to the gym every single week for years.” He also admitted, “Shoulders are big. Shoulders are a big deal.”
When asked directly about his glute routine, he laughed and told Vanity Fair, “I do a lot of dumbbell squats, like elevated dumbbell squats, so I go really deep. That’s kind of it. My parents have big butts.”
The internet couldn’t stop talking about the glow-up, with one user writing, “From non binary drag performer to hunk is crazy.”
27points