In her groundbreaking role as the first female lead in a Marvel movie, 'Captain Marvel' (2019), Brie Larson was determined not to appear weak. Despite considering herself "not super athletic," she dedicated nine months to rigorous training, successfully gaining 15 pounds (7 kg) of muscle to achieve her superhero form, earning much-deserved admiration for her impressive transformation.

For his role in 'The Wolverine' (2013), Hugh Jackman took his portrayal of the iconic character to a whole new level by getting remarkably ripped. To achieve this, he adopted a diet plan suggested by Dwayne Johnson, requiring him to consume a whopping 6,000 calories a day, accompanied by a rigorous workout routine. The result was an impressive transformation that truly embodied the essence of his comic book counterpart.

In his role as Apollo Creed's son in 'Creed' (2015), Michael B. Jordan displayed serious dedication to his craft. He transformed his physique by gaining an impressive 24 pounds (11 kg) of muscle over the course of a year. His commitment involved rigorous training for two to three hours daily and adhering to an incredibly bland diet, showcasing his remarkable dedication to the role.

In the iconic movie '300' (2007), Gerard Butler led the pack of impressively buff men, captivating audiences with their intense physiques. Butler underwent a grueling four-month training regime to prepare for the role, and his remarkable results became known as the '300 diet', popularized for its impressive effectiveness.

In 2008, Tom Hardy tackled the role of infamous criminal "Charles Bronson". To embody the character, Hardy adopted a unique approach, building muscle with exercises that could be performed in a jail cell. He followed a diet consisting of chicken, rice, pizza, ice cream, and cola, remarkably gaining 42 pounds (19 kg) in just seven weeks.

In preparation for his role in 'Southpaw' (2015), Jake Gyllenhaal underwent an impressive transformation, gaining 15 pounds (7 kg) of pure muscle through intense boxing training. His dedication paid off, as both his portrayal as an actor and a boxer received critical acclaim.

Kumail Nanjiani gained around 20 pounds of muscle to play Kingo in 'Eternals' (2021). His transformation involved daily strength training and a diet rich in protein, making waves in Hollywood due to his comedic roots.

Efron reduced his body fat to around 5-6% while building muscle for 'Baywatch' (2017). He shed about 10-12 pounds while gaining lean muscle definition, achieving a chiseled look through HIIT and a strict, low-carb diet.

For 'Atomic Blonde' (2017), Theron trained rigorously with martial arts, weightlifting, and tactical combat training, focusing on building functional strength and agility for the film’s intense fight scenes rather than gaining or losing significant weight.

Robbie trained in gymnastics, weightlifting, and martial arts to achieve a lean, athletic look for "Harley Quinn" in 'Suicide Squad' (2016). She focused on building strength and agility without major weight changes to handle the film’s heavy stunts.