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.

For 'The Batman,' Pattinson gained around 10-15 pounds of muscle, focusing on functional strength with bodyweight exercises and cardio to portray a lean yet powerful "Bruce Wayne."

For 'Challengers' (2024), Mike Faist underwent a transformation to portray a professional tennis player. Faist trained intensively in tennis to look authentic on screen and reportedly gained 30 pounds for an athletic physique suited for the court. His training involved worked out for four hours a day for 12 weeks, and daily tennis practice to build endurance and skill for the role.

For their roles in Ridley Scott’s 'Gladiator' sequel (2024), Paul Mescal and Pedro Pascal both bulked up to portray strong, battle-ready characters. Mescal reportedly added around 20 pounds of muscle through a combination of strength and endurance training, while Pascal focused on functional strength and stamina to take on the grueling action sequences. Both actors followed a high-protein diet to support their rigorous training.