Bradley Cooper is known for his handsome boyish looks, but when the Hollywood actor took on former Navy SEAL Chris Kyle in American Sniper, he had to use an intense workout to get the job done.

Bradley Cooper’s workout was a huge challenge. Not only did the actor have to pack on 40 pounds of muscle, but he also only had 10 weeks to undergo his body transformation.

Cooper was also suffering from back and shoulder problems at the time, making his goals even more difficult.

To accomplish this Herculean task, Cooper began seeing trainer Jason Walsh, who had previously helped Cooper’s friend and fellow actor John Krasinski bulk up. Walsh developed a training regimen for Cooper that helped him gain a lot of weight, getting up to Kyle’s massive size without compromising his health.

Cooper was eating between 5,000 and 6,000 calories each day, which is more than double what the average man eats. For Cooper, it was important to be upping his calorie intake, as opposed to eating healthier.