Mark Wahlberg's "Pain and Gain" movie has made him gain 40 pounds in 7 weeks and it was no easy feat. The actor said he had to eat 10 to 12 times a day to increase his weight from 165 pounds to 205 pounds! So, how did the actor manage to achieve this muscular built?

We unveil the secrets here. Mark Walhberg's "Pain and Gain" workout with his personal trainer Bryan Nguyen was a 5-day routine with mostly old-school workouts.

Mark Wahlberg's "Pain and Gain" workout was all about lifting really heavy weights to gain body weight fast, Popworkouts unveils the mystery.

Nguyen says about Mark Wahlberg, "I really respect him for the fact that as an athlete, he's able to bring himself to that level of intensity ... for lack of a better word, to dominate."

To add on to his physical training, mental strength is a must which is undeniable in case of Mark Wahlberg. Nguyen adds, "You can't deny mindset," he explains.

"You can't deny that variable of intensity, commitment, and pride," BodyBuilding.com quoted Nguyen.

Mark Wahlberg's "Pain and Gain" body secrets were also revealed by the actor himself in an interview with Muscle and Fitness. The actor, during the said interview, talked about his experience working with The Rock and his workout schedule.

Mark Wahlberg says, "I was training five days a week. I'd start with benching, and then I'd do my squats and lunges, then I'd do a lot of old-school stuff. I'd literally do a row of machines at the Sports Club/LA."

"One set of every single machine all the way down the row. I'd leave the hotel at 4:30 in the morning-just as the nightclubs were letting out on South Beach. I'd walk in the gym as the door opened at 5:00 AM every day, " he added.