Want to get as ripped as Jake Gyllenhaal in Southpaw? This is how he did it.

Coming less than a year after Jake Gyllenhaal's turn as a skinny creep in Nightcrawler, the actor's physical transformation in Southpaw — in which he plays a professional boxer — is nothing short of astonishing. Beefed up to bulky, muscular proportions, Gyllenhaal is totally credible as the kind of guy who could send just about anybody sprawling to the mat.

But how did he get into fighting shape so fast? As you'd expect, it wasn't easy — but a series of interviews have offered some insights for any masochists looking to replicate Gyllenhaal's eight months of training:

1. Develop an insane exercise routine

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People has an exhaustive rundown of Gyllenhaal's six-hour-a-day workout routine, which was developed by trainer Terry Claybon. Gyllenhaal's primary concern was ensuring that he came across like a real boxer, so his workout routine was similar to the kind of training practiced by actual professional fighters. Among many other boxing drills, every day included:

• 15 minutes of jumping rope
• 5 to 8 miles of running
• 500 to 2000 sit-ups
• 100 pull-ups and dips
• 20 flips of a 300-pound tractor tire

2. Keep your energy up with the right kind of food

The idea of an actor crash-training for an extremely role usually conjures up images of strict diets — but Gyllenhaal's workout routine was so intense that the primary concern was keeping his body rested and fueled enough to endure his physical training. Gyllenhaal's diet consisted of carbs in the morning and protein in the evening.

3. Have a reliable partner

"I said, 'Jake, you have to train like a fighter,'" said Antoine Fuqua, the director of Southpaw. "I can't have you faking it. You have to be in the gym twice a day, every day, even on Sundays."

With his leading man undergoing such a drastic physical transformation, Fuqua made an unusual decision: undergoing his own crash-course in boxing training alongside Gyllenhaal. "It was amazing to have your director with you, pushing you every day," said Gyllenhall. "Sometimes if I was too tired, he'd go, 'Well, we're there at 8:30,' or 'We're there at 4:30 a.m.' That motivation, and that sacrifice, is what drove both of us."

4. Say goodbye to your significant other

Gyllenhaal's training routine was so all-consuming that Antoine Fuqua believes it led to Gyllenhaal's breakup with then-girlfriend Alyssa Miller. "Literally. I think he broke up with his girlfriend because he was just in the gym every day," said Fuqua. "He was training like a fighter."