When Britney Spears debuted her sexy new video for "Criminal," we were as surprised as everyone else at the amount of flesh flashed in the clip by … her boyfriend, Jason Trawick. We've seen Brit's banging bod before – the Joseph Kahn-directed video for "Womanizer" opens with the superstar fully nude, arms strategically draped across her chest, on a bench in a steam room, for crying out loud – but this is our first real look at what her man's rocking under those fancy suits he wears to escort her to awards shows.

So what's Mr. Trawick got going on? Turns out, he's just as fit as his lady love. "He’s a mesomorph body type, so his body type is one that gains muscle easily," Hollywood trainer Jeanette Jenkins tells MTV News of Trawick's transformation from the typical guy next door to muscle-bound hunk (as illustrated above).

"Even in that before picture he doesn’t have a lot of body fat. He’s got a little bit of a belly. But he still, his density. I can see the density of his muscle," says Jenkins, who has helped sculpt the fit bods of Serena Williams, Robin Thicke, "Up All Night" star Christina Applegate, Kendra Wilkinson and Terrell Owens. "He was a classic out-of-shape mesomorph. Him and Britney Spears have the same body type. With mesomorph, when they get out of shape, when you gain just like five or ten pounds of body fat, you look so much more overweight because it’s the fat over the muscle. … But they have the muscle and muscles is what burns fat. So it’s like, once they start training, their body transforms very quickly."

For his part, "Criminal" video director Chris Marrs Piliero, who wasn't into the idea of Trawick co-starring with Spears in the video at first, was as surprised as everyone else at how sculpted the talent agent (who represented Spears until they decided to part ways professionally in May 2010) was when he showed up on set. Read on to hear what he had to say and for Jenkins' how-to guide to a Trawick-style transformation (she thinks you can do it in six months if you work hard!).

Chris Marrs Piliero talking about Jason Trawick's body transformation:

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Jenkins believes that if people commit to a dedicated-but-doable workout plan, they can get results like Trawick's in as little as six months, saying, "For sure and they can do it the healthy way – two hours a day for training, four days a week. It sounds like a lot but it’s not. … It doesn’t have to be two hours at the same time. You could be doing, you know, cardio in the morning and weight training at night."

Talking about Trawick, Jenkins again recommends separating the cardio routine from the weight training to maximize the effects of the workout. "If he was my client I would have him separate. In the morning I would have him doing cardio as soon as he wakes up to get him into that fat burning mode," she says. "Then weight training in the evening followed by his meal immediately after he’s done."

She believes that for the average working Joe keeping the weight training in the evening – and always eating afterward – is key to muscle building because rest is integral to the process.

"You need specific hormones to be released also to do proper recovery and you get that while you’re sleeping. So that’s why a lot of athletes, they actually do their weight training in the morning, they eat and they take a nap," Jenkins says. "If someone has to work a regular job, they can’t always do that. So I’d have them do the cardio in the morning to give them an energy boost to boost their metabolism for the day so they’re burning fat. Eating healthy meals throughout the day. Then in the evening doing heavy weight training, which means he’d be lifting, you know, between six to ten reps of three to five sets – separating the body parts throughout the week – and then getting proteins right after his weight training and getting lots of rest."

Seems simple enough. And if it means we can look half as good as Trawick in just six months, we're certainly game to give it a try.

"Criminal":

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