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02/14/2013 at 04:30 PM ET

kate upton 300x400 How Kate Upton Got In Shape for Her ‘Sports Illustrated’ Cover (We’re Tired Just Thinking About It)Courtesy Sports Illustrated

What’s harder than posing almost naked in the freezing cold in Antarctica? Preparing to pose almost naked in the freezing cold in Antarctica.

We chatted with David Kirsch, the trainer who primed Kate Upton for her second Sports Illustrated cover, and let’s just say: Upton must be exhausted.

Kirsch began working with the supermodel back in August, and for the first two weeks, Upton met with him for sessions twice a day. From then on, the model exercised five to six days per week for one and half to two hours until the photo shoot in December.

“[She did] boot camp circuit training mixed in with cardio,” Kirsch tells PEOPLE. “Running, rowing and the elliptical.” He adds that there are six regions a model needs to focus on for an SI: Swimsuit Edition shoot: “Legs, inner thighs, hips, butt, abs and arms. Anything that shows when you’re wearing a bathing suit. Which is … everything!” (Especially when that bathing suit is as tiny as some of the ones Upton sported!)

It wasn’t just the constant sweat sessions that got Upton ready to strip down; she was also extremely careful about what she ate. “She followed my ABC’s — no alcohol, bread or processed carbs – and no sugar — 24/7 with no cheat days,” the trainer reveals.

Along with not eating pasta, pizza, candy or apparently anything else that tastes delicious, Upton did Kirsch’s seven-day cleanse for two weeks out of every month they worked together. And during the other two weeks? She regularly drank protein shakes and green drinks to stay energized.

Despite all that, Kirsch says Upton didn’t complain once throughout the exhaustive process. Though, the same can’t be said about Upton while she was kneeling on an iceberg in nothing but a string bikini. But can you really blame her?

Tell us: What’s your take on Kate Upton’s workout regimen and diet? Worth it or way too intense?

–Jennifer Cress

PHOTOS: FIND OUT MORE CELEB FITNESS TRICKS!

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