We aren't sure which is hotter: Olivia Munn's fight scenes in X-Men: Apocalypse (out this month) or that latex suit she's sporting. Either way, we're digging her toned frame.

Her secret: the Swiss Ball Inchworm, says Ken C. Tran of Dax Gym in Montreal, who, along with trainer Karine Lemieux, helped transform the 35-year-old into the badass Psylocke. "It's a great core workout and hamstring stretch, and it improves muscle strength and endurance in your shoulders, arms, chest, and thighs," he says. Using a Swiss ball ($30, amazon.com), do 3 sets of decreasing reps (4, 3, 2), adding more as you improve, 3 times a week.

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How to do the Swiss Ball Inchworm:

Start in a push-up position with hands on the floor and toes close together on a Swiss ball ("A" in the image below). Keeping legs straight, lift butt, and roll ball forward as far as you can toward hands ("B" in the image). Walk hands forward, lowering back down to "A." To make it harder, add a push-up before performing the next rep.