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The benefit: This is one of the most challenging exercises for your entire core—from your shoulders to your hips. If you think your abs are strong, test them on this exercise to find out if they’re really strong.
How to do it: Lie on your back on a Swiss ball so that your upper back is firmly on the ball. Raise your hips so that your body forms a straight line from your knees to your shoulders. Hold your arms straight out from your sides. (It helps to hold a pole or broomstick across your body.) Without allowing your hips or arms to sag, roll across the ball to the left as far as you can. Reverse directions and roll as far as you can to the right. Continue back and forth for 30 seconds.