Joel Harper demos the flapper exercise.

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The Flapper
(Strengthens upper, middle, and lower back)

With your feet together and knees slightly bent, lean forward, bending at the waist until your back is flat and as parallel to the floor as possible. (If you've got a bad back, stay up higher.) Keeping your arms straight and your elbows unlocked, bring your arms out to the side, parallel to the ground; pause, then lower them, bringing your hands together. Do 40 times.