Circuit Three: Plank and Straight-Arm Kickback Reps: 10, alternating sides Start in a plank position holding a dumbbell in each hand. Open your feet wider than hip width for a stronger base of support. Lift your left arm behind you as high as you can. Bring the left arm back into plank to complete one rep. Repeat with the right arms for another rep. Image Source: POPSUGAR Photography