Arrow Arm Crunch WORKS: ABS, WAIST 1. Start on your back with your knees bent, feet flat on the floor. Focus on using your abs to lift your upper body off the floor as you straighten your arms and bring your hands together (like an arrow pointing to the center of your legs). 2. Reach to the left side, then back to the center, then to the right side and back to the center. Repeat for 30 seconds, rest, then do another 30-second set.