Sit erect, knees bent and feet flat on the ground. Extend your arms forward at chest height, palms down. Inhale, then exhale as you tuck your tailbone, "hollow" your abs, and roll back 45 degrees toward the ground. Reach diagonally backward with your left arm, using your abs to control the movement, and pulse your arm back 3 times in this position, exhaling with each pulse. Inhale as you sit back up, lengthening your spine. Switch sides and repeat. Do 5 reps on each side.