Lie facedown on the floor, hands next to sides, and tighten your glutes. Lift your upper body off floor, and pull your shoulder blades down and back. Extend the left arm in front of you, bicep next to your left ear, as you lean to the right and reach your right hand back toward your right foot (you should feel all the muscles along your left side engage). Switch to the other side, bringing left arm down to your side to reach back toward left foot as you lean to the left, and extend right arm out with biceps next to right ear. Continue for 30 seconds.