2 sets x 12-17 reps (increase number of sets as you get stronger)
Lie prone with your hips and lower abs on a fit ball (picture your body as a flat board—no sagging allowed). Your legs should be spread for stability and the toes of your shoes to the ground. Your arms should be out front of your chin, folded so that your hands are holding your elbows. This position requires that your entire body is flexed, but make sure to keep your neck relaxed, head in the neutral position and shoulder blades pulled together and down toward your lower back. You are going to raise the upper body about 15 degrees by extending your spine and contracting the lower back muscles (think of extending your head out to the wall and up, rather than just up to the ceiling). You should feel the muscles tighten, but no pinching whatsoever. Hold for a second and then slowly lower the trunk back to the start position.