Lie on your back on an exercise mat. Rest your calves on a physioball (medium or large) so your legs are elevated. Doing this protects your lower back and helps flatten your lower back on the mat. Your arms are gently crossed across your chest. Using your abdominal muscles, curl up off the mat and twist to the right, feeling a muscular contraction on your right side. Make sure you're not using your neck muscles to assist. Your neck should be relaxed. Lower your torso to the mat and relax. Repeat on the other side, curling up off the mat and twisting to the left, feeling a muscular contraction on your left side. Lower your torso to the mat and relax.