Get in a prone position on the floor, hands behind your head. Begin by crunching and rotating your torso. As you twist and lift your trunk, bring your opposing knee toward your chest. Touch opposite elbow to opposite knee. Perform each rep on a quick but controlled tempo.
Progression: Perform rotational sit-outs. Start with your body in a push-up position, with feet and hands shoulder-width apart. Under control, take one leg and sweep it underneath your body, rotating so that you are almost in a seated position with your opposing hand and foot supporting your weight. The hand opposite your sweeping leg reaches for the ceil-ing. Alternate sides for six to 12 reps.
Regression: Perform single-side McGill sit-ups. Lie in a supine position, with hands behind your head. On the working side, bring your knee up, with your foot flat on the floor and as close to your glute as possible. Extend your non-working leg. Breathe out and perform a crunch by visualizing the “row” of abs on your working side contracting. Perform the crunches and actively feel the muscles lengthen and shorten during the movement.
Expert Tip: Fully touching your knee to your elbow will elicit a more powerful contraction than a partial rep.