Reason: "Your transverse abdominis muscle acts like a corset when dropping the legs to protect and support the body and spine ...

However, many common ab exercises like sit-ups can be tricky ... Then, lift your legs while bending your knees into a tabletop position, stacked over your hips at a 90-degree angle.

To maximize this exercise, however, be sure to avoid working from a strict tabletop position. Instead of a totally flat back, focus on creating a longer shoulder-to-toe anti-rotational challenge ...