So today, for the reasons stated above, we are back to abs. One of the coolest and best ab exercises I have found is a variation of the plank. All by itself the plank is tortuously fantastic, but this one added move makes it wicked good.
Start in the traditional plank position, on your toes, forearms on the floor.
Alternate bending each leg to the side, bringing your knee to your waist, still maintaining plank position with your arms and other leg.
That is it! Seems simple, right? Try it and let me know how that works out for you.