What is the single best ABS exercise?
While there is no single best abs exercise, crunches do not work as well as people think. In fact, neither do stability ball (swiss ball) crunches or leg lifts. Strength coaches and fitness experts a like agree that those exercises do not challenge the stability of your body against gravity. John Romaniello, a strength coach and owner of romanfitnesssystems.com says exercises that force you to brace your spine and pelvis activate more muscle fibers than any type of crunching movement, which helps build the definition you desire.
The most common stabilization exercise is the plank (shown below). An exercise where you hold your body in a push-up position, while lowering your body to rest on your forearms instead of your hands.
The plank can be modified or progressed to meet any fitness level!