Tired of doing sit-ups? Try these innovative ab moves from our favorite trainers to really chisel your core. Bonus tip: Do these after your favorite cardio routine for the best burn.
The jackknife is a killer ab exercise that will really get your abs burning while testing your flexibility. To perform a jackknife, lay on your back with your legs straight and your arms extending over your head. On an exhale, keep your legs and arms straight as you bring them together in a jackknife position, letting your shoulder blades come off the floor. Inhale as you return to the start. The jackknife is an especially difficult exercise as the arm and leg movements work both your upper and lower abs at once, leaving your entire core on fire.