The Jack Knife is an incredibly challenging exercise that works multiple muscle groups to develop a strong, fit core. This exercise incorporates your lower back, abdominal muscles, legs and nearly your entire upper body.
Position yourself in a plank position on a core stability ball. Next, guide the ball toward your upper body by pulling your legs into your chest. Extend your legs back out to the starting position and repeat. Perform 3 sets of 12-15 reps.
Since this exercise utilizes your entire body, it can be used as a warm up before starting your regular strength training or cardiovascular routine. Additionally, you can incorporate this challenging exercise into your abdominal workout for phenomenal results.
If you are a beginner, you can begin by holding a plank position on the floor for 30 second intervals. Once you master a floor plank, move up to a plank on the ball. Once you master the art of holding your balance on the ball, you can advance to the jack knife.