SWISS BALL JACK KNIFES
The jack knife is a fantastic exercise to strengthen the core area. Lie with your stomach on a Swiss ball and place your hands on the ground out in front of you. Walk your hands forward and allow the ball to roll down your body towards your legs. Stop when the ball reaches just below your knees. Pause here and make sure your body is completely straight, with your abs braced to counteract a downward sag in your stomach. Now roll the ball, bringing your knees in towards your chest. Pause, and roll the ball back to its starting point. When you feel more confident, start with the ball lower down your shins and then, harder still, try it with your feet on the ball, as pictured.