This is for core stability. Lie in a prone position on the ball with your hips and belly on top of the ball. Feet and hands should be grounded. Engage the abs, glutes, and lower back and raise the right arm and left leg until they are in alignment (straight line from finger tips to toes). Hold for one to two seconds. Return to starting position. This exercise can be continued by going back and forth between opposing sides or sticking to the same side for required repetitions.