MUSCLES ENGAGED Abdominals The abdominal muscles (abs) provide movement and support to your core area. The deeper and closer to the spine the particular abdominal muscle is, the more effect over body posture it will have, and this often contributes significantly to a healthy back. Obliques Many people put a lot of focus on working their abs but forget their surrounding neighbors; the oblique muscles. Obliques serve as stabilizers, and are used in almost every physical activity. Exercising your obliques should be a very important part of your workout program. Equipment Used Stability Ball A stability or exercise ball is a ball constructed of soft elastic and filled with air until firm.Most stability balls range from a diameter of approximately 35 to 85 centimeters (14 to 34 inches). Bench A weight training bench is a piece of equipment that has a resemblance to a normal (e.g. park) bench, but is cushioned and designed for use in the weight room. Exercise Instructions Step 1 Start in a push-up plank position with your hands on the ball and your feet up on the bench. Step 2 Pull your knee into your chest and contract your abs and obliques. Step 3 Complete the recommended number of reps then switch sides.