MUSCLES ENGAGED 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. 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. 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). Exercise Instructions Step 1 Start in a plank position with your forearms placed on two seperate stability balls. Make sure to keep your hips down and tucked and your core tight. Step 2 Pull the ball into your body and meet it with a knee from the same side. Make sure to keep your core tight and your abs and obliques fully contracted when your knee touches the ball. Step 3 Push the ball back to the starting postion and lower your leg back down. Switch sides and repeat the action.