MUSCLES ENGAGED Quadriceps The quadriceps (quads) are a group of four muscles on the front of the thigh. They allow your knee to straighten and provide stability when standing. Your quads are the most important muscle group for maintaining the ability to stand and to walk independently. Glutes Gluteal Muscles (Glutes) are one of the strongest muscles in the body and are the connecting point between your legs and back muscles. Glutes are used in a variety of actions from moving the leg to extending and rotating the hip, as well as extending and rotating the trunk of the body. 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 Place the stability ball between the small of your back and a wall. Put one foot behind you against the wall and the other in front of your body. Be sure that your knee does not extend past the foot. Step 2 Keeping your back straight, lower your body until your front knee is bent at a 90 degree angle. Step 3 Lift the body back up to the starting position using the quadricep muscles. Repeat the action.