MUSCLES ENGAGED Back (upper) You can’t see your back without a lot of effort, but this doesn't mean you shouldn’t train it. Back exercises consisting of both back stretching and back strengthening is very important to your health and overcoming back pain. 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. 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). Cable Machine The cable machine is a piece of equipment used in weight training or functional training. A wide variety of exercises can be performed using the apparatus. Exercise Instructions Step 1 Start standing up on the Bosu with a slight bend in you knees. Keep your back straight and grip the handle with your thumb up. Step 2 Pull the cable to the side of your chest and squeeze your shoulder blade in the back. Step 3 Extend your arm back out to the starting position.