MUSCLES ENGAGED Chest Strengthening the chest muscles will help you push things easily and effortlessly. The muscles in your chest help stabilize your shoulder joint, which reduces your vulnerability shoulder joint injuries. Working your chest muscles also has an aesthetic factor (body contouring). Triceps Triceps are an often forgotten muscle group. Triceps are located on the opposite side of the biceps at the back of the upper arm. Well strengthened and defined triceps make the arm look bigger and sleeker (reducing the "flabby arm" look). 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 on your back with your shoulder blades in the center of the stability ball. Hold the dumbbells at at 45 degree angle at the armpit and the elbow. Keep your hips up and your core engaged throughout the entire exercise. Step 2 Press the dumbells up above your chest and slightly towards the center. Make sure to keep your core engaged and your hips up during the press. Step 3 Lower the dumbbells back down to the starting position using the same tempo and control used during the press.