MUSCLES ENGAGED Shoulders The shoulder is the most movable joint in the body. However, it is an unstable joint because of the range of motion allowed. This instability increases the likelihood of joint injury, often leading to a degenerative process in which tissues break down and no longer function well. Equipment Used Dumbbells The dumbbell, a type of free weight, is a piece of equipment used in weight training. It can be used individually or in pairs (one for each hand). Dumbbells vary in weight from 3lbs. up to 150lbs. Bosu The BOSU balance trainer stands for "Both Sides Utilized" and is most often used for balance training, various athletic drills and aerobic activities. Exercise Instructions Step 1 Start in a kneeling position on the Bosu with both feet off of the floor, your back straight and your shoulders pulled back in the shoulder girdle. Step 2 Raise the dumbbells up to shoulder height, pause and lower them back down to the side of your hips. Step 3 Repeat the action and make sure to keep your core engaged throughout the entire exercise.