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. Back (middle) Middle back muscles are very important as they help to support and strengthen the core muscles at the front of your body. 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 on top of the Bosu while holding a dumbbell in front of you in both hands. Step 2 Keep your back straight and a soft bend in your knees. Raise the dumbbell up in front of you to head height. Step 3 Lower the dumbbell back down to the starting position and repeat.