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 (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. Exercise Instructions Step 1 Start on your front side with your head and collarbone raised off of the floor. Step 2 Place your arms out in front of you with your palms facing and your thumbs up. Step 3 Pull your arms back, rotating through your shoulders and touch your hands together with the back or your palms facing.