MUSCLES ENGAGED Glutes Gluteal Muscles (Glutes) are one of the strongest muscles in the body and are the connecting point between your legs and back muscles. Glutes are used in a variety of actions from moving the leg to extending and rotating the hip, as well as extending and rotating the trunk of the body. 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. Exercise Instructions Step 1 Start on all fours with your back straight and your mid-section tight. Step 2 While keeping one arm and one leg on the floor, lengthen the opposite arm and leg to a full extension. Contract the muscles in the rear of the shoulder, lower back and buttocks. Step 3 Return to the starting position and repeat the action.