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. Quadriceps The quadriceps (quads) are a group of four muscles on the front of the thigh. They allow your knee to straighten and provide stability when standing. Your quads are the most important muscle group for maintaining the ability to stand and to walk independently. Exercise Instructions Step 1 Start in a standing postion with your feet shoulder width and you hands to your side. Step 2 Place both hands on the floor in front of you and jump out into a push-up position. Step 3 Jump back up towards your hands and stand back up to the starting position.