MUSCLES ENGAGED 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. 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 in a standing position with your feet shoulder width apart and your hands at your sides. Step 2 Place your hands on the floor and jump out into a push-up up position. Keep your back flat and your abs tight. Step 3 Jump back up with both feet at the same time and stand back up to the starting position.