MUSCLES ENGAGED Abdominals The abdominal muscles (abs) provide movement and support to your core area. The deeper and closer to the spine the particular abdominal muscle is, the more effect over body posture it will have, and this often contributes significantly to a healthy back. 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 plank position on your forearms with your feet shoulder width apart and your lower back flat. Step 2 Press your body up to a push-up position and then lower yourself back down into the plank. Step 3 Do all the reps on one side or alternate sides for the recommended number of reps.