This exercise adds difficulty to the traditional push-up. The declined version of the push-up is great for shaping and strengthening the chest muscles. The chest is scientifically named the pectoralis. There are two muscles that make up the pectoralis: pectoralis major and minor. The pectoralis major is always the prime mover during chest exercises.

Start by placing your toes on an aerobic step. Use both arms to support your upper body. Place your arms approximately shoulder width apart. Your body should be perfectly straight.
Next, slowly lower your chest to the floor. Then push back up to the starting position. Be sure to breathe out as you push your body up.