According to T Nation, push-ups are a great exercise for working many different muscle regions, including the abdomen, arms, chest and back. Depending on the type and form of push-up performed, different muscle groups and stabilizing muscles are worked.
T Nation states that while performing push-ups, the rectus abdominus works to help prevent the hips from sagging, while the oblique muscles work to prevent lateral shifting and twisting. Different hand positions also play an important role. For example, placing the hands together to form a narrower base causes the triceps and pectoral muscles to activate more. Alternating the hands on a Swiss or Bosu ball provides the greatest challenge to the rectus abdominus and oblique muscles.