Pushups are a great way to strengthen your core while enhancing upper body strength. The core not only involves the abdominals but includes the muscles of the lumbar, thoracic and cervical spine, along with the pelvic girdle and hip joint. The pushups in the video demonstrate the involvement of the core for stabilization and performance. These are just a few examples. Be sure to progress accordingly. Watch for compensations such as, low back arching, shoulders elevating or range of motion limitations. If any compensations occur, be sure to regress.