This is a posterior reach superset with a trunk rotation using band tubing. This helps to develop your rectus abdominis and internal and external obliques. Most people are accustomed to hearing this called your core region.
During the posterior reach I am basically letting the cables pull me back from a neutral position with arms overhead as if I were to attempt to do a back handspring. As I am doing this I bend my knees and shoot them forward to release any extra tension on my lower back and then I return to a neutral position while keeping my arms straight throughout the whole movement. Contrary to popular belief, the main function of the rectus abdominis is not to flex your spine (e.g. crunches) but to prevent hyperextension which is basically what a posterior reach is. Although crunches are great in developing your abs, the posterior reach has more functional value. During the trunk rotation I am basically rotating my upper torso while trying to keep my pelvis neutral. As you see it is a short range of motion but more than enough to get those internal and external obliques.
