To perform a standing abdominal crunches find a vertical portion of machine and loop a band around it and choke it off at the machine. Grab the end of the band with your hands and turn and face away from the machine. Put your hands behind your head and hold them there up against the back of your head. Perform a crunch down till your back is parallel with the floor flexing your abdominal muscles at the bottom. Control the motion back till you are standing straight again. Depending on your bodyweight, you may need to brace your back up against the machine that the band is looped around. This exercise is great for building abdominal strength. You can easily twist your body to left or right to work the corresponding obliques on either side.
Standing Band Ab Crunches Exercise - Start Position
Standing Band Ab Crunches Exercise - Finish Position