In this variation of the plank you are holding a higher percentage of your bodyweight than a plank on the floor, and you also have increased stability from the ball. Therefore please do not attempt this unless you can hold a stable plank with good technique on the floor for at least 30 secs. I recommend that you first try an incline plank with your feet on a box, bed or chair before moving to a swiss ball. This can also be done on a TRX system.