Plank on the Ball
Extended Arm Plank
This is a very difficult exercise,demanding an unusual degree of balance and effort. Start by kneeling in front of the ball and placing both hands on it.
Proceed to slowly straighten the legs out, gradually taking the weight from the knees and distributing it between your hands and feet. Keep your feet and hands apart to enhance stability. Hold the position for 30 seconds. If you feel you're going to fall, quickly bend your knees.