I was thinking along the same line as Belina .. how much air is in it? If the ball is overinflated and hard as a rock, there will be no "give" or flexible support. Also, how big is it, ie the diameter when inflated? If the ball is too big for you, then it will be very difficult for you to maintain proper balance and alignment on it. At 5'3", you should be using a 55 cm ball. The bigger 65 cm balls (like the purple ones sold at Walmart and Canadian Tire) are intended for persons over 5'6" .. although I'm sure they don't indicate this anywhere on the package .

If your ball is a larger one .. just deflate it a bit. When you sit on the ball, your hips and knees should bend at 90° angles with your feet flat on the floor .. like this ..

. Besides making it a better height for you, the softer ball will provide more flexible support under your hips and low back when doing crunches. When the ball is too big, your hips tend to be angled downward in an effort to keep your feet flat on the floor. This means your thighs and low back are doing all the work, not your abs


hth


Doreen