What Size Ball?
under 5′0” – 45 cm ball
under 5′10” – 55 cm ball
under 6′2” – 65 cm ball
over 6′3” – 75 cm ball
When you sit on it, knees should be @ 90 degrees
Target sells a good GoFit Exercise Ball for $19.99-$24.99
Description: Challenge your body and get a great all-over workout with this GoFit exercise ball. The ball provides an unstable surface so you train not only the primary muscle groups, but the small stabilizing muscles as well. Combine the ball workout with some cardio and resistance to complete your exercise regime.
NOT A TENNIS PLAYER? No Problem! Skip exercises 24-27 and you have 24 great fitness ball exercises!