The wide saddle shape is easy to sit on or roll over, because it only moves in two directions. Challenges the user to balance their core for an active learning posture. Recommended for daily excercise, positioning and therpay programs. Designed to improve motor and balancing skills. The unique design allows a therapist and client to both sit on. For best size: measure from Armpit to fingertips for closest height of ball. A must have therapy ball for anyone with balance, and attention needs.