Gymnic Sit'N'Gym Therapy Ball with Built in Legs, 13-1/2 Inches, Clear with Stars B.R.Q. models (Burst Resistance Quality) resist puncture from any source, however in case of a puncture, ball deflates slowly. Active users work on aerobic exercises, stretching, strengthening and relaxation, and classroom students get the same benefits while actively sitting. Virtually every muscle in the core and legs is used. Recommended weight is a maximum of 270 pounds. Choose a size by measuring the individual's arm length (arm pit to finger tips) and ordering the closest ball size. Product belongs to the Medical Device Class I. Balls develop balance, coordination, postural control, sensory integration, and fitness all in 1 design Ideal for children with SI, ADD, low tone or processing disorders Legs keep ball still and in place when not in use Made of super-strong latex-free vinyl material and is surface washable