Economical burst-resistant balls provide versatile workouts for rehabilitation and exercise These exercise balls help improve core stabilization by training the muscles of the spinal column as the body works to stay in balance. Ideal for exercises involving flexion, extension, equilibrium reactions and postural adjustments. Made of nonslip, heavy-duty vinyl, these balls deflate slowly if punctured. These balls are for indoor use only and can be used while seated, standing, on the floor or against a wall. Norco? Exercise Balls are tested to support up to 550 lbs. (250 kg). Not intended for heavy lifting.