j/fit Ergonomic Comfort/Stability Balance Ball Fitness Chair Designed by health and fitness professionals to strengthen your back and improve posture. Increases activation of your core muscles improving posture throughout the day. New innovative ergonomic shape is more comfortable than conventional ball chairs with more surface seating area. Helps to align your spine and relieve back pain. Accommodates heights from 5' to 6' 1" | Risers sold separately to add additional height of 1-2" per riser.