The ergonomic structure of K-Med Leverage-Bracing Support Chair uses your weight as leverage to brace your back for correct posture and lessen your weight load onto the lumbar and backbone. K-Med chair’s spherical bottom and elastic backrest brace up your pelvis, lumbar, back together to restore your backbone upright in any postures. It is perfect for students and teachers, office workers, game players, and those who usually sit long time and highly recommended for patients with lumbar pain, spinal curvature. * The function of the product is to brace your lumbar and backbone, not for comfort. The tightening feeling of the self-bracing chair is to protect you, not because of small size. K-Med chair's stable and elastic body is made of Polyamide resin to withstand the compressive load up to 800 lbs. * Size - Large : width 17.12 inches / Medium : width 14.96 in / Small : width 12.52 in * How to Use : Step 01 Place the product 5 inches apart from the back of your main chair. Step 02 Be sure to press your hip and lumbar to the product. It keeps K-Med chair to brace you all the time you sit. Step 03 Your weight gives leverage to the product to brace your lumbar and back.