TheraBand Pro Series Exercise and Stability Ball with 55 cm Diameter, Professional Slow Deflate & Burst Resistant Fitness Ball for Improved Posture, Balance, Yoga, Pilates, Core Stability, Red Strengthens muscles, improves posture, balance, and core stability, helps prevent back and spine pain 55cm diameter (22") is designed for individuals from 5'1" - 5'6" tall