New In Box Silver One Exercise Ball (55cm) Extra Thick Professional Grade Balance & Stability Ball - Pump Included 55 CM Ball in Blue Pump and Exercise Guide Improves balance & stability - Perfect for home exercise, yoga, pregnancy or to improve your core strength. Replace your office desk chair for improved posture and to relieve lower back pain. -Strenghtens core muscle & improves coordination. - It engages the core muscles by forcing the body to respond to the instability. - You can also use your balance balls as a tool for stretching while performing yoga or pilates exercises. - Use with weight training to add challange and engage more of the bodies muscles.