The Stability Exercise Ball is just what you need to strengthen and tone your abs, core, and back. Sit on it at work or at home to improve your posture and strengthen your legs. Use it when you exercise at home or the gym for a variety of balance, strength, and flexibility moves, either on the floor or while standing. Groundwork exercises include Swiss ball crunches, plank holds, push-ups and reverse extensions. Standing exercises include squats, lunges, hip circles and more! This black 55cm ball, which also comes in blue, is suitable for people between 4'11-in. and 5'4-in. tall; check out our 65cm ball if you are between 5'5-in. and 5'11-in.. Pregnant women will also enjoy this as it can improve flexibility and relieve tightness.