• A high-quality ball made of thick rubber or plastic manufactured by a reputable fitness company. Cheap balls have been known to pop while people are using them, which can lead to serious injury.
• The right size ball. As a guideline, people under 5 feet 6 inches should choose a 55 cm ball; those 6 feet 2 inches and taller should choose a 75 cm ball, and those in between should choose a 65 cm ball. When you sit on the ball, your hips should be slightly higher than your knees.