Get ready to strengthen your core and challenge your entire body with the ProForm PFSB6514 Anti-Burst Stay Ball. ProForm' s patented technology utilizes a small amount of weight inside the ball that dynamically moves around during movements to challenge the entire body and increase the workout intensity. Dynamically shifting weight requires more balance and strength through the full range of motion, which helps with balance, strength and functional performance. The ProForm Anti-burst Stay ball also stays in place and won't roll away from you between exercises or while you take a rest between sets. The included workout DVD will help you get a total-body toning workout from Day 1.