Perfect Fitness Ab Carver Pro Roller for Core Workouts Ultra-wide ab roller with built-in resistance and ergonomic handles to help maximize results of ab roll-out exercises Interior kinetic engine uses a carbon steel spring to provide resistance and amplify abdominal and arm workout Ultra-wide wheel tread offers stability when carving left, right or center for targeted work on obliques Ergonomic hand grips are angled to activate arm and core muscles; handles are removable for easy storage and transport Includes high-density foam kneepad for superior comfort; downloadable 21-day workout plan; 1-year manufacturer warranty