The Perfect Fitness Ab Carver Pro is an ab roller with built-in resistance to help maximize muscle growth and definition in abdominals and arms. A kinetic engine, comprised of a durable carbon steel spring, offers resistance on the roll out and assistance on the roll back to amplify ab and arm workouts. Perfect Fitness Ab Carver Pro features an ultra-wide wheel tread that increases stability when carving left or right to work obliques. Ergonomic hand grips are angled to help activate arm and core muscles; handles are removable for easy storage and transport. Durable, high-density foam knee pads are included for superior comfort while carving. Downloadable 21 day Perfect Fitness Ab Carver Pro workout plan also included. 1-year manufacturer .