The Automatic Rebound Can Strengthen Your Abs, Core, Trunk, Back, And Shoulders With This Durable And Portable Design. The Features A Spring-Loaded Mechanism That Allows It To Rebound Automatically, Making It Easier To Control And Maintain Balance. It Also Comes With Knee Pads For Extra Comfort And Protection.Works The Abs, Core And Torso; Supports The Back, Shoulders And Chest Muscles.Wider And More Stable Double Wheel Design, Supercharged Spring, Ergonomically Designed Elbow Rest.