Experience reactive impact Improves muscle tone and definition while enhancing cardiovascular fitness XCO Trainer® exercises strengthen the entire 3-dimensional structure of muscle, surrounding connective tissue and stabilizes the joints. Ideal for shoulder strengthening and rehabilitation. Produces results based on the principles of reactive impact. Its sleek design consists of a closed aluminum tube filled with a special granulate. As you move the tube in different directions, each movement creates a delayed soft-impact as the granulate shifts in the tube. Small -1 lb. Medium -1.5 lb. Large - 2 lb. X-Large - 2.5 lb. Exercise chart is included.