A long, cylindrical bag suspended by a chain, covered with leather, and filled with either a fibrous material or water. They weigh from 50 to 150 pounds. It is used by boxers to practice their punches, footwork, and stepping. It helps to build muscles in the upper body, wrists and hands. It also helps build endurance. Boxers punch it, move around it, and push it back, just as they would an opponent.