A barbell includes a bar assembly that includes a sleeve rotatably fitted over a rotating-locking mechanism at an end of a shaft; and an end cap attached to an open end of the sleeve to enclose the rotating-locking mechanism and the end of the shaft inside the sleeve, in which the rotating-locking mechanism includes a supporting ring rotatably fitted over the shaft and a joining ring attached to the end of the shaft, in which the supporting ring abuts, on one side, a shoulder on an inner surface of the sleeve and, on the other side, the joining ring.