Abstract: A weight lifting system includes a handle unit having a handle bar, two head units attached to two end sections of the handle bar in a manner that allows the two head units to rotate about a longitudinal axis of the handle bar, two screw rods disposed through holes in the two head units into hollow sections in the handle bar, wherein the two screw rods have threads of opposite directions, two thread-engaging mechanisms fixedly disposed at the two end sections of the handle bar to fit snugly on the threads of the two screw rods, and a lock mechanism disposed in a head unit for controlling rotation of the handle bar; and a plurality pairs of weight discs, wherein each of the weight discs has a center hole configured to accommodate one of the two screw rods.

Abstract: 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.

Abstract: A weight lifting system includes a handle bar and two weight plates. The handle bar is made of a first material and is attached to the two weight plates by inserting each of two ends of the handle bar in a hole in each of the two weight plates, wherein at least one of the two weight plates comprises a center portion made of a second material and a peripheral portion made of a third material, wherein the third material is different from both the first material and the second material, wherein the center portion comprises the hole, in which one of the two ends of the handle bar is inserted, and the center portion is welded to the handle bar.

Abstract: 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.