Abstract: A plyometric exercise device having an elongated shaft, a hand-grip attached to the shaft, and counterweights at the two opposing ends of the elongated shaft, for use in strength development of a user's shoulder and shoulder muscles is described. Also described are methods of using such a plyometric exercise device. In use, the user typically grasps the device and moves their arm up and down, while the exercise device oscillates in phase with the user's movements in an omni-directional manner. This omni-directional movement provides both eccentric and concentric muscle contraction in the shoulder of the user, and may act to strengthen the shoulder.