This patent discloses an exercise device to strengthen and rehabilitate an arm. The exercise device may include a splint, a container, and a ball. The container may include a container shell having a container shell interior surface surrounding a container shell void. The container shell interior surface may form a spherical surface having a container shell interior center. The ball may be positioned within the container shell void and include a ball center where, when the exercise device is moved by the arm, both the container and the ball rotate together with the ball center additionally moving around a circumference that follows a circumference of the container shell interior surface. The container may be attached to the splint so that the container shell interior center may be positioned outside of a hand grab radius of a hand of the arm when the exercise device is attached to the arm.