Abstract: A series of weights in various sizes and configurations, where a fluid, including but not limited to water, moves and shifts inside the hollow body or bodies of the weight, thereby providing a shifting center-of-gravity to the device during use. This shifting requires greater effort from the user to maintain stability, and results in faster and greater muscular development over a standard set of weights with a fixed center of gravity. The body may comprise any desired shape or form, such as an oval, rectangle, square, or circle, and may have rounded corners or ends in order to promote flow of the fluid or water inside the body. The body also may comprise one or more connectors extending between body parts. One or more handles may be affixed to the body.