A fitness device for strength training can include: a clamshell housing including a front portion and a back portion. The front portion and the back portion can mate together to define an internal volume. The clamshell housing includes first handle portions extending circumferentially around the front portion and second handle portions extending circumferentially around the back portion. The first and second handle portions mate together to define a plurality of handles. The fitness device includes a sealed container defining a fluid chamber. The sealed container can be fixedly received within the internal volume defined by the front portion and the back portion of the clamshell housing. The fluid chamber of the sealed container can contain: a gaseous component, a first fluid component, and a second fluid component.