Abstract: An exercise device for has a rigid body defining a chamber, at least one first fluid mass disposed to move within the chamber in response to movement of the rigid body during exercise, thereby increasing the effective mass of the device by dynamic movement of the fluid mass during rhythmic exercise, one or more handles for gripping of the device during exercise, and a set of one or more weight adjusting elements that can be removably attached in order to adjust the static base weight of the exercise device. Exercise devices may be constructed for use of one hand or two hands.