Abstract: A dumbbell is provided which is collapsible for storage and/or convenient transportability and can be expanded, when required for purposes of exercising, by introduction therein of fluid such as water and sand. The dumbbell comprises a hollow, collapsible container comprising a closed loop of hollow tube having an elliptical or doughnut shape, a hollow handle traversing the gap between the inner walls of the closed loop and a fluid inlet provided with a plug seal. The outer peripheral wall of the closed loop is provided with accordion pleats biased into the closed portion but expandable against the bias under the influence of pressure generated by introduction of fluid into the container. The amount of fluid so introduced is a matter of choice of the user to achieve the desired overall weight of the device. Advantageously the dumbbells are integrally molded from thermoplastic resin.