Described is an apparatus for performing power exercises with one or more weights, wherein a weight consists of a reservoir for filling with liquid and/or air. This reservoir, referred to below as weight reservoir, serves as weight resistance for a power exercise and is connected by means of a flexible liquid conduit to a liquid displacing device. This liquid displacing device can carry liquid into the weight reservoir and remove it from the weight reservoir, whereby the weight of the weight reservoir, and thus the resistance of the power exercise, becomes greater or smaller. The operation of this liquid displacing device can be carried out by the user while performing the exercise in order to adjust the weight to his or her wishes without having to interrupt the power exercise for this purpose. The invention can be applied to power exercises with free weights and power exercises wherein the weight reservoir is provided with a conducting device. A buffer tank and dumbbell suitable for application in such an apparatus also form an aspect of the invention, in addition to a method for performing one or more power exercises wherein such an apparatus is used.