The invention relates to a method for exercising muscles with the aid of an exercise apparatus and, where appropriate, for measuring exercise conditions, where the person exercising loads the relevant muscles by increasing or decreasing the rotational energy (E(kin)), kinetic energy, of at least one rotatably mounted flywheel, by means of a traction element which is wound up and designed for acting on the flywheel (1), the flywheel (1, 1a) being braked in a controlled manner by means of a brake element (40). The invention also relates to an exercise apparatus for exercising muscles.