A prosthesis or orthosis has a first body and a second body rotatable relative to one another, a passive mechanical converting mechanism with a third body arranged movably with respect to the first body, and an elastic element arranged between the third and the second body. The mechanical converting mechanism is configured for converting an angular change between the first body and the second body into a change of load on the elastic element. There is further provided a ratio adapting device interacting with the converting mechanism and configured for modifying the conversion ratio by which the change of load on the elastic element is performed.
