A substantially flexible implant holder for holding a substantially tubular implant structure during fatigue testing of the implant structure, the implant holder having a substantially elongate cavity for occupation by the tubular implant structure and a cavity-surrounding part which extends from at least a first longitudinal end of the cavity to at least a second longitudinal end of the cavity, the cavity-surrounding part having a stiffness which gradually changes from a relatively high stiffness adjacent each of the longitudinal ends of the cavity to a relatively low stiffness adjacent a middle portion which is situated between the two longitudinal ends of the cavity.