Abstract: A multi-axis fatigue testing device includes a multi-axis test fixture having a multiple input, multiple output mechanical linkage driven by a plurality of actuators and a controller operating each of the plurality of actuators in real time and in synchronization to produce user-defined multiple fatigue cycle profiles. At least one of the actuators driving the mechanical linkage acts against an artificial load characterized by a stiffness. The stiffness is selected to increase a resonance frequency of the test fixture to allow fatigue testing at higher frequencies for a wider range of samples.