Abstract: An apparatus and method for force-controlled fatigue testing of a specimen or material. A driver is used to generate a load force which is applied to the test specimen. Physical property changes of the test specimen are measured over time and a feedback signal is generated as a function of the measured physical property changes. A motion command signal is computed as a function of the feedback signal. A computer processes the feedback signal and emits the motion command signal to an actuator. The driver responds to the motion command signal and maintains the load force at an approximately constant magnitude during the physical property changes of the test specimen.