An actuator control system, mechanical testing system, and method for adaptive control of an actuator of a mechanical testing device may include determining a stiffness of a medium that the actuator is moving through and/or load gain of the actuator, wherein the stiffness and load gain is determined by generating a waveform to actuate the actuator until a load sensor signal and/or a displacement sensor signal is received, and controllably moving the actuator through the medium according to a predefined constant velocity by calculating a current request using the stiffness of the medium, and/or adjusting the load of the actuator in accordance with a constant load ramp rate.