The present invention is a mechanical element, commonly referred to as a “Jack Spring” that is based upon the concept of adding and subtracting coils from a spring. In particular, with the method and apparatus of the present invention, by changing the number of coils in a spring, the actual or intrinsic stiffness of the spring is structurally changed. A very simple and practical method is used to adjust the number of coils. The Jack Spring actuator of the present invention is based upon adjusting the effective structure of a spring.