From Equilibrium Point to Optimal Control

In the mid sixties, Feldman (1966) reported on experiments on feedback control processes that stabilize the human arm. In a typical test, the elbow flexors (or extensors) would be loaded and the subject was asked to maintain a predetermined elbow angle. After a sudden decrease of the load, the forearm would settle at a new position. The experiments were repeated for the same initial elbow position and load, but each time the change in the load was different. The set of points that resulted consisted of two variables: elbow angle θ and force ƒ. These points formed an exponential-like curve