Coping with disturbances

Motion systems must cope with internal and external disturbances affecting the envisioned movement program. In science responses to disturbances are used to characterize system properties. Recently, evidence has been collected that self-stability due to the mechanical response of a system can greatly contribute to safe guarding proper operation of the system and to follow up an envisioned task. Here we review research in our laboratory on the kinematic response of standing subjects to sudden pulls inflicted by a motor, and the kinetics of runners crossing a track with a bump. We find that in both cases the first responses are dominated by system compliance. Thereby damage is avoided and the tasks are secured. Preparation to the observed disturbance does not seem to have the goal to compensate quickly but to enhance the scope of the reaction and its economy.