Selfstability of Musculoskeletal Systems: Optimal Co-activation is Task Dependent

摘要

Human and animal locomotion represents a highly complex control problem. Internal and external disturbances increase these difficulties. Biological systems adapt the pure mechanical properties of muscles and passive structures to support stability and to cope with these disturbances. Stability only based on mechanical properties without neuronal feedback is called self-stabilization. The biomechanical model of a general joint with one extensor and one flexor muscle is based on a Hill-type muscle model and the geometry is adapted to different situations. The definition of stability in the mathematical sense is given using the framework of dynamical systems. Different aspects of stability are discussed, and mathematical methods to provide more detailed information about stability will be sketched. The question is, whether a high or a low co-activation of the elbow muscles should be used to minimize the maximal acceleration or deflection. In the present study, a waiter is considered who should not spill the water in the glass while moving. The mathematical analysis will show that the answer depends on the position of the upper arm.