ABSTRACT

The force produced by muscles can be modulated by controlling the number of fibers that are activated in parallel, a process known as recruitment. This modulation of force enables optimized efficiency over a wide range of loads and contraction velocities as well as accelerations. For the human body, there are more than 800 skeletal muscles-each of which is composed of one hundred or more individual motor units. For example, biceps brachii have about 750-800 such motor units. Each motor unit represents a single independently actuated degree of freedom (DoF). How do we control so many independently actuated degrees of freedom? General Considerations of Control Problem

By definition, sensors and actuators in both biological and artificial systems are connected to each other through a feedback-control system. As shown in the figure, the control system processes sensory data and, subsequently, sends commands to the motor system. Finally, the feedback loop is closed by the effects caused by the actuators and “everything else”, defining new state of measured quantities.