In engineering, the degrees of freedom of a system are the minimum of independent co-coordinates that are needed to specify uniquely the state of configuration of a system, without violating how its parts are interrelated. The arm has seven degrees of freedom: three at the shoulder (flexion-extension, abduction-adduction, rotation about its axis), one at the elbow (flexion-extension), one at the radio-ulnar joint and two at the wrist. At the level of muscles, the arm has 26 degrees of freedom in that there ten muscles at the shoulder, six at the elbow, four at the radio-ulnar joint and six at the wrist. Thus, the problem of controlling the movements of the arm would be reduced if the basic units to be controlled by the brain were joints rather than individual muscles (or motor units). Bernstein‘s solution to the problem was to propose that what the brain controls are functional groupings of muscles or what he termed coordinative structures
See Biomechanical degrees of freedom, Constraint, Coordinative structure, Kinematics, Motor control, Motor development, Motor unit, Movement (or motor) coordination, Non-univocality principle, Open system, Order parameter, Organism-environment mutualism, Synergy