Neuromuscular-skeletal constraints in the coordination of prono-supination Factores neuro-músculo-esquéleticos en la coordinación de movimientos de pronosupinación

Objective: To examine how changes in the position of the axis of rotation of the forearm alter both stability of unimanual coordination and activation patterns of muscles that contribute to pronation and supination of the forearm. Participants: 15 participants generated pronation and supination movements of the forearm in time with a metronome (frequencies from 1.75 Hz to 3.5 Hz). Methods: All the subjects were required to coordinate either maximum pronation or maximum supination with each beat of the metronome. Kinematic data (angular displacement) of the forearm were recorded. The axis of rotation was either coincident with the long axis of the forearm, above this axis, or below this axis. The time of onset of every pattern change was calculated to determine the stability of each mode of coordination. In 4 participants the electromyographic activity of pronator teres, brachial biceps, flexor carpi radialis and extensor carpi radialis and kinematic data of the forearm were recorded and synchronised. Results: The stability of the pronate-on the-beat pattern was greatest when the axis of rotation of the movement was below the long axis of the forearm. In contrast, the stability of the supinate-on-the-beat pattern was greatest when the axis of rotation of the movement was above the long axis of the forearm. The relative dominance of the pronation and supination phases of forearm rotation co-varies with the degree of engagement of flexor carpi radialis and extensor carpi radialis longus. Conclusion: The relative stability of pronate-on-the-beat and supinate-on-the beat patterns are contingent upon mechanical context. Changes in mechanical context alter the activation patterns of muscles that contribute to pronation and supination of the forearm, particularly flexor carpi radialis