Bilateral reaching to asymmetrical targets: muscle and joint dynamic interlimb adaptations.

A combined analysis of time, electromyographic, and joint torque measures was used to explore the force control processes underlying the dissociation of arm reaching movements performed bilaterally to targets of varying amplitude. Limb movements appeared closely coupled at movement initiation, which was confirmed by a strong tendency of the agonist muscles to remain synchronized despite any interlimb asymmetry in final target distance. On the other hand, interlimb decoupling occurred later as a result of the difference in the antagonists' timing of activation between the limbs. The partitioning of the net joint torque revealed that muscle activity is regulated in response to the intersegmental dynamics of the limb. It is proposed that spatial decoupling of asymmetrical movements becomes possible through postinitiation feedback processes which regulate muscle recruitment phenomena.