Bilateral reaching to asymmetrical targets: Muscle and joint dynamic interlimb adaptations

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