A musculotendon contribution for multijoint hand control.

For multijoint arm control, intersegmental dynamic properties have been observed to play a significant role. This paper focuses on the contribution of viscoelastic musculotendon properties during coordinated hand movements. Specifically, the musculotendon passive stiffness torque is shown to be more than 90% of the total passive torque, based on two-link planar model dynamics, during repetitive hand movements. Furthermore, a large difference in the contribution to joint torque was observed depending on the relationship between wrist and finger phasic movements. With the wrist and finger in phase, the peak-to-peak stiffness torque was 24 N-cm, while it was only 6 N-cm with the wrist and finger out of phase. Despite the difference in the musculotendon dynamics between in-phase and out-of-phase coordination patterns, when they spanned similar angular excursions, the movement variance remained the same. We hypothesize that the interactive musculotendon torque contribution is accommodated by the neural controller and is utilized to achieve task-dependant impedance of the hand.