An analysis of static and dynamic joint torques in elbow flexion-extension movements

The goal of this study was to quantify shoulder, elbow and wrist dynamic and static torques in the elbow flexion-extension movements. The movements were supervised and produced by using an industrial robot manipulator that was capable of imposing a programmed arc trajectory at various velocities in the sagittal plane of the seated human subject. The muscles of the right arm being measured, were kept passive at all times of the experiment, to allow smooth guidance of the arm along a desired path. These programmed trajectories allowed a very good motion repeatability, which is not possible in normal unconstrained movements. All four velocity and acceleration profiles were taken into account and applied to matrices describing the different dynamic components in the upper extremity motion. A range of velocities which correspond to everyday movements was tested. The results reveal that the gravitational torque contributions have a prominent effect on the arm dynamics at low elbow velocities ((qoverdot) approximate to 0.25 rad/s). At these speeds the velocity and acceleration dependent terms can justifiably be discarded. However, at higher motion velocities ((qoverdot) approximate to 1 rad/s) the inertial and Coriolis-centrifugal contributions become non-negligible. Their effect is furthermore increased with speed and accompanied accelerations. (C) 2003 Elsevier B.V. All rights reserved.