Effect of spinal cord injury at C6–C7 on global upper-limb coordination during grasping: Manipulability approach

This study describes an analysis of the upper-limb coordination through the calculation of manipulability indices borrowed from robotics. From the current arm posture as input data, this original approach allows the quantification of the hand capacities to generate linear velocities represented with a 3D ellipsoid from which two indices were derived. Its volume that represents the global velocity generation capacities and its isotropy that characterizes preferential direction for velocity generation were assessed during multi-directional reach-to-grasp task performed by subjects suffering from spinal cord injury (SCI) at C6–C7 and control subjects. Results showed that subjects with a SCI presented higher values for the ellipsoid volume independently of the movement direction suggesting a modification of their motor coordination. Secondly, some similarities of the ellipsoid isotropy were found between the two groups suggesting that despite the injury, some aspects of the coordination remained or were recovered.