Trajectories of target reaching arm movements in individuals with spinal cord injury: Effect of external trunk support
Design: Deficits in trunk control due to spinal cord injury (SCI) lead to slower target-reaching movements of the hand. We investigated whether the movement path is also affected, and whether providing external support for the trunk can abolish the kinematic differences.Objective: To compare movement trajectories between individuals with SCI and neurologically normal individuals, with and without external trunk support.Setting: Neural Control/Biomechanics Laboratory, University of Illinois, Chicago, USA.Methods: Five subjects with levels of injury between C7 and T4 were tested 3–8 years post-injury, and compared with five control subjects. Two targets were employed. Trajectories were recorded by a motion-capture system using infrared emitting markers. Peak speed and path curvature were calculated for the fingertip and for the acromion.Results: Compared with control subjects, the subjects with SCI exhibited lower peak speed of the fingertip but not of the acromion, and less straight paths for both. When the trunk was supported externally, the difference in fingertip speed persisted. The support abolished the difference in path curvature for the fingertip but accentuated that for the acromion.Conclusion: The slower hand movements of individuals with SCI are not simply time-scaled versions of those of normal subjects, and the provision of trunk support does not erase the kinematic differences between the reaching movements of the two groups.