Effect of increased load on scapular kinematics during manual wheelchair propulsion in individuals with paraplegia and tetraplegia.

Repetitive loading of the upper extremity musculature during activities like wheelchair propulsion can lead to fatigue of surrounding musculature causing irregular segment kinematics. The goal of this study was to determine the effect of increase in load on the kinematics of the scapula in users with paraplegia and tetraplegia. Data were collected on 18 participants (11 with paraplegia and 7 with tetraplegia) using an electromagnetic motion tracking system (100Hz) and force sensing pushrim (200Hz). The participants propelled under no load and loaded conditions at their customary propulsion velocity. On average a 60N increase in force was elicited with the experimental protocol. Users with tetraplegia showed significant increases (p<.05) in the rate of change of scapular angles in the upward/downward rotation and the retraction/protraction direction under the loaded conditions, whereas users with paraplegia only showed difference in the retraction/protraction rotation direction. Overall both user populations moved towards position of increased downward rotation, anterior tilt and protraction with increase in load hence increasing the risk of impingement. This experiment adds depth to our understanding of dynamic scapular kinematics during wheelchair propulsion under different loading conditions and differences in scapular control between users with paraplegia and tetraplegia.