A method for analyzing center of pressure during manual wheelchair propulsion

Little published information is available on joint kinetics during wheelchair propulsion. This is partially due to the lack of appropriate instrumentation and techniques. Biomechanical-mechanical techniques may be developed to assist in the amelioration of upper extremity pain among wheelchair users, Elbow, wrist, and hand pain have been reported to exist among 16, 13, and 11% of manual wheelchair users, respectively. This paper focuses on methods for determining the location of the pushrim center of pressure during wheelchair propulsion. Wheelchair propulsion is accomplished by bilateral simultaneous repetitive motion of the upper extremities. The pushrim is grasped or struck and pushed downward and forward, in turn, rotating the wheels. During the propulsive phase, the hand is capable of exerting a three-dimensional moment against the pushrim. The moments and forces exerted on the pushrim were measured by a specialized wheelchair wheel, the SMART/sup wheel/. The center of pressure (COP) for the upper extremities is found in three planes parallel to the frontal, sagittal, and transverse anatomical planes, This calculation of the COP is analogous to the calculation of the COP for lower extremity gait analysis using a force plate. One difference is that the hand has the ability to pull on the pushrim and, therefore, the upper extremity COP does not necessarily reside within the projection of the hand. Another difference is that with a force plate, there is only one plane of interest (the plane of the force plate), and three are used for the complete analysis of the upper extremity. Kinetic data were collected using the SMART/sup Wheel/ from three subjects who are wheelchair users. Kinematic data were also collected concurrently using a PEEKS video analysis system. Graphs of the COP from the sagittal plane show great variability, which is probably due to the low medial-lateral forces exerted against the pushrim. Frontal COP graphs show less variability and indicate that with these three subjects the line of action for the anterior-posterior force component is located between 10 and 15 cm lateral to the pushrim and a variable distance above or below the location of the 2nd metacarpal-phalangeal joint. Future studies with more subjects may show force offset to be a modality in the cause of carpal-tunnel syndrome.