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Overuse injury (repetitive strain injury) of upper extremity is remarkably common in individuals who use manual wheelchair as daily living. Previous studies have related the long-term wheelchair propulsion with the upper extremity injuries. Most published studies simplified the movement of upper extremity via two-dimensional description and their results have indicated the need of three-dimensional analysis. Seat of wheelchair is an important interface in providing the force needed for propelling the wheelchair. Different seat position will change the interface of users and the wheelchair. The purpose of this study is to investigate the effect of seat position changes on the kinematics and kinetics of upper extremity with full three- dimensional description. A 3 by 3 matrix of seat positions was used. We hypothesize that the differences in kinematics and kinetics of upper extremity appeared at different seat position. Thirteen ambulatory men were instructed to propel the wheelchair on the level ground. A standard type manual wheelchair with an instrumented wheel consists of a six-component load cell was used to collect the forces and moments applied on the handrim by users directly. Several reflective markers were placed on the subject used to define the segments of upper extremity for calculating joint kinematics and kinetics of upper extremity via the inverse dynamics method. ExpertVisionTM system was used to collect the trajectory data of the markers while the subject was propelling the wheelchair on the level ground. The isolated joint moment data collected in this study were expressed in terms of a wheelchair propulsion strength rating (WPSR). The WPSR is defined as the ratio between joint moment generated during propulsion and that generated during a maximum isometric strength test at each direction, as an index indicating the percentage of loading. The maximum isolated isometric moments of each subject were evaluated by the Kin-ComTM AP dynamometer. Multivariate ANOVA was used to analyze all parameters in relation to the seat height and seat axle horizontal position. Comparisons were made for the individual effect of seat height and seat axle horizontal position, also the interaction of these two factors. The effect of seat position changes appeared significantly for joint range of motion and WPSR, but no significant difference found in temporal parameters and propulsion efficiency. The movement pattern of wheelchair propulsion can be described more detail by the three-dimensional data-acquisition system, both in kinematics and kinetics. This study supports the hypothesis that the kinematics and kinetics of wheelchair propulsion would be affected by seat position changes. High WPSR in the shoulder and wrist joints match the high incidence of shoulder and wrist over-use injury.
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