| Thousands of individuals who rely on wheelchairs experience shoulder joint pain or injury. The onset of pain or injury is devastating and can negatively impact an individual's quality of life, level of independence, and well-being. It is incumbent for research scientists, engineers, and therapists to be armed with the tools necessary for evaluating shoulder stresses during activities of daily living, especially those that involve weight-bearing on the upper extremities.; Propelling a manual wheelchair is a strenuous and repetitious activity that encourages multi-planar joint movements. In the first of four independent studies presented in this dissertation, a new approach was undertaken to analyze time-series propulsion data. This new method, the autoregressive modeling technique, was used to fully describe force waveforms mathematically and investigate asymmetry in propulsion. The findings of this study revealed that the autoregressive modeling method was more specific than discrete-point methods in detecting anomalies among curves. Future applications of this method may provide greater insight into upper extremity injury mechanisms.; In the second study, a biomechanical shoulder model was utilized to document the maximum shoulder stresses and ranges of motion during two speeds of wheelchair propulsion. It was encouraging to find that the model produced variables that were consistent, reproducible, and different between sides. The findings revealed that high shoulder forces and moments are often present while the shoulder is also in an ‘impingement position’.; The third study investigated differences in the shoulder biomechanical variables when the origins of the local coordinate systems defining the motion were moved to the theoretical joint center positions. Large differences were found in shoulder kinematics whereas the changes in the kinetic variables were minimal. Future kinematic studies should consider internal joint centers.; In the last study, scapular position data were collected in various static arm positions with a digitizing stylus. The results of this study indicated significant relationships among the arm, torso and scapular angles. Moreover, a series of regression equations were derived for predicting scapular orientation during propulsion. A more detailed model may be necessary to identify the biomechanical factors that predispose wheelchair users to shoulder joint pain and injury. |
