Effect of Wheelchair Seat Stiffness on Back Muscle Fatigue During Wheelchair Propulsion

The purpose of this thesis was to identify and analyze differences in back muscle activity with different seat stiffnesses during wheelchair propulsion. It was hypothesized that because the seats offered differing degrees of stability, they would require differing stabilizing efforts using back musculature by the individual. Ten normal and nine paraplegic subjects were tested on five different wheelchair seat support surfaces of differing stiffness while performing wheelchair propulsion on a stationary wheelchair ergometer. The myoelectric activity of the erector spinae muscles in the lumbar region was studied quantitatively using EMG data with surface electrodes during wheelchair propulsion over three time periods for each cushion. An EMG power spectrum analysis was employed to measure trunk muscle fatigue caused by the instability of the different wheelchair seat support surfaces. No significant differences were found in the overall fatigue pattern response of EMG muscle activity across the five cushion types within each group. In other words, no single cushion stiffness was found to be better than any other in terms of stability as measured by EMG back muscle activity. Significant differences in EMG fatigue patterns across the three work (wheelchair propulsion) periods were found within the paraplegic group, but not for the normal group. These differences in fatigue patterns found within the paraplegic subjects were significant only within each individual cushion, but not statistically significant when compared across the five cushions. Results indicate that EMG data are useful in studying changes in activity of the trunk muscles in relation to the stiffness of the seat support for the wheelchair. Furthermore, results support previous studies that no single cushion is ideal for all people with severe physical disability and that factors other than tissue pressure need to be considered in the prescription of a wheelchair cushion. It is further concluded that objective evaluation data, such as EMG analyses, and clinical assessment combined together provide a more effective means for individualized cushion prescription.