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Abstract
Manual wheelchair users rely on their upper extremities for mobility. The wheelchair user controls movement of the wheelchair through the handrims, which are tubular hoops attached to the wheels. There is a high incidence of upper extremity overuse injuries among the manual wheelchair population. Associations have been found between incidence of injury and handrim loading characterisitcs such as the impact and peak force. Impact loading is defined as the rate at which the handrim is loaded during the beginning of the push. One of the proposed methods to reduce impact and peak loading is the use of a compliant handrim, a handrim that can displace relative to the wheel when impacted by the hand during the push. In an exploratory study, translational compliance was found to reduce impact loading while rotational compliance tended to increase impact loading. The velocity of the hand at impact was not affected by handrim compliance and was found to lag the tangential velocity of the handrim. Metabolic demand was found to be reduced for two of the compliant handrim conditions. Increasing compliance was found to adversely affect control, comfort, and perceived effort required during use. A dynamic model was created to explore the effect of compliance on propulsion efficiency. Impact velocity of the hand was not predicted to have an appreciable effect on efficiency. Translational compliance was predicted to adversely affect efficiency, while rotational compliance resulted in an improved efficiency within a band of compliance values. A Variable Compliant Handrim Prototype (VCHP) was designed and used to experimentally tune the compliance level. Three isotropic compliance levels were established based on the exploration study recommendations. All of the subjects found the lowest compliance level (152 lb/in) to be acceptable; acceptance decreased as compliance was increased. The 152 lb/in compliance level was found to reduce peak loading on steeper grades and to reduce impact loading on low to mid-level grades. As compliance was increased from the 152 lb/in level, trends in the resulting propulsion outcomes suggest that users were adapting by increasing their handrim forces. A compliance level was identified that maximizes user acceptance while attenuating impact loading. Future work will include adapting and further optimizing the compliant handrim such that it can be used on a wide variety of wheelchair wheels. Use of compliant handrims is hoped to prevent or delay the development of upper extremity injuries.
