Despite many applicable developments in the field of ergonomically improved manual drive wheelchairs, the standard fixed pushrim remains the most prevalent method of propulsion. These ubiquitous fixed pushdm drives, while inexpensive and intuitively simple to operate, contribute to several common repetitive motion injuries. Among manual wheelchair users surveyed, prevalence of shoulder pain is seen to be between 31 percent and 73 percent, and carpal tunnel syndrome (CTS) to be between 49 percent and 73 percent. The prevalence of these injuries is associated with the large wrist flexion under load, the downward pressure on the pushrim, the muscle imbalance from the uni-directional stresses of continuous push motions applied to the pushdm, and the large number of repetitions of the push motion. When pain reaches a certain level of discomfort, the wheelchair dependent individual generally starts using a powered chair, thus losing a valuable cardiovascular exercise. Responding to the needs of this large user population, 1.5 million in the US alone, it is our long-term objective to provide a wheelchair propulsion system utilizing a pushrim of improved kinematics. The improved kinematic design will allow up to a 50 percent reduction of push strokes for a given distance traveled. Additionally, it will allow the user the option of a mode of operation that will essentially eliminate wrist flexion under load and lessen forces on the shoulder, while retaining traditional pushrim operation for fine control. The concept has the potential to allow embodiment as fully self-contained wheel assemblies that would be field retrofittable to a large number of existing wheelchairs. We have developed a pushrim drive concept that will enable the long-term objectives slated above. It is the specific aim of this proposal to design, fabricate, and test a transmission mechanism, contained entirely within the wheel hub, such that the needed utility will be demonstrated.
