While the traditional wheelchair design, employing pushrims for propulsion, is simple and reliable, it is unfortunately inefficient and injurious. Research conducted at HERL has shown that only about half of the force being applied to the pushrim produces useful torque. In addition, researchers have associated several common injuries with pushrim propulsion. Surveys of manual wheelchair users show the prevalence of shoulder pain to be between 31 and 73% and of Carpal Tunnel Syndrome to be between 49 and 73%. A lever drive wheelchair transmission has the potential to reduce all of the risk factors for wrist and shoulder injuries. This Phase I program has demonstrated a lever drive with a mechanical efficiency of over 90%. The improvement in propulsion efficiency, coupled with the improved biomechanics of the lever drive, could substantially reduce new wrist and shoulder injuries, ameliorate existing injuries and allow some individuals the option of continuing to use a manual wheelchair. In this proposed Phase II program, we will continue engineering development of the lever drive transmission begun in Phase I, incorporating shift-on-the-fly capability and dynamic braking. Metabolic testing will be conducted on two models to document improvements in propulsion efficiency and in biomechanics.
Wheelchairs are in widespread use throughout the world. In the US alone, there are around 1.5 million wheelchair users. Of these, it is estimated that one half will eventually develop CTS and/or shoulder injuries such as rotator cuff tears. A wheelchair that could reduce the number of these injuries or allow injured users to continue to use a manual whelchair would find broad acceptance.
