Approximately 3.26 million Americans are wheelchair bound, and an estimated 83% of this population are manual wheelchair users (MWUs) [1,2]. MWUs exhibit a high incidence of self-reported shoulder pain that increases with duration of wheelchair use and is attributed to excessive mechanical loading of the glenohumeral (shoulder) joint during wheelchair locomotion [3]. Various modified wheelchair systems have been developed to ease upper extremity work during wheelchair locomotion including powered, push-assisted, lever-driven, and geared wheelchairs. With the ability to maintain standard manual wheelchair wheel esthetics, cost, and weight, geared wheels could be an easily adoptable assistive technology to reduce glenohumeral joint forces and torques in MWUs. IntelliWheels, Inc., Champaign, IL, has created a variety of geared wheels that use a planetary gear train between the hand rim and the wheel to allow for different gear ratios.
To assess joint loads in the user, inverse dynamics...
