Biomechanics and the wheelchair.

Wheelchair biomechanics involves the study of how a wheelchair user imparts power to the wheels to achieve mobility. Because a wheelchair can coast, power input need not be continuous, but each power strike can be followed by a period of recovery, with the stroking frequency depending on user preferences and the coasting characteristics of the wheelchair. The latter is described in terms of rolling resistance, wind resistance and the slope of the surface. From these three factors the power required to propel the wheelchair is determined, and must be matched by the power output of the user. The efficiency of propulsion is the ratio of this power output to the metabolic cost and is typically in the order of 5% in normal use. The features required in a wheelchair depend upon user characteristics and intended activities. The ideal wheelchair for an individual will have the features that closely match these characteristics and activities. Thus prescription is not just choosing a wheelchair, but choosing the components of the wheelchair that best serve the intended purpose. In this paper, each component is examined for available options and how these options effect the performance of the wheelchair for the individual. The components include wheels, tyres, castors, frames, bearings, materials, construction details, seats, backrests, armrests, foot and legrests, headrests, wheel locks, running brakes, handrims, levers, accessories, adjustments and detachable parts. Each component is considered in relation to performance characteristics including rolling resistance, versatility, weight, comfort, stability, maneouvrability, transfer, stowage, durability and maintenance. Where they exist, wheelchair standards are referred to as a source of information regarding these characteristics.