Until recently, there were essentially two systems of seated wheeled mobility: conventional manual wheelchairs that relied solely on the user or helper to propel the chair and power mobility (both wheelchairs and scooters) using motors to drive the wheels. Manual wheelchairs are relatively lightweight (typically 17-40 lbs for an adult), easy to manipulate, and can be transported in most vehicles without special adaptations. Yet by relying solely on the user's own physical power, many environments are not practically accessible. Carpets, rough terrain and even small inclines or slopes increase the effort and energy cost of mobility.1-4 A growing body of evidence suggests that the repetitive stress of manual wheeling has serious negative consequences.5-9 Cooper et al. concluded that manual wheelchair users are particularly susceptible to a variety of bone, joint, and repetitive motion injuries that may not have time to adequately heal when manual wheelchairs are the primary mode of mobility.8 Boninger et al. recommended that peak forces imposed on the upper limb during wheeling and push frequency be minimized in order to prevent or forestall the injury related to long term wheelchair use. 5 Power mobility demands very little of the user's strength and endurance, but this may not be desirable in all instances. 10 Physical inactivity appears to occur disproportionately among those with disabilities, contributing to obesity and a cycle of deconditioning and further decline. 8 Further limitations of power mobility include the weight of the devices (typically 150 lbs or greater) and difficulty in transporting the devices10, 11. Often, expensive vehicle modifications and mechanical lifts are required. To address the limitations of conventional manual and power mobility, a third option has emerged, power-assist wheels (PAWs). When PAWs are attached to a manual wheelchair or in systems where the PAW is integral to the wheelchair, the term pushrim-activated power assist wheelchair (PAPAW) is often used. PAWs require users to stroke the pushrims to activate small, lightweight motors that drive the wheels for a brief period of time (seconds). To keep PAWs moving, users must continue to stroke the pushrim as they would if they were propelling a conventional manual chair. Compared to manual wheeling, use of PAWs requires less user strength and endurance to propel which is especially beneficial on inclines, uneven terrain, and carpeted surfaces.11,13,14 Compared to conventional power wheelchairs, PAWs are lighter and thus likely to be easier to transport.11 Laboratory studies have demonstrated that PAWs require less effort and energy compared to conventional manual mobility, as manifested by lower heart rate, less activation from upper limb and trunk muscles, reduced stroke frequency and range of motion, less perceived exertion, and less oxygen consumption. 11,13-18 It should be noted that PAPAWs are heavier than comparable manual wheelchairs, and thus more challenging to transport, and may not be as intuitive to propel. They are also more expensive than comparable manual wheelchairs, and require recharging and battery maintenance. Despite the apparent utility of PAWs, little is known about their actual impact on users' daily life experiences and events. Although there are many dimensions of enablement, it is appealing to use distance travelled as a primary outcome to measure the impact of PAWs on users' lives since the central purpose of wheeled mobility devices is to facilitate travel. In other words, a key question is whether wheelers travel farther when given an opportunity to use PAWs than when in their own conventional wheelchairs. Except differences in participant sample, Fitzgerald el al (7 manual wheelers with paraplegia) and Ding et al (15 with tetraplegia) used similar methodology to investigate the impact of PAPAWs in wheelers' every-day lives. 19,20 Both studies employed a cross-over design with subjects acting as their own controls. During the 2-week baseline phase, wheelers' activity in their own manual wheelchairs was monitored with both a data logger and survey instruments. This was compared to the 2-week intervention phase, where users were given a Yamaha JWII PAPAW which was selected to be similar to the users' own chairs. During the experimental phase, the users were free to use either their own chair or the PAPAW. Results of these 2 studies showed that users chose to use the PAPAWs and their personal wheelchairs at similar frequency during the PAPAW phase of the trial. The distances travelled were not significantly different between the PAPAW and manual chairs, although the participants travelled more quickly in the PAPAWs. The PAPAWs did not result in significantly greater community participation, satisfaction, or psychological impact compared to users' own manual wheelchairs. Limitations to these studies acknowledged by the authors included a small sample size and the two-week time frame for each phase, which may not have been adequate to detect the effects of the intervention. The authors suggested that future studies should include larger, more diverse samples and measurements collected over longer periods of time. With this in mind, we decided to investigate the impact of power assist wheels over 16-weeks and tested the following hypotheses: Wheelers would travel significantly farther during the intervention phase than the baseline or follow-up periods. Baseline wheelchair performance would not predict the response to the intervention. Those with worse hand function would have more trouble controlling the PAWs, and therefore would see a significantly smaller change of distance in the intervention compared to baseline and follow-up than those with more normal hand function. The distance travelled during the first two weeks after receiving the PAWS would be significantly less than in the following 6 weeks since wheelers would need a period to adjust to the PAWs. The most functional wheelers (those with the highest ability to wheel in a test of wheelchair performance) would show the most difficulty adjusting, since their current manual wheelchair use was more likely to be satisfactory.