Abstract
For people with physical disabilities, manual wheelchairs are essential enablers of mobility, participation in society, and a healthy lifestyle. Their most general design offers great flexibility and direct feedback, but has been described to be inefficient and demands good coordination of the upper extremities while critically influencing users’ actions. Multiple research groups have used Inertial Measurement Units (IMUs) to quantify physical activities in wheelchairs arguing that knowledge over behavioural patterns in manual wheelchair usage can guide technological development and improved designs. The present study investigates turning behaviour among fulltime wheelchair users, laying the foundation of the development of novel steering systems that allow directing kinetic energy by means other than braking. Three wearable sensors were installed on the wheelchairs of 14 individuals for tracking movement over an entire week. During detected “moving windows”, phases where the velocities of the two rear wheels differed by more than 0.05 m/s were considered as turns. Kinematic characteristics for both turns-on-the-spot as well as for moving turns were then derived from the previously reconstructed wheeled path. For the grand total of 334 km of recorded wheelchair movement, a turn was detected every 3.6 m, which equates to about 900 turns per day on average and shows that changing and adjusting direction is fundamental in wheelchair practice. For moving turns, a median turning radius of 1.09 m and a median turning angle of 39° were found. With a median of 89°, typical turning angles were considerably larger for turns-on-the-spot, which accounted for roughly a quarter of the recognised turns and often started from a standstill. These results suggest that a frequent pattern in daily wheelchair usage is to initiate movement with an orienting turn-on-the-spot, and cover distances with short, straightforward sections while adjusting direction in small and tight moving turns. As large bends often require simultaneous pushing and breaking, this is, perhaps, the result of users intuitively optimising energy efficiency, but more research is needed to understand how the design of the assistive devices implicitly directs users’ movement.
Highlights
According to the World Health Organisation, approximately 1% of the population with musculoskeletal impairments or disabilities, or worldwide more than 65 million people rely on a wheelchair for mobility (WHO, 2008)
Wheelchairs generally use four independent wheels and are push-rim controlled, meaning that hand-rims on the large rear wheels act as the interface for propelling and navigating the system: pushing forward on both sides simultaneously results in a forward motion, while braking on one side causes a turn to the respective direction
Individuals who have relied on a manual wheelchair for mobility for a duration of at least 6 months before the measurements were included in this study
Summary
According to the World Health Organisation, approximately 1% of the population with musculoskeletal impairments or disabilities, or worldwide more than 65 million people rely on a wheelchair for mobility (WHO, 2008). The same report highlights the critical role of an adequate assistive device for people with disabilities to become mobile, participate fully and, above all, remain healthy, which emphasises the multifaceted relationship between the wheelchair and the manifold activities users engage in. While wheelchairs are central to users’ independence, opportunities, and health, almost 90% are surprisingly simple, mechanical devices (van der Woude et al, 2001). Offering great flexibility and direct visual, proprioceptive and kinaesthetic feedback (van der Woude et al, 2006), such a configuration has been described to render wheelchair ambulation a challenging, frustrating and hugely inefficient process (Reid et al, 1990; Lee Kirby et al, 1999) that requires the constant use of both hands, a specific set of skills and good coordination of the upper extremities. Wheelchair users are often required to take a detour to avoid steps or, on a more fine-grained level, might find themselves adapting to topographical features, as even slightly uneven surfaces cause “veering off” in conventional wheelchair designs (Storch, 2015)
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