Hills, L.M.; (2011) Every push matters. Masters thesis , UCL (University College London).

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Abstract

Rear axle adjustment has an effect on the stability of a user’s wheelchair. On delivery, a wheelchair’s axle is usually set in its most rearward and most stable position, with guidelines and cautionary advice on its forward adjustment. This is contrary to current clinical recommendations, which advise practitioners to; ‘adjust the rear axle as far forwards as possible without compromising the stability of the user’ (Paralyzed Veterans of America 2005). Thus, clinicians adjust the rear axle forward incrementally, working with the wheelchair user, in order to maintain safety and maximise performance. Theoretically, a more forward axle position has been shown to decrease rolling resistance by reducing the weight transferred through the front castors (Brubaker 1986). Therefore, most clinicians assume that moving the rear axle forward will make the wheelchair significantly easier to propel. This study was undertaken to investigate if this is true in straight line pushing tasks; propulsion on lino, propulsion on artificial turf (Astro), ascending a 1:12 ramp and ascending a 3” kerb. Following rear axle adjustment from the most stable position to the least stable position, castor and pushrim forces were recorded during each propulsion cycle. Tasks were performed by a group of eight experienced manual wheelchair users, all of whom had a spinal cord injury below the level of T1. To assist in the clinical application of the data a ‘Performance Capacity Ratio’ developed by Nicholson and colleagues (Nicholson,G et al. 2006), was used. This investigated the relationship between a person’s functional performance and their capacity to perform mobility tasks when the Rear Axle Position (RAP) was adjusted. This was expressed as a percentage, to gauge whether a person exceeds their ‘comfort zone’ when performing different pushing tasks. The ‘comfort zone’ was defined as 80% of the maximum voluntary push force a person was capable of. The study has shown that RAP does affect capacity to perform and that subjects were more likely to exceed their comfort zone when performing tasks in a more stable set up. It concludes that terrain impacts on capacity to perform, as wheelchair users are more likely to reach and exceed their capacity on terrain which imposes the greatest resistance. The synchronisation of the pushrim and castor force measurements allowed a detailed examination of how the forces changed during a typical propulsion stroke, and how this related to castor loading. It was found that castor loading was significantly affected by the Rear Axle Position (RAP), but this did not translate directly into differences in propulsion forces required to overcome increased rolling resistance for all tasks, except the kerb.

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