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What Matters When Scripting a Manual Wheelchair?

Scripting ultra-lightweight manual chairs can be a challenge – what frame material do you choose? What frame design? And then there are all the measurements that you need to get…

When first learning to script manual wheelchairs, it can be hard to know what to focus on, however a recently published article by Lin and Sprigle can help give us some direction.


TiLite ZR wheelchair with purple anodised accents

Lin and Sprigle’s study researched the operator and wheelchair factors on wheelchair propulsion effort, taking a group of 36 people and exploring which factors influenced their propulsion effort over a modified figure eight course.

Lin and Sprigle were keen to explore which factors really matter to everyday wheelchair users. The modified figure eight course was compromised of both tile and carpet surfaces, and thought to be more reflective of the stopping, starting and turning that wheelchair users do in their daily lives. The study group was made up of 23 existing manual wheelchair users who completed the study in their own chairs, and 13 able bodied people who were randomly assigned a pre-configured chair.

Both operator and wheelchair factors were explored. Operator factors included aerobic capacity, muscle strength, maximum propulsion strength and their shoulder position relative to the axle. Wheelchair factors included the mass of the chair, the weight distribution over the chair – given as a percentage weight over the rear wheel, and system friction. 

These factors were assessed over two separate sessions and included five minutes of propelling around the modified figure eight course. The results from these were then statistically analysed, and which factors that influenced propulsion effort identified.   

The results of this study showed that shoulder position of the user relative to the axle, and weight distribution of the chair had the largest influence on propulsion effort, particularly on the tiled surface. So, in other words, where the axle position was placed and where this position was relative to the user’s shoulders mattered.  And in this case, it mattered more than the overall weight of the wheelchair and the fitness of the user.

This result obviously applies to these particular testing conditions. Under different conditions, factors such as the user’s strength and fitness may have more influence.  Of note, the influence of weight distribution and axle position was less pronounced when the person was propelling on carpet, where the carpet itself was a significant factor in the person’s propelling efficiency. The chairs used in the study had a variety of castors and rear wheels with different amounts of friction produced which also produced some impact when propelling on carpet but was not as significant.

The weight distribution on a chair is related to the axle position, with a more forward axle position resulting in more weight over the rear wheels, and vice versa – where the influence of weight distribution on turning resistance is most noticeable when too much weight is towards the front of the chair.

Man in TiLite ZR wheelchair with ROHO Agility backrest on the backdrop of a harbour

The axle position relative to the shoulder is crucial for maximising the ergonomics of the person self-propelling, with both the axle position relative to the back posts and the height relative to the user being important. Establishing where to set the axle position for new users is often challenging. A more forward axle position results in a chair that is more ‘tippy’ which can be difficult for a new user to manage, while a more rearward axle position can result in a chair that feels ‘heavy’ to push and turn.

This is where adjustable chairs are useful and the axle position can be changed as a user becomes more confident in using their chair, allowing the chair to be configured for optimal efficiency over time.

The seating used on the wheelchair can also contribute to the relative axle position. A change of cushion can change the user’s height relative to the wheel, while a change of back support, or changing between a solid back support and an upholstery back (not to mention an upholstery back that becomes saggy with time) can change how far forward the axle sits.

Another factor that impacts on weight distribution on the chair is the body shape of the user itself – a person who has had both legs amputated above the knees will have no weight towards the front of the chair, while a person with oedematous legs may have more than usual. A bilateral above knee amputee can be challenging to set up as the chair needs to be stable, yet the rear wheel placed in a position to ensure efficient self-propelling. For this group, learning good wheelchair skills is important, while others may need anti-tips to ensure stability of the chair when using on uneven surfaces.

So, what is the one thing we need to get right when scripting a manual chair? The position of the axle – this can make a world of difference to the end user and how easy their chair is to manage. Not sure how to get this right? Consider starting with an adjustable chair and ask your local supplier or dealer with help to set it up. Then trial the chair in the places the person needs to use the chair to ensure that the set-up is just right.

Still wondering about the weight of the wheelchair? We’ll come back to this in a later blog!

A boy in a TiLite Pilot wheelchair

Reference

Jui-Te Lin & Stephen Sprigle (2020) The influence of operator and wheelchair factors on wheelchair propulsion effort, Disability and Rehabilitation: Assistive Technology, 15:3


Clinical Education Specialist Rachel Maher

Rachel Maher
Clinical Education Specialist

Rachel Maher graduated from the University of Otago in 2003 with a Bachelor of Physiotherapy, and a Post Graduate Diploma in Physiotherapy (Neurorehabilitation) in 2010. 

Rachel gained experience in inpatient rehabilitation and community Physiotherapy, before moving into a Child Development Service.

Rachel moved into a Wheelchair and Seating Outreach Advisor role at Enable New Zealand in 2014, complementing her clinical knowledge with experience in NZ Ministry of Health funding processes.

Rachel joined Permobil in June 2020, and is passionate about education and working collaboratively to achieve the best result for our end users.

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