A look at the why and how of power add-on units

Published: 13 July 2023
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Written by
Bianca Brady
Bachelor of Applied Science (Occupational Therapy)
Astris PME Clinical Education Coordinator

For manual wheelchair users, the benefits of using a power add-on unit go beyond preservation of shoulder health or facilitating long distance propulsion. There are many secondary benefits of this set up which additionally preserve and aim to maintain independence in other areas of daily life and wellbeing, too.

A systematic review in 2016, explored factors influencing participation of wheelchair users in their social and community environments. The scope to change outcomes by addressing some factors or accommodating for others was also identified. When looking at the “modifiable” factors, there is a wide range where the use of a power add-on unit can improve participation and access. Some examples include:

  • being able to provide effective propulsion in the presence of reduced hand grip strength.
  • managing energy expenditure by augmenting or replacing the need for manual propulsion.
  • managing fear of risk /risk of shoulder injury with sustained and repetitive manual propulsion.
  • Reducing dependence on others by providing opportunity for independent mobility.

These primary benefits then promote greater opportunity for participation and access and many secondary benefits can be gained. Particularly contributing to being engaged with the community, motivation to access community environments and preservation of shoulder health for independence in daily living tasks and overall, helping to achieve positive life outcomes.

What about exercise and fitness?

Occasionally, a question is raised on using a power add-on unit and removing the opportunity for long distance self-propelling, and with it, the perceived potential benefits on cardiovascular and respiratory function. There is little evidence outlining the impact on cardiovascular or respiratory function when comparing manual self-propelling against the use of a power add-on unit. There is no statistically significant data that shows using a power add-on unit negatively impacts a user in this way when compared to self-propelling, however further research continues to be recommended. What is available though, is extensive research on shoulder health for manual wheelchair users who self-propel, and the risks associated with sustained, repetitive manual propulsion. There is a high prevalence (30-70%) of manual wheelchair users with a spinal cord injury sustaining a repetitive strain injury in their shoulder (Gil-Agudi et al, 2014).  It is also important to note that propulsion biomechanics does not differ significantly between athletic users (those with significantly greater levels and intensity or physical activity per week) and non-athletic users in their daily manual wheelchair (S.J, Briley, et al, 2020).

If weighing up the perceived potential benefits of long-distance self-propelling against use of a power add-on unit, consider the known risk to shoulder health and the complications that can arise from an injury impacting function and quality of life.

Don’t forget to consider the frame and system set up

It is also important to note that using a power add-on unit is only one out of five ways to address the need to preserve shoulder health and function for manual wheelchair users. Attention and consideration of the whole system should be reviewed and using a power add-on unit on a sub-optimal system should be avoided. Some power add-on units significantly increase the demands on the frame. Check the strength, durability and vibration dampening properties against the chosen unit and environment/s of use. Careful consideration of wheelchair frame components can also promote efficiency of the whole system or cause barriers and sub-optimal use.

Where to start to narrow down the options

With multiple options currently available for consideration, how do you start to identify a suitable unit? Power adds on units can be broken down into 2 categories:

  1. those that offer partial assistance (augmenting the user’s manual propulsion) such as rear mount (Alber Smoov, SmartDrive, Klaxon Twist), hand-rim activated (Alber E-Motion) and front mount with no handlebar (Klaxon Twist).
  2. those that provide full assistance (removing the need for manual propulsion), such as joystick conversion (Alber E-Fix, Todo, i-Xpress) and front mount with handlebar (Klaxon Klick or Twist).

It is a good idea to consider this first, after evaluations and discussions have occurred between the clinician and the user.  This collaborative approach can help ensure the needs and capabilities of the user along with the parameters of the unit are suited.  It will also look into how this set up will achieve the desired goals and outcomes in the intended environment/s of use. For example, does the front castor need to be lifted off the ground to overcome barriers in the community.

Following this, the type of set up can be narrowed down. Most units will offer one type of set up, either rear mount, hand rim activated, joystick control, or front mount with handlebar and one which offers a combination depending on the goals and intended environments of use.

A note on transitioning from one environment to another with a power add-on unit

Considering if a manual wheelchair user is changing environments throughout the day and if power is needed in each environment, could highlight the need for a power add-on unit that offers multiple set ups. For example, consider the need to access outdoor community areas and then office spaces, places of learning, shopping centres, or even air travel and use on a trip. There is also evidence to support an emerging trend for user transitioning from one environment to another and finding themselves limited when the power add-on unit is not suitable for use in the new environment. Funding bodies will often only approve one type of power add-on unit. In looking to optimise a user’s engagement and participation, having an option that can cross over from one environment to another can help achieve this. With careful consideration, there is significant potential to address multiple factors influencing participation to optimise someone's life outcomes.

References:

  • Briley, S.J.,  Vegter, R. J. K., Tolfrey, V. L., & Mason, B. S. (2020). Propulsion biomechanics do not differ between athletic and nonathletic manual wheelchair users in their daily wheelchairs. Journal of Biomechanics, 104, 109725–109725. https://doi.org/10.1016/j.jbiomech.2020.109725
  • Dhaliwal, Manveer & Janssen, Sara & Kuik, Kylie & Giesbrecht, Edward. (2022). Choosing a Power Assist Device. 10.13140/RG.2.2.32593.45924.
  • Khalili, Jonathan, C., Hocking, N., Van Der Loos, M., Mortenson, B., & Borisoff, J. F. (2022). Perception of autonomy among people who use wheeled mobility assistive devices: Dependence on the type of wheeled assistive technology. Assistive Technology, 34(6), 725–733. https://doi.org/10.1080/10400435.2021.1934611
  • Gil-Agudo, Á., Solís-Mozos, M., Crespo-Ruiz, B., Del-Ama Eng, A. J., Pérez-Rizo, E., Segura-Fragoso, A., & Jiménez-Díaz, F. (2014).Echographic and kinetic changes in the shoulder joint after manual wheelchair propulsion under two different workload settings. Frontiers in bioengineering and biotechnology, 2, 77. https://doi-org.ezproxy.uws.edu.au/10.3389/fbioe.2014.00077
  • Smith, E., Sakakibara, B. M., & Miller, W. C. (2016). A review of factors influencing participation in social and community activities for wheelchair users. Disability and Rehabilitation: Assistive Technology, 11(5), 361–374. https://doi.org/10.3109/17483107.2014.989420
  • Waugh, K., Crane, B., Johnson Taylor, S., Cwiertnia, S., Saftler Savage, F., Davis, K., Brown, L., & Christie, S. (2013). Glossary of wheelchair terms - NCART. NCART. https://www.ncart.us/uploads/userfiles/files/documents/glossary-of-wheelchair-terms.pdf

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