What We Will Be Covering
- Alternate Drive Mechanisms
- Providing assist for self-propulsion of a manual wheelchair
- Lever drives
- Arm-crank drives
- Geared hubs
- Reverse pushrim drives
- Push rim-activated power assist drives
We are going to be focusing on power add on options as well as a few other options to help optimize self-propulsion for people who are using manual wheelchairs. This is a really exciting cutting-edge area it is helpful to you and to the clients whom you serve. We are going to talk about a category of seating and mobility equipment called alternative or alternate drive mechanisms. This is not a very consistent term. You might hear a lot of different terminology around this area, but this is the term that is utilized in our latest text on seating and wheeled mobility. We are going to talk about how these alternate drive mechanisms provide assistance for self-propulsion of a manual chair using either a lever drive, an arm-crank drive, geared hubs, a reverse pushrim drive, or those PAPAWs, push rim-activated power assist drives.
SMS Series
- This is part of a series of webinars designed to prepare the participant for the Seating and Mobility Specialist examination
- And… develop more advanced seating and wheeled mobility skills
The Seating and Mobility Specialist certification is offered through RESNA. They have two certifications, the ATP, or Assistive Technology Professional, as well as the SMS or Seating and Mobility Specialist. If you are pursuing your Seating and Mobility Specialist certification, you have to already have received your ATP. We do have a series of courses on occupationaltherapy.com designed to prepare you for that particular certification, and again this series is designed to provide more advanced information in preparation for the SMS. But, regardless of whether you are interested in one of those certifications, I really hope this does help you develop more advanced seating and wheeled mobility skills because that helps any of us do our job even better.
Mobility Hierarchy
There is a mobility hierarchy as seen in Figure 1.
Figure 1. Mobility hierarchy.
Depending on the client, we may start with a more dependent manual wheelchair, something that a caregiver pushes for the client. The client is unable to move on their own. From there, we try to determine if a client can be independent with a manual chair and propel it on their own. One of the courses in this series talks about ultralight manual wheelchairs which are specifically designed to optimize self-propulsion. We also have alternate drive mechanisms. These are designed to improve the efficiency of a manual wheelchair for self-propulsion. Finally, we have power wheelchair options for someone who cannot use any of the other options in order to achieve independent mobility.
Alternative Drive Mechanisms
- Goal:
- Improved mechanical efficiency
- Maintain the transportability, versatility, and aesthetics of a manual wheelchair
(DiGiovine & Berner, 2018)
Our goal with these options is to improve the mechanical efficiency of the system. Manual wheelchairs have been around for quite a while now, but they have not really changed that much. If we look at really early models, the seating and wheel position may have changed, but the overall design has remained the same. The seated person grasps a wheel and pushes it forward to make the wheelchair move. We have had design changes like demonstrated in the ultralights to optimize that propulsion but some of the strategies we're going to talk about today are an attempt to change the efficiency of how this wheelchair works. Can we give this a mechanical advantage so the user has to exert less effort, and again as a result is more efficient in their propulsion?
Figure 2. Example of an alternative drive mechanism (NuDrive Air).
With this option, we can maintain the ability of the client or caregivers to transport this device. It gives a little more flexibility to the user. Additionally, many people are going to prefer the aesthetics of their manual chair as opposed to a power wheelchair.
Who Is This Appropriate For?
- It is well documented that people who self-propel a manual wheelchair, even an appropriately configured ultralightweight manual wheelchair (MWC), are prone to:
- Repetitive stress injuries
- Shoulders, wrists
- Pain
- Repetitive stress injuries
- This can worsen to the point that mobility is compromised.
It is well documented that people who self-propel a manual wheelchair, even if we have set it up as well as we can, that people who self-propel are prone to pain and repetitive stress injuries, particularly of the shoulders and wrists.
Figure 3. Example of an ultralight wheelchair (Quickie Q7).
We are all aging including people with a disability. This is really becoming a problem. Many years ago, if someone sustained a spinal cord injury, for example, their average lifespan was only six years. Now people who have sustained a spinal cord injury may live close to a typical lifespan, and this person may be propelling for decades. It is very important that we keep this in mind that even if this person is doing just fine with their self-propulsion right now. They are at high risk of these repetitive stress injuries and pain, and this can worsen to a point where this person can no longer use their manual chair at all. If there are some things we can do preventatively so this person can stay with manual mobility as long as possible, then that is part of our job. Who could benefit from these alternative options?
- A person who can self-propel, but:
- Has upper extremity injury and/or pain
- Has decreased cardiopulmonary function
- Has decreased strength and endurance
- Is less efficient in mobility secondary to aging with a disability or aging in general
- Is a long-term MWC user who may have lost efficiency
- Is an MWC user who cannot manage slopes, varied terrain and/or long-distances without assistance
These additional options to increase the efficiency of a chair are designed for a person who can self-propel but perhaps has upper extremity injury and/or pain or is at high risk for that. It might be a little harder to convince someone who is successful and not experiencing injury or pain right now to consider these options. It may also be difficult to convince a funding source to consider these options unless there is already an existing issue. But, if this person has an upper extremity injury, pain, or decreased cardiopulmonary function, this could be a great justification for this equipment. They may say, "I can only push so far so long with so much effort before it just takes too much of a cardiovascular toll on my body. Or, "My heart and breathing rates raise up too high." This person may simply have decreased strength and endurance. A person who is less efficient in mobility secondary to aging with a disability or aging, in general, would be another category. They do not have the same strength and endurance. Some of our clients may have been very efficient with their mobility in the past, but they are now getting older and aging with a disability. They are not doing as good a job as they used to in terms of overall time, distance, and effort. It might be a manual wheelchair user who does fairly well over smooth level surfaces but is now having difficulty with slopes, varied terrain, and/or long distances without help. And perhaps, this person is propelling through the community and accessing ramps. They might have difficulty with having enough strength to get up a ramp and preventing themselves from rolling back down. They also might have difficulty slowing themselves so they do not go barreling down the ramp when they exit the building. Longer distances or bumpy roads can be too challenging as well.
Non-powered Options
- Geared systems
- Lever systems
- Arm-crank systems
We have several different non-powered options, as much as the title of our course today is power add on, we are talking in general about alternate drive mechanisms and that includes non-powered and powered options. Let's start with these, and this includes geared systems, lever systems, and arm-crank systems.
Geared Systems
- Gear system between the handrim and the wheel
- Geared hubs
- Reverse pushrim drives
A gear system sits between the handrim and the wheel, and consists of either a geared hub or something called a reverse pushrim drive.
