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Once you recognize that the mobility outcomes produced by a person using a wheelchair is the result of the interactions of a Complex Adaptive System, the next step is to recognize the recurring patterns of behavior that are produced by the interactions of the system. When a distinct pattern repeats itself on a regular basis, it is known as a template or a system archetype. Due to the variability inherent to complex systems, they can create multiple archetypes (repeating patterns of behavior).
In terms of active manual wheelchairs, there are several distinct archetypes. These archetypes can be identified by the combination of the wheelchair user’s mobility outcome, wheelchair geometry, and the user’s seated posture. They are created by the cause and effect interactions of the wheelchair system.
The archetypes are not the result one any one particular factor in the system. Commonly grouped factors tend to result in a certain type of archetype. But this is not always the case, due to the influence of the other factors that make up the system. This is the hallmark of complex systems. There is no certainty of the exact outcome produced by the system.
These archetypes exist separate from judgements of “good” or “bad”. What is “good” for one person, may be “bad” for another or vice versa. Archetypes are identifiable patterns of behavior that arise from the system. They provide distinct examples of different outcomes from a complex system.
The following are three wheelchair system archetypes that I have identified in active manual wheelchair users:
Stability First – The primary goal (outcome) of the design of this system is to prevent the wheelchair user from falling in any direction, forwards, backwards, or sideways. Specific cause and effect interactions are:
Drive wheels mounted far rearward to increase the wheelchair’s backward stability.
Anti-tipping devices to prevent the wheelchair from tipping over backward.
High and reclined backrest to provide back support and to reduce the risk of the user’s upper body from falling forward.
Armrests and backrest side wings to increase trunk lateral stability.
Seatbelt to prevent the user from falling forward out of the wheelchair.
Due to the combined effect of the above, the wheelchair user typically has difficulty self-propelling the wheelchair on anything but flat and smooth surfaces. Therefore, this archetype commonly includes:
Push handles for an attendant.
Larger front casters for rolling over rough surfaces while being pushed, or from the user not being able to wheelie.
Power assist device.
The Stability First archetype results in a wheelchair user who is unlikely to fall in some manner or direction. Due to the setup of their wheelchair and other factors, they tend to have great difficulty propelling their wheelchairs on anything but smooth and level surfaces.
Stability First is more likely to be associated with higher levels of SCI injuries who have limited to no trunk control. Therefore, they are at a higher risk of trunk instability and falling. It is also associated with wheelchair users who perceive themselves, or are perceived by the medical community, as having a higher risk of falling. Having comfortable and supportive seating is also a main consideration.
Mobility First – Where the Stability First archetype exchanges mobility for stability and comfort, the Mobility First archetype sacrifices stability and comfort for maximum wheelchair mobility. The design of the Mobility First system is pretty much the opposite of Stability First.
Drive wheels mounted forward close to the users center of gravity to increase the wheelchair’s dynamic mobility.
No anti-tipping devices to enable on-demand wheelies.
Low backrest to provide full arm/shoulder/back mobility for propelling.
Vertical (not reclined) backrest to provide support for proper posture for propelling.
No armrests or backrest side wings to provide full access to the drive wheels.
No seatbelt to provide unrestrained body mobility.
Due to the combined effect of the above, the wheelchair user is typically able to independently self-propel on typical terrain. Therefore, this archetype commonly has:
No push handles.
Smaller front casters for less caster flutter at high speed and a more compact wheelchair design.
No power assist device.
The Mobility First archetype results in a wheelchair user who is at a higher risk of falling in some manner or direction. They tend to have minimal difficulty propelling their wheelchairs on typical terrain and are therefore comparatively mobile and active in their environment.
Mobility First is more likely to be associated with lower levels of SCI injuries and other people who have full or substantial volitional trunk control and stability. It is also associated with wheelchair users who accept the risk of inherent wheelchair instability for the gain of greater mobility.
Stability Slumping - This archetype has wide variability within it. It is described as having more mobility than Stability First and less than Mobility First. While also having less stability than Stability First and more stability than Mobility First. The wheelchair geometry/setup tends to be the middle ground between these two opposing archetypes.
The name, Stability Slumping, arises from the wheelchair user purposely, or unconsciously, sitting in a somewhat slumped posture to create more upper body stability. The slumping occurs as the wheelchair user moves their hips forward in the seat which causes their lower back to recline into the backrest. By moving their hips forward, the center of mass of the wheelchair is moved forward relative to the rear axle creating more backward stability (the wheelchair is less likely to flip over backward). In addition, the reclining position makes it less likely for the user’s trunk to fall forward.
As a result, the wheelchair user typically leans forward with their head and shoulders to compensate for their reclined lower back. The outcome is a forward head and rounded shoulders posture. The wheelchair user’s spine creates a C shape. They have posterior pelvic tilt.
This slumped position increases the user’s trunk static stability at the cost of poor posture and greatly reduced power generation for propelling. The greater the slumping, the greater the resulting stability, and the more reduction in propelling power.
Stability Slumping is the wheelchair user’s (sometimes unconscious) response to their trunk instability. Therefore, it is more likely to be seen in people with little to no voluntary trunk control. They feel more stable in this position, so they naturally assume it. Their specific wheelchair setup my also (unknowingly) encourage slumping.
The three mentioned wheelchair system archetypes are commonly observed in manual wheelchair users. As with all archetypes, they are not absolute descriptions, nor do these three archetypes describe all manual wheelchair users.
Studying each archetype represents an opportunity to better understand how the cause and effect interactions of the complex wheelchair system create different outcomes as the system variables change.