SCI Roundup: Ultralights & Propulsion
Putting the Push in Propulsion
When aiming for efficient ultralightweight propulsion, what ultimate
goals should be kept in mind? Long-term ability to self-propel? Improved daily functioning? Reduced risk of injury or pain?
David Boninger, Ph.D., VP of Out-Front, says the ultimate long-term
goals are “all of the above — meaning that each of the goals is critical. One
goal is to enable an individual to remain in a manual chair longer because he
or she remains able to self-propel. Another central goal is to reduce the risk of
pain and injury. If we can successfully reduce pain and injury, then we’ll be
assured of achieving another critical goal — improved daily functioning and
independence. These goals are closely related to one another: Improved daily
function and continued independence rests on minimizing pain and injury.”
Despite the large scope of the goals, Boninger adds that the formula for
achieving is less complicated.
“One key part of the formula is to reduce the stress and strain of each
push on the handrim,” he says.
Thousands of Times Per Day
“In any given day, a person propelling their chair pushes on their handrim
2,000 to 3,000 times,” Boninger says. “So, anything that improves that
interface — that makes the push less stressful — can make a huge difference…
2,000 to 3,000 times a day!”
An effective way to reduce the strain of propulsion is to significantly
reduce the number of pushes.
“This is achieved by using longer, smoother pushes on the handrim,
which will help to reduce push frequency and minimize forces,” Boninger
says. “Fewer pushes means less repetitive stress. This formula stems
directly from recommendations in the clinical practice guideline for the
Preservation of Upper Limb Function Following Spinal Cord Injury.”
Evaluating the Trade-Offs
Using ergonomic components can help tip the push/strain equation in
favor of consumers — but as is often the case with mobility systems, there
might be trade-offs to think about. For example, will changing components
add weight to the chair, thereby making it heavier to push? Will
new components make the chair wider, which could lead to maneuverability
or accessibility problems?
What give-and-take considerations need to be considered?
“When we think about aftermarket components that can impact
propulsion techniques and ultimately help us achieve the goals we
discussed earlier, we definitely want to be aware of what other aspects of
the chair are affected when these components are added,” Boninger says.
“With ergonomic handrims, for example, people are typically most interested
in whether or not there are any meaningful changes in the width
and weight of the chair.”
Fortunately, Boninger adds that today’s ergonomic handrims
frequently don’t add width to the chair, depending on consumer preference
and how the handrims and wheels are configured.
And when considering weight that ergonomic components can add,
Boninger says it’s important to consider the overall picture.
“It is really important to keep in mind that the small changes in weight
are more than off set by the benefits of ergonomic handrims,” he notes.
In the case of his own Out-Front products, “These handrims have been
heavily researched and tested, and time and time again, we find that the
ergonomic benefits — like not needing to grip the rim as hard and not
needing to grab the tire — far outweigh any small differences in weight.”
Boninger adds that using ergonomic pushrims aren’t the only factor in
improving propulsion, but can be part of an equation that can make a big
“When it comes to efficient propulsion, many factors come into play, but
the primary interface or focal point for propulsion is the hand meeting the
handrim,” he says. “So, an ergonomic handrim is certainly a key component
capable of making a huge difference in propulsion efficiency. But
it’s not just the handrim — it’s also proper posture and positioning, so
that one’s arms are in the right position to most eff ectively achieve a long,
smooth push on the handrim. When the proper ingredients are in place —
an ergonomic handrim, proper positioning, an ultralight, well-fitted chair
— then the difference can be huge, and it can light up the face of someone
experiencing these ingredients for the first time.”
This article originally appeared in the June 2012 issue of Mobility Management.