Page 18 - Mobility Management, October 2018

ATP Series
Setting Up for Success
level — is ‘You need to fit the chair like a ski boot.’ It has to be an extension [of the person]. You don’t want slop with your foot to your ski boot; you’re not going to turn effectively. That’s one of the best lessons I’ve learned from Brad about not going too wide [with the seat] and how the chair is an extension of your body. Trunk rotation causes the chair to move, if your hips aren’t slopping around in your chair.”
Weight Distribution: The Best Equation
Another critical aspect to successful self propulsion is the effi- cient distribution of body weight, which can affect how easily and effectively the wheelchair can be propelled.
“I think I’m using a little more aggressive center of gravity,” Anderson said of his setup, “because as I’m getting older, I can’t sit up as straight as I used to. So I keep the chair very light on the front. I try to run 80 percent of my weight over the rear wheels, and I do that so the chair’s very maneuverable. I’m not front loading the casters. I actually bought pads that are used for balancing cars to balance the weight of the chair so there’s 75 to 80 percent of my weight over the rear wheels.”
Anderson emphasized that such fine-tuning — even involving what seem to be very minimal adjustments — can make an enormous difference.
“If there is an audience that benefits from really fine-tuning the chair, it’s individuals that have upper-body weakness, whether
If there is an audience that benefits from really fine-tuning the chair, it’s individuals that have upper-body weakness, whether it’s in their arms or in their trunk — Josh Anderson
it’s just in their arms or in their trunk. Calibrating to that fine detail, a quarter of an inch forward or rearward for the center of gravity, is a big deal. It’s only a small percentage of weight differ- ence, transferring weight front to rear, but you’re talking about somebody who’s got compromised strength. If that front end is just a little bit lighter but still stable enough that I don’t feel I’m going to flip over backwards, then it makes a huge difference
in my ability to turn the chair. It makes a big difference that I don’t need to have camber, so I can fit through a really narrow doorway if I’m in Europe or in Asia in particular.”
“A rule of thumb,” Black said, “would be that 80 percent of
the weight be over those axles. When you put weight over the axle, you create better wheel access. Any time I move that wheel further behind me, it starts putting more forces on the front of the chair, and when the front of the chair has more forces and is front loaded, that’s when we create problems with people flipping forward. It stops the rolling dynamics of the product, and it’s unsafe.
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“When people start having problems leaning forward, they actually lose a lot of rolling dynamics, so they tend to stay back in their chair. They tend to slide back into posterior pelvic tilt to create that length, so it also affects your seating and positioning. All of these things happen when you’re not balanced over that wheel.”
In the 1990s, Black recalled, “the trend was having these short chairs, short wheelbases, so you had a shorter turning radius. But we found that your only room for defense is to move your wheels back, which takes the wheels away from you and creates more bad postures of people sliding into posterior pelvic tilt. We figured out that when you start balancing that wheel over the top of the body, what happens is now it doesn’t matter how long your chair is. If I can move my wheel 3" forward, I can grow the front of my chair 3" more. For every inch, you take forces off that front end. That’s a good thing.”
Like Anderson, Black also believes in balancing a wheelchair the way a racecar is balanced.
“The closer you can get the chair’s center of mass to the user’s center of mass, the more successes you’re going to have,” he said. “Then when you extend that wheelbase to create that stability, it’s really going to make you more efficient. So the trend now is to have longer chairs in the front, moving that wheel underneath you to create a more efficient rolling dynamic for a product.
“The most important thing for any manual chair is the fit of the product. The wheel access, the balance and stability create a better-performing product. When you get injured, the first year that you’re in a chair, you’re going to slide into balance. So you might as well create balance off the bat. If you can create balance for somebody, you’re going to fix a lot of seating needs.”
Hand Placement: Optimizing Each Push
Efficient propulsion also depends on the interaction between the client’s hands and the chair’s handrims. Wheelchair users with quadriplegia might be unable to grip a handrim in the same way that someone with paraplegia can.
“My handrims are a big deal,” Anderson said. “I use Q-Grips, Neoprene-coated handrims. They’re not vinyl or plastic, and they’re much more tactile. As somebody who pushes off of fric- tion, I think they’re fantastic. I get a great deal of friction from the handrims.”
Anderson said the Neoprene coating doesn’t build up heat the way vinyl can, particularly when going downhill. “When they get wet, I still have good tactile feel to them; vinyl just becomes like glass. Plus, durability is important. I literally change chairs and keep the same wheels and handrims because my mind has gotten used to every little nick and scratch in the Neoprene, yet they don’t get damaged to where they’re unusable.”
“For somebody who has weakness and limited hand func- tion,” Black said, “the most important thing is to get that wheel even more aggressive and in the right position early on in their disability so they can get the wheel to start rotating. If you can get the wheel to start rotating, then you settle into your balance.”
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