Focus on Ultralights

What Camber Can Do for Performance

Chuck Aoki competing at the Tokyo Paralympic Games

CHUCK AOKI: SHUTTERSTOCK/MARCO CICCOLELLA

Significant camber is clearly visible in the sports chair used by Chuck Aoki, a three-time United States Paralympian in wheelchair rugby, seen here competing at the Tokyo Paralympic Games last year.

Even sports fans with little understanding of ultralightweight wheelchair setup will immediately notice that the rear wheels of chairs used for rugby, basketball or tennis look very different than the wheels on everyday manual wheelchairs.

They’re seeing camber, what United Spinal Association defines as “an angling that brings the top of the wheels closer to each other” (spinalcord.org). With camber applied, a chair’s rear wheels are no longer perpendicular to the ground.

Camber can offer many functional benefits… but as with all wheelchair setup choices, adding camber to a system is a matter of careful balance.

Less Energy & Effort Expended

Lauren Rosen, PT, MPT, MSMS, ATP/SMS, is the Program Coordinator for the Motion Analysis Center at St. Joseph’s Children’s Hospital of Tampa, Fla.

“It’s the angle between the top of the wheel and the bottom of the wheel,” Rosen said, in explaining camber. “Camber helps with stability, and it helps with turns. That’s why when you see the sports chairs — tennis, basketball, rugby — they all have a huge amount of camber in them. Because that makes you super stable, and that makes you turn on a dime. Those are two things you need for playing all of those sports, especially basketball and rugby, where there’s chair-to-chair contact.”

But wheelchair stability is crucial to efficiency and function, even if your clients aren’t aiming to compete in the Paralympics.

“It makes the chair feel more stable laterally,” Rosen said. “It’s not going to stop fore/aft tipping; that’s about center of gravity and casters, etc. But camber makes the chair more stable laterally, so if I need to pick something up off the ground or reach to the side, it makes my chair more stable.”

Camber also makes turning the wheelchair a more effortless endeavor. “It puts less of the tire in contact with the ground, so it turns easier,” Rosen said.

How Much Camber Is Ideal?

So if adding camber to a system makes the wheelchair easier to turn and also makes it laterally more stable, what’s the down side?

Well, splaying the rear wheels outward can make a wheelchair substantially wider. The more camber it has, the wider the chair gets.

Camber is measured in degrees, and Rosen pointed out, “[In sports chairs], it’s like 15° or 20°. It’s a significant amount. For a lot of those guys and girls, they have to take at least one if not both wheels off to get through a door.

“That’s why you see a lot of them bringing their day chair and their rugby chair, because that rugby chair won’t go everywhere. That’s why they don’t leave their day chair at home and just travel in the rugby chair, because it’s ridiculous to try to make it through doors in something with that much camber.”

Larger amounts of camber can interfere with accessibility. Smaller amounts of camber, though, can offer multiple benefits without causing doorway problems.

“The only reason I would ever give somebody a chair with 0° camber is if I’m worried about them getting through a door — if they’re wide and their chair is wide, and I’m worried about door access,” Rosen said. Basically, everybody else she sets up in her clinic “gets 2° to 4° of camber because the chair rolls better. The wheels are closer to your body, so you have better wheel access. It just makes for a more stable base.”

Such modest amounts of camber, Rosen added, are not readily noticeable, unless you know what to look for. “With 2° to 4° of camber — you really don’t see it. It’s not obvious that there’s camber in the wheels, unless you’re actually specifically looking. Anybody who would look at the chair would not think there was camber at 2° or 4°.

“But if you push a chair with 0°, 2°, and 4° of camber, you’d feel the difference.”

Because Everything Matters in Manual Wheelchairs

Camber can make those rear wheels easier to reach, a real benefit especially to very young ultralightweight wheelchair users with shorter arms.

“If I really know there’s never going to be a door access issue because you’re super small, I’ll go with 4° [of camber], because you’ll come back and tell me it’s easier to push,” Rosen said. “It gets the wheel a little closer to him up at the top so he’s not having to abduct so much, and it’s an easier turn. If I make [an adult wheelchair] just a smidgen too wide, you can’t get into your house. In kids’ [wheelchairs], I don’t have to think about that.”

Despite its great potential impact, Rosen added that camber is just one element in the science and art of optimally setting up an ultralightweight wheelchair, whether it’s for a world-class athlete, a weekend warrior, or a giggling preschooler whose main goal is keeping up with siblings.

“Some of it being easier to push is [due to] the rest of my setup,” she said.

“Everything matters on a manual chair. I can put your center of gravity in a great place, but if I give you no camber, you’re going to feel like it’s hard to push. If I put your seat depth in the wrong place and make you sit uncomfortably, having perfect camber doesn’t make a difference.

“I can give you the lightest-weight chair on the market, whatever that is today, and if I don’t set up everything right, it can feel just as bad as pushing a steel chair.”

This article originally appeared in the Jan/Feb 2022 issue of Mobility Management.

About the Author

Laurie Watanabe is the editor of Mobility Management. She can be reached at lwatanabe@1105media.com.

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