With arms churning, shoulders lurching, and wrists twisting for the essential grip on the handrim, it’s easy to see why manual wheelchair users have high rates of carpal tunnel syndrome and shoulder injuries. Only it’s not so easy to see.

Manual wheelchair users can propel their wheels hundreds of rotations just to ambulate along a city block, and sometimes quite rapidly when it comes to, for example, crossing a busy street – a fact that makes measuring those movements difficult. It’s a challenge that is being answered by Beckman Institute faculty member Jacob Sosnoff.  

Thanks to the Americans with Disabilities Act (ADA) and a societal change in how they are viewed, people in wheelchairs have greater access to buildings, educational opportunities, and many other things life has to offer than they did 20 or even 10 years ago. What they haven’t had is science that takes a detailed look at the motion required to propel a manual wheelchair.

Sosnoff is changing that. Last year, he set up an experiment that used the motion capture suite at Beckman’s Illinois Simulator Laboratory (ISL) to glean information on the repetitive movements of manual wheelchair users in a way that’s never been done before.

The motion capture technology is the same as that used to create digital movie characters like Gollum from Lord of the Rings. Markers placed at certain points of the body were recorded by the suite’s ten cameras that can capture images at thousands of frames per second; the digital information from those points is then turned into a finely detailed graphic representation of a wheelchair user’s propulsion motion in the form of hundreds of digital, overlapping ellipses.

“An observer in real time can’t see motion irregularities and the reason you can’t see them is that it happens only once in maybe a hundred revolutions and involves very subtle variances in motion,” ISL director Hank Kaczmarski said. “Our motion capture system is capturing images at a thousand frames a second; researchers can then take the data offline and parse out these subtle differences.”

The initial focus of this project was to see if the technology and experimental set-up in the motion capture suite were effective. The answer was yes, and the results included a finding that showed differences in the propulsion patterns of experienced and novice wheelchair users.

Sosnoff, who is an Assistant Professor in the Department of Kinesiology and Community Health at the University of Illinois, collaborated on the wheelchair propulsion study with Elizabeth Hsiao-Wecksler from the Department of Mechanical Science and Engineering. A member of Beckman’s Human Perception and Performance group, Sosnoff’s research interests include aging, disability, mobility, and perceptual-motor variability.

“Predominately I’m trying to understand how we control our movements, literally how our brain controls our movements,” Sosnoff said. “I come from a behavioral standpoint. I look at behaviors to try and understand how we move, and within that I am very interested in motor variability.”

Sosnoff said that every time people do a common or repetitive movement, such as writing their name, each time there are slight fluctuations in that movement.

“What I’ve been looking at most recently is to try and see if those fluctuations in the movement, from fine movements like writing, to more complex movements like wheelchair propulsion, and see if that variability is indicative of some dysfunction,” Sosnoff said. “The analogy I like to give, especially for the wheelchair work, is that the amount of variability we see in movement can be related to muscular-skeletal pain. The idea with the study I’m doing at ISL is to see if variability in wheelchair propulsion is related to shoulder pain.”  

Sosnoff said his current research directions are based on a decision he made a few years ago to focus less on the theoretical and more on work that could translate into helping people.

“I started off from a theoretical motor control sense,” Sosnoff said. “It gets to the point where there are probably a dozen people in the world doing the same type of work that I was doing and understood the theoretical application I was doing it in. I sort of got tired taking to myself so I wanted to apply this knowledge, this theoretical training, to a real-world problem.”

That decision – along with his personal background and home department setting – naturally led Sosnoff into doing studies on the physical mechanics of wheelchair users. A concern for the struggles people with disabilities face on an everyday is ingrained in Sosnoff, even though he is not disabled and chose a career path in academia and research.     

“Related to this, my family business growing up was manufacturing artificial limbs and braces so I’ve always been around people with mobility disabilities,” Sosnoff said. “I was around this my whole life and, due to interacting with wheelchair athletes on campus, started doing some reading.

“I realized that no one had looked at variability in wheelchair propulsion, which essentially was the green light. My grandfather likes to tell the story about how he used to carve prosthetics out of wood and now you literally scan the stump and then it gets made somewhere and shipped out. So the technology has changed.”

But the issues facing people in wheelchairs haven’t. Studies have shown that shoulder injuries and carpal tunnel syndrome for manual wheelchair users are common.

“Upwards of 60 to 70 percent of manual wheelchair users develop shoulder pain,” Sosnoff said. “For individuals who walk, if we hurt our shoulder, we essentially stop the activity, whether it’s swimming, racquetball, whatever, that caused it. If someone is depending on their wheelchair for mobility, they are not fortunate enough to be able to stop that movement.”

As with any research, the first step is to understand the problem at its most basic element, and doing that required ISL’s motion capture technology and movement analysis techniques developed by Hsiao-Wecksler for studying human gait that Sosnoff applied to the wheelchair study.

For the experiment, 23 markers were placed on the arms and upper body of the test subjects, and on the stationary wheelchair, which sat on a roller that allowed test subjects to rotate the wheels. The test subjects, which included those with no experience using a wheelchair, and very experienced users, pushed for a couple of minutes on the passive wheelchair and their movements were recorded in order to look at the variability of that repetitive push motion. The researchers also analyzed differences in the experienced and inexperienced groups involving those with and those without shoulder pain.

“The idea is that individuals with pain will have different variability profiles than individuals without pain,” Sosnoff said. “Of course that doesn’t show causality. We don’t know that the change in variability in people with and without pain caused the pain, but it gives us evidence to go look at it further.  

“Coming from a kinesiology motor control perspective, I envision that there are good ways to move and bad ways to move. That is essentially what this project is trying to look at: the variability in wheelchair propulsion; is that related to shoulder pain?”

One obvious difference shown by the subjects in Sosnoff’s experiment was between the ellipse of an experienced versus a novice wheelchair user. The digital images showed a variation from the motion for novice users when it came to the top of the rotation – the place where the hands were readjusted on the handrim for the next revolution.

  The idea for the wheelchair study also has roots in Sosnoff’s home college of Applied Health Sciences, which also includes the Division of Disability Resources and Educational Services that supports people with disabilities on campus. It is a setting that allowed him to interact with students with disabilities, including wheelchair athletes, and learn about the challenges they face.  

“We intermingled and we had some students who were on the wheelchair team,” Sosnoff said. “It just sort of happened. It was the right place at the right time. I became aware of the shoulder pain issue and, doing some research, I found that no one had looked at it from the perspective that I take. I saw the door wide open so to speak.”

It is research that, Sosnoff hopes, will lead to solutions for the problem of manual wheelchair user injuries.

“I was trained as a theoretical motor control person and one of the reasons I got into this project, in addition to being one of the few in the world and not talking to anyone about my research, was I realized that with all of this training and this work I wasn’t necessarily helping anyone,” Sosnoff said. “So applying these theories to actually help somebody is definitely a personal goal, but also an educational goal. Would these interventions work? That’s my hope. My goal is to do random clinical trials to see if we can help shoulder pain, gait dysfunction, any mobility disability.”

            Sosnoff is also collaborating with Beckman Institute Director Art Kramer and researcher Mark Neider on a project that involves putting wheelchairs in ISL’s CAVE™ immersive virtual reality environment. The CAVE had been playing host to a research line looking at pedestrian distraction that had subjects walk on a treadmill set inside the virtual reality environment’s wall-sized screens that displaying a virtual street crossing.

“We’re replacing the full-size treadmill with a kid’s treadmill and then the kid’s treadmill with a roller assembly for stationary wheelchair testing,” Sosnoff said.

            In that study, as with the wheelchair propulsion research, Sosnoff will be breaking new scientific ground in order to potentially help people.

            “Historically people who looked at locomotion mainly looked, for obvious reasons, at walking and running,” Sosnoff said. “But with the graying of America and increased trauma care we are ending up with more and more people using wheelchairs for mobility.”

And, Sosnoff adds, there has been little interdisciplinary work in this area. It was through the expertise of Hsiao-Wecksler in mechanical science and engineering, his own background in kinesiology, and the capabilities of the motion capture suite that made this research possible.

“The problems we face as a society or as scientists are so complex, to think that you can solve them with training from a specific field is fairly naïve,” Sosnoff said. “Every discipline has strengths and I think you need to take those strengths and bring them together to solve these bigger issues and make bigger jumps in science.

“I think if we try to tackle it from just one perspective at a time it will a, take us longer, and b, we’ll end up with bodies of science that don’t necessarily talk to each other. So the answer could very well be out there in the engineering field or the kinesiology field and there needs to be some cross-breeding so speak to get the final answer out. We can skip that step and do it in an interdisciplinary way to start with.”