Long-term use of a manual wheelchair is a disaster for the shoulders. Impingement, rotator cuff issues, degenerative joint disease, and pinched nerves are just some of the problems that crop up and debilitate after years of pushing a wheelchair.
It's the pushing that's the problem, as Salim Nasser realized when he was a mechanical engineering student at Florida International University. “I wanted to do something that I was personally interested in,” he said. “I'm in a wheelchair and knew some of the problems.” So, for his senior design project he created a chair that would go forward when pulled.
To make it move in this seemingly paradoxical way, Nasser quickly settled on a design that used a hub with planetary gears. “It was the obvious solution for me, the simplest way to reverse that motion,” he said. “I didn't have to think about it more than once.” It was this design — its simplicity, viability, and extraordinary effectiveness at minimizing shoulder problems for those in wheelchairs — that won Nasser SAE's Create the Future Design Contest in 2010.
The award helped Nasser find a financial partner and go from prototype to product in a matter of five years. Now wheel-chair bound people all over the country are pulling on their wheels to go forward and saving their shoulders from a world of pain in the process.
The Rowheel has come a long way since its first inception. “I had to completely redesign it, so that it was manufacturable, and cost-effective,” said Nasser. “It had to be reliable, light-weight enough to transfer to cars, and it had to look good.”
To lighten the hub, Nasser tried a variety of materials and manufacturing methods before settling on thixomolding (essentially an injection molding process done with magnesium in a semisolid state). The result was a more rugged hub, pounds lighter, and a good 80 dollars cheaper than machining from aluminum. To keep the gears themselves light and low maintenance, they are now self-lubricating and made of nylon and Delrin. To further lower the weight and increase reliability Nasser switched to wire race bearings that are made in house. The initial first commercial version of a Rowheel had a high gear ratio which made it fast and responsive but better suited to those with good upper body strength. A second version, which uses a low gear ratio makes it easier to propel than standard wheelchairs and is the more popular and simpler of the two.
Using Rowheels actually builds shoulder strength. On a traditional chair, the harder you push the greater the risk of injury to the shoulders. But Rowheel users can go as fast as they want. “The harder you pull, the better it is — the motion is completely benign to those issues,” said Nasser. A study published in the Journal of Spinal Cord Medicine confirmed the benefits to the shoulders of anyone switching from a forward-push wheelchair to a Rowheel.
Despite the successes, though, Rowheels are still far from commonplace. “Muscle memory works against us,” said Nasser. “Physical therapists, when they see it, a light bulb goes off in their heads — they know. But for longtime users, we're asking them to do exactly the opposite of what they've been doing for years. It's like asking you to walk backward to go forward. A lot of people freak out.”
There is one group of people that don't need any convincing: anyone who's already experienced shoulder pain or injury from wheelchair usage. “The moment they sit in it they notice the difference,” said Nasser. “It's instantaneous.”
Michael Abrams is a science and engineering writer based in New Jersey.
2010 GRAND PRIZE WINNER
INNOVATOR: Salim Nasser, Founder, Rowheel
INNOVATION: The Rowheel Wheelchair Propulsion System helps manual wheelchair users increase their mobility while decreasing upper body, repetitive stress injuries.
IMPACT: Easier wheelchair usage for those who suffer from muscle pain, torn rotator cuffs, joint degeneration, and carpal tunnel syndrome.
Enter the 20th Anniversary Contest: www.createthefuturecontest.com