ATP Series

Midline Matters

How a different location can improve function for some PWC users

Vituvian Man


While much about complex rehab seating and positioning remains a mystery to those outside the industry, popular fitness movements such as CrossFit have made concepts of midline or core strength and stability part of mainstream conversation.

Take this excerpt from an Invictus Fitness post called “What Is Core to Extremity?” by Bryce Smith: “The core serves as a muscular corset that works as a unit to provide stability both with and without movement. All motions are generated from the core and translated to the extremities. Core to extremity means that the bridge that connects your upper body to your lower body is tight and secure with no loose ends and no broken beams. The midline is the bridge that allows efficient and safe force transfer.”

For complex rehab clients, core stability is crucial for function, such as the ability to sit in a position that enables them to propel a manual wheelchair. For power wheelchair users, core stability can make it possible to reach and effectively use a joystick or other type of driving control.

And for some power chair users, moving the driving control front and center — to midline, around the belly button — can make a huge difference in function.

The Big Deal About Midline

Generally speaking, we have greater strength close to our bodies than farther away. Imagine lifting a gallon jug of water with one hand and extending your arm so the jug is at arm’s length from your body. Then imagine lifting that same jug, but keeping your arm and the jug close to your body, right around your midsection. Which position is easier to maintain and is less fatiguing?

The loss of distal strength — that is, strength farther away from the body — before the loss of proximal (closer to the core of the body) strength is common in some types of muscular dystrophy, for example. But Michael Flowers, CEO/President of Active Controls, noted that this tendency can also present in wheelchair users with other diagnoses.

“That rule really applies to all of the neurological disabilities,” Flowers said. “It’s not really restricted to any particular one.”

Active Controls is best known for its centrally located power wheelchair driving controls — controls positioned not on the end of an armrest, which is the standard joystick location, but closer to the power chair user’s core or midline.

“It was serendipitous,” Flowers said of finding that midline location. “We had developed the JoyBar handlebar control” — a power chair control that looks like a scooter tiller — “and the only way to put a handlebar control on a power wheelchair is to put it at midline, just like a scooter handlebar is always in the center of the front of the scooter.”

After developing a modular system for that handlebar control, Flowers recalls saying to a colleague, “This is just a connection. We can put any type of control up here, including a joystick.” That colleague responded, “If we can do a joystick, we can do alternative driving controls.”

Flowers added that there’s a very practical reason that midline-mounted controls can be easier for some power chair users to operate. As Active Controls was designing its products, Flowers noted, “I said, ‘If we do a joystick, we can do supports on each side of the joystick to support the lower arm and relieve the stress and the strain on the forearm and the heel of the hand.’ That would make it so much easier to drive a power wheelchair. That’s how it all evolved.

“When we did that and developed the gel pads for [the supports], we found that [midline controls are] not just for people who can’t drive from the armrests. By supporting the lower arm and the heel of the hand, you are using less muscles. We confirmed that with the clinical study we did at MossRehab Hospital [available on the Web site]. The doctor who did the study [Alberto Esquenazi, M.D., MossRehab] used muscle sensors to see which muscles were firing when you drive from an armrest, and then he compared it to driving at midline with lower-arm supports. And he confirmed that the muscles that fire are basically in the shoulder and the neck — so that’s your trapezoids. And it confirmed that you have less muscle usage when you drive at midline with a lower-arm support. That equals less fatigue and longer [power chair] usage during the day.”

Variations on the Midline Location

So if operating a joystick or other power chair driving control from a midline location can require less effort and cause less fatigue, why not just move all power chair driving controls front and center?

Because, as is seemingly always the case with complex rehab technology clients, what works for one person or even most people isn’t the best answer for everyone.

As Education Coordinator for Adaptive Switch Laboratories (ASL), Byron Guisbert is well versed not just in alternative driving controls, but in making them work optimally for each power chair user.

“Everyone is different,” Guisbert said. “Somewhere, sometime, the ‘standard’ joystick position just happened to be at the end of an armrest in almost exactly the same position on every manufacturer’s [power chair]. I agree that there are individuals who could benefit from having it placed elsewhere, but that could be inches left or right.

“For me, where the joystick is positioned is dependent on what joystick, how much stability someone needs for their upper extremities, how their hand needs to be positioned, where their visual field is capable. What function are they using to move the joystick — shoulder, arm, hand, fingers, etc.?”

Guisbert pointed out that mounting power chair controls in a midline location requires those controls to swing away to allow for transferring in and out of the chair. Some swing-away mounts “swing away when you don’t want them to swing away,” he said. And those mounts need to be able to return those power controls to the exact same spot every time. It’s not just a matter of a power chair user being finicky: It’s a matter of having learned how to use those controls exactly where they were. Having controls in a different location, even one just slightly different, could make it difficult or impossible for the power chair user to function.

“The one thing they don’t like is change,” Guisbert said of complex rehab power chair users.

Finding Each User’s Functional Sweet Spot

Guisbert noted that power chair consumers with complex seating needs develop unique ways to use their power chair controls.

“The standard method became mounting [controls] on an armrest, but they were standard for spinal cord injuries,” Guisbert said of how joysticks originally came to be located. “And if they had shoulder movement, that was awesome, because they laid their hand on the armrest and they drove.

“But for me, it’s always a question of who am I working with? Am I working with someone who’s using the shoulder, the entire chest to use the joystick? Some people are even rotating their trunk. You might find somebody using a hand-over-hand [method], where they’re using both hands to utilize a joystick and actually rocking the joystick itself. Are they rocking it by using the weight of their hands?”

Flowers agreed: Every power chair user is different.

“It extends beyond just the operation of the chair, and that’s what to me has always been intriguing about driving in a position that is most comfortable for you,” he said. “Every one of us has a different sweet spot.” Active Controls’ Ergo ReJoy, Flowers noted, gives seating teams greater ability to find that “sweet spot.”

“We always try to get as close to the core, or the belly button, as possible to start,” Flowers said. “But what we’ve found is that you can actually move [the controls] all around and firmly position it where anybody’s hand naturally falls in front of their body. Usually, it’s going to be within 2" or 3" of the core, and most people are going to be right in the center. However, there are some people that have shorter arms, and reaching over to the center isn’t a natural feel for them. And you really want the person’s elbow supported by the armrest at the same time, because that also relieves the muscle usage in the trapezoid.

“If you balance the position where they drive from, you balance the position of the rest of the body.”

Guisbert’s additional concerns, beyond how functional a power chair user would be with midline controls, were the environmental accessibility restrictions that can come from having controls mounted front and center.

“For anything you do that’s awesome, there’s something that you’re hindering,” he pointed out, about midline mounting and perhaps about complex rehab technology choices in general. “For me, midline joysticks almost eliminated pulling [up] to a table. That’s almost priceless to me — for everybody to be in the same place, whether I’m in a chair or out of a chair. If I’m eating at the table, I want [them to be able to.]. If I’m working at a workspace, they should be able to acquire that.”

Guisbert acknowledged that if a power chair user was highly functional with midline-mounted controls, he wouldn’t rule that positioning out. But he cautioned against generic questions such as “What mounting controls position should you use for cerebral palsy clients?”, because having a diagnosis does not make everyone with that diagnosis exactly the same.

“These are all individuals,” he said. “It all depends on the family, the person, if they’re using their shoulder. If they put the joystick midline and are using their right arm, all of a sudden they might be pushing to the left a little more aggressively than they would be going forward.”

So as with everything else in complex rehab, midline mounting can be helpful to some power chair users, but each client is a case unto themselves.

And Guisbert is fine with that.

“To me, joystick users — they don’t need us,” he said of power chair consumers who can efficiently use standard controls. “I’m glad they have us, but for the people that need us the most, we’ve got to figure out where they do their best function.”

This article originally appeared in the Jan/Feb 2020 issue of Mobility Management.

In Support of Upper-Extremity Positioning