A successful wheeled mobility intervention is the culmination of dozens of measurements and the optimal combination of hundreds of components, all brought together in precisely the best way.
Of all the numbers to come out of a seating evaluation, seat-to-floor measurements might seem among the most basic — merely the inches or centimeters from the floor to either the front or back of the wheelchair’s seat.
But even slight differences in seat-to-floor heights can impact so much of a wheelchair rider’s day, from accessing the environment to transferring and performing activities of daily living. Plus, so many factors — such as the client’s height — are out of the seating team’s control. What seat-to-floor goals should seating teams strive for as they choose wheelchair frames, seating and other components? And what factors impact seat-to-floor heights in the first place?
Understanding seat-to-floor height
Alli Speight, OT, ATP, Motion Composites’ director of clinical education and training, pointed out that “seat-to-floor height” can refer to different sets of measurements.
“If you’re just focusing on the wheelchair and the frame itself, that’s typical seat-to-floor height,” Speight said. “When you’re talking about the whole system together — because of course, frames and seating should never be looked at separately — and you add that cushion on top of it, then you’re looking at finished seat-to-floor height. So your seating and your cushion will have an impact on seat-to-floor height as well.”
And of course, the seating team is usually working with two seat-to-floor heights — front and back — for every wheelchair, because even standard chairs, such as ones in restaurants or convention center ballrooms, aren’t perfectly level.
“Most chairs for able-bodied people have a difference of about one inch from front to back,” Speight said. While that difference is all about comfort and sitting tolerance for restaurant patrons, for wheelchair users, seat-to-floor differences front to back can be all about seated stability or optimal positioning for self propulsion.
Another truth — and challenge — about seat-to-floor height is that so many factors impact it.
Speight noted that even small components can make a difference: “A combination of caster forks and stem bolts in that caster system can have an impact on seat-to-floor height.”
Jessica Presperin Pedersen, OTD, MBA, OTR/L, ATP/SMS, North American director of clinical education for Sunrise Medical, said the wheelchair rider, the rider’s environment, and seating materials and surfaces can all affect a wheelchair’s ultimate seat-to-floor height. “The client’s height, including anatomical lower-leg measurement — popliteal to heel — account for lower-extremity (LE) positioning in regard to placement of the footplate. LE range of motion — e.g., hamstring tightness, amount of knee flexion — will affect footrest-to-seat height, which is a factor of required seat-to-floor height.”
Different types of seating can also impact the ultimate seat-to-floor height. Pedersen pointed out that typical seat cushion heights are 2″, 3″, 4″, with custom-molded systems potentially being even taller.
“Consider the amount of immersion into the seat cushion, or if an offloading cushion is used, then the actual seated height on the cushion may vary,” she noted. “We need to consider how the height of the cushion affects the overall seated height of the client.”
Power wheelchairs have additional components that can add to seat-to-floor height.
“Group 24 batteries are taller than other batteries and require a higher seat-to-floor height,” Pedersen said as an example. So could power seating systems. “Consider the space needs of seating actuators — i.e., power seat elevation — between the base and the seat pan.”
Why seat-to-floor height matters
An inch here, a half-inch there: Do these measurements truly make a difference in a wheelchair user’s day-to-day life?
“For a lot of people, it can impact their ability to transfer,” Speight said. “So do they need a specific seat-to-floor height for their wheelchair to do bed transfers? Or to allow them to do stand-pivot transfers independently or with minimal assistance?
“At the same time, they need to be functional within their environment. So it needs to work within their environment — with tables, chairs, other things they may be using during the day.”
Speight said the typical seat-to-floor on a standard chair of around 18″ is where seating teams can begin.
“Some of those norms, although they might not be ideal for someone in a disability, set certain standards that we can start to work around,” she said. But then she immediately mentioned the very low seat-to-floor heights needed for clients who foot propel. “Wheelchairs for foot propellers with those hemi-height frames can get as low as 12″ off the floor, floor to rail,” she said.
While those super-low hemi heights do position foot propellers for optimal heel strikes, they also make transfers more difficult. “It’s really hard to get up to do those transfers,” she said. “Your chairs in your kitchen or your toilet is potentially going to be higher. Toilets in some people’s homes are upwards of 21″. When you’re trying to work with the environment, the standards have been set for able-bodied people. But your transfers are absolutely going to matter.”
Christie Hamstra, PT, DPT, ATP, Motion Composites’ clinical educator, pointed out that transfers are also different for every client. She referenced a client with a T10 spinal cord injury who drove a standard-height pickup truck.
“He goes right up there, opens the door, grabs a handle, and swings himself up,” she said of his efficient and apparently easy transfer routine. “So again, it has a lot to do with [seat-to-floor height], but it also has to do with what is the person’s preference? How are they going to end up interacting with their environment? It comes down to many factors.”
What is the ‘ideal’ seat-to-floor height?
Seat-to-floor height can have an enormous impact on propulsion efficiency for ultralightweight wheelchair riders. “It needs to be ideal for their positioning, because what they do with those lower extremities, with their pelvis, where it sits within the wheelchair, could impact how someone sits within their chair as well,” Speight said. “So you do have to look at how someone’s propelling, where they’re going to sit within their wheels, how they’re going to transfer, how it’s going to function in their environment — and they somehow all have to come together.”
Hamstra added that seat-to-footplate height is yet another measurement to consider.
She told of seeing sample manufacturer wheelchairs being rolled up a ramp at an event. “The footplates were hitting the ground because these demos are set up in specific way to probably just roll straight, but not to go up an incline,” she explained. “So you have to think about how all of that geometry works as well. They kind of have to play along together.”
“You need a proper seat-to-floor height,” Speight said. “But your ground clearance is going to be dictated based on your lower leg length, or the frame, or the hangers that you have. And so because you need to be positioned properly with those plus your ground clearance, you might have to have a certain seat-to-floor height. But then it needs to work with everything else you have to do.”
Pedersen pointed out different factors for the seating team to consider, based on manual vs. power mobility.
“For active manual wheelchair configuration, the goal is for optimal propulsion, which means the client’s reach to the rear wheels should be considered when determining seat-to-floor height,” she said. “The rear seat-to-floor height and center of gravity play an important role in aligning the upper extremities. The front seat-to-floor height is determined by the amount of seat slope needed for trunk balance and how much ground clearance is needed to accommodate the client’s lower leg length — which can vary depending on the front frame angle (amount of ‘tuck’ of the lower legs).”
For power chair users, “the [seat-to-floor height] would be based on the person’s functional goals and to allow access under tables/desks and ensure vehicle clearance,” Pedersen added. Transfers are still a talking point, but power seating can ease those transitions. “Level transfers to various surfaces — bed, toilet, vehicle seat — are often a goal which can also be accommodated by power seat functions, i.e., power seat elevation.”
Pediatric seat-to-floor considerations
Erica Walling, MPT, ATP/SMS, is the clinical education manager in the U.S. Southeast for Sunrise Medical USA. “Seat-to-floor height for a child is going to be determined more by the functional goals of the child and family,” she said. “Factors to consider are transfers, environmental access and peer interaction. Consider functional goals and build the chair around them for optimal propulsion.”
Walling recalled working with a young child who had spina bifida and whose wheelchair, given the child’s age, had a low seat-to-floor height. “He was an active user, a self-propeller. He was in an ultralightweight manual chair configured to be successful in all environments and for optimal propulsion. His mom was upset that he couldn’t sit at the same height as everybody else at the dinner table.” If that were the goal, the seat-to-floor height would have been raised to 18″, compromising other functional activities.
Being a mom herself, Walling has used a booster seat for her child, so she made that suggestion. “It was a lot of back-and-forth education with her about how important [the lower seat-to-floor height] was for his propulsion vs. making him sit way high on top of his chair so that he could reach the table. We talked about environmental modifications, like putting a little block for him to roll up onto at the table. Considerations like that, I think, are important.”
For younger children, Pedersen added, “We want that ideal position for propulsion, and then I think a little more stability front-loading, because they often try to reach towards the floor. And they’ll try crawling onto the chair to get in.
“So a lot of times, we’ll balance the casters a little bit more off to the side to give that stability. And then we might have a little bit of length at the front, so that might change the seat-to-floor height a bit so they can access [the chair] that way.”
Ultimately, though, pediatric seat-to-floor height can be an outlier.
“Nobody can predict how one kid is going to grow versus another, even based on genetics, growth curves and growth expectancies,” Hamstra said. “The norms don’t really exist for pediatrics. So is this kid going to be able to get up and down [from the chair], and if so, then we need to have it a little bit lower to the floor. Are they going to be getting up and down out of the chair? Or is someone going to be lifting them up and down? Those are all things that you need to think about for the more active and independent [child]. We want them to be doing it on their own. So whether it’s the seat-to-floor height being lower to the ground, or there’s a decent position on the footplate so they can transition between the seat to the footplate to floor and then back up — I think those are things you can do as well if you have to compromise and make the seat-to-floor height a little bit higher.”
The art of the compromise
Seat-to-floor heights are determined by a range of components and measurements. But in the end, finding the optimal seat-to-floor height will typically require compromise.
“So your ideal seat-to-floor for a certain activity of daily living might be one [measurement], but you have to compromise on that seat-to-floor height for another activity,” Speight explained.
“Many manual wheelchair users request higher seat-to-floor heights to assist with transfers,” Pedersen said. “However, it is not always recommended to raise the seat-to-floor height for this purpose if it compromises propulsion and reach to the rear wheels. Instead, recommend physical therapy for transfer training with an optimally configured manual wheelchair.”
Asked for best-practice tips, she said, “Consider the goals of the client — transfers, environmental access, upper-extremity reach — while ensuring that the client’s anatomical measurements match the configuration of the mobility device without compromising function. For manual wheelchair configuration, the primary goal should be optimal propulsion for preserving upper-extremity function, as well as balancing stability with maneuverability. Transfer techniques can be learned, and therefore optimal propulsion should be prioritized over attempting to match seat-to-floor heights to transfer surfaces if it compromises the rider’s reach to the rear wheels.”
Hamstra suggested that having some adjustability in an ultralightweight wheelchair — particularly for newly injured or diagnosed clients — can be helpful as those clients learn to navigate the world while on wheels.
“At least initially, while they’re trying to figure out where it is that they’re going to be [functionally], I think [some adjustability] is always a good thing,” she explained. As an example, she described “a young kid his first chair. Right after his injury, he wanted to be really high so that he would be closer to [the heights of] standing people. Then he figured out no, that doesn’t work.”
As with all complex seating and mobility situations, determining the best seat-to-floor height for a particular client is certainly a mixture of science — taking accurate measurements and considering range of motion, for example — and compromise, as higher seat-to-floor heights are great for certain situations, and not so great for others. Achieving the best seat-to-floor height is also a matter of noticing the details. For example, Speight pointed out that something as simple as a different pair of shoes can add an inch to a client’s height and significantly change that client’s heel strike if that client is foot propelling.
Given all the variables, Speight added, “My rule of thumb: I would try to demo [the seat-to-floor height] as close as possible. I would try to mimic how they’re going to be in it. Are they successful? Do we have the right positioning with it? We spend a lot of time talking about transfers. But for proper positioning, that difference of front to rear seat-to-floor height — and what that does to your pelvis, and how you sit, and then how that plays with the back angle for that positioning — if that’s what allows someone to be independent, to be functional, that gives them the stability to be able to go about their day, that’s top priority.”
This story originally appeared in Mobility Management’s Seating & Positioning Handbook, published as a digital edition ebook. Access the rest of the ebook here.