How Wheelchair Setup Affects Performance Ian Denison PT ATP

By the end of this session participants will:- Wheelchair Setup By the end of this session participants will:- Understand the importance of appropriate selection and set up of a wheelchair. Be 60 minutes older Wished they had gone to bed last night instead of the wee hours today Gained first hand knowledge of the benefits of regular weight shifts PT by Training OT by experience Frustrated Engineer at heart I began comparing wheelchairs fifteen years ago and have spent a lot of time analyzing the factors that contribute to their performance. This presentation will deal with the mobility aspect of a complete solution. Joanne and her buddy have covered seating in detail. It is important to establish the seating needs of your client before looking at the mobility side of the equation. This can be as easy as selecting a cushion or as involved as a foam in place tilting power seat. Either way, always establish your clients seating needs first.

Considerations in Creating a Solution ADL Mobility Positioning Psycho-Social issues Transfers Careful consideration of all these factors will help to make a mobility device work for an individual. In preparing for this presentation one of the OT’s I spoke with said that about 90% of her clients had chairs and weren’t using them. 1

ADL Factor Removing and retrieving components Reaching Proximity Access

Mobility Factor Who is doing the propulsion Surfaces Inclines Transitions Confined spaces

Positioning Factor Interacting with people and environment Posture Comfort

Psycho Social Factor Recreational and Vocational limitations Interacting with people How do you feel How do you look

Transfers Factor Removing and retrieving components Ease of moving within chair Height Proximity Space Stability

Options Affecting Suitability to Task As previously mentioned this presentation is concerned with meeting the mobility needs of the client. Imagine that we have already established an appropriate seating system and whittled the choices down to a specific folding manual lightweight wheelchair (Q2) No mean feat when you consider there are more than one hundred manual chairs to choose from.

Options Affecting Suitability to Task 4 frames 11 frame widths 9 sling depths 7 frame lengths 11 backrests 11 hangers 6 footplates 3 tubes 22 casters 10 forks 6 armrests 2 axles 20 wheel types 8 tire types 9 handrims 6 wheel locks 4 push handles 2 side guards OVER 6.6 QUADRILLION CONFIGURATIONS AVAILABLE

Adjustments 24 axle positions 4 different camber settings 8 back angle settings 5 back heights 6 caster positions 5 footrest heights 6 armrest heights 5,750,000 adjustments

Other Options 28 Colours 2 spoke guard colours 4 seat belts 6 arm pads

Number of Ways to Set up a Q2 Frame >100,000,000,000,000,000,000,000,000 I hope this doesn’t intimidate anyone who’s about to order their first wheelchair. That is over one nonillion different ways to spec a Q2

Number of Ways to Set up a Q2 Frame >100,000,000,000,000,000,000,000,000 Putting things in perspective Population of the Earth 7,300,000,000 To put that figure in perspective it is estimated that the population of earth today is 7.3 billion.

Number of Ways to Set up a Q2 Frame >100,000,000,000,000,000,000,000,000 EACH PERSON CAN HAVE 150 BILLION UNIQUE CHAIRS. Putting things in perspective Population of the Earth 7,300,000,000 To put that figure in perspective it is estimated that the population of earth in today is 7.3 billion.

INFLUENCING FACTORS Camber Casters Rigid / folding Tires Toeing error Weight Weight distribution These are some factors that influence chair performance, take a second to organize them from most to least important – write numbers 1 through 7 next to the factor

Common Elements These are things that should be done to all chairs regardless of how they will be used. Mobility ADL Regardless of the specific mobility needs of the client there are elements common to all chairs that should be optimized to improve the chances that the client will have the best possible chance of success in terms of efficient mobility. Transfers Positioning

Common Element Minimize rolling resistance Caster stem - vertical Bearings – reduce drag, minimal play Toeing - eliminate The one thing that should be common to every chair set up is to reduce the effort required to move the chair. Rolling resistance determines the energy required to propel a chair up to speeds of about 2 metres per second, at which point air resistance plays an increasingly significant role.   Rolling resistance is the combined drag created by tires, casters and bearings. It stays fairly constant whatever the speed of the wheelchair.

Caster Stem Caster stem Stems should be vertical when viewed from the front and side except in exceptional circumstances.

Caster Stem Vertical stem When the stem is vertical the front of the chair stays at the same height regardless of the caster position and steering effort is minimal

Caster Stem Stem leaning forwards In this setting the chair will be difficult to turn, the caster will always try to assume the trailing position. And the front of the chair will be tilted down while wheeling forwards.

Caster Stem Stem leaning forwards In this setting the chair will be difficult to turn, the caster will always try to assume the trailing position. And the front of the chair will be tilted down while wheeling forwards.

Caster Stem Angle and front seat height with stem vertical In this setting the chair will be difficult to turn, the caster will always try to assume the trailing position. And the front of the chair will be tilted down while wheeling forwards.

Caster Stem Angle and front seat height with stem leaning forwards In this setting the chair will be difficult to turn, the caster will always try to assume the trailing position. And the front of the chair will be tilted down while wheeling forwards.

Caster Stem Stem leaning backwards wheeling In this setting the caster will want to lead and the chair will be difficult to keep straight. Each time the wheeler starts to roll he will have to effectively push the chair up hill.

Caster Stem Stem leaning backwards resting In this setting the caster will want to lead and the chair will be difficult to keep straight. Each time the wheeler starts to roll he will have to effectively push the chair up hill.

Bearings Cross section of hub All wheels should spin freely and should roll back a little bit after they stop spinning. Axle nuts should be tightened to reduce sideways play at the bearing without making the bearing bind. (If this happens the wheel will not spin back when it stops after being gently spun.) The caster stem bolt can be slightly over tightened to help reduce flutter. When tightening the axle nut of a quick release wheel make sure the plunger extends fully when the wheel is in place (the wheel can fall off if the plunger doesn’t extend).

Toeing View from above Direction of travel Toed out Contact patch The contact patch of the wheels should be parallel and pointing in the same direction as the wheeler Toeing error is a condition that occurs when the wheels are not facing in the direction of travel of the wheelchair. It is sometimes found in new chairs but more frequently when chairs with camber have the rear wheel position adjusted. Contact patch Toed in

Toeing A 1 degree toeing error increases energy expenditure by 50% A chair should never have a toeing error.

Custom Elements Chair Size Chair Frame Geometry Wheel Caster Armrests Footrests Wheel locks, anti tippers Positioning ADL Mobility Transfers These Elements have an upside and a down side and it is a good clinician who is able to make compromises that utilize the clients strengths and support their weaknesses.

Chair Size Width plus “8” plus camber 27” is magic number 1” too wide costs 10% Transfer height Distance to span Clothing Transportation Table height / ground clearance Hip / trunk width Positioning ADL Mobility Transfers Width plus 8 plus camber 27 is magic number chairs wider than this have trouble with narrow doorways 1” too wide costs 10% Transfer height compatible with destination height Distance to span how close can you get to destination Clothing do you need extra width to accommodate clothing Transportation, what kind of vehicles will be used and who is putting the chair in Table height knees under and feet off ground Consider trunk as well as hip width when sizing a chair remember backs and cushions can overhang if frame will accomadate

Chair Frame Folding versus rigid. Tilt and or recline Exotic material Transportation Storage Positioning ADL Mobility Transfers Chair only folds when you are not in it. Rigid chairs are always best when you are wheeling. Only consider benefits when chair not being used. Tilt and or recline – T and R is lethal. T only is better for nearly everyone. Care giver has to be trained in how to use. Exotic material over rated hardly an issue when used inside Transportation where will the chair be in a vehicle, what shape does it have to be to fit Storage

Geometry Horizontal wheel position (C of G) Vertical wheel position Camber Seat Angle Back Angle Positioning ADL Mobility Transfers And we will only consider part of the geometry element. Horizontal wheel location and camber have the biggest impact on a chairs characteristics inside.

Geometry - Horizontal Wheel Position More weight on the drive wheels and less on the auxiliary wheels (casters and anti tippers) makes the chair roll with less effort. However putting all the weight on the rear wheels has functional limitations such as making the chair too tippy reducing space for transfers etc and a compromise has to be made based on the clients needs and strengths. The rolling resistance doubles when the centre of gravity is moved from directly over the rear wheels, to mid way between the wheels and casters. Smoother ride

Geometry - Horizontal Wheel Position More room to transfer More stable platform Easier to push/manoeuvre More wheel Shorter chair Thresholds easier Carpets easier Easier for attendant Moving the wheels back creates more room for sliding transfers and a more stable platform. Moving the wheels forward puts the wheeler in a more efficient position to reach a larger arc of the rim. And makes the chair shorter.

Geometry –Camber Further distance to bridge Need for wider doors Bigger chair Hand protection Side stability More natural stroke The camber adjustment assumes that the tops of the wheels are kept the same distance apart from each other. In studies that we performed using able bodied and people with sci there was no difference in energy cost whether the camber was 0, 3 or 6 degrees.Nearly all people sampled preferred to wheel the chair with 6 degrees of camber. A chair that fits someone 16” wide at the hips will be 30” wide at the wheels. One with no camber will be only 24” wide.

Custom Elements Tire Selection (applies to casters too) Shock Absorption Traction Rolling Resistance Durability Puncture Resistance Wheel lock function Positioning ADL Mobility Transfers While we have already established that we want to minimize rolling resistance in all circumstances how this is achieved varies depending on the environment and the relative importance of the other roles tires are asked to perform. Inflate tires to maximum pressure if wheeling on hard surfaces. Deflate tires to between 10 and 20 psi if wheeling on soft ground or carpet

Tire Selection Shock Absorption In wheelchairs shock absorption is achieved through. Suspension Pneumatic tires Wheels Frame design Cushion selection Shock absorbing frames, wheels and suspension are expensive. A cushions main function is hardly related to it’s shock absorbing qualities Pneumatic tires are a relatively cost effective way of getting some vibration reduction. When contrasting the shock absorbing qualities of tires it is worth remembering that air filled tires absorb shock throughout the entire tire whereas only the material between the rim and ground absorbs shock in an airless tire.

Tire Selection Traction Not synonymous with friction Pneumatics better than non pneumatics Tread design Tread composition Traction and friction are different when considering a tire. You want enough traction so that the wheel and ground do not experience wheel spin or skidding (shear) Pneumatic tires provide better traction than solids A lugged tire will provide a bigger surface area on soft, conforming terrain. Soft - tacky tires will grip better but wear quicker.

Distance Rolled (in metres) by Various Tires on Hard Smooth Surface

Distance Rolled (in metres) by Various Tires on Hard Smooth Surface

Distance Rolled (in metres) by Various Tires on Hard Smooth Surface

Distance Rolled (in metres) by Various Tires on Hard Smooth Surface

Tire Selection Rolling Resistance Solid { Pneumatic { Tires provide a wheelchair’s only contact with the floor. They transmit motive force, braking force, absorb shock and are responsible to a large degree in determining the rolling resistance. THEY ARE KIND OF IMPORTANT In order to match a wheelchair to a client it is important to know the effect that each component or setting has on the performance of a wheelchair. During the course of our investigations we discovered these facts about tires. Solid tires have almost twice the rolling resistance of conventional tires on hard surfaces High pressure tires have 10% less rolling resistance than conventional tires. An average user experiences two punctures a year Rolling resistance increases by an average of 12% when tire pressures are reduced to half of the recommended setting. For those of you who care this just qualifies as statistically significant and since rolling resistance is directly related to energy expenditure it is very clinically relevant. The cause of rolling resistance produced by the tire is the combined deformation of the wheel, tire and road surface at the contact point. Energy is lost (and rolling resistance occurs) when these structures do not spring back elastically (hysteresis), failing to return all the energy to the wheelchair. Wide treaded tires perform best on soft and/or rough terrain e.g. grass, snow, sand and gravel etc. On soft ground, most of the energy is lost deforming the ground. A large contact patch spreads the weight over a larger area and produces a relatively low rolling resistance. Solid { Pneumatic {

Tire Selection Air loss over time 1 month So if maintaining tires at 50% or more of the recommended pressure results in reasonable everyday performance:- How often should tires be reinflated. 7 sets of tires were inflated to recommended pressures and checked on a regular basis. The air loss curves suggest that tires can be left at least a month before needing air. Monthly inflation should be adequate but for optimum performance weekly is better. If tires squish when squeezed pressures are way low. Incidentally air is lost through microscopic pores in the rubber not through the valve.

Tire Selection Distance rolled by Cheng Shin and V Trak tires Smooth hard surface Hard low pile carpet Thick plush carpet 4.2 m 6.4 m Regular tires at 65psi Cheng Shin’s and HP Primo V Traks at 100psi were tested on linoleum and on carpet. The carpet was exceptionally dense low pile, ideal carpet for wheeling on. Distance rolled on linoleum was 34% greater with the hp tires. On carpet however both tires performed identically. On softer surfaces the standard tires actually perform better. The reduction in distance rolled for both tires on carpet was equivalent to dropping tire pressures to 10 psi on a hard surface. 2.4 m 2.4 m 1.4 m 0.9 m

Tire Selection Footprint: What is the big deal? Rolling Resistance is wasted energy Some of the energy is lost in the form of noise - most is lost in the form of heat. Some of the heat energy is lost at the bearings, at loose spokes, where the tire attaches to the rim and where the tire touches the ground. Movement and deformation generate heat and with most tires and wheels the majority of the deformation occurs at the interface between the tire and ground. If the ground is hard the tire deforms If the ground is soft the ground deforms Regardless of which bit gives the result is the same - rolling resistance. Hard, thin tires are best suited to hard surfaces because they don’t deform.On soft surfaces however a thin hard tire will dig in, a big soft tire with a large footprint on the other hand will float on the surface and cause the ground to deform less than a narrow hard one resulting in lower rolling resistance. So why isn’t a hard thin solid tire the best alternative, hysteresis, intimate fit, shape.

Tire Selection Footprint: Using changing characteristics to your advantage? Knowledge of how a tire responds to air pressure can be used to the consumers advantage. The Xtreme tire on the left has a stiff side wall made of Kevlar fibres and tends to hold its shape as air is lost. The V trak has a relatively soft side wall and tends to squish out as air is lost. The Xtreme would be a good selection for someone who isn’t very diligent about keeping their tire pressures up. The V trak is a better choice for someone who is diligent about inflating tires monthly and / or wants the flexibility to reduce tire pressure for temporary use on soft terrain.

Tire Selection Pneumatic tires perform better (except flats) Pressure not significant until 50% or less. Reinflate tires monthly. Tires under inflated by 75% perform better on soft terrain. Over inflated tires less puncture prone. Dense carpet same as reducing pressure to 10 psi on hard surface. So to summarize here are a few Selection about tire pressure.

Caster Selection Parasitic Rolling resistance Thresholds Foot clearance Stability for transfers Shock absorption Or more accurately increase the speed at which flutter occurs

Caster Flutter The following factors reduce the tendency to flutter: Increased trail Minimize bearing play Caster stem at 90 degrees More weight on wheel Lighter wheel Smaller wheel Round wheel Wider foot print Or more accurately increase the speed at which flutter occurs

Push handles Who is pushing What else are they used for Hooking Transfers carrying Head protection

Armrests

Footrests

Anti tippers

Wheel locks