What affects the manoeuvrability and self-propelling efficiency of a manual wheelchair? There are a whole host of variables that have influence, and we’ll cover some of them in this article. We’ll go into more detail in future articles.
The main objective of a wheelchair is for the user to have maximum functionality, comfort and mobility. An inadequate wheelchair, as well as being uncomfortable, can cause sliding, leaning to the side, or generally uncomfortable postures, which can cause problems in the long run. It may also put certain muscle groups at risk of injury or result in a position that is not strong or efficient for self-propelling. The shoulder is not a particularly stable or strong joint of the body, yet self-propelling a wheelchair is asking the shoulders to provide the engine behind the wheelchair’s motion. Think how many times those shoulders are going to be used. Soft tissue injury around the shoulder is a real risk, therefore anything that can be done to increase the efficiency of the push, or reduce the strength required to push, will reduce the risk of injury. That is why it should always be the chair that should fit your needs and not the other way around.
When assessing the suitability of a wheelchair, four factors need to be considered. How the weight is distributed between the wheels, what the centre of gravity is, the ground on which it is to be used, and the technical aspects (size, material, wheel type etc…).
The weight distribution between the front and rear wheels
The weight distribution of a wheelchair user refers to the proportion by which the weight is divided between the front and rear wheels. Generally, the greater the amount of weight on the front wheels, the greater friction will be, so it will require more effort to move it, although you will have greater stability.
A traditional 50% rear-wheel and front-wheel distribution (typical of standard wheelchairs) will guarantee stability, but will also require more effort to move - more appropriate if you are not going to self-propel yourself. An 80% distribution on the rear wheel and 20% on the front, will give you great efficiency, and will be more active.
Centre of gravity adjustment
This can be the difference between a chair that can be self-propelled, and one that can’t. It is important that the centre of gravity (COG) be set appropriately so that maximum efficiency can be gained, whilst maintaining some kind of stability.
Most active wheelchairs will have centre of gravity adjustment. This could be achieved by moving the rear wheels forward/backward on the frame, or by moving the weight of the user forward/backward on the frame. Both have the same effect.
Being able to move the centre of gravity of your wheelchair will allow the maximum adjustment of weight distribution. Generally, light aluminium chairs allow you to adjust it by moving the rear wheel position forwards, backwards, upwards and downwards. The further back and upwards you position the centre of gravity, the more weight you will give to the rear wheels achieving more mobility but less stability. It is advisable to adjust the centre of gravity of your wheelchair to meet your needs.
The rear wheels and tyres play a key role in the mobility of your wheelchair. Wheels provide the interface between your pushing force and the wheelchair therefore they need considerable attention when prescribing your wheelchair. A strong wheel will flex less than a less strong wheel, therefore transferring more of your pushing force into forward movement. You’ll get a slightly harder ride from a stiff wheel but this is unlikely to be noticeable. Cheaper wheels will flex slightly during every push, absorbing some of your pushing energy resulting in a less efficient push. They’re also more likely to suffer broken spokes or buckled rims.
Tyres cause a lot of debate, especially in NHS wheelchair services who are trying to save costs on repairs. When choosing a tyre material, pneumatic ones are more comfortable and allow shock absorption, and provide less rolling resistance. The big benefit of solid tyres is the guarantee of never getting a puncture! The size of the wheel needs to be considered in combination with the height of the user, and the rear seat height of the wheelchair. Taller users are more likely to gain benefit from a larger wheel (25 or 26”), especially if their rear seat to floor height is quite high.
The distance between the casters and the rear wheels will greatly influence mobility and stability. The smaller the wheelbase, the better the wheelchair will turn and the more manoeuvrable it will be, however, as in all previous cases, greater mobility is usually synonymous with less stability.
Smaller casters will provide quicker, more efficient turning particularly on flat, hard surfaces. This is why sports wheelchairs will always have very small casters. Outside, or on rough terrain, it is better that the front wheels are bigger because the contact surface with the ground is bigger and so the imperfections of the terrain can be absorbed. Most active user wheelchairs will have 4 or 5” casters, a compromise between the very small and the very large.