Manual Wheelchairs - World Health Organization

46 I guIdelInes on the provIsIon of manual wheelchaIrs In less resourced settIngs
2.4 Functional performance
Functional performance is how a wheelchair performs for different users in different environments.
The functional performance of a wheelchair is determined by its unique design and features. There
are many compromises to consider when designing or selecting for different uses.
This section provides information on the key features of a wheelchair that affects the main categories
of performance and how to evaluate them. It also outlines compromises that need to be considered
when choosing different design features.
To meet the functional performance needs of individual users, a range of wheelchair designs and
sizes are needed.
2.4.1 Wheelchair stability
Wheelchair stability affects how safe the wheelchair is, and how well the user can carry out activities
in the wheelchair. Wheelchair tipping causes many injuries for users (4).
• Static stability relates to the stability of the wheelchair when it is not moving. This determines
whether the wheelchair will tip over (where some wheels lose contact with the ground) when
the user, for example, leans over to pick something up off of the ground or transfers into or out
of his or her wheelchair.
• Dynamic stability relates to the stability of the wheelchair when moving. This determines whether
the user can ride over bumps or sloped surfaces without tipping.
The design features used to increase wheelchair stability have secondary effects on other functional
performance characteristics. For example, moving the front castor wheel forward increases stability
but reduces the manoeuvrability of the wheelchair in confined spaces. These relationships are
described below.
General stability is affected by the position of the combined centre of gravity of the user and
the wheelchair relative to its wheelbase. A way of increasing general stability and its associated
advantages and disadvantages are shown in Table 2.2.
Table 2.2. Aim: to increase stability in all directions
Advantages Disadvantages
By lowering the seat and thus the centre of gravity of the user
n It may be easier for the user to reach objects on the floor.
n The seat (and the user’s knees) will be more likely to fit
under desks and tables.
n Users will be more able to use their feet to assist with
propulsion (if they are able).
n Being lower may make it harder to reach objects above.
n The posture may be less comfortable and may increase
the pressure on the user’s seat (a cause of pressure
sores).
n The user’s pushing position may be worse and access to
the hand rims more difficult.