ISO 16840-13:2021

INTERNATIONAL ISO
STANDARD 16840-13
First edition
2021-06
Wheelchair seating —
Part 13:
Determination of the lateral stability
property of a seat cushion
Reference number
©
ISO 2021
© ISO 2021
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ii © ISO 2021 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviations. 2
5 Apparatus . 2
5.1 RCLI . 2
5.2 RCLI cover . 2
5.3 Stability test rig . 2
5.4 Tilt angle measurement device . 3
6 Test environment . 3
7 Preparation and setup of cushion . 4
7.1 Choice of cushion . 4
7.2 Preconditioning the cushion . 4
8 Cushion lateral stability test method . 4
8.1 General . 4
8.2 Test procedure . 4
8.3 Method of calculation . 5
8.4 Test report . 6
Annex A (informative) Method for using pressure mapping to characterize behaviour of
reaction forces during the stability property test . 7
Bibliography . 9
Foreword
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iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 173, Assistive products, Subcommittee
SC 1, Wheelchairs.
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iv © ISO 2021 – All rights reserved

Introduction
The seat cushion, as the base of support for the wheelchair occupant, affects postural stability by
resisting moments when the occupant’s centre of mass is displaced. Research exploring the influence of
cushion design and setup on pelvic orientation and measures of postural stability is limited. Standard
test methods, highlighted in ISO 16840-2, should be used to characterize tissue integrity management
properties of wheelchair seat cushions such as immersion, envelopment, hysteresis, impact damping,
recovery, and horizontal stiffness.
This document provides details of test equipment and a method for the measurement of the cushion’s
ability to resist movements contributing to pelvic obliquity. Changes in pelvic obliquity, as a result of a
shift in the centre of mass, can affect stability and mobility depending on the response of the cushion,
the occupant’s core muscle strength, etc. Moments in the test method are created by shifting a vertical
load laterally on the top surface of a standard rigid cushion loading indenter (RCLI) simulating the
buttocks and upper thighs. The test method described in this document is intended to differentiate
lateral stability performance between cushions and is not appropriate for ranking cushions nor for
directly matching this characteristic with an individual occupant’s requirements. The link to clinical
efficacy, although implied, has not been validated. It is intended that this document will evolve when
the evidence of clinical relevance is confirmed. Test conditions (e.g. the RCLI) simulate a symmetric
anatomy. The loads used in this document are based on the 40th to 60th percentile wheelchair occupant
and are not intended to characterize any cushion properties under bariatric loading conditions or to
assess the weight capacity of a cushion.
There are other stability issues of relevance to the occupant, but which are not addressed in this
document. For example, because the positions of the occupant’s thighs, lower legs, and feet can
counterbalance any instability elements of the cushion, an anterior-posterior stability test carries
lesser significance to the occupant and is not included. This document also does not address aspects
of wheelchair sitting stability related to the resistance or assistance that the cushion provides to the
occupant regaining a neutral pelvis following a lateral tilt as viewed in the frontal plane. Additionally,
edge stability is not assessed. In some cases, the occupant will benefit from the stability provided by
the cushion’s edge (i.e. a strengthened edge could be of benefit in supporting the required functional
posture while the occupant is seated on the cushion). In other cases, the occupant could prefer lesser
stability at the edge to assist in transferring off the cushion.
INTERNATIONAL STANDARD ISO 16840-13:2021(E)
Wheelchair seating —
Part 13:
Determination of the lateral stability property of a seat
cushion
1 Scope
This document specifies apparatus, test methods, and disclosure requirements for determination of
lateral stability properties of wheelchair seat cushions by measuring the response from the cushion to
a shift in the centre of mass of the load on the cushion. It provides a method of determining changes in
a particular physical and mechanical property of the cushion. It does not provide information specific
to cushion performance for a particular individual user. It does not provide information related to
anterior-posterior stability, nor to stability contributions from cushion edges.
NOTE 1 Test conditions simulate a symmetric anatomy.
NOTE 2 Loads are intended to represent those seen under the pelvis of a 40th to 60th percentile wheelchair
user.
This document is applicable to cushions used in situations other than a wheelchair.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 7176-26, Wheelchairs — Part 26: Vocabulary
ISO 16840-2:2018, Wheelchair seating — Part 2: Determination of physical and mechanical characteristics
of seat cushions intended to manage tissue integrity
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 16840-2 and ISO 7176-26 and
the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
cushion lateral stability
cushion’s ability to resist tilting of the pelvis as viewed in the frontal plane caused by a shifting centre
of mass of occupant in a lateral direction
3.2
cushion stability test live load
portion of the total apparatus weight applied to the test cushion that translates in the horizontal plane
to shift the centre of mass of the load relative to the test cushion during the test procedure
Note 1 to entry: Example of a live load are keys 4, 5 and 6 of Figure 1.
3.3
cushion stability test dead load
portion of the total apparatus weight applied to the test cushion that does not translate in the horizontal
plane relative to the test cushion during the test procedure
Note 1 to entry: Example of a dead load are keys 7 and 8 of Figure 1.
4 Abbreviations
RCLI Rigid Cushion Loading Indenter
5 Apparatus
5.1 RCLI
An RCLI as specified in ISO 16840-2:2018, Annex A and D.
5.2
...