ISO 16840-1:2006
(Main)Wheelchair seating — Part 1: Vocabulary, reference axis convention and measures for body segments, posture and postural support surfaces
Wheelchair seating — Part 1: Vocabulary, reference axis convention and measures for body segments, posture and postural support surfaces
ISO 16840-1:2006 applies to seating intended to provide postural support within a wheelchair. It specifies: a global coordinate system that permits the determination and recording of a person's posture while seated in a wheelchair; the standard terms and definitions for use in describing both the posture and the anthropometrics of a person seated in a wheelchair; the terms and definitions for describing the dimensions, location and orientation of seating support surfaces, which together comprise the body support system. ISO 16840-1:2006 does not specify any methods for use in measuring a person's seated posture, nor does it define terms for dynamic physiological movements (such as flexion or extension). ISO 16840-1:2006 might be applicable to seating other than that intended to be used within a wheelchair.
Sièges de fauteuils roulants — Partie 1: Vocabulaire, convention des axes de référence et mesures des segments corporels, des surfaces de posture et du siège
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 16840-1
First edition
2006-03-15
Wheelchair seating —
Part 1:
Vocabulary, reference axis convention
and measures for body segments,
posture and postural support surfaces
Sièges de fauteuils roulants —
Partie 1: Vocabulaire, convention des axes de référence et mesures
des segments corporels, des surfaces de posture et du siège
Reference number
ISO 16840-1:2006(E)
©
ISO 2006
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ISO 16840-1:2006(E)
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© ISO 2006
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ISO 16840-1:2006(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 General terms and definitions . 1
3 Abbreviated terms and subscripts. 6
3.1 Abbreviated terms . 6
3.2 Subscripts . 6
4 Global coordinate system principles. 7
4.1 General. 7
4.2 Structure . 7
5 Terms and definitions of an integrated geometric reference system . 7
5.1 General. 7
5.2 Global coordinate system. 8
5.3 Wheelchair axis system (WAS) . 9
5.4 Support surface axis system (SSAS). 10
5.5 Seated anatomical axis system (SAAS) . 11
6 Terms and definitions of support surface measures. 12
6.1 General. 12
6.2 Terms and definitions of support surface measures in the sagittal view. 13
6.3 Terms and definitions of support surface measures in the frontal view. 20
6.4 Terms and definitions of support surface measures in the transverse view. 26
7 Terms and definitions of body measures of a seated person . 30
7.1 General. 30
7.2 Terms and definitions of body measures in the sagittal plane. 31
7.3 Terms and definitions of body measures in the frontal view. 41
7.4 Terms and definitions of body measures in the transverse plane . 50
Annex A (normative) Definition of reference lines for common seating support surfaces . 56
Annex B (normative) Calculations of joint centres. 63
Annex C (informative) Abdominal and sternal body segment lines for use in sagittal and frontal
body measures. 68
Bibliography . 74
Alphabetical index . 75
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ISO 16840-1:2006(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 16840-1 was prepared by Technical Committee ISO/TC 173, Assistive products for persons with disability,
Subcommittee SC 1, Wheelchairs.
ISO 16840 consists of the following parts, under the general title Wheelchair seating:
Part 1: Vocabulary, reference axis convention and measures for body segments, posture and postural
support surfaces
Part 2: Determination of physical and mechanical characteristics of devices intended to manage tissue
integrity — Seat cushions
Part 3: Determination of static, impact and repetitive load strengths for postural support devices
The following parts are under preparation:
Part 4: Seating systems for use in motor vehicles
Part 5: Determination of pressure relief characteristics of seat cushions intended to manage tissue
integrity
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ISO 16840-1:2006(E)
Introduction
The development of wheelchair seating as a sub-specialty of rehabilitation services has been occurring over
the last several decades. This practice involves the selection and provision of wheelchair seating products that
provide improved body support, movement control, and injury prevention for the wheelchair user. Inherent in
this selection process is the measurement and communication of the anthropometrics and postural measures
of the seated person, as well as the orientation, location and linear measures of the person's seating support
surfaces.
However, there has been tremendous variation in the use of the terminology and definitions related to the
clinical measures of a seated individual. Standard definitions and terms are lacking for communicating critical
postural information and support surface parameters in a way that is uniformly useful to service providers,
researchers, manufacturers, wheelchair users and purchasers when selecting and providing wheelchair
seating devices.
The purpose of this part of 16840 is to specify standardised geometric terms and definitions for describing and
quantifying a person’s anthropometric measures and seated posture, as well as the spatial orientation and
dimensions of a person’s seating support surfaces. This also allows for the systematic monitoring of a
person's seated posture change over time.
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INTERNATIONAL STANDARD ISO 16840-1:2006(E)
Wheelchair seating —
Part 1:
Vocabulary, reference axis convention and measures for body
segments, posture and postural support surfaces
1 Scope
This part of ISO 16840 applies to seating intended to provide postural support within a wheelchair. It specifies:
a) a global coordinate system that permits the determination and recording of a person's posture while
seated in a wheelchair;
b) the standard terms and definitions for use in describing both the posture and the anthropometrics of a
person seated in a wheelchair;
c) the terms and definitions for describing the dimensions, location and orientation of seating support
surfaces, which together comprise the body support system.
This part of ISO 16840 does not specify any methods for use in measuring a person's seated posture, nor
does it define terms for dynamic physiological movements (such as flexion or extension).
This part of 16840 might be applicable to seating other than that intended to be used within a wheelchair.
2 General terms and definitions
2.1
absolute angle
angle which represents the orientation in space of a body segment or support surface reference plane relative
to the gravitational axis system
NOTE See 5.2.
2.2
body centreline
vertical line falling on the midsagittal plane of the body, as viewed in the frontal plane
2.3
body segment line
line defined by two designated body landmarks, either palpated or calculated, used in determining angular
positions of body segments
2.4
contact surface
surface of the seating support in contact with the seated person's body
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ISO 16840-1:2006(E)
2.5
depth
linear dimension of a seating support surface measured in the Y direction on a line parallel to the support
surface reference plane
See Figure 1.
Figure 1 — Examples of depth
2.6
length
linear dimension of a seating support surface measured in the Z direction on a line parallel to the support
surface reference plane
See Figure 2.
Figure 2 — Examples of length
2.7
reference position
fixed hypothetical baseline position to which other positions may be referenced
2.8
relative angle
angle formed between two body segment lines or two support surface reference lines
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ISO 16840-1:2006(E)
2.9
seated anatomical axis system
SAAS
axis system used to define the orientation of the body segments in space and to each other
2.10
seated reference position
SRP
orthogonal seated position to which other positions may be referenced
2.11
support surface axis system
SSAS
axis system used to define the orientation, location and linear dimensions of seating support surfaces
2.12
support surface geometric centre
SSGC
point of intersection of two or more lines joining the furthest points from the edges of a contact surface,
measured along the surface
See Figure 3.
a) Asymmetric contoured surface b) Planar surface
Key
1 line along the contoured surface
2 support surface geometric centre (SSGC)
Figure 3 — Illustration of the SSGC on curved and planar support surfaces
2.13
support surface reference line
designated line passing through the support surface geometric centre used in measurement of the absolute
and relative angles of the seating support surface
2.14
support surface reference position
SSRP
fixed hypothetical baseline position of support surfaces in the three orthogonal planes to which other positions
may be referenced
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ISO 16840-1:2006(E)
2.15
support surface reference plane
plane passing through the SSGC tangential to the surface curvature at the SSGC radius at the point of the
SSGC
See Figure 4.
NOTE The tangent to the radius of a planar surface is parallel to the surface.
a) Symmetrical contoured b) Asymmetrical contoured c) Planar surface
support surface support surfaces
Key
1 support surface reference plane
2 radius of the support surface curve at the SSGC
3 SSGC
Figure 4 — Examples of support surface reference planes for contoured and planar surfaces
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ISO 16840-1:2006(E)
2.16
thickness
linear dimension of a seating support surface measured perpendicular to the support surface reference plane
See Figure 5.
Figure 5 — Examples of thickness
2.17
wheelchair axis system
WAS
axis system which may be used to define the orientation and location of the person and any items attached to
or contained within a wheelchair base relative to that base
2.18
width
linear dimension of a seating support surface measured in the X direction on a line parallel to the support
surface reference plane
See Figure 6.
Figure 6 — Examples of width
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ISO 16840-1:2006(E)
3 Abbreviated terms and subscripts
3.1 Abbreviated terms
AS anterior support
ASIS anterior superior iliac spine
IS inferior support
LS lateral support
MS medial support
PS posterior support
PSIS posterior superior iliac spine
SAAS seated anatomical axis system
SSAS support surface axis system
SRP seated reference position
SSGC support surface geometric centre
SSRP support surface reference position
WAS wheelchair axis system
3.2 Subscripts
d depth
ed effective depth
el effective length
ew effective width
fang frontal angle
floc frontal location
L left
l length
R right
sang sagittal angle
sloc sagittal location
t thickness
tang transverse angle
tloc transverse location
w width
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ISO 16840-1:2006(E)
4 Global coordinate system principles
4.1 General
This part of 16840 is based on a three-dimensional global coordinate system applied separately to the
wheelchair, the seating support surfaces and the wheelchair user. Separately and/or collectively this
coordinate system allows for measurement in the three traditional orthogonal planes of locations, linear
measures, and angles of the body segments of a person and the seating support surfaces.
The measures of a person (either linear or angular) will not necessarily be identical to those of the seating
support surfaces. The prescription of a seating support surface should be determined through clinical
interpretation or translation of the measures of a person into those appropriate for support surfaces that will
adequately support a person in a desired posture.
4.2 Structure
Clause 5 specifies the integrated geometric reference system upon which all the following definitions for this
part of ISO 16840 are based. Next, the measurement definitions for seating support surfaces, and the body
measures are specified. They are each defined using the three orthogonal planes, sagittal, frontal and
transverse. For each plane, a standard reference position (SSRP or SRP), and definitions for measures of
support surface locations, linear dimensions, absolute angles and relative angles (where appropriate) are
specified.
5 Terms and definitions of an integrated geometric reference system
5.1 General
The following are terms and definitions for an integrated geometric reference system that permits the
measurement of a person's seated posture. The measured seated posture can then be recorded relative to
the person's seating support surfaces, and finally, in relation to the global reference (the wheelchair frame) in
which the person is seated.
Five interrelated components comprise the integrated geometric reference system:
a) the wheelchair axis system (WAS) defines a fixed global reference system, specified by the geometry of
each person's wheelchair after configuration of that wheelchair for the specific person;
b) the support surface axis system (SSAS) defines the coordinate conventions used to specify the support
surface reference position;
c) the support surface reference position (SSRP) defines a fixed hypothetical position of the support
surfaces to which other positions may be referenced;
d) the seated anatomical axis system (SAAS) defines the geometric measures used to specify and record
the positions of a person's body segments relative to the seated reference position;
e) the seated reference position (SRP) defines a fixed hypothetical position of the seated person to which
other positions may be referenced.
The integration and application of these interrelated geometric systems allow the systematic measurement
and recording of a person's wheelchair-seated posture. Subsequent measurements will allow the systematic
monitoring of seated posture change over time.
Of fundamental importance are the selection and consistent use of an axis system. This convention, termed
the global coordinate system, then allows the systematic integration of the above measurements.
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ISO 16840-1:2006(E)
For all measurements, when a line or coordinate position does not fall on one of the three defined orthogonal
planes, the line or coordinate position is projected to the appropriate plane and then measurements are taken.
NOTE This simplification reduces all three-dimensional measures to two measurements, which is consistent with
current clinical practice.
5.2 Global coordinate system
5.2.1 Basis
The global coordinate system is based on a gravitational axis system in which the +Z axis has been
designated as the upward vertical axis. Both X and Y axes are at right angles to Z and to each other. The
location of the origin for the global coordinate system is described in 5.3.
5.2.2 Direction of axes
The right-hand directional rule is used to define the directions of the coordinate axes, specifically, thumb
vertical along the positive (+) Z axis, index finger defines the positive (+) X axis, and the middle finger defines
the positive (+) Y axis
See Figure 7.
Figure 7 — Right-hand directional rule defines positive directions of axes X, Y and Z
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ISO 16840-1:2006(E)
5.2.3 Orthogonal planes
The three axes, X, Y, and Z, create three orthogonal planes, YZ (sagittal), ZX (frontal), and XY (transverse),
illustrated in Figure 8.
a) Sagittal (YZ) plane b Frontal (ZX) plane c) Transverse (XY) plane
Figure 8 — Three axes and created orthogonal planes
5.2.4 360° measurement convention
A 360° measurement notation is used throughout the integrated measurement system. This system specifies
that all angular measures start at the positive Z axis (or positive Y axis in the transverse view) and proceed to
360° in a clockwise direction according to the left-hand screw rule
See Figure 9.
NOTE There are no negative angles with the 360° notation.
Figure 9 — 360° measurement notation system
5.3 Wheelchair axis system (WAS)
The WAS serves as the global reference system based on the axis convention defined in 5.2, and denoted
with a subscript “c”. It establishes the absolute (global) reference origin (0,0,0 ) for the global coordinate
c
system.
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ISO 16840-1:2006(E)
The global origin (0,0,0 ) is located on the floor directly below the midpoint of a line passing through the axles
c
of the rear-most pair of non-castored wheels, or drive wheels, on the wheelchair frame (see Figure 10). In the
case of an adjustable rear axle or drive wheel axle, the location of the axle should be configured as desired for
the user and this location should be disclosed and established as the 0,0,0 origin. In any case, where the
c
above description cannot be applied, the 0,0,0 point shall be ascribed and specified.
c
a) Side view (sagittal) b) Front view (frontal) c) Top view (transverse)
Figure 10 — Location of global origin as defined by the wheelchair frame geometry
5.4 Support surface axis system (SSAS)
5.4.1 General
The SSAS is a geometric axis system based on the axis convention defined in 5.2, but denoted with a
subscript “s”. The SSAS is used to specify the orientation, coordinate locations and linear dimensions, of
seating support surfaces in the three orthogonal planes.
5.4.2 Location of the SSAS origin
The SSAS origin (0,0,0 ) is the point at which a line, passing through the SSGC and parallel to the reference
s
plane of the rearmost seat support surface intersects the reference plane of the lowest back support surface.
See Figure 11.
a) Side view (sagittal) b) Front view (frontal) c) Top view (transverse)
Figure 11 — Support surface axis system
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ISO 16840-1:2006(E)
5.4.3 Coordinate locations of support surfaces
The coordinate locations of support surfaces are defined by values along the two axes in each orthogonal
plane. These locations are measured between the 0,0,0 origin and the support surface geometric centres of
s
each support surface. For each support surface in Figure 11, the support surface geometric centres (SSGC)
are shown.
5.4.4 Orientation of individual support surfaces
The absolute angle of a support surface is measured about an axis passing through the SSGC. When
specifying the absolute angle of a support surface in any of the orthogonal planes, a reference line, lying along
the plane of the support surface of interest, is extended from the support surface geometric centre. As
specified in Annex A, this reference line extends in a direction which allows measurement of the support
surface angle so that it can be correlated with the absolute angle of the body segment it supports. Figures 16,
21 and 24 illustrate absolute angle measures of selected support surfaces in the three planes.
5.5 Seated anatomical axis system (SAAS)
The SAAS is a geometric axis system based on the axis convention defined in 5.2 but denoted with a
subscript “p” The SAAS is used to specify linear body measures, and orientation in space of a person's body
segments in the three orthogonal planes.
5.5.1 Location of the SAAS origin
The SAAS origin (0,0,0 ) is the point at which the Z axis crosses the midpoint of a line joining the right and left
p
hip joint centres.
See Figure 12.
5.5.2 Body segments
Lines joining anatomical landmarks and/or computed joint centres define the body segments of postural
interest. Tables 1 (7.2.1), 4 (7.3.1) and 6 (7.4.1) define the anatomical landmarks, body segments and
segment lines in each of the three planes. The spatial orientation of the body segments relative to the axis
system defines the person's seated posture. Deviations of body segment lines from the designated reference
axis, projected to the three orthogonal planes, permit the measurement of absolute body segment angles.
5.5.3 Orientation of body segments
The origin for the axis system may be transposed to various defined locations on the body, usually joint
centres, thereby allowing measurements of body segment orientations relative to the reference axis (absolute
angles), or to each other (relative angles). The absolute angle of a body segment is measured about an axis
passing through the anatomical centre of rotation of that segment. Tables 2 (7.2.2), 5 (7.3.2) and 7 (7.4.2)
specify the points of rotation for each body segment in each plane.
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ISO 16840-1:2006(E)
a) Side view (sagittal) b) Front view (frontal) c) Top view (transverse)
Figure 12 — Seated anatomical axis system
6 Terms and definitions of support surface measures
6.1 General
6.1.1 Generic support surfaces with abbreviations
Definitions in this clause permit the quantification of the location, linear measures, and spatial orientation of a
seated person's support surfaces in the sagittal, frontal and transverse planes.
Generic support surfaces with abbreviations are used to represent various types of commonly used actual
support surfaces. All support surface designations refer to the part of the support surface in contact with the
person's body when in a seated position.
PS indicates a generic support surface in contact with a posterior surface of the body.
AS indicates a generic support surface in contact with the anterior surface of the body.
LS indicates a generic support surface in contact with a lateral surface of the body.
MS indicates a generic support surface in contact with a medial surface of the body.
SS indicates a generic support surface in contact with a superior surface of the body.
IS indicates a generic support surface in contact with an inferior surface of the body.
6.1.2 Coordinate locations of support surfaces
The axis system for defining the location of each support surface is specified in 5.4. Locations in each view
are defined by two coordinates (X,Y; Z,X; or Y,Z) measured from the 0,0,0 origin of the support surface axis
s
system (SSAS) to the support surface geometric centre (SSGC) of the support surface of interest.
NOTE The conventional medical terms inferior-superior indicate locations in the positive or negative Z direction; the
terms anterior-posterior indicate locations in the positive or negative Y direction; and the terms lateral-medial indicate
locations in the positive or negative X direction from the 0,0,0 origin.
s
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ISO 16840-1:2006(E)
6.1.3 Absolute and relative angles of support surfaces
Absolute angular orientations of seating support surfaces are values measured in accordance with the 360°
measurement convention. Tables A.1, A.2, and A.3 in Annex A define the axial orientation of the reference
lines for typical support surfaces in the SSRP in each of the three orthogonal planes. The direction of
extension of the reference line has been defined in such a manner that the angular measure of the support
surface correlates to the angular measure of the body segment being supported. Absolute angle
measurement definitions are provided for all three orthogonal planes. Relative angle definitions are provided
for the sagittal plane only since relative angles in the other two planes are rarely used in practice.
6.1.4 Linear measures of support surfaces
To differentiate between overall dimensions and intended contact surface dimensions, the word “effective” is
added to a term to indicate that the dimension describes the intended contact surface of the support surface.
The subscripts “l”, “w”, “d” and “t” are used to indicate length, width, depth and thickness, respectively. The
subscripts “el”, “ew”, and “ed” are used to indicate effective
...
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