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Dear Biomch-L readers,
Last year, I was asked to send a memo to the Dutch Normalisation Commission
for NEN2738 ("Human Physical Load -- Terms and Definitions") on joint and
segment attitude representation, following the preceding debates on this list
and during the ESB Meeting in Aarhus/DK -- see the BIOMCH-L archives for
February, March, and August, 1990. [Contrary to the Biomch-L debate, the
memo had a length of one page only; it summarized the pro's and con's of the
Cardanic and (my preferred) `helical' angles.]
This morning, I received a copy of the published Norm (1st printing, 1 March
1991), following earlier, oral information that the various attitude represen-
tation conventions were considered too difficult to be included at the present
time. I believe that some of the definitions in NEN2738 (up for revision in 5
years) deserve to be posted on Biomch-L, and I hope that the open issues on
joint rotation centres, on laboratory, segment, and `joint' coordinate systems,
and on Cardanic/Eulerian, `helical' or other representations might be resolved
by that time.
In the Introduction, Norm NEN2738 is justified by reference to Dutch unemploy-
ment figures: chronic pain in the movement apparatus is t h e major cause
for unemployment benefits. By the end of 1986, 27% of long-term unemployed
people were classified under the heading "deviations of the movement appara-
tus", the largest of the 17 existing categories (Dutch unemployment benefits
start after one year of `sick leave', with different rules and categories).
Newly admitted persons for unemployment benefits in 1986 ranked highest in
this category (34%), followed by "psyche" (25%), "heart and vessel diseases"
(11%), "accidents" (5%), etc. I suspect that the first and last categories
could be merged to some extent, thus increasing the 34% figure.
While NEN2738 is concerned with p h y s i c a l loading, other aspects
should not be ignored. Its final items ( and ) are reminders of
the Norm's purpose and of the single-mindedness of a purely physical (bio-
mechanical?) approach. Clearly, when assessing unemployment elegibility,
all relevant factors should be considered.
The costs to society of unemployment, both humanly and economically, are
enormous, and justify unambiguous definitions for prevention, diagnosis,
and treatment. Among these, the definitions of 3-D joint and body-segment
coordinate systems, postures/orientations, and displacements are quite
relevant. The aims of NEN2738 are in particular:
a) to contribute to the unambiguous use of terms concerning physical load;
b) to normalise measurement methods for physical loading -- dorsal loading
especially. This is deemed important:
- for improving the exchangeability and comparability of scientific
research findings;
- for new regulations and legislation regarding physical loading in
occupational situations;
- for providing measurement methods that can be applied in practice.
In this context, I wish to remind you of Peter R. Cavanagh's 15 April dead-
line on proposals for the ISB Standardization and Terminology Committee .
The translations into English below are my own, and personal comments are
between square brackets [...]. The complete text (I do not know whether an
English version is/will be available) may be obtained from the Netherlands
Normalisation Institute, P.O. Box 5059, NL-2600 GB DELFT, The Netherlands,
Tel. +31.(0)15.690 390, FAX +31.(0)15.690 190, Telex 38144.
Herman J. Woltring
Brussellaan 29, NL-5628 TB EINDHOVEN, The Netherlands
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Netherlands Norm NEN2738, UDC 658.382.041:001.4, 1 March 1991
HUMAN PHYSICAL LOAD -- TERMS AND DEFINITIONS
Normcommission 302 02 "Physical Load"
.....
7 HEALTH EFFECTS
7.1 G e n e r a l
7.2 P h y s i o l o g i c a l E f f e c t s
7.3 B i o m e c h a n i c a l E f f e c t s
7.3.1 G e n e r a l T e r m s
[mechanics, kinematics, dynamics, statics, biomechanics, body support
planes and points, weight distribution, lever/moment arm of power,
right/left handed/leggedness, standing leg, force accrueing rate]
7.3.2 B i o m e c h a n i c a l M o d e l o f t h e H u m a n B o d y
7.3.2.1 biomechanical model; macromodel; body model: A mechanical equiva-
lent of the human body existing of links (body segments) and rotation points
(joints). By way of example, figure 1 [n/i] provides 18 links and 15 rotation
points. [n/i = not included.]
Elucidation
For conducting a biomechanical analysis of a person who is carrying out
his task, the human body is viewed as a mechanical system consisting of
more or less rigid body segments, connected together in the joints --
the rotation points. In this model, the joint axes are viewed as fixed
rotation points, whose positions are determined by means of external
corporal landmarks. [how can an axis be a point??]
Translations in the joints are not considered in this model. The con-
necting elements between two rotation points or between a rotation point
and the distal end of an extremity or of the head constitute the links
with known lengths and weights. The length of a link determined in this
manner has a maximal error of 5% [cf. D.B. Chaffin & G.B.J. Anderson,
Occupational Biomechanics, New York: Wiley, 1984].
A macromodel was adopted by means of which calculations can be carried
out in practical situations. This model cannot be used without further
=> considerations in pathological cases. [But then, how should this model
=> be used to assess unemployment eligibility in practical, pathological
=> cases???]
7.3.2.2 rotation point: Point about which the links make circular movements.
Elucidation
The rotation points represent the corresponding joints in the link model.
The positions of the rotation points are determined by means of palpable
body landmarks.
[specific rotation points are defined: head/neck, neck/trunk, L5/S1,
shoulder/upper arm, elbow, wrist, hip, knee, and ankle]
7.3.2.3 link, segment: Body part to which a mass, length and centre of gravity
are attributed in correspondence with the values belonging to that body part
according to an anthropometric table. [Inertial moments are n o t consi-
dered in NEN2738.]
[further, specific definitions: head, neck, trunk, pelvis, upper and
lower legs and arms, foot, hand, shoulder; rigid and deformable links]
7.3.2.6 link length: The distance between two adjacent rotation points
or from a rotation point to the end of the link (head, hand and foot).
Elucidation
Link length may be smaller than the length of the corresponding body part.
.....
7.3.2.8 angle between links; joint angle: Angle between the longitudinal
axes of adjacent segments.
Elucidation
The angle between the links when in the anatomical posture is 0 degrees
("extended posture", except for the foot). Angular orientation is in
=> conformance with a right-handed orthogonal, coordinate system. [This
=> seems to entail different signs for ab/adduction and endo/exorotation
=> between the left and right extremities.]
[Under the customary Cardanic convention, with ab/adduction the `floating
angle' and endo/exorotation about the distal segment's longitudinal axis,
the joint angle cosine is equal to the product of the flexion/extension
and ab/adduction angle cosines. Derivation of an equivalent relation for
the `helical' angles is left to to readership.]
7.3.3 coordinate system: A reference system for describing positions and
movements of objects in space or with respect to each other.
7.3.3.1 reference coordinate system; laboratory system: An orthogonal
coordinate system, the origin of which coincides with the projection on
the working floor of the midpoint of the line interconnecting the ankles
[with the subject in the anatomical position]. The positive X-axis is
oriented forwardly, the positive Y-axis points to the left [as seen by
the subject, not by someone facing him/her], and the positive Z-axis
points orthogonally upward from the XY-plane (see figure 2 [n/i]).
Elucidation
There is no normalisation in the biomechanical literature on the
positioning of the coordinate system to be used [various examples
are provided].
7.3.3.2 anatomical posture: Straight-standing attitude, facing straight
forward, feet in parallel and about 10 cm apart, knees in extension, the
arms suspended alongside the body with the palms facing forward, and body
weight distributed evenly over both feet (see figure 2 [n/i]).
7.3.3.3 local coordinate system: An orthogonal coordinate system whose
origin coincides with a rotation point and whose axes are defined on body
segments in the positions [postures, orientations -- positions and atti-
tudes?] corresponding to the anatomical posture (see figure 3 [n/i]).
7.3.3.4 corporal axes and planes in the anatomical posture
7.3.3.4.1 longitudinal axis; length axis: Axis in the longitudinal direction
of the body, of a body segment or link through the centre of gravity. [NB:
if the c.o.g. is important, why choosing the origin of a local coordinate
system at a rotation point , cf. also the definition of link length
as the distance between rotation points ?].
7.3.3.4.2 frontal axis; transversal axis: Axis normal to the longitudinal
axis running from the left to the right side of the body [as seen by the
subject].
7.3.3.4.3 sagittal axis: Axis normal to the plane through the longitudinal
and frontal axes, running from the rear to the front end of the body.
7.3.3.4.4 sagittal plane: A plane normal to the frontal axis. [This seems
confusing: should some named line not be normal to the plane with the same
name?]
7.3.3.4.5 median plane; midsagittal plane: Saggittal plane that separates the
body in almost equal left and right halves.
7.3.3.4.6 transversal plane (horizontal plane): A plane normal to the longi-
tudinal axis.
7.3.3.4.7 frontal plane: A plane normal to the sagittal axis.
7.3.4 position and direction as relative notions:
[specific definitions for caudal/inferior, cranial/superior, dorsal/posterior,
ventral/anterior, medial, lateral, distal, proximal]
7.3.5 movement: A displacement with respect to a specific point of reference.
Elucidation [* see footnote below]
The direction of movement is viewed with respect to the anatomical posture.
7.3.5.1 rotation: Circular movement about a point or axis [thus not necessa-
rily "orthopaedic" or axial rotation, cf. ].
7.3.5.1.1 flexion: Rotation (bending) about a frontal axis.
7.3.5.1.2 anteflexion: Flexion in the ventral direction.
7.3.5.1.3 retroflexion: Flexion into the dorsal direction.
7.3.5.1.4 extension: Stretching (rotation about a frontal axis), so as to
reduce the angle with an other link (goes to 0 degrees [cf. ])
corresponding to the anatomical posture.
7.3.5.1.5 abduction: Rotation about a sagittal axis into the lateral
direction (concerns the extremities).
7.3.5.1.7 lateral flexion: Abduction of the head or trunk.
7.3.5.1.8 endorotation: Rotation of the ventral side to median.
7.3.5.1.9 exorotation: Rotation of the ventral side to lateral.
7.3.5.1.10 axial rotation: Rotation about the longitudinal axis.
7.3.6 force: The influence on an object that changes the rest or motion
state of an object or that is necessary to maintain a specific posture
or movement.
7.6.3.1 external force: Force acting on the object from outside
[specific definitions for gravity, line of gravity, friction force,
carrying force, support force, and ground reaction force]
7.6.3.2 internal force: Force working on the structures in the body
[some overlap seems possible with ; perhaps, "on" should
be replaced by "between"].
7.6.3.2.1 joint reaction force: The reaction force working on the
cartilageous planes of the joint.
7.6.3.2.2 muscle force: The force exercised by a muscle on its insertion
points.
7.3.6.2.3 intra-abdominal force: The force originating from the intra-
abdominal pressure and working on a (transversal) section of the intra-
abdominal cavity.
7.4 D e l e t e r i o u s e f f e c t s :
- sickness absence;
- health damage.
7.5 B e h a v i o u r a l E f f e c t s :
- psychological effects;
- psychophysiological effects;
- sociological effects.
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[*] "There are six sorts of movement: generation, destruction, increase,
diminution, alteration, and change of place."
Aristotle (384 BC), Categoriae 15a, 14.