The Anthropometry of the Manual Work Spuce for the Seated Subject

29 Pages·2005·2.28 MB·English

The Anthropometry of the Manual Work Spuce
for the Seated Subject'
WILFRID TAYLOR DEMPSTER, W. CREIGHTON GABEL2 AND
WILLIAM J. L. FELTS3
Department of Anatomy, University of Michigan, Ann Arbor
This paper is an exploration of the isms involved. (A link is the straight line
space-geometry of hand motions as they or core line through a body segment be-
relate to young men in the seated posture. tween adjacent joint hinge points; it is the
It is primarily a presentation in functional mechanical unit of body motion.) Older
anthropometry, but the information de- sources that cannot be ignored in a func-
rived should have practical use in improv- tional-anatomical-anthropometric study of
ing the design of work areas. The pilot of this type are: Fischer ('07), Fick ('ll),
an airplane, the driver of an automobile, Strasser ('17), Braus ('21), Lanz and
the assembly worker or the machine oper- Wachsmuth ('35),a nd Mollier ('38). The
ator all perform critical tasks with their Albert-Strasser globographic technique (Al-
hands. Controls and switches or objects bert, 1876; Dempster, '56) for demonstrat-
upon which work is to be done must not ing the range of individual joint move-
merely be within reach, they should also ment has provided useful background ma-
terial. Equivalent work on living subjects
be placed in the best possible spatial posi-
is not available. Joint range studies on
tion relative to the operator. This ideal
living subjects are typified by papers by
position has not yet been prescribed.
Gilliland ('21 ) , Sinelnikoff and Grigoro-
A detailed job analysis of a specific man-
witsch ('31 ) , Glanville and Kreezer ( '37 ) ,
ual operation should of course improve the
Dempster ('55a) and Barter, Emanuel and
work area materially, but this information
Truett ('57). These studies are rather in-
has little transfer value to another situa-
complete for certain joints and are not
tion. Our work is concerned with the gen-
wholly satisfactory. Further work relating
eral range of hand motion, and we have
to age, sex, race, and occupation is war-
attempted to find principles applicable to
ranted.
all work situations involving the seated
During the past decade or so, various
position.
authors have touched on aspects of the
The approach is anthropometric-but in
work place. Motion and time study work-
an entirely different sense from traditional
ers (Barnes, '49; Branson, '52), psycholo-
anthropometry. Our measurements of the
gists (Chapanis, Garner and Morgan, '49;
space within reach of the seated subject
Hick and Bates, '50; McFarland, '53), en-
for all possible upper limb postures repre-
gineers ( Wallichs and Hulverscheidt, '35;
sent an approach to a dynamic anthro-
Davis, '49; MacNeil, '54), and physiolo-
pometry. The method of measurement is
gists (Taylor and Blaschke, '51) have di-
indirect, and it involves a certain novelty
rected attention to spatial aspects of hand
in anthropometric procedure; this shows
action. Dynamometric studies on hand
up especially in the methods of gathering
forces by Hugh-Jones ('45) and by Darcus
raw data, of making measurements, and
of treating data.
'This work was conducted under contracts
A study of the functional-anatomical
with the Wright Air Development Center (An-
background for limb motion paralleled this thropometry Section), Wright-Patterson Air Force
study. Relevant work (Dempster, '55a, Base, Ohio.
'55b, '56) involved a study of the motions Present Address: Department of Anthropol-
ogy, Northwestern University, Evanston, Ill.
of the major limb joints and a clarification
Present Address: Department of Anatomy,
of the characteristics of the link mechan- University of Minnesota, Minneapolis.
289
290 W. T. DEMPSTER AND OTHERS
('51), Salter and Darcus ('52), Darcus in effect, is the zero point on an x, y, z
and Salter ('53), Gaughran and Dempster coordinate system, to which are related
('55), Whitney ('58), and Dempster ('58) the variable distance and angulation of
are relevant also. Randall, Damon et al. the hand point as it travels in its outermost
('46) and especially King, Morrow and range over the surface of the space en-
Vollmer ('47), King ('48, '52), McFarland velope.
et al. ('53) and McFarland, Damon and The hand is a complex anatomical struc-
Stout ('55, '58) have considered dimen- ture; if a part of it is to be a reference
sional problems of the seated subject. point, a precise posture must be assumed.
Commonly these references relate to em- Our approach starts with the recognition
pirical studies designed to meet specific that the hand in a position of rest reflects
problems of military and industrial per- a balanced system of minimal forces. This
sonnel. is a sort of mean hand posture from which
other postures, including those involving
Orientation
finger activities, are deviations. Of course,
If a part of the body such as the feet or there is no one rest position; it varies with
buttocks is placed motionless on a support- how the hand rests with relation to the
ing surface, the relative range of motion forearm and with the degrees of wrist
of some more mobile part, as the hand, flexion or extension. When, however, the
may be defined in terms of a space geome- hand and forearm lie passively and supine
try related to the immovable region. In on a horizontal support with the wrist
effect, the body can be regarded as if it straight, the rest position is fairly average.
were within a three-dimensional Cartesian This rest posture is approximately the
coordinate system which has its origin at same as when the hand lightly grips a
a point on the supporting surface; the po- cylindrical rod of about 30 mm (1 1/8")
tential motion of any moving point-for diameter. In our work the gripping of a
instance some point on the hand-may be standard rod proved an easy way of getting
located within a region or space envelope the hand to assume a position comparable
with boundaries that may be scaled off to the mean rest posture. Now, when the
relative to the x, y, and z coordinates. In hand gripped such a rod and the hand and
the present study, the subjects were al- forearm hung inert and vertically, the grip
ways seated. The envelope has a specific angle for 40 men relative to the long axis
size, shape, and relation to the seat, trunk of the forearm was found to be 102" 6"
and legs; like the atom or solar system, (obtuse angle on the radial side). (The
however, it is bounded by an intangible grip axis was also about 14" more supine
surface which in this instance represents than a line between the radial and ulnar
the extreme range of motion of the refer- styloids in the semi-prone position [Demp-
ence point of the hand in different direc- ster, '55al. ) The grip angulation increased
tions. The space itself is merely the re- as rods of notably larger diameters were
gion of potential position of the hand point. grasped, but it was little changed for ob-
In order to visualize the space envelope jects down to the size of a pencil.
and its modifications for different condi- In this study the axis of the grip was
tions, both the seat and the hand refer- regarded as the core line of a 30 mm rod
ence points must be clearly identified. held in the hand. The thumb, or radial
For the seated subject the most stable end of the rod, was used as a pole of refer-
body region is that part touching the seat. ence. A point on the axis of the rod at the
In our procedures the subject's head lay level of the third finger was arbitrarily
in contact with a dental head rest, the taken as the hand point or grip center-
back was against the wooden seat back, hereafter called "grip point."
the buttocks were well back on the seat, It is the outermost range of this grip
and the thighs were directed forward; point which, according to our usage, con-
thus the trunk was relatively stable for all stitutes the surface of the space envelope.
hand positions. We have selected the mid- At the surface of the space envelope as
sagittal point of the junction of the seat defined by the grip point, the fingers or
and back as a reference ("R") point. This, any other part of the hand may momentar-
ANTHROPOMETRY OF THE WORK SPACE 291
ily lie exterior to the grip point and to this We employ the term kinetosphere, from
extent they will project outside of the hineto, movement, plus sphere, region of,
space envelope; similarly, the subject’s as an aid in analyzing the work area.
body, and parts of the arm in certain posi- The term applies to the total range of
tions, lies outside. Since the position of translational movement of the end member
rest of the hand is a generalized mean of a series of links relative to an “ Rp oint;
posture, the space envelope for the index moreover it applies only to the arbitrary
finger tip of the pointing hand, or for the situation in which the end member is
pinch position of the fingers, can be de- continually maintained in a constant an-
rived by adding appropriate dimensions gular orientation relative to a system of
to the front surface of the space envelope reference coordinates. In this study the
for the resting hand (and subtracting from hand was always directed straight for-
the rear surface). ward; other kinetospheres could be defined
The hand mass of the seated subject for study with the hand pointing up, to the
may be moved in either of two ways; it left, or down.
can move by rotation or by translation. In One should appreciate the nominal char-
rotational or angular movement, the hand acter of the kinetosphere. It is not merely
may be turned or twisted so that the angle another word for the work area but a con-
of the grip axis is changed relative to the cept which defines the space-shape which
Cartesian system (or the floor or walls of a encloses a specific class of hand motion,
room). In translational movements, how- translational movement only, so that it
ever, the grip angle remains constant; the can be analyzed. The dimensions of such
hand in translational movement may be an envelope may be measured, and its
moved in a straight or curved line in any shape may be reconstructed. The bound-
direction, but there is no angular change ary outlines of sections through the kineto-
in the grip axis relative to the room. The spheres can be grouped and compared, and
hand may move through three degrees of similar kinetospheres from different indi-
freedom for translational movement-up viduals can be combined and averaged.
and down, right and left, forward and The variability from subject to subject can
backward. It may also move through three be treated statistically. But kinetospheres
additional degrees of rotational freedom- have no existence apart from a rigidly im-
rotation in the sagittal plane, rotation in posed set of conditions, which limit the
a coronal plane, or rotation in a transverse hand to purely translatory types of mo-
plane; but it has only these 6 degrees of tion. The value of the concept is both in
freedom for potential movements. In our its use as an analytical tool for exploring
approach, translational movements of the body motion and in its ability for defining
hand, it will be seen, will receive primary the space requirements for types of hand
attention. motion. The designer of planned work
When the hand, as the end member of areas should thus be aided practically.
a chain of extremity links, is kept in a Each arbitrary hand orientation has on-
constant angular orientation relative to a ly one kinetosphere. When a group of
fixed “ R point, movements at the wrist, kinetospheres representing a related ser-
elbow and shoulder permit an extensive ies of hand orientations, i.e., different
range of translational hand movement. classes of grip rotation for the same direc-
The space envelope enclosing the total tion of hand pointing (viz., forward), are
range of such translational movements added to one another, we call the cumula-
has a distinctive shape, which results from tive pattern a strophosphere from strophe,
the unique combination of both the range a turning or twisting, plus sphere, region
and freedom of joint rotation by all of the of. The related series of hand grip orien-
upper limb joints and the limitation im- tations may represent a series of discrete
posed by the constant orientation of the wrist tilts in the sagittal plane (relative
hand. The relative dimensions of the limb to the room); the series may involve a
segments in different people, of course, prone to supine twist about an antero-
also have a determinant relation to the posterior hand axis (again relative to the
shape but this effect is small. room), or a wrist movement may be con-
292 W. T. DEMPSTER AND OTHERS
cerned with side-to-side hand postures it described a circuit at the extreme limit
about a vertical axis. The term applies of movement. In his hand he held an
to the space envelope, which permits three appliance consisting of a screen grid and
degrees of translational freedom for the an adjustable hand grip (referred to later)
hand plus one degree of rotational free- which assured that the grip axis was main-
dom relative to fixed coordinates. (Other tained in some standard orientation
strophospheres, not studied, can be visual- throughout the circuit. Then the seat
ized-the hand and forearm pointing up, and subject were advanced a measured
in, out, or down, in each instance includ- distance relative to the plane of the screen,
ing a systematic grouping of rotational and a new hand circuit was photographed.
motions.) When one or two additional The subject was moved forward progres-
degrees of rotational freedom are included, sively in this step-wise fashion and addi-
the complexity increases, since the se- tional hand circuits were recorded for
quence of adding involves 6 possibilities each position of the seat and subject until
of combinations; thus the value of the each level of the whole kinetosphere had
analysis breaks down.
been photographed. The photographic re-
Through kinetospheres and stropho-
cords provided a group of equally spaced
spheres, however, one may dissect the
frontal serial sections through the kineto-
work area in terms of the hand positions
sphere. From these, a variety of data could
which are possible in different regions of
be derived, including three-dimensional
the total space within reach.
models.
A more extensive term ergosphere, from
The seat on which the subject sat was
ergo, work, plus sphere, region of, or work
of wood, and it had a back and a headrest.
area, may apply to the total range of pos-
The basic plan was that of the Air Force
sible hand positions relative to an “R”
fighter cockpit of the early 1950’s. The
point; we would apply the term ergosphere
seat was 15 in. deep and 11 in. wide; be-
to the hand space representing wholly un-
cause of the narrow seat back, the sub-
restricted movement for any and all hand
ject’s elbows and shoulders were unim-
and forearm orientations-the only con-
peded, thus the posterior range of the
dition would be that the subject’s back
grip point was not artificially reduced. The
and buttocks had the constant relationship
seat was tilted 6” to the horizontal. The
to the “ R point.
back was 26 in. high, and it tilted back
METHODS 17” from the vertical. At the top of the
Twenty-two male college students (ages seat back, an adjustable dental headrest
17-33) formed the study sample. In build was mounted. The position of the foot-
they ranged from median to muscular; rest and foot platform relative to the seat
rotund and thin types were excluded. The could be adjusted by oblique upward and
more significant mean dimensions were : forward movements as in the airplane
stature-175.7 +- 4.5 cm (69.4 in.); sitting cockpit, so that individuals of different
height-91.5 2 3.2 cm (36.1 in.); acro- heights could be accomodated comfortably.
mial height (sitting)-61.3 -C 3.2 cm Through adjustments of the height of the
(24.2 in.); and upper limb length (acro- foot platform, the vertical distance be-
mion to dactylion 111-arm straight, hori- tween eye level and heel was made a stand-
zontal, and forward)-72.8 c 2.9 cm ard 39.5 in. for each subject.
(28.7 in.). As shown in figure 1, several wire grids
Our primary records (fig. 1) were a (1 X 2 in. mesh) were suspended from an
series of photographic negatives-time ex- overhead horizontal bar parallel to the
posures in the dark-which showed the picture plane of the camera to provide a
path of movement of a small light at the frontal reference plane behind which the
hand (i.e., over the “grip point”) as it hand could move. A large 5 X 7 ft. mirror
was moved by the subject. The subject sat set at 45”-0n the subject’s left-showed
facing the camera in a special seat and, a side view of the grid, subject and seat.
€or the first record, he moved his hand The hand appliance (fig. 2), which was
over a wire screen at arm’s length so that constructed for the left hand only, con-
ANTHROPOMETRY OF THE WORK SPACE 293
sisted of a handle-a 30 mm aluminum be attached at one or another of a number
rod-and a small rectangular orientation of selected angulations relative to the hand
grid. Scotch-lite reflective tape was added grip. When the grip was held firmly in
to the vertical midline and the horizontal the subject’s left hand and the forearm,
borders of the grid to enhance visibility wrist and grip were aimed straight ahead,
in the photographs. Dental moulding com- with the grip vertical, the grid was initially
pound was shaped about the aluminum set upright in the frontal plane (i.e., 0’).
rod to provide a good fit for the thumb, After this initial adjustment, 7 other grid
palm and fingers of the left hand; thus positions (fig. 2) were obtained by screw-
the handle could be grasped in only one ing the grid to the ball at other standard
way. An aluminum ball at the thumb end angulations. In each position the grid
of the grip had a series of threaded taps and the grip were oriented at a specific an-
by which the small rectangular grid could gulation to one another. When the grid
Fig. 1 Method for recording extreme movements of the “grip point” of the hand in the plane of
the wire screens. The figure at the right is a 45” mirror image of the subject shown front view. Dur-
ing a time exposure a flashing light at the level of the grip point marks out a path of movement. The
hand grid assures a vertical hand grip orientation. Fixed reference lights lie over the sternum; other
moving lights are attached to the shoulder and elbow.
294 W. T. DEMPSTER AND OTHERS
PRONE
Fig. 2 Hand grip and reference grid designed to keep the hand in a fixed orientation while hand
movements were recorded. The 8 standard hand orientations studied are illustrated.
was held upright in the frontal plane (for over the shoulder and elbow joints. A
instance, behind and parallel to the hang- flashing rate of 6 per second, controlled
ing grids of figure l), the hand grip axis by an electronic system, allowed easy dif-
of necessity assumed some fixed angula- ferentiation of traces when more than one
tion to the vertical. Five grip orientations appeared on the film. A Graflex camera at
in the sagittal plane (relative to the room) 15 ft. distance from the reference plane
were permitted and these were: 30" back of the suspended wire grids included a field
(i.e., -30"; upper end of the grip directed like figure 1. A red lens-filter transparent
backward and upward), 0" vertical, 30" to neon light was fitted to the camera, and
forward, 60" forward and 90" forward a low-intensity blue light that did not re-
(i.e., the grip was horizontal and directed cord through the filter was used for gen-
forward). In adidtion to the 0" position, eral illumination of the otherwise dark-
three other positions in the coronal plane ened room. Dark backgrounds were pro-
were permitted by the ball at the hand vided for both the direct and mirror-image
grip. These were the prone and supine views.
positions and a vertical position with the For the record-taking, the subject sat
thumb downward-the invert or 180" squarely against the seat back and head-
position. rest, and he directed his arm straight for-
A 1/25 watt neon glow lamp was ad- ward with the shoulder protruded and the
justed to the hand grid, so that its position grid of the hand grip held behind and par-
in photographic records lay at or near the allel to the suspended reference grids.
center of the grip, i.e., the "grip point." While the arm was in this position, the
Sometimes other lamps also were fitted seat was moved forward or back until the
ANTHROPOMETRY OF THE WORK SPACE 295
distance between the grid plane and the Since the records were intended to show
“R” point of the seat was as short as pos- the range of hand motion, it was import-
sible-a three-inch or less clearance was ant that adventitious trunk movements did
permitted for the movements of the hand not augment the motion. Figure 1 shows
grip. The actual seat-to-grid distance was a yoke of sheet lead lying on the sternum
measured and recorded. When this ad- with flashing neon lights over the manu-
justment was made, the reference grid at brium and xyphoid. Where the photo neg-
the hand was 3 in. or closer to the zero atives showed that the lights had moved as
grids. much as 1.5 in. during the clockwise and
The first photo record was taken with counterclockwise movements of the hand,
the neon lights flashing as the subject the record was later repeated.
slowly moved his hand clockwise in the The photo negatives for each subject-
frontal plane-then counterclockwise- grid distance were projected in an enlarger
through the widest possible complete cir- to exactly 1/5 natural size. Tracings of
cuit. The hand grid was to be kept con- each negative were made on paper sep-
stantly in its upright orientation just be- arately, including neon light paths as well
hind the reference grid; this was critical as orienting landmarks and dimension
since a constant grip orientation was es- marks in the background. Next, as a sep-
sential if the hand motion were to be arate operation, a mean circuit was drawn
strictly translational. In the faint blue in between the tracings of the clockwise
light of the room, the camera operator and counterclockwise circuits of the neon
could see both the direct and mirror-view light; this mean circuit was thereafter
of the subject; the mirror-view showed the taken arbitrarily as the definitive record
reference grid edge-on, and any deviations of “extreme” hand movement in the plane
from the frontal plane could be seen. Any of reference.
sidewise tilting of the grid could be seen Planimeter measurements of the area of
directly. If any significant deviations were each mean circuit were then made from
seen, the camera operator could direct the the tracings. These areas were next plotted
subject to repeat the record. After prac- as ordinates on graph paper (fig. 5) with
tice runs in both the clockwise and count- a spacing along the abscissa comparable
erclockwise directions, the camera was to the distance between sections; the loca-
opened and the path of both circuits of tion of the “ R point and reference grid
the neon lamp was recorded. At some time was also drawn on the graph. Two correc-
during the movement, a speed-lamp (= tions were necessary before the graph was
strobe) flash was set off to illuminate the strictly accurate; first, the mean antero-
whole view including an instantaneous posterior distance between the hand light
image of both the direct and side views of and the reference grids (as seen side view,
the subject (fig. 1). fig. 1) had to be measured; secondly, the
When a new film (super XX, film pack) distance between the light (or reference
was in place for a second exposure, the grid) and the grip point-different for
seat and subject were moved a fixed stand- each grip orientation-had to be added.
ard distance (three or 6 in.) closer to the After these corrections had been plotted
reference grid, and a new pattern of hand relative to the reference grid position, the
movement was photographed. After each plot was properly related to the grip point.
exposure, the seat and subject were ad- An accurate area-to-distance curve could
vanced by the standard distance until the now be constructed (fig. 5). The area un-
subject no longer had space to move his der the curve, as measured by planimeter,
hand between the reference grids and his corresponded (at one-fifth scale) to the
body. One or another panel of the grid volume of the kinetosphere.
in front of the subject was then raised or, In addition, through a treatment of mo-
if they touched him, removed. Movements ments along an antero-posterior axis (i.e.,
of the hand at the side of or behind the areas of sections x distances from a zero
body were traced over a single grid at the point) the fore-to-back distance of the cen-
left of the body. troid, or center of gravity, of the kineto-
296 W. T. DEMPSTER AND OTHERS
sphere could be calculated and located rel- ing” of the contours of two section cut-
ative to the grid plane and to the “ R p oint outs-the ones just anterior to and poste-
of the seat. rior to the centroid.
Next through the suspension of card- The three sections cutting the kineto-
board cutouts, the locations of the centers sphere in mutually perpendicular planes
of gravity were found for two sections- that intersected the centroid could be in-
that just directly ahead of and that im- terpreted as easily as three-dimensional
mediately behind the kinetosphere cen- plastic reconstructions; the shapes could
troid. The centers of gravity of the two be compared, by superimposing section
sections were located relative to a vertical outlines; the contours could be superim-
coordinate corresponding to the mid-sagit- posed and summated to give generalized
tal plane of the subject and a standard patterns for a group of individuals, or they
transverse coordinate near the shoulder could be grouped to show strophosphere
level; then tracings of the two sections patterns.
were superimposed and, by appropriate Actual three-dimensional reconstructions
“weighting,” a new “mean” section con- were made from tracings through repre-
tour with its center of gravity was drawn sentative kinetospheres. Much like the
in for the correct antero-posterior distance wax plate reconstructions of embryologists,
of the kinetosphere centroid. We assumed these models were made from slices of
that this section-centroid would have ver- Styrofoam plastic (12 X 12 X 0.6 or 1.2
tical and horizontal coordinates compar- in.); the thicknesses of the plates of foam
able to those of the whole kinetosphere. plastic were just 1/5 of the three or 6-in.
With this approximation, it became pos- distance that the subject was moved be-
sible to relocate the centroid of the whole tween records.
kinetosphere relative to the “R” point of In the initial photography, each of the
the seat-anteriorly, laterally, and ver- 22 subjects went through the procedures
tic ally. 8 times; each time represented a different
A convenient way of comparing kineto- hand orientation and hence a different
spheres involved the use of sagittal, front- kinetosphere. From each group of records
al, and horizontal sections through the (i.e., one kinetosphere for one subject),
centroid. This required a reconstruction we had as working data: (1) a group of
of contours from measurements derived 7 or 8 (or more) frontal tracings of mean
from the sections. The technique involved hand range having a known antero-poste-
first the marking of the horizontal fore- rior spacing, (2) plots representing sagit-
and-aft projection of the centroid of a ki- tal, frontal and transverse sections through
netosphere upon each tracing in a series the kinetosphere at centroid level, and (3)
of sections. Then, at points directly above area and volume data based on planimet-
and below the centroid on each section, ric measurements.
the distances to the section outline were Since the data relating to a single in-
measured. These measurements were next dividual were of limited practical inter-
plotted as ordinates on graph paper (above est, our data were typically summated or
and below a horizontal line indicating cen- averaged in some way. For numerical
troid level) ; the horizontal spacing was data, such as planimeter measurements of
comparable to that between sections. sections, kinetosphere volumes, and dis-
When the points were connected, the plot tances, individual records were simply av-
represented a sagittal section through a eraged. Where shapes were involved, com-
kinetosphere at centroid level. The “R” posite mean section contours were neces-
point, kinetosphere centroid, and other sary. The sagittal, horizontal, or frontal
points were added also. Comparable plots plots (through a centroid) of different in-
showing transverse measurements at cen- dividuals, as mentioned above, were super-
troid level permitted the development of imposed relative to the seat coordinants
a horizontal section through the kineto- (and other landmarks in the original pho-
sphere. A coronal section through cen- tographs) and traced in different colors,
troid level was determined, as mentioned to avoid confusion, on tracing paper or on
above (previous paragraph), by a “weight- translucent plastic; centroid locations
ANTHROPOMETRY OF THE WORK SPACE 297
were indicated also. The mean centroid mean deviation rather than standard de-
location for all of the similar kinetospheres viation has been used as a simple measure
together could be found through a con- to compare the variability of one region
sideration of their moments. After this of the space-shape with another; M.D. =
point had been located, 8-10 lines were VD/n).
drawn radiating out from the common cen- In gathering and processing the data,
troid to the contours of the superimposed utmost attention was paid to obtaining cor-
colored tracings. Along each of the radi-
rect orientations and dimensions. For this
ating lines, measurements were made of reason, the results obtained from the ma-
the distance from the centroid to each of
terial at one-fifth scale could be projected
the intersecting contours. These distances
back to natural size with no appreciable
were then averaged to give a mean dis-
loss of accuracy.
tance, and this was marked as a point on
All our records were taken from the left
the radiating line. A mean contour could
hand. Since the two hands should have
then be drawn through the points. In ad-
about the same range of movement, the
dition to the average contour, the distances
mirror image is roughly comparable to a
of the individual contours from the aver-
age were measured along the radii, and direct record. Thus, when right-hand ki-
the mean deviation was calculated. It netospheres are implied, they are simply
should be noted that the plus and minus mirror images.
4
Fig. 3 Seven contour outlines show the range of movement of the prone hand over a series of
frontal planes spaced at 6-inch intervals. The relative position of the seat and subject are shown also;
the lights attached to the yoke over the sternum indicated whether or not trunk movement contributed
to hand range.
298 W. T. DEMPSTER AND OTHERS
RESULTS knee and thigh contact intruded. The
Section contours and kinetosphere highest contour came to lie above the left
shapes shoulder. At the next section, there was
not room for forearm and wrist movement
Since the basic data for this study con-
between the body and the reference plane.
sisted of a group of mean tracings of
This limitation to hand movement pro-
frontal-plane serial sections through each
duced a definite posterior surface to that
of the 8 kinetospheres of 22 different men, portion of the kinetosphere in front of the
the general character and implications of
trunk region. Until the trunk hindered
the sections themselves must be appre-
movement, knee and thigh contact and the
ciated. The sections illustrated (fig. 3) maximum amount of abduction, flexion,
represent the range of motion of the grip
extension, or adduction permitted at the
joint of the prone hand directed forward
wrist joint were the limiting features to
for one of our subjects.
movements in the coronal plane.
After trunk contact with the wrist and
Superimposition of sections
forearm, the only territory free for addi-
The sections were superimposed rela- tional limb and hand movement was later-
tive to both the midline of the seat and a al to the trunk on the test-limb side of the
transverse line (near shoulder level) body. These contours became narrow ver-
through a landmark at camera height in tical ellipses, with the upper pole tending
the background of the original photo. One to deviate toward the head. Movement
sees a series of 7 rounded or irregular was restricted on the left because of in-
closed outlines which varied in size and ability to increase wrist abduction. Other
orientation relative to the subject’s body. boundaries were due to limited wrist flex-
The contours in this instance represented ion (above), to the amount of wrist ex-
sections at a 6-inch spacing through the tension permitted (below), and to body
kinetosphere. The first section, that far- contact (medially). At the extreme poste-
thest forward from the body, was ordi- rior range, shoulder retraction and elbow
narily roughly circular. If the subject flexion reached a maximum. It should
could scarcely reach the grid, the diameter be noted that the narrow seat back used
was small; in a larger contour, the first sec- did not restrict movement of the shoulder
tion could, as shown, have an irregular and elbow and that the hand could move
lower boundary over the knees. The limits about at the side of and even slightly
of forward movement for the maximally behind the body without artificial contact
protruded shoulder were determined by the restraints.
fact that the hand, because of the obliqui-
Total shape
ty of the arm in a wider circuit, would
move away from the plane of the hanging Although serial sections are informative,
reference grids. the three-dimensional character of the ki-
As the subject-to-grid distance was short- netospheres can be shown initially to better
ened, the size of the circuits increased- advantage by reconstructed plastic mod-
particularly in the upper range. As the els, such as that in figure 4. The model
seat-grid distance was further reduced, represented a smoothed composite of the
ligamentous restraints to wrist abduction mean space envelope for the prone hand.
on the test-limb side and limits to adduc- The principal bulk of the kinetosphere lay
tion on the far side defined medial and in front of the trunk and above the knee
lateral boundaries for movements of the and thighs, extending a full head higher
prone hand. At the same time, a lower than the mean sitting height, and its max-
limit was imposed by contact with the imum height was again above the left
knees or thighs. An upper limit was de- shoulder. The kinetosphere bulged medi-
termined by maximum shoulder elevation ally and laterally-mainly laterally-and
and by the tendency of the raised limb to it had a “wing” projecting to the left and
retract from the grid plane. The limita- backward to a point a little behind the seat
tions mentioned restricted movements to R-point. For the prone hand, much of the
broad, elliptical contours, except where restraint medially and laterally was caused