close

Вход

Забыли?

вход по аккаунту

?

Arm lengths and arm reaches Some interrelationships of structural and functional body dimensions.

код для вставкиСкачать
Arm Lengths and Arm Reaches: Some Interrelationships
of Structural and Functional Body Dimensions
HOWARD W. STOUDT
D e p a r t m e n t of Physiology, Hci~vcir-dSchool of Pzihlic H e a l t h , Bostoii,
M n s s a c h u s e t t s 021 15
K E Y WORDS Anthropometry . Applied physical
ogy . Arm reaches . Measurement prediction.
anthropol-
ABSTRACT
Structural measurements of the human body have for the most
part been of little practical use as indicators of such functional body dimensions
as arm reaches. These dimensions, which define the area around the body to
which a person can reach given certain specified conditions and constraints
are often critical for the design and layout of workspaces. However, they are
relatively difficult and time-consuming to obtain, usually requiring specially
constructed measuring systems for each differing design situation, as well as
resurveys for each physically distinct population.
An alternate approach, described here, investigates the interrelationships between these two classes of measurements with the aim of predicting functional
reaches from structural body dimensions. In the present study traditional structural measurements and 117 functional arm reaches were obtained on 100
subjects. Correlations between the two types of measures are reported. Regression equations are presented which can predict functional arm reaches from
two structural body dimensions on anthropometrically differing populations
under a fixed set of workspace conditions.
Measures of anatomic arm length, such a s
shoulder-elbow or elbow-fingertip lengths,
have long been included in the battery of
dimensions taken in traditional anthropometric surveys. Such measurements, however, while useful for various purposes in
human biology, have generally been of
relatively little utility to those concerned
not primarily with the length of a person’s
arms, but rather with what he could do
with them, i.e., how far he can reach and
perform some specified task. These sorts
of data are of considerable importance to
the applied physical anthropologist, and to
all of those concerned with any aspect of
the design and layout of work and living
spaces, such as human engineers, industrial designers, and architects.
As a partial solution to this problem,
some anthropometric surveys have included certain limited kinds of arm reach measurements, usually two or three dimensions on the outstretched arm. Hertzberg
et al. (’54), for example, have measured:
(1) “arm reach from wall,” a wall-tofingertip dimension taken with both shoulAM. J. PHYS.ANTXAOP.,38: 151-162.
ders against the wall and the arm extended horizontally; (2) “maximum reach from
wall,” with the left shoulder against the
wall and the right shoulder thrust maximally forward; and ( 3 ) “functional reach,”
as in (1) above but with the tips of the
thumb and forefinger pressed together.
Similar reach measurements have also
been included in more recent anthropometric surveys (Clauser et al., ’72; White
and Churchill, ’71) with the addition of
a vertical reach with the arm extended
overhead.
Such “reach’ dimensions are also unfortunately of only limited use to the designer, since they describe a rather specific
type of reach to a single point immediately
in front of, or directly above, the subject.
These dimensions tell us nothing of what
other reaches might be to a myriad of
other points surrounding the subject though rough guesses or crude extrapolations can be made in some cases.
The kind of functional arm reach, as opposed to anatomic length, with which we
are concerned here, can best be defined as
151
152
HOWARD W. STOUDT
the distance between some fixed reference
point, either anatomic or extra-anatomic,
and a point in the area surrounding the
body to which a person can reach and perform some task such as touching, grasping
or manipulating. These reaches are determined not only by arm lengths, and other
measures of body size such as shoulder
height, but by many other variables as
well. The more critical of these relate to
biomechanical considerations such as the
range of motion at the joints of the body
and, perhaps more importantly, to the
position of the body when the reach is
being made. Body position, in turn, is affected by a series of non-biologic variables.
In the seated position these are: (1) the
characteristics of the seat including height
above the floor and angulation of seat surface and backrest; (2) constraints, if any,
to body movement, i.e., lap belts or shoulder harnesses, or objects in the immediate
environment such as control wheels, levers,
panels, etc.; (3) the specific reaching task
to be undertaken, whether a fingertip
button-push, whole hand grasp, or the
manipulation of objects with two hands,
etc.; and (4) the kind of effort required in
the reach, i.e., easy comfortable reach,
comfortable maximum reach, absolute maximum reach, etc.
Taking into account all the possible interactions of these variables and their resulting effects upon human arm reaches,
it can be seen that the measurement of
such reaches, and the systematic presentation of the data so that they can be most
effectively utilized, is indeed a formidable
task. We must remember that the equipment designer needs biologic data on human body movement which can resolve
specific questions such as the maximum
and minimum permissible limits, as well
as the optimum locations, of all controls
located i n the workspace.
In the past such determinations have
usually been made empirically, on a trial
and error basis. The results, while often
adequate for most people, were also often
inadequate for some people. It has become
increasingly apparent that for certain design areas at least, a more definite assurance of adequacy for all or virtually all
users was needed. Unfortunately, the complexity of the problem, and the seeming
impossibility of obtaining any generalized
sort of reach data applicable to a variety
of different conditions, has required each
different design area to have its own special reach study to account for the individual characteristics of that population, in
that workspace, performing that task.
PREVIOUS RESEARCH
The earliest applied anthropometric
study that attempted to deal sytematically with this problem was that of King,
Morrow, and Vollmer (‘47) who measured
139 subjects to determine the outer boundaries for the operation of manual controls. The subjects were seated in a standard pilot’s seat with a locked lap belt and
shoulder harness. The subject kept his
back against the backrest cushion, his
body in a n “easy sitting position.” The
measuring device consisted of a vertical
rod on a horizontal support. Each subject
reached for and touched points at different levels on the vertical rod as it was
moved toward him from different angles
to the right or left. Measurements were
made at six inch vertical levels from eight
inches below to 52 inches above a seat reference point, and at zero degrees and eight
other angles to the right and left of the
midline. The seat reference point (SRP)
was defined by the intersection of the
planes of the seat surface and backrest in
the midline. The measurements were made
horizontally at each level from the vertical
axis through the SRP to the maximum
point of reach. The resulting data were
presented in means and standard deviations for the reaches attained a t each level
and angle. A later study extrapolated the
values of these reaches to those that could
have been made if 18 inches of forward
shoulder movement had been permitted
(King, ’48).
Emanuel and Dempsey (‘55) continued
this general approach in a n Air Force
study of the effects on arm reach of a partial pressure flying suit. Reaches were
made both in shirtsleeves, and while wearing the partial pressure suit, at angular
increments of 15” to the right, from 0 ” to
135 along various horizontal planes. The
basic measuring device used has been described in detail by Dempsey (‘53). This
earlier data on military populations has
been largely superseded by the work of
O ,
153
ARM LENGTHS AND ARM REACHES
Kennedy ('64), who determined the outer
boundaries of grasping-reach envelopes
for a shirt-sleeved operator. Utilizing twenty male subjects, right arm reach was
measured on each of 12 horizontal planes
separated by five inch intervals from five
inches below to 50 inches above the SRP.
On each of these planes the measurements were taken at angular increments
of 15" to the right of the midline, 0" to
180°, and to the left of the midline to
165'. Hence, measurements were made
at a total of 24 vertical planes intersecting
with 12 horizontal planes, or 288 measurements for each of the 20 subjects.
The measuring apparatus consisted of a
hard wooden seat which rotated under a
wooden arch with measuring staves radiating toward the seated operator a t 15"
intervals. The task of each subject was to
grasp a knob on the end of each of these
staves and then to push the stave away as
far as he could until his arm was fully
extended without pulling his right shoulder
away from the backrest. The resulting
data were presented in tabular and graphical form for the first, fifth, fiftieth, and
ninety-fifth percentile reaches along horizontals radiating out from a vertical line
through the SRP.
Dempster and his associates (Dempster,
'55; Dempster, Gabel and Felts, '59) have
presented a n excellent theoretical and
methodological approach to the problem of
functional reaches and "kinetospheres,"
or the three-dimensional space envelopes
that surround the body, and which define
the limits of reach of the hands or feet.
While invaluable for a n understanding of
the biomechanical basis of reach, these
studies were not primarily concerned with
obtaining reach data for specific applications and hence have been of limited practical utility.
A somewhat different mechanical device
for obtaining arm reaches has been described by Wright ('63), but without applicable data. Ely, Thompson and Orlansky
('63)have presented summary data on arm
reaches in graphical form which are intended to aid the designer in locating controls within the workspace. Though perhaps useful as rough guides or indicators,
these data are somewhat lacking in specificity and may be difficult to apply, especially
since the means of determining the data
and the characteristics of the population
which they represent are not stated.
The only other major focus of interest
in arm reach studies has been the National Highway Traffic Safety Administration,
Department of Transportation, and the
U.S. automotive industry, who have been
jointly concerned with the locations of
controls that must be reached by drivers
wearing lap and upper torso restraints.
The culmination of rather extensive recent
studies carried out within the industry has
been summarized by Hammond and Roe
('72). Similar, parallel efforts have been
undertaken by Woodson et al. ('71). The
intent here has been to establish specific
guidelines for the locations of controls in
different kinds of vehicles which will be
adequate for specified percentages of the
driving population.
METHODS
In general then, the purpose of previous
arm reach studies has been either to develop methodologies or techniques for obtaining the data, or to obtain specific data
to answer immediate practical questions.
The investigation of the interrelationships
of structural and functional body dimensions has been largely ignored, though
such findings should ultimately be of considerable practical interest to all concerned
with equipment and workspace design.
What is needed here, ideally, is some way
of satisfactorily predicting functional arm
reaches from a battery of easily obtained
structural measurements, and a complementary set of workspace conditions, thus
obviating the necessity of a special study,
usually expensive and time-consuming,
for each new problem area.
Though the present study (Stoudt et al.,
'70) was primarily a n initial attempt to
provide data to assist in establishing the
outer permissible limits for the location of
controls in motor vehicles, it was also possible to investigate certain aspects of the
problem of predicting functional reaches
from structural body dimensions. A small
series of anatomic measurements was,
therefore, obtained on each subject on
whom the functional reach measurements
were made. These structural dimensions
were selected from those basic, commonly
taken measurements that might be expect-
154
HOWARD W. STOUDT
ed to affect in some way a person's ability
to reach. These measurements were: height,
sitting height, shoulder height, shoulder
(biacromial) breadth, anterior arm length,
elbow-fingertip length, and shoulder-elbow
length. In addition, weight, age, and handedness of each subject were recorded a s
was the preferred fore-and-aft seat adjustment.
The functional reach measurements were
selected primarily to define the areas in
which hand controls are most likely to be
located. This includes the region to the
driver's front and sides, from slightly
above the floor level to the top of the windshield. It was, therefore, decided to establish the lower vertical limits of the area
for the measurement of arm reach at six
inches above the floor and the upper limits
at 42 inches. (Since the present measuring
system is indexed to a reference point 9
inches above the floor, the upper and lower
vertical limits are expressed as 33 inches
and - 3 inches, respectively.) Within this
36 inch vertical range, measurements of
functional arm reach were taken at fourinch intervals, thus making in effect a
series of ten parallel horizontal planes
through the driver's workspace. The selection of the four-inch vertical intervals
makes possible the accurate interpolation
of reach values falling between any of the
measured vertical values.
Once the vertical conditions of measurement were determined, the lateral constraints of the measuring system were established. Since most controls used by the
driver are located in the general area to
his front, it was decided to take measurements at 0" (midsagittal plane), and a t
lo", 2 0 ° , 30°,40" and 50" to the right.
Beyond this area reaches are apt to be
less critical, though still of potential concern, so the interval of measurement was
increased here to include the additional
conditions of 70" and 90" to the right.
All the above measurements were made
with the right hand. Past studies of functional arm reach have generally assumed
that left arm reaches were, for all practical purposes, a mirror image of those for
the right arm, a n acceptable assumption
where any constraints on movement were
equal for the left and right sides of the
body. However, the realities of the present
situation are that the points of attachment
in the vehicle of the upper torso restraint
system, and its positioning on the body
can differentially affect the reach capability of the right and left arms. Hence i t
was necessary to make a separate series
of measurements for left arm reaches to
the left.
The resulting system of measurement
for functional arm reaches can best be
visualized as ten horizontal planes intersecting with 12 vertical planes, giving a
total of 120 different measuring conditions
or locations. Each horizontal plane, for
example, the one 33 inches above the H
point, will thus have measurements taken
at O " , 10" right and left, 20" right and
left, etc. In practice these 120 measurements have been reduced by 3 to 117 owing
to the impossibility of obtaining any reaches for many subjects at the lower level at
0" and 10" right and left.
The mechanical aspects of the measuring system are shown in figures 1 and 2.
The seat itself pivots about a vertical axis
through the measuring reference point to
attain the various reach angles to the
right or left. In addition, a vertical bar
rolls freely back and forth along two horizontal bars positioned directly over the
seat. The bottom of this bar is vertically
adjustable to each of the desired horizontal planes on which the measurements are
made.
After the subject was seated comfortably i n a normal position, the lap belt was
tightened and the shoulder harness adjusted with exactly four inches of slack. The
measuring chair was then positioned for
the 0" measurements, and the adjustable
vertical bar placed for the highest, or 33
inch, level. The subject was then told that
the white button at the base of this bar
would be pushed toward him until he
could easily reach it with the thumb-tip of
his outstretched hand and arm, with his
back against the backrest. He was then
asked to push the button as far away as
he comfortably could, leaning forward until restrained by the shoulder harness. The
vertical bar was then lowered to the next
level at 29 inches, the bar brought forward to the subject, and this arm reach
made a s above. This was repeated until
all of the ten vertical levels were completed
for the 0" reach angle. The chair was
then rotated 10" to the left. The button
ARM LENGTHS AND ARM REACHES
Fig. 1
155
Arm reach at 0 degrees, 33 inches above reference point.
to which the subject was reaching was
now located 10" to the right of his 0" center line. The vertical bar was raised to the
33 inch level, the arm reach measurement
taken and the bar dropped to the 29 inch
level. This same procedure was followed
until all reach angles were measured. The
thumb-tip reach utilized here is admittedly one rather specialized reach condition,
but it is a basic, easily defined one, and
more importantly, one for which it is possible to derive a standard series of correction factors to obtain any other desired
kind of reach, i.e., thumb-forefinger grasp,
full-hand grasp, etc.
In figure 1, the reach is being made a t
0 " in the midsagittal plane to the 33 inch
level above the reference point, the latter
indicated by the small white ball on the
vertical rod in front of the hip. In figure
2, the subject is reaching 40" to the right
of the midsagittal plane to a vertical level
nine inches above the reference point.
This reference, or H, point is intended to
correspond to the hinge point of the hip
and thigh. Anatomically it approximates
the palpable maximum lateral protrusion
of the greater trochanter. In practice,
however, it is very precisely defined and
located by a three-dimensional manikin
constructed for the Society of Automotive
Engineers ('70), and widely used by the
automotive industry a s a n initial design
point in vehicle seating and control placement. This H point, which defines one end
of our functional arm reach dimensions,
was established by placing the threedimensional manikin in the measuring
156
HOWARD W. STOUDT
Fig. 2
Arm reach at 40 degrees right, 9 inches above reference point.
seat used in these studies. Most importantly, however, it is a precisely fixed point
which can be easily located and measured
with accuracy and reliability. Other such
points might serve as well. (For more precise details of the construction and operation of the measuring apparatus, as well
as the rationale for the inclusion of its
various aspects, see Stoudt et al., '70).
Each of the reaches attained by the subjects was recorded photographically with a
35 mm camera equipped with a 250 exposure power-operated film transport. All
photographs were taken under identical
conditions of alignment of measuring seat,
reach target and camera. Every subject
thus had a single 35 mm frame taken a t
the farthest reach point attainable at each
of 117 different positions. To extract the
reach measurements from each of these
photographs, a Grafacon Model lOlOA was
used, which was interfaced with a small
PDP-8/S computer. The Grafacon is,
briefly, a n electronic tablet ten and onequarter inches square containing a grid
of 100 lines to the inch i n both the axes.
Any point on this tablet when touched by
the tip of a n electronic stylus can be defined in terms of the values of the coordinates of that point. Thus the computation
of the distance between any two points on
the tablet surface is a matter of simple
trigonometry.
To determine the arm reach measurements, the first slide in the film strip was
projected onto the Grafacon tablet. The
two reference points in this film, the H
point and the fingertip reach point, were
ARM LENGTHS AND ARM REACHES
then touched in turn by the electronic
stylus, the coordinates were processed
through the computer, and recorded both
on paper punch tape and on teletype
printout. The next photograph was then
automatically displayed by means of a
stepping motor on the slide projector. The
projector-to-tablet distance was set to permit the largest projection of that area of
the slides needed for data analysis. For
ease in computation and in running standardization checks of the system, the ratio
of Grafacon to “real world’ distances was
set at precisely 1:8, i.e., any eight inch dimension will, when photographed under
standardized conditions and projected
from a slide onto the Grafacon surface,
measure exactly one inch. The accuracy
with which repeated measurements of the
coordinates of the same point on a projected slide could be made was commonly
of the order of one coordinate line, or less.
Rarely was the difference as great as two
lines. Since there are 100 lines to an inch,
a reliability factor for repeated measurements on the tablet is about f 0.01 inch.
Applying the 1:8 conversion to obtain real
world measurement our factor increases
to about t 0.08 inch, or still less than
k 0.1 inch for the determination of most
coordinates.
RESULTS
Data were obtained in this study on 100
subjects, 50 males and 50 females, who
were selected to approximate the distribution of the general adult driving population in height and weight as determined
by the National Health Examination Survey (Stoudt et al., ’65). On each subject
the eight structural measurements previously noted, plus age and weight, were
obtained, as were the 117 functional reach
measurements. The correlations between
these two classes of measurements show
some interesting associations, especially in
view of a statement from the earliest study
of arm reaches by King, Morrow and Vollmer (‘47), that “. . . no one anthropometric
measurement is a satisfactory predictor for
effective reach. Prediction on the basis of
a combination of anthropometric measurements, although theoretically possible,
cannot be considered practicable.” Such a
position is no longer tenable in view of the
157
findings from this study, as well as those
of Kennedy (‘64). Table 1 presents correlation coefficients for the 9 structural
anthropometric variables plus age, and a
selected group of 24 (of 117) of the more
critical, or useful, functional reach dimensions.
In summarizing these findings we note
that age is very poorly if at all related to
reach capability. In the series of 117 correlation coefficients, almost all ranged between 0.0 and 0.1. Of these extremely low
correlations, 49 were negative, the rest
positive (only with age did any negative
correlations with reach measurements appear - all others were positive).
Correlations between weight and the
117 reach measurements were only moderate, ranging between about 0.2 and 0.5
and averaging around 0.4. Height was substantially better, varying generally between 0.5 and 0.7, and averaging over
0.6. Here, as elsewhere, the location of the
reach area affected the correlations. The
highest single correlation with height,
0.820, was found at the highest reach
level, 90” to the right. The lowest correlations, on the other hand, generally in the
0.400s and the very lowest at 0.378, were
almost always reaches to the very lowest
level.
Anterior arm length also showed uniformly high correlations with functional
reach, though often not quite so high as
stature. The values here also ranged between 0.5 and 0.7, averaging over 0.6.
Though it may seem unusual that arm
length, seemingly more closely related to
arm reach than stature, should not be
more closely correlated, the answer probably lies in the greater lack of reliability
of this measurement, being partly influenced by the extent to which the subject
presses his shoulder back against the wall
when the measurement is being taken.
Elbow-fingertip length suffers from no
such problems. It is an easy measurement
to take accurately, has high reliability,
and is clearly one of the major components
of arm reach. It shows, overall, probably
the highest general correlation with the
117 functional reaches. The intercorrelations are for the most part around 0.6 and
0.7. Shoulder-elbow height, another component of overall arm length, rather closely parallels the pattern of elbow-fingertip
0.028
0.029
0.033
-0.034
0.050
0.031
0.052
0.012
0.071
0.050
0.069
0.048
17
13
9
5
17
13
9
5
17
13
9
5
30
40
50
0.007
- 0.053
- 0.069
0.413
0.396
0.364
0.344
0.439
0.392
0.409
0.351
0.470
0.445
0.438
0.386
0.425
0.406
0.363
0.314
- 0.008
17
13
9
5
0.583
0.540
0.495
0.470
0.600
0.567
0.573
0.540
0.601
0.601
0.580
0.573
0.625
0.592
0.588
0.587
0.645
0.613
0.623
0.600
0.607
0.562
0.554
0.523
0.633
0.603
0.602
0.569
0.620
0.564
0.556
0.519
0.581
0.527
0.541
0.475
0.563
0.533
0.455
0.431
0.521
0.466
0.458
0.438
0.478
0.460
0.426
0.384
0.632
0.623
0.618
0.586
0.585
0.539
0.539
0.499
0.620
0.585
0.602
0.588
0.558
0.535
0.506
0.506
0.489
0.484
0.475
0.613
0.439
0.439
0.443
0.419
0.426
0.406
0.404
0.331
0.397
0.344
0.323
0.314
0.513
0.482
0.445
0.424
0.522
0.461
0.471
0.388
0.498
0.464
0.405
0.382
0.439
0.436
0.412
0.335
0.516
0.478
0.450
0.387
0.588
0.551
0.536
0.502
0.496
0.450
0.461
0.482
0.603
0.588
0.571
0.591
0.633
0.613
0.610
0.627
0.619
0.624
0.608
0.625
0.415
0.389
0.359
0.333
0.496
0.463
0.409
0.363
0.359
0.334
0.403
0.363
0.581
0.543
0.510
0.483
0.401
0.445
0.446
0.452
0.421
0.438
0.445
0.521
0.616
0.598
0.577
0.596
Heel pointH point
Shoulder
height
0.633
0.621
0.609
0.630
0.614
0.612
0.583
0.589
0.611
0.600
0.567
0.588
0.617
0.590
0.560
0.571
20
-0.147
- 0.109
0.631
0.607
0.585
0.597
0.396
0.363
0.304
0.222
- 0.043
- 0.066
17
13
9
5
10
0.593
0.546
0.576
0.197
-0.165
5
0.497
0.466
0.443
0.389
0.604
0.567
0.603
0.581
0.580
0.281
-0.110
9
0.506
0.467
0.598
0.599
13
0.583
0.501
0.629
0.634
0.585
0.594
0.354
-0.107
0.629
0.643
0.437
-0.056
17
0
Sitting
height
erect
Biacromial
breadth
Sboulderelbow
length
Elbowfingertip
length
Anterior
arm
length
Height
Weight
Height
(inches)
Angle
(degrees)
Age
Functional arm reach
(from “H” point)
Correlation coefficients f o r selected f u n c t i o n a l a r m reaches a n d s h u c t u r a l body d i m e n s i o n s , age, w e i g h t a n d seat a d j u s t m e n t
TABLE 1
v)
U
c3
3c
ARM LENGTHS AND ARM REACHES
length in its correlation with the various
functional arm reaches though the values
are usually slightly lower. It is possibly a
slightly less reliable measure than elbowfingertip length and is in terms of gross
size a somewhat smaller dimension.
Sitting height erect also correlates reasonably well with functional arm reach,
though not quite so well as stature or the
various segments of arm length. The range
is generally between 0.4 and 0.7. The pattern of the correlation of shoulder height
with functional arm reach is, not surprisingly, similar to that of sitting height. The
values of the correlations are, however,
somewhat lower, ranging generally between 0.4 and 0.6, averaging perhaps 0.4
plus. Shoulder breadth, or biacromial diameter, demonstrates the lowest intercorrelations of any of the anthropometric variables except weight. It varies usually
between 0.3 and 0.5.
The H point to heel point distance as
measured horizontally on the floor plane
from a vertical line dropped from the H
point is not a n anatomical dimension, but
rather an indicator of fore-and-aft seat
adjustment. As such, it is determined primarily by leg length and hence general
body size, and also by personal preferences
in seating comfort. The correlations are
moderately high, mostly around 0.4 and
0.5. Obviously longer reaches are indeed
positively associated with more rearward
seat adjustments.
To determine to what extent it is possible to predict dynamic measurements
from traditional anthropometric measurements, the eight static dimensions taken
in this phase of the study were included
in a regression analysis with a selected
group of functional arm reach measurements. The functional measurements selected were those which defined the most
commonly used area for the location of
controls in a vehicle, the region around
the instrument panel to the front and
sides of the driver. Four levels were selected for each of six angles for a total of 24
functional reach points to be predicted.
The levels were 17, 13, 9 and 5 inches
above the H point, and the angles were
O " , and lo", 2 0 " , 30°, 40°, and 50" to the
right.
The method employed was that of stepwise regression, in which one attempts
159
to obtain the best linear prediction of a
variable Y (in this case, functional arm
reach) from a series of X variables (structural measurements). It is important to
include only those independent variables
which are likely to contribute to the effectiveness of the linear relationship. Secondly, only those structural measurenients
should be utilized that are either commonly available, or can be relatively easily obtained, Obscure measurements, or those
difficult to take, are less useful. The eight
measurements included here meet the above
two criteria.
In addition, in developing the equations
the number of structural measurements
should be kept as small as possible. Too
many variables are undesirable, not only
because of possible difficulties in obtaining the data, but more importantly because
a smaller number of variables, perhaps
two or three, can often serve just as effectively as predictors. Theoretically only
those structural measurements should be
included which show a high correlation
with the dependent variable and a low correlation with each other. If two independent variables have a fairly high correlation with the dependent variable and a
low correlation with each other, both measure different aspects of the dependent
variable and both will contribute substantially to prediction. In anthropometry,
however, body heights and lengths, which
might be supposed to be the best predictors of functional reaches, are within
themselves, fairly highly correlated.
The basic data employed here consist of
values from 100 subjects for each of the 24
different functional reach positions and
the eight independent variables. Each of
these reach positions were run in turn
against the structural variables, and in
each case, those variables which contributed least to prediction were eliminated
step by step. In all of the 24 reach positions, the results were similar, Two measurements consistently emerged at the
end of each calculation that were clearly
superior for predictive purposes. With
these two static dimensions in the equations, none of the remaining six improved
the accuracy of prediction in any substantial way. These two measurements are:
elbow-fingertip length, and shoulder-elbow
length, both components of arm length
160
HOWARD W. STOUDT
and reach. In spite of the relatively high
intercorrelation of these two measures,
they nevertheless proved to be the best two
predictors when coupled together.
The resulting prediction equations are
presented in table 2. Here the arm reach
(in inches, the unit presently preferred by
designers) is computed from a constant followed by weightings for variables X (elbow-fingertip length) and Y (shoulder-elbow length). The latter measurements are
retained in millimeters since these are the
units in which they are normally obtained
from the anthropometer. The values that
result from the application of these equations are the average, or roughly fiftieth
percentile, reaches as measured from H
point to the thumb tip of the outstretched
hand. However, these equations predict
less accurately at the extremes of the
reach distributions. For this reason the
appropriate standard deviations obtained
in the analysis of the original reach data
have been included for each prediction
equation. With these standard deviations
it is possible to estimate given percentiles
from the predicted mean values as follows:
for the fifth and ninety-fifth percentiles,
1.645 X S.D. is subtracted or added, respectively to the mean; for the 1st and
ninety-ninth percentiles, 2.326 X S.D.
(see Damon, Stoudt, and McFarland, '66).
TABLE 2
Formulae f o r predicting functional a r m reaches f r o m structural body m e a s u r e m e n t s
u n d e r certain specified conditions"
Arm reach location
Angle
Height
Prediction formulae
S.D.
10
10
10
10
17
13
9
5
20
20
20
20
17
13
9
5
30
30
30
30
17
13
9
5
+ 0 . 0 2 3 +~ 0 . 0 2 9 ~
+ 0 . 0 2 2 ~+ 0.032;
+ 0 . 0 2 2 ~+ 0 . 0 3 3 ~
+ 0 . 0 2 8 ~+ 0 . 0 2 4 ~
0.94 + 0 . 0 2 5 ~
+0.028~
8.24 + 0 . 0 2 8 ~+ 0 . 0 2 6 ~
6.17 + 0 . 0 3 0 ~
+0.024~
2.99 + 0 . 0 3 2 ~+ 0 . 0 2 5 ~
1.21 + 0 . 0 3 0 ~
+0.023~
8.88 + 0.028x + 0 . 0 2 7 ~
7.87+ 0 . 0 3 1 +
~ 0.021~
3.21 + 0 . 0 3 3 +
~ 0.026~
+0.034~
10.77 + 0 . 0 2 4 ~
+0.035~
8.67 + 0 . 0 2 4 ~
7.45 + 0 . 0 2 8 ~+ 0 . 0 2 8 ~
2.98 + 0 . 0 3 1 f~0 . 0 3 2 ~
40
40
40
40
17
13
9
5
11.05+0.027x+O.O32y
8.16 0 . 0 2 2 ~ 0.042~
5.67 0 . 0 2 8 ~ 0 . 0 3 6 ~
5.57 0 . 0 2 7 ~ 0 . 0 3 2 ~
2.28
2.46
2.53
2.50
50
50
50
50
17
12.38f 0 . 0 2 8 +O.O29y
~
11.82 0 . 0 2 3 ~ 0 . 0 3 2 ~
9.02 0 . 0 2 6 ~ 0 . 0 3 1 ~
7.31 0.029~ 0.027~
2.41
2.59
2.61
2.81
0
0
0
0
17
13
9
5
13
9
5
10.37
8.31
5.55
3.86
+
+
+
+
+
+
+
+
+
+
+
+
2.11
2.21
2.26
2.33
2.13
2.29
2.36
2.41
2.21
2.30
2.29
2.47
2.30
2.31
2.37
2.57
Arm reaches in inches from reference H point
Angles in degrees right from reference H point
Heights in inches above reference H point
x = elbow-fingertip length i n mm
y = shoulder-elbow length in mm
* The specific conditions for which the measurement predictions are valid are: (1) a hard, non-deformable seat with a seat surface angle 17.5O from the horizontal, and a backrest angle 25O from the vertical;
(2) a n H point 9.0" above the floor, 3.8" from the seat surface, and 5.3" from the backrest (see text and
Stoudt et al., '70 for more specific details).
ARM LENGTHS AND ARM REACHES
Details of the specific stepwise regression
analysis utilized here are available in Neff
('69).
CONCLUSIONS
Functional arm reaches can be predicted from as few as two structural body
measurements with a degree of accuracy
that should be satisfactory for most design problems involving control location
and workspace layout. At present such
predictions can only be made within the
context of a fixed workspace configuration; that is, for each anthropometrically
distinct population, we can accurately predict the changes in functional arm reaches
that can be attained in that workspace.
However, prediction formulae determined
under one set of workspace conditions
will not necessarily still be valid if one or
more of those conditions are significantly
changed. What is needed now is a mathematical model of human reaching behavior which will take into account the effects of changes in any relevant workspace
variable and, in conjunction with limited
structural anthropometric data, generate
the desired functional reach dimensions.
LITERATURE CITED
Clauser, C. E., P. E. Tucker, J. T. McConville, E.
Churchill, L. L. Laubach and J . A. Reardon
1972
Anthropometry of air force women.
AMRL-TR-70-5, Wright-Patterson Air Force
Base, Ohio, pp. 1-1 157.
Damon, A., H. W. Stoudt and R. A. McFarland
1966 The H u m a n Body i n Equipment Design.
Harvard University Press, Cambridge, pp.
1-355.
Dempsey, C. A. 1953 Development of a workspace measuring device. WADC Tech. Rept.
55-53, Wright-Patterson Air Force Base, Ohio,
pp. 1-12.
Dempster, W. T. 1955 Space requirements of
the seated operator: geometrical, kinematic, and
mechanical aspects of the body with special reference to the limbs. WADC Tech. Rept. 55-159,
Wright-Patterson Air Force Base, Ohio, pp.
1-254.
Dempster, W. T., W. C. Gabel and W. J . L. Felts
1959 The anthropometry of the manual work
space for the seated subject. Am. J. Phys.
Anthrop., 17: 2 8 S 3 1 7 .
161
Ely, J. H., R. M. Thomson and J. Orlansky 1963
Layout of work places. In: Human Engineering
Guide to Equipment Design. Chapter 7, C. T.
Morgan, A. Chapanis, J. S. Cook, 111, a n d M. W.
Lund, eds. McGraw-Hill, New York, pp. 281320.
Emanuel, I., and C. A. Dempsey 1955 Unpublished data, Wright-Patterson Air Froce Base,
Ohio.
Hammond, D. C., and R. W. Roe 1972 SAE controls reach study. Paper 721099, Society of Automotive Engineers, Automotive Engineering
Congress, Detroit, Michigan, pp. 1-21.
Hertzberg, H. T. E., G. S. Daniels and E. Churchill
1954 Anthropometry of flying personnel 1950. WADC Tech. Rept. 52-321, Wright-Patterson Air Force Base, Ohio, pp. 1-134.
Kennedy, K. W. 1964 Reach capability of the
USAF population. Phase 1 . The outer boundaries of grasping reach envelopes for the shirtsleeved, seated operator. AMRL-TDR-64-59,
Wright-Patterson Air Force Base, Ohio, pp.
1-83.
King, B. G. 1948 Measurements of m a n for
making machinery. Am. J . Phys. Anthrop., 6:
341-351.
King, B. G., D. J. Morrow and E. P. Vollmer 1947
Cockpit studies - the boundaries of the maxim u m area for the operation of manual controls.
Report No. 3, Project X-651, Naval Medical Research Institute, National Naval Medical Center, Bethesda, Maryland, pp. 1-26.
Neff, R. K. 1969 Stepwise Regression, COPS&
Health Sciences Computing Center, Harvard
School of Public Health, Boston.
Society of Automotive Engineers 1970 Manikins
for use in defining vehicle seating accommodation. SAE Standard JS26, 1970 SAE Handbook,
New York.
Stoudt, H. W., A. Damon, R. A. McFarland and
J. Roberts 1965 Weight, height and selected
body dimensions of adults. United States 19601962. Public Health Service Publication No. 1000
-Series 11 - No. 8, Washington, D.C.
Stoudt, H. W., T. J. Crowley, R. A. McFarland,
A. Ryan, B. Gruber and C. Ray 1970 Static
and dynamic measurements of motor vehicle
drivers. FH-11-6569, National Highway Safety
Bureau, Washington, D.C., pp. 1-237.
White, R. M., and E. Churchill 1971 The body
size of soldiers. U . S. Army anthropometry1966. Tech. Rept. 72-51-CE. U. S. Army Natick
Laboratories, Natick, Massachusetts, pp. 1-329.
Woodson, W. E., D. W. Conover,'B. F. Pierce,
P. H. Selby and G. J. Pearson 1971 Driver eye
position and control reach anthropometrics.
Vol. 1. Static eye position, control reach and
control force studies. Rpt. MFI 71-117, Man
Factors, Inc. San Diego.
Wright, I. B. 1963 Applications of a system of
functional anthropometry in pressure suit design. J. Brit. Interplanetary SOC.,19: 31-41.
Документ
Категория
Без категории
Просмотров
3
Размер файла
937 Кб
Теги
structure, dimensions, interrelationship, length, arm, body, reaches, function
1/--страниц
Пожаловаться на содержимое документа