I MEASUREMENT OF SITTING AREA

malo subjects siting on the ecg lee nS ee ee
ibjects sitting on it
form (Fig 1). Note thatthe platom extends

4
Tg rertre

Figure 2. Sitting area (average per age groups)

Fi 2-shows an increase in sitting area
witheage up to 40 after which there isa Sealy



Per cent
of total
sitting .

Location

Table IV. Summary Data of Sitting Pressures

Area 1 Area It
10-60 Ibs/int 4-9 Ibs/in? ©
35 45
Under ischial == Near
tuberosities

tuberosities

Area Ht Area 1V
83 Iba/int 4% lbs/in?
210 38.0
Adjacent to” Peripheral
periphery

Table V. Subjects 1, 2, 5, 6, 8 of the Preceding Test were Used in This
Experiment.

Subject

COW IOm

Area I
10-60 lbs,

Area we
8.96 88.22
0 0

096 = 10.12

6.80
5.62

Area It
4-9 Ibs.

Area We
871 ©3648
0 0

25.68

29.30
4448

27.18

4.60
Ib/in*

-~T-

Area Ill Area IV
%3 lbs. 3-8 lbs.
Area We. Area Wt.
33.57 7891 = 18,75
8042 134.13 31.14 20.60
5342 168.90 7661 38.30
29.70 30.70 T1LS51 = 24.88
275 1950 107.94 26.98
43.17 16.78 73.33 6 25.9
1.78 0.354
+ Ib/in® D/in*


Table II. Height, Weight, and Age of Subjects

GUN ONE NED m8 OU ED SOON ENB OD ot 9 62 m1 MD mt tt OF ot mt OF mt OF C8 ON mt 6D OF mt 08 09 mt tm SP mt 08 ms

Number

TRESRRNRASTHSSSRESRSIVASSU SSR TAB SBRERRETEGTESS

Pieler Lt et Pt Pope r penn

Number Age

SEERSERGSESSRERR SRB eas Rassecg

Weight

TN ok tO tk ot tO eH 2 Ct eat 8 08 mt 6 rat OF OF HF mt C8 mt OF A mi OF OF me OF mt

Number

PEPE EEELEELEEEELLCEEREPE ELL ECEEC EES TT 1}

Weight

MAMOUS Treen en

SESESSSRKALTe

He Number
(nce

~4-

Pex



Table I, Summary Date of Sitting Area

Range Meson
Figure 3 is a plot of weight and area. Note * 101-2684 1704
that there is a positive relation between weight we cn") 4
and area of contact. There is also a Weight (Ibe) 108-200 14
relationship between area and height ( Fig, 4). ariel eo-23 2
Age (yrs.) 17-14 36

copy Aner

.
’
petiig rtii, rly

L : a

[ my } vot
t a ; oe
e- Hse | ; an

Figure 3, Plot of related to weight and Figure 4. Plot of sitting related to height and
age (100 Subpee . a age (108 Subjects) bd
'

i


III. STUDY TO DETERMINE DISTRIBUTION OF
PRESSURE OVER THE SITTING AREA

Table I of this report shows that average sit-
ting pressure ranges from .69 to 1.23 Ibs/in’ but
Hertzberg” has pointed out that sitting pres-
sures under the ischial tuberosities may be as
high as 60 Ibs/in’. This phase of our study was
was conducted to extend the above observations
W determining distribution of pressure over

e entire sitting area,

Prints (Fig. 6a and 6b) were made of sitting
Pressure distribution using absorbent paper over
inked cord cloth. Density of ink transfer
‘was calibrated in Ibs/in* and ‘the sitting pres-
sure prints evaluated using a photometer.

Repeat prints of a single individual showed

_ the of inking the cloth to be reliable
and lucible.

Four areas of density were established:

Area I — Very black = 10-60 Ibs/sq. in. Since
the inking became solid with 10 Ibs. or over
it was not possible to define the

of pressure. However, Hertzberg found max-
imum pressures in very small areas under the

tuberosities to ran, up to 60 Ib/sq. in.
Hence, we assume that solid black areas re-
present pressures between 10 and 60 Ibs./sq.
in.

Area IT — Dark lines almost mergihg = 4-9 Ibs/
8q, in. ’

Area IIl—Dark lines deparated by distinct
white lines = %-3 Ibs, sq. in.

Area IV ~ Dark lines incomplete = 1/8°1/2 Ibs/
sq, in, .

Results on 5 subjects are presented in Tables
TV and V.

Figure 6a. Sitting pressure
prominent Tul

Figure 6b, Sting remae pent of subject without

Averages for the group show nearly half of
the body weight is concentrated on 8% of the
sitting area, area is located

body structure, this percent of weight concen-
tration ran ay high 2 708 while Geen a,
highest pressure readings found in the entire
sittin; area did not exceed the limit of Area III,
i 3 iba/in' (See Fig 6b), ‘


971138

f

AN ANALYSIS OF SITTING AREAS
AND PRESSURES OF MAN

B
=
-

AS AD No. 211

caratogen ay ASTIA

r FEDERAL AVIATION AGENCY

AERONAUTICAL CENTER
. OKLAHOMA CITY, OKLAHOMA
.

JANUARY 1962



While addition of these chair accessories may

weight on a sitting platform by
more hes hs no follow that the aver-
ag. sitting pressure is reduced by a correspond-

SEAT SUPPORT
ONLY

by

a
to]

xs
°

Area in Squore inches

Weight in Pounds
°

WITH ARM RES’

'& SEAT BACK

ing amount. Figure 7 presents a comparison of
weight, area, and average pressure for each of
the sitting conditions,

WITH. ARM REST

SEAT SUPPORT {SEAT SUPPORT [SEAT SUPPORT
FOOT SURPORT 1@ FOOT

te

i

7. Relationship of weight, area and pressure in various seating arrangements

iti

Table VII.
Platform with
back, foot rest
chair arms
Area
eat 1576
63.2 L8TT
a3 LTS
85.0 Lm
S20 “2.050
100.7 Lig
38.6 1441
» 36 2.103
68.1 1.783



.. Contact areas were made of individuals
“seated relaxed on a transparent platform and
made from the supporting

weight readings
scales. A foot rest (18” below platform), chair

IV. EVALUATION OF THE USE OF CHAIR ARMS, SEAT
BACK, AND FOOT REST AS AIDS FOR REDUCING
SITTING PRESSURES.

arms (9” above platform), and a chair back

Sitting
Platform
with —

Foot Rest
only (1)

Chair Arms
only (2)

Chair Back
only (3)

Table VI. Reduction of Body Weight on Sitting Area by
Adding Chair Arms, Back Support, and Foot

Rest to Sitting Platform.
Experimental Weight Loss
Singularly In Combination
Loss of Bod: Si Los
weit ee, aed
Siting Area with — Sitting Area
Foot Rest. (1) and
184g Chairs Arms (2) 30.85
Chaie Arms (2) and
12.48 Chair Back (3) 16.45
1
‘ Foot Rests (1) and ‘
a4 Chair Back (3) \ 31.38
Foot Rests. (1),
' Chaje Arms (2) and
| Chie Back (8) 304g

(15° back of vertical) were added individually
and in various combinations to determine their
effects on reducing body weight on the plat-
form scales. Results are presented in Table VI.

Arithmetic Addition of
Individual Accessories

Platform
with

Foot Rest
Chair Arms

Chair Arms
Chair Back

Foot Rest
‘Chair Back

Foot Rest
‘Chair Back

Lose of Body
Sitting Area

18.48
12.42

12.48
448

16.85
18.48
448

18.48
148.


‘I. VARIATIONS OF THE SITTING CONTACT AREA
WITH MAGNITUDE OF EXPERIMENTALLY .
APPLIED FORCES

Each of the nine subjects was supported over
@ transparent sitting platform by means of a
special chest hamess and lowered stepwise so
as to make the platform scales read 5, 10, 15,
20, 40, 60, 80, etc., up to total body weight
After the scales supported the subjects’ total
weight, loads on the sitting area were further
increased by having him hold additional
weights in his arms namely, 20, 40, and 60
). Contact area tracings were made
each increment of weight and are presented
in Figure 5. Very large weight loadings on the
buttocks and thighs, such as are luced by
the vertical component of force in a crash, were
not investi ted I However, it may be noted vce
in this ly that man reached his maximum Figure 5. Area of si

AREA in Severe tones

cy $0 820 860"
Py

Poors
x it incriments

supporting area with his own body weight. (a seb wich
Table III. Subjects for Phase II The nine subjects used in this study fell with-
‘ in the age-weight-hei; range of the total
Subject Age , Heteht Weight group of subjects t in the seated position.
1 7 12" am
a 8 oe" 14
3 28 "” + 309
4 3 ar / Ws
8 31 oy i 3
6 28 ese 180 .
7 u n* 200
8 4 es” 181
® 30 es” 130
Averege 98.1 7 18.4
¥
-5-


Tig,

I, MEASUREMENT OF SITTING AREA

Figure 2. Sitting area (average per age groups)

Figure 2 shows an increase in sitting area
with age up to 40 after which there is a steady

Figure 1. Platform for measuring sitting areas
,

*


Pg,

AN ANALYSIS OF SITTING AREAS
AND PRESSURES OF MAN
J. J. Swearingen, C. D. Wheelwright, J. D. Garner

Studies of sitting area on a plane rigid surface for a of 104 male subjects were
made, Area was found to vary with cn and weight und to. increase with age up to
40 years after which there is a steady decline. Means were 179.4 sq. in. for area and

82 pounds/sq. in. for average pressure.
Sitting contact area was found to increase with experimentally applied force of
magnitudes up to something less than body weight. .
Analysis of pressure distribution in the sitting area reveals that nearly half of the
is 8% of the This ‘s under
body weight i supported on sitting area. high pressure area or
Over one-third of the body weight on the sitting is removed by the addition of
a footrest, chair arma, and a slightly doping seat beck. © ad

force and area relationships in more complex
seating designs. ms

Four different kinds of measurements are

Teported: ,

L Measurement of sitting area of a
group of male subjects 17-74 years of
age.

IL. Variations. of the sitting contact area
with magnitude of experimentally ap-
pliéd forces.

‘ TIL. Determination of distribution of pressure
over the sitting area.

IV. Evaluation of the use of chair arms, seat
back, and foot rest as aids for reducing
sitting pressures.

-1-


AN ANALYSIS OF SITTING AREAS
AND PRESSURES OF MAN

* J. J. Swearingen
C. D. Wheelwright
J. D. Garner
© Chief, Protection end Survical Brench

62-1

¥ CIVIL AERO MEDICAL RESEARCH INSTITUTE
FEDERAL AVIATION AGENCY

OKLAHOMA CITY, OKLAHOMA
‘Temnary 1008



BIBLIOGRAPHY

1, HERTZBERG, H.T.E., 1955. Some con-

tributions of applied physical anthropol
to human engineeri Am. N. Y. "hee .
Sci. 63:61 .
+
v : '
, '
&
FEDERAL AVIATION AGENCY AC @1-1178 “-10-
oe :