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The Effect of Seat And Table Height On Joints Comfort Angles And Seat Pan Pressure
Western Michigan University and Kalamazoo Area Mathematics and Science Center
By Kaylie Butt
May 2015
Introduction
Research studies have been performed concerning student workstations in the past, but
very little concerning the comparison between different types of seating structures and the height
at which the table of their workstation rests. The independent variable for this study is the type of
seating structure used: a stool versus a seat with minimal back support. These two seating
structures were considered to be the most common types of chairs that a student would encounter
in a regular school day, specifically for mathematics workstations, which often receive the least
amount of study in scientific literature. Previous studies considered the amount of lumbar
support provided as well as the resulting pain as the main elements of an ideal seat, but the force
exerted on other areas of the body parts are involved as well (Grandjean, 1997). Several studies
elected to study the effect of seating structures such as exercise balls in order to exert less strain
on certain sections of the seat pan (McGill, 2006), yet none have performed a comparison using a
backless stool and a seat with back support. The dependent variables of this particular
experiment are both the weight distribution exerted on the seat pan as well as the height of the
table of the workstation. The height of an average worktable in the experiment school, KAMSC,
was measured and recorded to be 30 inches. The ergonomically correct height for writing is
estimated to be just above elbow height, as described in Fitting the task to the human: a textbook
of occupational ergonomics (Grandjean, 1997). Furthermore, the elbow height of a subject is
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measured by having elbows at an approximate 90 degree angle, with arms extended, palms
down, and shoulders relaxed; and the measurement is then recorded by calculating the length
between bottom of the palm to the pan of the chair. This numerical value, known as the
“ergonomic height” was used during experimentation to assist in creating a table height that
would contrast the table height measured in the actual mathematics workspace, this was also
known as the “actual height: which was 30 inches. The pressure map will find the difference
between the center of pressure value for each subject and equilibrium center of posture in the pan
of the seat. The pressure on the seat pan will signify whether or not there is an equal distribution
of weight on the seat; the more “centered” the weight of the body is, the less strain is a specific
area of the body, which is an important factor when selecting an ideal seat (Legg, 2007). To
acquire the distribution of the pan, the map will be split into four quadrants. Due to the different
heights and weights of each subject, the data will be normalized into a proportion of which the
pressure of each quadrant can be compared across subjects, table heights, and chairs. Studies
have shown us that there are certain comfortable angles while sitting that are specified to be
“most ergonomic”, meaning the safest and most natural state, as well as the position that allows
the least amount of harm. To acquire these angles, reflective balls were placed over each joint
and then a video of the subject was recorded while at the workstation. Using an image taken
during the video, a straight line was drawn connecting each ball to the nearest joint and the
angles of each were taken from their proposed 90 degree starting point. To determine whether or
not there are any specific benefits to one chair or the different table heights, the angles were
compared to the table of ergonomic comfort angles for sitting found in the textbook Bodyspace:
Anthropometry Ergonomics and the Design of Work (Pheasant, 2005), which gives us a range of
what the angles should be. This absolute value of the difference was then compared between
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table heights, seat types, and subjects. The amount of static force that is exerted on the postural
joints is also considered to be another variable as well. The 3D SSPP Statistic Program creates a
rudimentary, virtual model of each subject and evaluates the static force on the joints of the hip,
knee, shoulder, and ankle joints. The force put on each muscle can be measured by the angle; and
as the distance between the angle measure and 90 degrees increases, the amount of force exerted
upon the joint due to gravity, weight, and body height also increases. The result of the 3DSSPP
analysis is a total overall injury probability and the repercussions of the injuries.(van Niekerk,
2008). The purpose of this experiment was to determine whether or not the seating structures in a
mathematics workspace were best suited for the tables at which they were placed and what seat
or table heights were the “most ergonomically” suited to improve the workstation.
Method and Materials
Pressure map Computer compatible with the pressure map (FSA4) and 3D SSPP programs Camera (Laptop connected) Stool Chair with back support Measuring tape Platform that can be raised to adjust height of knee Tape measure Table (with adjustable height) Reflective markers (with attachments) Two cameras (at different angles) Scale Yard stick Pressure map markers (pennies and duct tape)
1. Both the stool and the plastic chair were acquired from KAMSC. Markers were placed on
the chair to assure that the pressure map was placed in the same place each time. These
markers were pennies placed at the edge of the chair in three places and the stool in four
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with the edge sticking up. Then on the map with two different colors of tape the
corresponding edges were taped on the pressure map to line up each time.
2. Each student then had their weight, height, and sitting height measured, their dominant
foot, hand, and eye were also recorded. Eye dominance was tested by closing one eye
slowly one after another while staring at a point. The eye that keeps the point focused in
the same spot as when both eyes are open is dominate.
3. The height of a regular school desk was taken and the height of the workstation during
the study is put at the same height (30 inches).
4. Two cameras were placed at two different angles to observe the subject, one directly
behind the student to look for tilt of the upper body and torso from left to right, and a
second along the line of the torso to see all the joints involved in the task to be analyzed
against standard joint comfort angles and by the 3DSSPP.
5. The student then is equipped with 7 reflective markers at the 7 joints involved. There was
a light turned on at this point at a 45 degree angle to reflect off the balls into to camera
depicted by Figure 1.
Figure 1 Set up for data collection video
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6. Each student first sat in the plastic chair first that has been equipped with the pressure
map and the table is set to 30 inches. The data will be collected moments after sitting
down and beginning write. They will be in the chair for 1minute. For this 1 minute they
will be working on a math activity
7. While they are still in the chair a photo will be taken for further evaluation.
8. Step 7 was repeated with the same chair but at an ergonomic height taken by raising the
table to the palm of the hand when at elbow height.
9. Steps 6-8 were also repeated for the stool.
10. This process was repeated a total of 12 times with 6 females and 6 males.
11. The data from the pressure map was taken out of the FSA pressure mat software and put
into excel. The data was then trimmed to the appropriate size of the edges of each chair to
prevent artifact tainting. This is extra pressure from outside forces not being the subjects
body, this includes front of legs if they are touching the front of the mate and the back in
the chair if the subject was leaning back.
12. The photos taken were placed under overhead slides and finding each reflective ball
representing the joints were identified with a large dot the carefully connected by straight
lines to its corresponding dot. (Ankle to knee, knee to hip, etc.)
13. The angles were each manually entered into 3D SSPP software and create a model using
the demographic information we took to collect data from the model. An injury analysis
was the result for each of the four trial of each subject.
14. Pan pressure and angle deviation were compared via MiniTab.
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15. A statistical test of significance was then performed to identify a relationship between the
variables. A matched t –test in MiniTab between the pan pressure map quadrants of the
actual height to the new ergonomic height as well as the actual height stool data to the
chair was used then to show the effects.
16. A matched pair t-test in MiniTab was also used for each difference of the body angles
from the stated ergonomic joint comfort angles for sitting found by subtracting the actual
angle from the suggested value.
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Results
To allow use to compare across subjects and chairs the percent of pressures was
calculated in four quadrants as a percent of total pressure. The percent was calculated from the
sum of pressures in the mat area bounded by the edge of the chair to prevent artifacts
intervention. It was split equally left to right and top to bottom. If it was an odd number the extra
row was divided by two and added to each side as seen in Figure 3 of the example of the chair
data. Figure1 shows example of the stool data. Percentages were then created by adding up the
different areas and putting it over the total.
Figure 2 FSA pan pressure map of stool
3 4 5 6 7 8 9 10 SUM
D 0 0 33.16 37.92 26.32 16.65 1.15 0 115.2
E 0 96.86 51.11 48.99 45.51 74.89 47.22 1.14 365.72
F 32.62 53.96 34.25 21.89 20.26 40.48 18.48 1.31 223.25
G 34.25 31.24 34.92 19.07 38.59 44.35 23.65 5.54 231.61
H 15.11 17.28 19.48 6.46 2.62 15.77 14.67 1.14 92.53
I 11.61 8.21 20.7 8.01 1.83 16.36 9.48 3.12 79.32
J 42.78 33.14 37.2 28.89 14.3 24.79 17.99 3.46 202.55
K 36.76 46.68 56.44 74.96 54.82 61.42 46.02 15.52 392.62
L 0 74.62 68.29 75.08 53.15 28.11 21.89 0 321.14
M 0 1.38 53.7 60.86 38.27 11.42 0 0 165.63
SUM 176.13367.37 414.25
388.13 302.67 342.24
209.55 31.23 2231.57
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2 3 4 5 6 7 8 9 10 11 12 13 14 SUM
B 38 34.59 20.56 25.02 44.3 50.02 74.52 40.44 33.14 38.43 11.02 0 0 337.45
C 87 101.76 50.63 15.38 15.15 20.34 40.71 27.77 19.31 28.31 31.2 3.28 0 252.08
D 119 84.32 41.99 13.33 12.84 20.17 22.74 18.98 21.82 34.12 40.15 34.39 11.49 272.02
E 73 70.83 56.96 27.23 27.57 27.72 43.51 33.84 36.38 56.08 81.55 62.86 40.3 494
F 46 41.03 18.64 16.08 3.48 0 10.34 12.97 12.84 20.04 86.37 70.74 42.11 293.61
G 19 3.81 1.5 2.35 0 0 0 4.58 11.35 44.26 74.9 94.91 79.88 313.73
H 0 0 0 0 0 0 0 0 0 14.47 40.96 48.14 43.64 147.21
I 0 0 0 0 0 0 0 0 1.16 47.42 60.86 67.41 62.94 239.79
J 0 0.86 4.22 13.53 9.35 2.26 10.9 18.05 28.98 70.76 93.12 88.62 78.88 418.67
K 21 16.94 19.62 34.12 41.29 31.99 25.27 41.08 52.66 115.7 117.1 83.88 69.06 631.8
L 14 26.46 26.16 33.18 39.44 31.81 12.71 29.4 37.78 86.88 71.85 55.09 46.41 470.71
M 31 25.73 37.28 28.12 32.54 32.55 15.83 15.18 29.44 64.66 44.87 21.26 7.3 329.03
N 13 23.31 14.17 10.14 23.12 23.78 24.46 19.63 16.15 33.48 29.34 4.66 0 198.93
O 0 4.75 5.5 17 23.85 24.31 20.55 16.1 11.7 23.46 7.13 0 0 149.6
SUM 461 434.39 297.23 235.48 272.93 265 301.54 278 312.71 678.1 790.4 635.2 482.01 5443.76
Figure 3 FSA pan pressure map of chair
Quadrant 1 is the top left corner represented by the color green in Figure 2 and 3.
Quadrant 2 top right (blue), quadrant 3is the bottom left (orange), and quadrant 4 is the bottom
right (red). The resulting values of the percentage are displayed in Table A2
Table 1 Descriptive statistics of FSA pan pressure percentages
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The optimal pressure percentage left to right and top to bottom should be 50% to 50%,
likewise each quadrant should be 25% to reduce stress and create a more natural ergonomic
sitting state. The statistic percentages (Table 2) demonstrated that in an actual classroom
scenario, the stool tended to have little to no symmetry, as compared to the chair by an average
of about 5 %. This means that the chair allows 5% more of the pressure to be distributed more
evenly than the stool. There was also a noticeable almost 6.5% difference in stools equal
distribution in the pan at the ergonomic height. There was also about a 1.8% difference from the
chair’s ergonomic height from the actual. In Table A7 we can also see that top (representing the
back of the stool) for the actual table height and stool is less the bottom (the front) .But the
proportions become closer to 50-50 when the height is changed to the ergonomic height by about
4%. The same is true for the chair as well on about 2% change in distribution.
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When using a paired t-test on the statistics of the stool at ergonomic height verses actual
height it was found a p-value of .038. On the other seat, the same test the p-value was .208. Since
the p value of the stools t-test is less than that of the alpha value .05 we are 95% confident that
we can reject the null hypothesis and show that there is a positive difference from the ergonomic
table height from the actual height. This is not true for the chair.
After evaluating the angles of the subjects by the given methods, the next step was to
compare them to the given joint ergonomic comfort angles (Pheasant, 2005). The ranges of the
back inclination, shoulder, elbow, knee, hip, and ankle angles were. To compare the deviation
from these ranges was 0 if it was within the range, and if not it was calculated by subtracting the
lower bound from the angle if it was below the range and the higher if above (Table A4).
When using the angles in the 3DSSPP software the in injury analysis showed that there
were only three areas of risk, the knee, ankle, and back inclination angles. We know this because
the angle was over the range given to us that the angle is suitable ergonomically (Figure A1,
Table A1). On top of that we saw many variations in knee and ankle angles due to placement
behind, around the chairs legs as well on the ground flat or on the rung of the stool. This cause
the data to be varied in standards causing analysis to be futile as was proven statistically by a
paired t -test between stool’s ergonomic height vs. actual heights p value or .239 and the chairs
similarly at .568. We focused on the deviations in the back inclination angles. The matched t-
test for the stool’s ergonomic height vs. actual height gave a p-value of. 032 and showed the
chair test showed a p-value of .049. We can reject both null hypotheses and see that by changing
the heights to the ergonomic height in both chairs had an effect.
Conclusion
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Since the paired t-test on the statistics of the stool at ergonomic height verses actual height had a
p-value of .038 which is less than the alpha value we concluded that that there was a change
from the actual height to the ergonomic height. This change was due to the raising of the table to
the elbow height suggested in the literature. The matched t-test for the stool’s ergonomic height
vs. actual height gave a p-value of. 032 and showed the chair test showed a p-value of .049. We
can reject both null hypotheses and see that by changing the heights to the ergonomic height in
both chairs had an effect. Thus showing again, that the height of the table to elbow height on the
stools has a positive effect and reduces stress caused by improper sitting. Although we have
evidence from the t-test of the back angles that the lowering was effective also. It is uncertain by
failing to reject the null hypothesis of the first t-test of the pan pressure. This is most likely due
to the fact that we could not lower the table to the exact height past 28 inches. Further study
should be done with this capability. Since we used matched t-scores we can also assume that the
sample size is large enough to be significantly sufficient Further study should also be done with
the ankle and knee angles a the 3DSSPP analysis should a problem but our analysis came up
inconclusive. My studies such as Designing chairs with mounted desktop for university students:
Ergonomics and comfort (Mohamad, 2010,) have done such studies and looked at foot and knee
rests.
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References
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References (continued)
10. McGill, S. M., N. S. Kavcic, and E. Harvey. "Sitting on a chair or an exercise ball: various
perspectives to guide decision making." Clinical Biomechanics21.4 (2006): 353-
360.
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mounted desktop for university students: Ergonomics and comfort."International
Journal of Industrial Ergonomics 40.1 (2010): 8-18.
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Work, Third Edition CRC Press, 2005
13. van Niekerk, Sjan-Mari, et al. "Photographic measurement of upper-body sitting posture of
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Appendix
Table A1 3DSSPP Injury analysis full table
SubjectRun c1ah c1eh c2ah c2eh c1ah c1eh c2ah c2eh c1ah c1eh c2ah c2ehElbow 94 94 94 94 95 95 94 94 94 96 93 95Shoulder 99 99 99 99 99 99 99 99 99 99 99 99Torso 98 98 98 98 98 98 98 98 98 98 98 98Hip 96 96 74 84 85 95 96 96 69 87 94 84Knee 88 91 83 71 78 89 87 89 86 81 82 72Ankle 14 43 8 16 3 16 78 89 27 23 55 4Low Back 476.4 472.2 447.2 444.6 427.6 349.5 349.5 398.7 566 541 530 566SubjectRun c1ah c1eh c2ah c2eh c1ah c1eh c2ah c2eh c1ah c1eh c2ah c2ehElbow 95 94 94 94 93 93 96 94 95 95 96 96Shoulder 97 98 98 98 99 99 99 99 99 99 99 99Torso 98 98 98 98 98 98 98 98 98 98 98 98Hip 73 86 90 91 69 80 82 77 78 96 88 94Knee 89 82 71 71 75 74 79 81 77 86 81 89Ankle 55 83 24 73 35 71 24 50 89 89 65 76Low Back 522 554 533 522 480 551 513 547 531 535 497 566.8SubjectRun c1ah c1eh c2ah c2eh c1ah c1eh c2ah c2eh c1ah c1eh c2ah c2ehElbow 94 96 95 96 93 93 96 93 93 95 96 95Shoulder 99 99 99 99 99 99 99 99 99 99 99 99Torso 98 98 98 98 98 98 98 98 98 98 98 98Hip 91 89 77 83 89 70 78 73 91 96 83 87Knee 87 87 87 85 74 86 81 75 75 73 79 74Ankle 10 5 73 43 7 12 72 68 52 69 11 33Low Back 534 525 504 548 521 498 503 504 493 481 479 536SubjectRun c1ah c1eh c2ah c2eh c1ah c1eh c2ah c2eh c1ah c1eh c2ah c2ehElbow 94 94 94 94 95 95 94 94 93 96 96 96Shoulder 99 99 99 99 99 99 99 99 99 99 99 99Torso 98 98 98 98 98 98 98 98 98 98 98 98Hip 96 96 74 84 85 90 89 94 90 72 85 78Knee 88 91 83 71 78 89 87 89 78 88 76 87Ankle 14 43 8 16 3 17 78 89 85 21 76 6Low Back 476.4 472.2 447.2 444.6 427.6 349.5 349.5 398.7 478 482 514 508
11 12
1
7 8
4 5 6
9
10
32
Figure A1 3DSSPP injury analysis example
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Table A2 FSA Seat Pan Pressure map percentiles full table
Subject
Run c1ah c1eh c2ah c2eh c1ah c1eh c2ah c2eh c1ah c1eh c2ah c2ehTop 54% 60% 60% 56% 51% 53% 51% 60% 51% 56% 47% 49%
Bottom 44% 39% 31% 35% 47% 44% 46% 42% 48% 43% 51% 54%Q1 31% 33% 24% 21% 32% 26% 28% 15% 30% 31% 18% 17%Q2 23% 26% 36% 40% 25% 24% 21% 27% 21% 24% 10% 8%Q3 22% 19% 15% 17% 26% 29% 30% 34% 25% 20% 36% 41%Q4 22% 20% 16% 15% 15% 18% 18% 28% 23% 23% 33% 37%
Left 53% 52% 39% 37% 58% 55% 59% 48% 55% 51% 55% 58%Right 45% 46% 52% 54% 40% 42% 39% 54% 44% 48% 43% 45%
SubjectRun c1ah c1eh c2ah c2eh c1ah c1eh c2ah c2eh c1ah c1eh c2ah c2ehTop 51% 51% 52% 61% 71% 64% 45% 61% 52% 52% 53% 54%
Bottom 47% 49% 48% 40% 27% 33% 5% 40% 46% 46% 47% 46%Q1 36% 37% 20% 20% 22% 23% 2% 20% 18% 16% 9% 12%Q2 25% 30% 16% 26% 46% 37% 1% 26% 22% 25% 8% 9%Q3 26% 22% 36% 34% 24% 27% 44% 34% 29% 27% 45% 46%Q4 11% 13% 28% 19% 4% 10% 4% 19% 28% 30% 38% 34%
Left 62% 58% 56% 55% 47% 50% 46% 55% 47% 42% 55% 57%Right 36% 42% 44% 46% 50% 47% 4% 46% 51% 56% 46% 43%
SubjectRun c1ah c1eh c2ah c2eh c1ah c1eh c2ah c2eh c1ah c1eh c2ah c2ehTop 39% 36% 62% 45% 51% 52% 54% 44% 46% 67% 65% 42%
Bottom 59% 62% 48% 53% 47% 54% 53% 53% 52% 45% 47% 56%Q1 31% 39% 22% 25% 23% 30% 26% 33% 30% 20% 20% 29%Q2 21% 17% 29% 23% 28% 29% 31% 20% 16% 23% 25% 19%Q3 18% 19% 33% 21% 23% 23% 23% 25% 31% 44% 40% 23%Q4 28% 23% 25% 28% 25% 25% 27% 20% 21% 25% 26% 26%
Left 48% 57% 55% 46% 46% 53% 49% 57% 61% 64% 60% 53%Right 49% 41% 55% 52% 53% 54% 57% 40% 37% 48% 51% 45%
SubjectRun c1ah c1eh c2ah c2eh c1ah c1eh c2ah c2eh c1ah c1eh c2ah c2ehTop 40% 62% 55% 45% 51% 61% 58% 45% 36% 52% 45% 61%
Bottom 57% 48% 52% 51% 45% 49% 52% 51% 62% 54% 51% 49%Q1 30% 25% 11% 29% 35% 12% 17% 29% 39% 30% 29% 12%Q2 21% 17% 19% 18% 18% 27% 25% 18% 17% 29% 18% 27%Q3 20% 46% 35% 27% 34% 35% 34% 27% 19% 23% 27% 35%Q4 27% 23% 41% 21% 11% 37% 35% 21% 23% 25% 21% 37%
Left 50% 71% 47% 56% 68% 47% 51% 56% 57% 53% 56% 47%Right 47% 40% 60% 40% 28% 63% 59% 40% 41% 54% 40% 63%
54
1 2 3
10 11 12
7 8 9
6
Table A3 FSA Seat Pan Pressure map percentiles full table
Subject Chair and Table # Back inclination Hip Knee Shoulder Elbow Ankle side back1 Stool, Actual 20 109 69 51 112 98 91 Stool, Ergonomic 12 120 73 49 90 91 41 Chair, Actual 11 104 140 52 148 119 121 Chair, Ergonomic 15 111 140 63 90 122 52 Stool, Actual 18 107 72 18 102 122 82 Stool, Ergonomic 10 118 80 32 92 65 52 Chair, Actual 23 115 65 23 95 120 202 Chair, Ergonomic 22 92 117 20 90 98 53 Stool, Actual 18 111 84 37 132 98 23 Stool, Ergonomic 15 114 97 52 121 91 03 Chair, Actual 10 112 96 49 124 96 6
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3 Chair, Ergonomic 7 108 99 49 116 114 24 Stool, Actual 7 126 67 -5 100 56 -54 Stool, Ergonomic 3 124 69 -2 92 65 -34 Chair, Actual 25 108 69 61 121 81 -94 Chair, Ergonomic 12 104 70 53 114 75 -35 Stool, Actual 19 124 123 28 101 89 115 Stool, Ergonomic 15 134 118 23 96 83 35 Chair, Actual 26 106 69 33 91 59 -25 Chair, Ergonomic 20 91 92 31 73 90 -116 Stool, Actual 18 107 72 18 102 122 -36 Stool, Ergonomic 12 112 89 31 92 65 -36 Chair, Actual 24 96 79 59 120 76 -56 Chair, Ergonomic 29 99 88 62 110 90 -27 Stool, Actual 5 126 124 23 106 112 -57 Stool, Ergonomic 3 127 123 30 101 111 -27 Chair, Actual 24 90 45 20 89 103 -107 Chair, Ergonomic 15 89 91 39 110 90 -88 Stool, Actual 18 112 102 29 110 94 78 Stool, Ergonomic 12 121 100 38 113 120 48 Chair, Actual 16 91 72 43 106 90 78 Chair, Ergonomic 15 92 75 48 95 90 79 Stool, Actual 12 109 86 47 125 110 09 Stool, Ergonomic 10 112 86 36 124 110 -29 Chair, Actual 12 102 56 45 143 105 -19 Chair, Ergonomic 2 94 52 30 120 108 -6
10 Stool, Actual 4 130 69 42 119 66 410 Stool, Ergonomic 3 106 54 27 112 96 110 Chair, Actual -25 97 93 35 122 90 1010 Chair, Ergonomic -4 111 75 33 99 79 811 Stool, Actual 17 119 90 -8 76 90 311 Stool, Ergonomic 14 118 102 -6 79 90 611 Chair, Actual 5 96 55 0 97 78 411 Chair, Ergonomic 5 99 58 -10 64 87 412 Stool, Actual 4 130 70 40 119 66 412 Stool, Ergonomic 3 110 54 27 111 98 112 Chair, Actual 14 96 97 35 122 90 1012 Chair, Ergonomic 10 110 78 33 99 79 8
Table A4 Demographics
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*L represents the lowest height the table could go 28 inches. The eye, hand, and foot represent dominance.
Subject Hand Dominance Eye Dominance Foot Dominance Hieght Weight Elbow C1 Egro C2 Ergo Feet placed on Rung on stool1 right right right 162 138 16.5 35 low yes2 right right right 169.5 158 14.5 34 low no3 right right right 187.5 273 28.5 37 low no4 right right right 161.5 151.1 19 32 low yes5 right right right 173 230 24 34 low no6 right right right 163.2 1658 24 34 low yes7 left right left 167 190 30 33 low yes8 right right right 173 158.5 29 34.5 29 no9 left left left 170.5 130 23 32 low yes10 right left right 164 149 20 31.5 low yes11 right right right 172 142 22 33 low no12 right right right 167 165 31 34 low yes
Table A5 Difference of body angles to ergonomic joint comfort angle range (Pheasant 2005)
SubjectChair and
Table #Back
incline Hip Knee Shoulder Elbow Ankle1 Stool, Actual 0 0 -26 6 0 -2
1Stool,
Ergonomic -8 0 -22 4 0 -91 Chair, Actual -9 0 5 7 28 19
1Chair,
Ergonomic -5 0 5 18 0 222 Stool, Actual -2 0 -23 -12 0 22
2Stool,
Ergonomic -10 0 -15 -13 0 -352 Chair, Actual 0 0 -30 -22 0 20
2Chair,
Ergonomic 2 -3 0 -25 0 -23 Stool, Actual -2 0 -11 -8 10 -2
3Stool,
Ergonomic -5 0 0 7 1 -93 Chair, Actual -10 0 0 4 4 -4
3Chair,
Ergonomic -13 0 0 4 0 144 Stool, Actual -13 6 -28 5 0 -44
4Stool,
Ergonomic -17 4 -26 18 0 -354 Chair, Actual 0 0 -26 16 1 -19
4Chair,
Ergonomic -8 0 -25 8 0 -255 Stool, Actual -1 4 0 -17 0 -11
5Stool,
Ergonomic -5 14 0 -7 0 -175 Chair, Actual 0 0 -26 0 0 -415 Chair, 0 4 -3 0 7 -10
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Ergonomic6 Stool, Actual -2 0 -23 -12 0 22
6Stool,
Ergonomic -8 0 -6 0 0 -356 Chair, Actual 0 0 -16 14 0 -24
6Chair,
Ergonomic 0 0 -7 17 0 -107 Stool, Actual -15 6 0 -7 0 12
7Stool,
Ergonomic -17 7 0 0 0 117 Chair, Actual 0 5 -50 -10 0 3
7Chair,
Ergonomic -5 6 -4 0 0 -108 Stool, Actual -2 0 0 -1 0 -6
8Stool,
Ergonomic -8 1 0 0 0 208 Chair, Actual -4 4 -23 0 0 -10
8Chair,
Ergonomic -5 3 -20 3 0 -109 Stool, Actual -8 0 -9 2 5 10
9Stool,
Ergonomic -10 0 -9 0 4 109 Chair, Actual -8 0 -39 0 13 5
9Chair,
Ergonomic -18 1 -43 0 0 810 Stool, Actual -16 10 -26 -3 0 -34
10Stool,
Ergonomic -17 0 -41 -18 0 -410 Chair, Actual 0 0 -2 0 2 -10
10Chair,
Ergonomic -24 0 -20 0 0 -2111 Stool, Actual -3 0 -5 -38 -4 -10
11Stool,
Ergonomic -6 0 0 -36 -1 -1011 Chair, Actual -15 0 -40 -30 0 -22
11Chair,
Ergonomic -15 0 -37 -40 -16 -1312 Stool, Actual -16 10 -25 -5 0 -34
12Stool,
Ergonomic -17 0 -41 -3 0 -212 Chair, Actual -6 0 0 0 2 -10
12Chair,
Ergonomic -10 0 -17 0 0 -21
Table A6 Descriptive statistics of body angles
Butt 19
Variable Chair, Table N N* Mean SE Mean StDev Minimum Q1 MedianBack inclination Chair, Actual 12 0 13.75 4.06 14.08 -25.00 10.25 15.00 Chair, Ergonomic 12 0 12.33 2.63 9.11 -4.00 5.50 13.50 Stool, Actual 12 0 13.33 1.87 6.49 4.00 5.50 17.50 Stool, Ergonomic 12 0 9.33 1.43 4.94 3.00 3.00 11.00
BI Dev Chair, Actual 12 0 -4.33 1.50 5.19 -15.00 -8.75 -2.00 Chair, Ergonomic 12 0 -8.42 2.28 7.90 -24.00 -14.50 -6.50 Stool, Actual 12 0 -6.67 1.87 6.49 -16.00 -14.50 -2.50 Stool, Ergonomic 12 0 -10.67 1.43 4.94 -17.00 -17.00 -9.00
Hip Chair, Actual 12 0 101.08 2.32 8.05 90.00 96.00 99.50 Chair, Ergonomic 12 0 100.00 2.45 8.47 89.00 92.00 99.00 Stool, Actual 12 0 117.50 2.67 9.24 107.00 109.00 115.50 Stool, Ergonomic 12 0 118.00 2.27 7.87 106.00 112.00 118.00
H Dev Chair, Actual 12 0 0.750 0.509 1.765 0.000 0.000 0.000 Chair, Ergonomic 12 0 0.917 0.679 2.353 -3.000 0.000 0.000 Stool, Actual 12 0 3.00 1.17 4.05 0.00 0.00 0.00 Stool, Ergonomic 12 0 2.17 1.25 4.32 0.00 0.00 0.00
Knee Chair, Actual 12 0 78.00 7.40 25.63 45.00 58.25 70.50 Chair, Ergonomic 12 0 86.25 7.08 24.52 52.00 71.25 83.00 Stool, Actual 12 0 85.67 5.95 20.61 67.00 69.25 78.00 Stool, Ergonomic 12 0 87.08 6.46 22.37 54.00 70.00 87.50
K Dev Chair, Actual 12 0 -20.58 5.22 18.10 -50.00 -36.75 -24.50 Chair, Ergonomic 12 0 -14.25 4.43 15.36 -43.00 -23.75 -12.00 Stool, Actual 12 0 -14.67 3.33 11.54 -28.00 -25.75 -17.00 Stool, Ergonomic 12 0 -13.33 4.55 15.76 -41.00 -25.00 -7.50
Sholder Chair, Actual 12 0 37.92 5.07 17.57 0.00 25.50 39.00
Butt 20
Chair, Ergonomic 12 0 37.58 5.80 20.08 -10.00 30.25 36.00 Stool, Actual 12 0 26.67 5.44 18.83 -8.00 18.00 28.50 Stool, Ergonomic 12 0 28.08 4.99 17.30 -6.00 24.00 30.50
S Dev Chair, Actual 12 0 -1.75 3.86 13.36 -30.00 -7.50 0.00 Chair, Ergonomic 12 0 -1.25 4.69 16.26 -40.00 0.00 0.00 Stool, Actual 12 0 -7.50 3.44 11.90 -38.00 -12.00 -6.00 Stool, Ergonomic 12 0 -4.00 3.94 13.63 -36.00 -11.50 0.00
Elbow Chair, Actual 12 0 114.83 5.62 19.47 89.00 95.50 120.50 Chair, Ergonomic 12 0 98.33 4.98 17.24 64.00 90.00 99.00 Stool, Actual 12 0 108.67 4.21 14.57 76.00 101.25 108.00 Stool, Ergonomic 12 0 101.92 4.04 14.00 79.00 92.00 98.50
E Dev Chair, Actual 12 0 4.17 2.41 8.36 0.00 0.00 0.50 Chair, Ergonomic 12 0 -0.75 1.50 5.21 -16.00 0.00 0.00 Stool, Actual 12 0 0.917 0.996 3.450 -4.000 0.000 0.000 Stool, Ergonomic 12 0 0.333 0.355 1.231 -1.000 0.000 0.000
Ankle Chair, Actual 12 0 92.25 5.14 17.82 59.00 78.75 90.00 Chair, Ergonomic 12 0 93.50 4.19 14.51 75.00 81.00 90.00 Stool, Actual 12 0 93.58 6.30 21.81 56.00 71.75 96.00 Stool, Ergonomic 12 0 90.42 5.34 18.50 65.00 69.50 91.00
A Dev Chair, Actual 12 0 -7.75 5.14 17.82 -41.00 -21.25 -10.00 Chair, Ergonomic 12 0 -6.50 4.19 14.51 -25.00 -19.00 -10.00 Stool, Actual 12 0 -6.42 6.30 21.81 -44.00 -28.25 -4.00 Stool, Ergonomic 12 0 -9.58 5.34 18.50 -35.00 -30.50 -9.00
side back Chair, Actual 12 0 3.50 2.62 9.09 -10.00 -4.25 5.00 Chair, Ergonomic 12 0 0.75 1.90 6.57 -11.00 -5.25 3.00 Stool, Actual 12 0 2.92 1.55 5.37 -5.00 -2.25 3.50 Stool, Ergonomic 12 0 1.167 0.928 3.215 -3.000 -2.000 1.000Variable Chair, Table N N* Mean SE Mean StDev Minimum Q1 Median
Butt 21
Table A7 Descriptive statistics for angle deviation
Back inclination Chair, Actual 12 0 13.75 4.06 14.08 -25.00 10.25 15.00 Chair, Ergonomic 12 0 12.33 2.63 9.11 -4.00 5.50 13.50 Stool, Actual 12 0 13.33 1.87 6.49 4.00 5.50 17.50 Stool, Ergonomic 12 0 9.33 1.43 4.94 3.00 3.00 11.00
BI Dev Chair, Actual 12 0 -4.33 1.50 5.19 -15.00 -8.75 -2.00 Chair, Ergonomic 12 0 -8.42 2.28 7.90 -24.00 -14.50 -6.50 Stool, Actual 12 0 -6.67 1.87 6.49 -16.00 -14.50 -2.50 Stool, Ergonomic 12 0 -10.67 1.43 4.94 -17.00 -17.00 -9.00
Hip Chair, Actual 12 0 101.08 2.32 8.05 90.00 96.00 99.50 Chair, Ergonomic 12 0 100.00 2.45 8.47 89.00 92.00 99.00 Stool, Actual 12 0 117.50 2.67 9.24 107.00 109.00 115.50 Stool, Ergonomic 12 0 118.00 2.27 7.87 106.00 112.00 118.00
H Dev Chair, Actual 12 0 0.750 0.509 1.765 0.000 0.000 0.000 Chair, Ergonomic 12 0 0.917 0.679 2.353 -3.000 0.000 0.000 Stool, Actual 12 0 3.00 1.17 4.05 0.00 0.00 0.00 Stool, Ergonomic 12 0 2.17 1.25 4.32 0.00 0.00 0.00
Knee Chair, Actual 12 0 78.00 7.40 25.63 45.00 58.25 70.50 Chair, Ergonomic 12 0 86.25 7.08 24.52 52.00 71.25 83.00 Stool, Actual 12 0 85.67 5.95 20.61 67.00 69.25 78.00 Stool, Ergonomic 12 0 87.08 6.46 22.37 54.00 70.00 87.50
K Dev Chair, Actual 12 0 -20.58 5.22 18.10 -50.00 -36.75 -24.50 Chair, Ergonomic 12 0 -14.25 4.43 15.36 -43.00 -23.75 -12.00 Stool, Actual 12 0 -14.67 3.33 11.54 -28.00 -25.75 -17.00 Stool, Ergonomic 12 0 -13.33 4.55 15.76 -41.00 -25.00 -7.50
Sholder Chair, Actual 12 0 37.92 5.07 17.57 0.00 25.50 39.00 Chair, Ergonomic 12 0 37.58 5.80 20.08 -10.00 30.25 36.00 Stool, Actual 12 0 26.67 5.44 18.83 -8.00 18.00 28.50
Butt 22
Stool, Ergonomic 12 0 28.08 4.99 17.30 -6.00 24.00 30.50
S Dev Chair, Actual 12 0 -1.75 3.86 13.36 -30.00 -7.50 0.00 Chair, Ergonomic 12 0 -1.25 4.69 16.26 -40.00 0.00 0.00 Stool, Actual 12 0 -7.50 3.44 11.90 -38.00 -12.00 -6.00 Stool, Ergonomic 12 0 -4.00 3.94 13.63 -36.00 -11.50 0.00
Elbow Chair, Actual 12 0 114.83 5.62 19.47 89.00 95.50 120.50 Chair, Ergonomic 12 0 98.33 4.98 17.24 64.00 90.00 99.00 Stool, Actual 12 0 108.67 4.21 14.57 76.00 101.25 108.00 Stool, Ergonomic 12 0 101.92 4.04 14.00 79.00 92.00 98.50
E Dev Chair, Actual 12 0 4.17 2.41 8.36 0.00 0.00 0.50 Chair, Ergonomic 12 0 -0.75 1.50 5.21 -16.00 0.00 0.00 Stool, Actual 12 0 0.917 0.996 3.450 -4.000 0.000 0.000 Stool, Ergonomic 12 0 0.333 0.355 1.231 -1.000 0.000 0.000
Ankle Chair, Actual 12 0 92.25 5.14 17.82 59.00 78.75 90.00 Chair, Ergonomic 12 0 93.50 4.19 14.51 75.00 81.00 90.00 Stool, Actual 12 0 93.58 6.30 21.81 56.00 71.75 96.00 Stool, Ergonomic 12 0 90.42 5.34 18.50 65.00 69.50 91.00
A Dev Chair, Actual 12 0 -7.75 5.14 17.82 -41.00 -21.25 -10.00 Chair, Ergonomic 12 0 -6.50 4.19 14.51 -25.00 -19.00 -10.00 Stool, Actual 12 0 -6.42 6.30 21.81 -44.00 -28.25 -4.00 Stool, Ergonomic 12 0 -9.58 5.34 18.50 -35.00 -30.50 -9.00
side back Chair, Actual 12 0 3.50 2.62 9.09 -10.00 -4.25 5.00 Chair, Ergonomic 12 0 0.75 1.90 6.57 -11.00 -5.25 3.00 Stool, Actual 12 0 2.92 1.55 5.37 -5.00 -2.25 3.50 Stool, Ergonomic 12 0 1.167 0.928 3.215 -3.000 -2.000 1.000