The Effect of Seat And Table Height On Joints Comfort Angles And Seat Pan Pressure

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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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702.

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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.

12. Pheasant S., Haslegrave C. Bodyspace: Anthropometry, Ergonomics and the Design of

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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disorders 9.1 (2008): 113.

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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%


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%


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

The Effect of Seat And Table Height On Joints Comfort Angles And Seat Pan Pressure

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