Modification of computer table for ergonomic suitability for female users in
India
Ch. Snehalathaa, Batish, Sb and Sandhu, Pc, *
b
a
Department of Family Resource Management; Punjab Agricultural University; Ludhiana; India ([email protected])
Department of Family Resource Management; Punjab Agricultural University; Ludhiana; India ([email protected])
c
Department of Family Resource Management; Punjab Agricultural University; Ludhiana; India [email protected])
ABSTRACT:
Ten young females (well acquainted with computer work) were made to type a given script on existing
and modified computer table for 20 mins. Physiological parameters recorded were: heart rate (to work out
physiological cost of work), blood pressure (to know their cardiovascular responses), deviation from the natural
alignment of spine while at forward bending position, muscular grip of both left and right hand, physical and eye strain.
The results indicated that the computer table with 73 cms height and key board with 68 cms. height was found to be
ergonomically best computer table combination for an average stature Indian female (154.5 + 3.62 cms tall) because it
was least taxing to their body in terms of physiological cost of work, cardio vascular responses, angle of deviation, grip
strength, visual and physical fatigue; and gave higher satisfaction as compared to exiting one. Therefore, it is
recommended that computer tables should be designed in accordance with the anthropometric measurements of users.
Key words: Ergonomic suitability, physiological stresses, cardio vascular responses, visual fatigue.
1. INTRODUCTION
Unlike the development of other areas of scientific, technical and general interest, the computer
science, has grown up at a very fast pace. It has come like a storm and is here to stay and conquer. Since
computer has become popular with all kinds of population, its design, dimensions and placement should not
be ignored if optimum efficiency is to be attained. Continuous keyboard operation by the computer operators
will ultimately demand a good amount of medical expenditure associated with severe pain and mental agony,
resulting in high amount of indirect loss to the IT industries Cakir et al (1980). Increased use of computers in
the work place has caused a corresponding rise in health concerns directly related to their use.
There are number of risks which computer users are facing while working on existing computer
tables such as repetitive strain injuries ( RSI), occupational over use syndrome (OOS), cumulative trauma
disorders (CTD), general muscle strain and vision problems (Nag, 2002). It is, therefore, preferred to provide
a modified workstation to eliminate this particular problem based on ergonomic considerations. Variables of
workstation design include computer table, chair, document holder, wrist rest, mouse rest, foot rest etc. The
best design work environment is one, which keeps the body of worker in natural alignment, by putting
minimum stress on cardiovascular, muscular and respiratory systems.
An ergonomically designed workstation reduces the human efforts, enhances the work efficiency and
at the same time provides safety to the worker (Grandjean, 1988). Now a day’s women are also working with
computers in every field. They are spending lot of time with computers due to their professional
requirements. It has been found that physiological cost of work amounts to be more for female users than
males while working on the computer table which is available in the market ( Shraddha and Sehga, 2002).
Their study have also revealed that commonly sold computer tables in Indian markets are found to be most
taxing to female body and they are repeatedly experiencing repetitive strain injuries, occupational overuse
syndrome and cumulative trauma disorders apart from general muscle strain and vision problem. Therefore,
considering the importance of ergonomic design of computer table for improving work efficiency of female
users, the present study has been planned with the following objectives:
1.
To assess the physiological parameters (physiological cost of work, cardiovascular responses, angle of
deviation, grip strength and muscular and eye strain) caused while working with standard design of
computer table.
Sandhu ,P.et al./ The 9th Southeast Asian Ergonomics Society Conference (Page 2)
2.
2.
To modify and evaluate Computer table in terms of reduction in physiological parameters of female
users.
MATERIALS AND METHODS
This study was conducted in Punjab Agricultural University, Ludhiana (in Punjab state of India)
purposively and was conducted in two phases, phase – I included the survey (for gathering anthropometric
data and to know existing computer work stations); and phase II included laboratory experiments.
2.1
Survey
The total sample for the survey was 200 female computer users within the age range of 21-30 years
who used to work on computer for at least 2 hours daily. Relevant anthropometric data of respondents was
gathered to modify computer table according to their body dimensions.
2.2
Laboratory Experiments
2.2.1
Selection of Subjects
Ten female subjects were selected for laboratory experiments having all the physiological parameters
in close proximity to know the change in physiological parameters while working on modified and existing
computer table models. These subjects were falling within the permissible range of physiological parameters
and average stature of Indian women (ICMR, 1990). Their mean age was 25 ± 1.41 years, mean height
157.80 ± 3.62 cms, mean weight 54.35 ± 2.58 kgs, mean heart rate 79.36 ± 1.39 beats/min and mean blood
pressure 120.8 ± 1.28/mm Hg.
2.2.2
Selection of parameters
Heart rate (to work out physiological cost of work): Polar Heart Rate Monitor was used to measure heart
beats per minute.
Blood pressure (to know their cardiovascular responses): Sphygnomanometer was used to record systolic
and diastolic pressure.
Deviation from the natural alignment of spine while at forward bending position: A highly adjustable
Flexi curve was used, and the shape adapted was immediately drawn on paper and angle of deviation
measured with the help of protector:
Muscular grip of both left and right hand: The grip strength was measured with the help of Grip
Dynamometer.
Eye strain: Snellen Chart (an eye chart used by eye care professionals to measure visual acuity) was placed
at a standard distance (20 feet) and mistakes committed were recorded while reading the Chart.
Physical strain: A modified 5- point scale of ‘Rated Perceived Exertion’ as developed by Varghese et al
(1994) was used to calculate mean scores of physical fatigue, which scored 1 point for ‘Very light’, 2 for
‘Light’, 3 for ‘Moderately heavy’, 4 for ‘Heavy’ and 5 for ‘Very heavy’ physical fatigue.
2.2.3
Modification of Computer table
Relevant anthropometric data were used to modify the computer table.
Recommended distance between eye of user and monitor screen should be 40.6 cm as recommended
by (Charles et al, 1980). Height of the upper edge of the monitor screen should be 15° below sitting eye
height of the users with the distance of 40.6 cm and this works out to be 107.5 cm. It may be noted that
sitting eye height of users was 119.50 cm. Distance between base of monitor and upper edge of monitor
screen (used in present study) is 34.5 cm; and by subtracting 34.5 cm from 107.5 cm (eye level 15° below
sitting eye height) we get 73 cm. Hence computer table height should be 73 cm for the selected subjects.
Keyboard tray height should be at the elbow height in sitting posture, which is in case of selected subjects is
68 cm. Since computer work is a light activity for which no further lowering down of elbow height is
required so 68 cm keyboard height is just right for work efficiency. The accessories such as mouse rest,
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document holder cushion, UV-rays protector, foot rest, spot light were also provided while working on
modified computer table.
2.2.4
Collection of data
Most used computer table of 76 cm height with keyboard level height of 66 cm was selected to
conduct experiments under existing working conditions. These dimensions were based on results of the
survey conducted.
Resting parameters of subjects (heart rate, blood pressure, grip strength) were noted; before they
performed the typing (a set quantum of text) activity for 20 minutes; which were noted again during the
activity.
Heart Rate Monitor and Sphygnomanometer instruments were attached on respective body parts.
Heart rate at resting position was recorded for 5 minutes at the interval of 1 minute each. Blood pressure was
noted at the interval of 1 minute each for 3 minutes. Sphygnomanometer was removed and Grip
Dynamometer was given to the subjects and subjects were asked to hold and pull the handle of the Grip
Dynamometer up to their maximum strength with right hand and then with left hand. Thus grip strength of
the subjects was recorded for both the hands. Heart rate was noted during work at the interval of 5 minutes
each; the peak heart rate was also noted. Later these readings were averaged to get mean values. Flexicurve
was used to record the angle of deviation while at work.
Immediately after the completion of 20 minutes, subjects were made to sit in relaxed position and
heart rate recovery was recorded for 5 minutes at the interval of 1 minute each (or till the value touched
resting value) with the help of Heart Rate Monitor. Reading from Grip Dynamometer was also noted down
simultaneously. Scoring of Snellen Chart and ‘Rated Perceived Exertion Scale’ were also taken after
completion of the activity. Readings of subjects were taken in similar fashion when they worked on modified
table. Each experiment was repeated four times.
2.2.5
Assessment of physiological parameters
Physiological cost of work: Five values of working and resting heart rate (measured at the interval of 1
minute each) were averaged to work out average heart rate.
Average Heart Rate (AHR) = Average Working Heart Rate – Average Resting Heart Rate.
(Increase over base)
Total Cardiac Cost of Work (TCCW) = Cardiac Cost of Work (CCW) + Cardiac Cost of Recovery (CCR)
Where, CCW = AHR x duration of activity
AHR = Average Working Heart Rate – Average Resting Heart Rate
CCR= (Average Recovery Heart Rate- Average Resting Heart Rate) x duration of recovery
Total Cardiac Cost of Work
PCW = -----------------------------------Total time of activity
Blood Pressure: Five values of measured blood pressure were averaged each time to make final assessment.
Pulse Pressure: Pulse pressure was calculated from the systolic and diastolic blood pressure as given below
Pulse Pressure = Systolic Pressure – Diastolic Pressure
(mm Hg)
(mm Hg)
(mm Hg)
The systolic pressure was the upper limit of blood pressure and the diastolic pressure was the lower limit of
the blood pressure.
Average Mean Pressure = Diastolic Pressure + 1/3 Pulse Pressure
Grip Strength: The percent reduction in grip muscular strength (muscular fatigue) was calculated
from the following formula:
Sr-Sw
Percentage reduction in grip strength = ⎯⎯⎯⎯ х 100
Sr
Where, Sr = Strength of muscles at rest (Kgs)
Sw = Strength of muscles at work (Kgs)
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Angle of Deviation: It is calculated by following formula:
x required angle
Measure y
x = 360° - y
Fig. 1: Postural deviation
2.3
Analysis of Data
Weighted means score were calculated for summing up intensity of fatigue/ physical strain (scoring
done on ‘Rated Perceived Exertion Scale’) and eye strain (mistakes committed on Snellen Chart).
Percentile values of anthropometric measurements were calculated, for data presentation and Paired
‘t’ test was applied in order to find if significant differences occurred while working on existing and
improved model of computer table.
3.
RESULTS AND DISCUSSION
Ergonomic evaluation of modified computer table has been done in relation to physiological cost of
work, cardiovascular responses, angle of deviation, grip strength and physical and eye strain while working
with the existing and modified computer table by selected female subjects.
3.1
Physiological Cost of Work
Table 1:
Parameters
Heart rate
(beats\min)
Total Cardiac
cost of work
Physiological
cost of work
(PCW)
Reduction in physiological cost of work of selected subjects while working on existing and
modified computer table
Physiological Stresses
Average
reduction
Percent
reduction
‘t’ value
Existing
Computer table
85.44 ± 0.45
Modified
Computer table
81.7 ± 0.29
7.66 ± 0.86
4.22
4.58 *
131.51 ± 39.50
65.02 ± 23.28
66.49 ± 12.81
50.55
5.05 *
6.58 ± 1.97
3.25 ± 1.16
3.33 ± 2.02
52.69
5.05 *
*Significant at 5 % level of significance
Mean values of heart rate, total cardiac cost of work (TCCW) and physiological cost of work (PCW)
of working on existing and modified computer table have been depicted in Table 3.1. It is seen from the table
that mean heart rate increased up to 85.44 beats/minutes during the activity. Thus the percent increase was
7.66 beats/minutes. Further these values differed while subjects worked on modified computer table. During
activity heart beats increased up to 81.7 beats/minutes. Thus the reduction in percent increase in heart rate
was found to be 4.22 while working on modified computer table over existing model of Computer table. The
results were found to be significant at 5 percent level of significance, which means that the modified
computer table is effective to bring down heart rate significantly. Thus it can be concluded that modified
computer table was highly effective in minimizing increase in heart rate of subjects.
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Data given in Table 3.1 unveils the TCCW of selected female computer users while working on
existing and modified computer table model too. It is seen that while working on existing computer table
average TCCW was 131.51 beats where as while working on modified computer table these decreased to 65.02
beats indicating average reduction of 66.49 beats thus the percent reduction was 50.55 while working on
modified Computer table over existing model of Computer table. ‘t’ values were found to be significantly
different indicating that there is difference between existing and modified computer table. Thus it can be
concluded that modified Computer table was significantly effective for reduction in total cardiac cost of
work.
Physiological cost of work while performing the typing activity on existing and modified computer
table have also been highlighted in Table 3.1. It is seen from the table that PCW while typing on existing
model of Computer table was 6.58 beats/min where as while typing on modified Computer table it was
reduced to 3.25 beats/min indicating average reduction of 3.33 beats/min. Thus the percent reduction was
52.69. Results were found to be significantly different at 5 per cent level of significance indicating that
modified Computer table was significantly effective for reducing physiological cost of work.
3.2
Angle of Deviation
A good working posture is one, which can be sustained with a minimum static muscular effort and in
which it is possible to perform the task more effectively and with least muscular effort. Angle of deviation
was measured in degrees for cervical region and thoracic region. Average values of angle of deviation with
respect to while working on existing and modified computer table have been given in Table 3.2.
Reduction in Angle of deviation
181
188
7
3.46
±1.66
1.41
3.12*
Thoracic
Region
196.7
206.8
10.1
6.16
±1.75
192.1
199.4
7.3
3.70
±1.85
2.46
2.07*
Angle at
working
4.87
±1.30
Angle at
normal
position
8.9
Percent
increase
191.9
Increase
over base
183
Angle at
working
Cervical
region
Angle at
normal
position
Percent
increase
Modified Computer table
Increase
over base
Parameters
(Degrees)
Existing computer table
‘t’ value
Reduction in angle of deviation of selected subjects while working on existing and
modified computer table
Reduction in percent
increase
Table 2:
*Significant at 5 % level of significance
It is seen from Table 3.2 that angle at normal position in cervical region was 183° where as during
the activity it deviated up to 191.9° indicating increase over base of 8.9°. Thus the per cent increase was
4.87°. Further angle of deviation differed while subjects worked on modified Computer table. The angle at
normal position was 181° and during activity it is deviated up to 188° indicating increase over base of 7°.
Thus the per cent increase was 3.46. Reduction in per cent increase in angle of deviation was found to be
1.41° with the use of modified computer table. The results were found to be significant at 5 per cent level of
significance. Thus it can be concluded that modified Computer table is effective for reduction in angle of
deviation for cervical region.
Table 3.2 also show that in thoracic region angle at normal position was 196.7° whereas during the
activity it deviated up to 206.8° while working on existing Computer table indicating increase over base of
10.1°. Thus the percent increase was 6.16. Further these values are different while respondents worked on
modified Computer table that is angle at normal position was 192.1° and during activity it was deviated up to
199.4° indicating increase over base of 7.3°. Thus the percent increase was 3.70. Reduction in percent
increase in angle of deviation was found to be 2.46 with the use of modified Computer table. Results were
found to be significantly different at 5 per cent level of significance indicating that there is difference
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Sandhu ,P.et al./ The 9th Southeast Asian Ergonomics Society Conference (Page 6)
between existing and modified Computer Table. Thus it can be concluded that modified Computer table was
significantly effective for reduction in angle of deviation for thoracic region.
3.3
Muscular Grip Strength
Table 3: Reduction in muscular grip strength of selected subjects while working on existing and
modified computer table
Reduction in
grip strength
Muscular grip strength
Existing
Modified
Computer table
Computer table
Average
reduction
Percent
reduction
‘t’ value
Left hand
13.66 ± 4.38
5.69 ± 1.98
7.97 ± 5.30
58.34
4.50 *
Right hand
14.52 ± 5.23
6.95 ± 2.44
7.57 ± 4.38
52.20
5.19 *
*Significant at 5 % level of significance
Data given in Table 3.3 reveals that the average muscular grip strength of left hand was 13.66 Kgs
and that of at right hand was 14.52 Kgs after doing typing work on existing computer table whereas after
typing on in modified Computer table it was 5.69 Kgs for left hand and 6.95 Kgs is for right hand indicating
average reduction of 7.97 Kgs and 7.57 Kgs respectively. Thus the per cent reduction was 58.34 Kgs for left
hand and 52.20 Kgs for right hand. The percent reduction for right hand was less. The reason might be that
right hand is involved more while working on Computer. The results were found to be significantly different
at 5 per cent level of significance indicating that as compared to existing model of Computer table, modified
Computer table is more effective.
3.4 Blood pressure
The data obtained on blood pressure is given in Table 3.4. It contains the mean values for systolic,
diastolic, pulse pressure and average mean pressure at rest as well as while working on existing and modified
computer table. Table indicates that at resting position the values for systolic, diastolic, pulse pressure,
average mean pressure were 120.8 mm/Hg, 78.2 mm/Hg, 41.7 mm/Hg, and 92.09 mm/Hg. These values
increased up to 122 mm/Hg for systolic, 80 mm/Hg diastolic, 42 mm/Hg pulse pressure, and 93.86 mm/Hg
average mean pressure while working on existing computer table indicating increase over base as 1.2 mm/Hg
systolic, 1.8 mm/Hg diastolic, 0.3 mm/Hg pulse pressure, 1.77 mm/Hg for average mean pressure. Thus the
percent increase was 0.99 for systolic, 2.30 diastolic, 0.71 pulse pressure and 1.92 for average mean pressure.
Table 4: Reduction in blood pressure of selected subjects while working on existing and modified
computer table
Existing
computer table
Modified
computer table
Blood Pressure(mm/Hg)
PARAMETERS
At rest
During activity
Systolic
(mm.Hg)
120.8 ± 1.28
Diastolic
(mm.Hg)
78.2 ± 0.63
Pulse
pressure
41.7 ± 1.49
122 ± 0.66
80 ± 0.66
42± 0.94
93.86 ± 0.65
1.2
1.8
0.3
1.77
0.99 ± 1.34
2.30 ± 0.82
0.71 ± 2.54
1.92 ± 0.64
120.8 ± 1.28
78.2 ± 0.63
41.7 ± 1.49
92.09 ± 0.56
121 ± 1.05
79 ± 1.01
42 ± 0.94
92.09 ± 0.56
0.2
0.8
0.3
0.9
0.16 ± 0.66
1.01 ± 1.62
0.71 ± 3.35
0.97 ± 0.56
0.83
0.91
1.29
0.84
0
1.07
0.8
2.59
Increase over base
Percent increase
At rest
During activity
Increase over base
Percent increase
Reduction in percent increase
‘t’ Value
Average mean
pressure
92.09 ± 0.56
*Significant at 5 % level of significance
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Sandhu ,P.et al./ The 9th Southeast Asian Ergonomics Society Conference (Page 7)
While working on modified computer table these values increased up to systolic 121 mm/Hg,
diastolic 79 mm/Hg, pulse pressure 42 mm/Hg and average pulse pressure 92.09 mm/Hg indicating increase
over base 0.2 mm/Hg, 0.8 mm/Hg,0.3 mm/Hg and 0.9 mm/Hg. Percent increase was 0.16 mm/Hg, 1.01
mm/Hg, 0.71 mm/Hg and 0.97 mm/Hg in modified computer table over existing one. Thus the percent
reduction for systolic came out to be 0.91, for diastolic 1.29, nil for pulse pressure and for average mean
pressure it was 0.8 respectively. However the results were found to be non significant, indicating that there is
no stress on cardiovascular responses under existing and modified work conditions. The present findings are
in line with those of Shraddha1 and Sehgal (2002) who also reported that there is not much increase in pulse
pressure while working on Computer.
3.5
Physical and Visual fatigue
Data in this regard given is in Table 3.5 which indicates that mean score concerning physical fatigue
of selected subjects was found to be 3.3 after working on existing model of Computer table where as after
working on modified model of Computer table mean score came down to 1.8 indicating average mean
reduction of 1.5 and the percent reduction was worked out 45.45. The results were found to be significantly
different at 5 per cent level of significance indicating that there are differences between existing and
modified computer table with regards to physical fatigue experienced by subjects.
Table 5: Physical fatigue and Visual fatigue (Mean score) experienced by subjects while working on
existing and modified computer table
Parameters
With existing
computer table
With modified
computer table
Average
reduction
Percent
Reduction
‘t’ value
3.3
1.8
1.5
45.45
3.04 *
2.9
1.6
1.3
44.82
0.89 *
Physical fatigue
(based on RPE scale)
Visual fatigue
(based on Snellen Chart)
*Significant at 5 % level of significance
Further the table indicates that for Visual fatigue mean score was 2.9 after working on existing
model Computer table whereas mean score came out to be 1.6 after working on modified model of Computer
table indicating average reduction of 1.3. Thus the per cent reduction was 44.82. ‘t’ values were found to be
significantly different indicating that there are differences between existing and modified computer table
with regards to visual fatigue experienced by the respondents. Thus it can be concluded that modified
Computer Table was significantly effective for reduction in Visual fatigue.
4. CONCLUSION
From the above study, it can be concluded that computer table should be in accordance with
anthropometric measurements of users as these reduce physiological cost of the worker in terms of reduction
in cardiovascular stresses, visual and physical strain, minimal angle of deviation as measured in degrees for
cervical region and thoracic region and better muscular grip of both hands. Reduced costs of work thereby
enhance the work efficiency of female workers as well as provide health safety too.
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Medical Research; New Delhi.
[5] Nag PK (2002) Ergonomics of human computer interaction. National Institute of Occupational Health, Ahmedabad.
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