Louisiana State University LSU Digital Commons LSU Master's eses Graduate School 2015 A Comparative Assessment of Ergonomic Risk Factors in University Personnel Using RULA and REBA Aiming to Study the Cause and Effect Relationship Nabila Chowdhury Louisiana State University and Agricultural and Mechanical College, [email protected]Follow this and additional works at: hps://digitalcommons.lsu.edu/gradschool_theses Part of the Mechanical Engineering Commons is esis is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Master's eses by an authorized graduate school editor of LSU Digital Commons. For more information, please contact [email protected]. Recommended Citation Chowdhury, Nabila, "A Comparative Assessment of Ergonomic Risk Factors in University Personnel Using RULA and REBA Aiming to Study the Cause and Effect Relationship" (2015). LSU Master's eses. 2314. hps://digitalcommons.lsu.edu/gradschool_theses/2314
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Louisiana State UniversityLSU Digital Commons
LSU Master's Theses Graduate School
2015
A Comparative Assessment of Ergonomic RiskFactors in University Personnel Using RULA andREBA Aiming to Study the Cause and EffectRelationshipNabila ChowdhuryLouisiana State University and Agricultural and Mechanical College, [email protected]
Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_theses
Part of the Mechanical Engineering Commons
This Thesis is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSUMaster's Theses by an authorized graduate school editor of LSU Digital Commons. For more information, please contact [email protected].
Recommended CitationChowdhury, Nabila, "A Comparative Assessment of Ergonomic Risk Factors in University Personnel Using RULA and REBA Aimingto Study the Cause and Effect Relationship" (2015). LSU Master's Theses. 2314.https://digitalcommons.lsu.edu/gradschool_theses/2314
A COMPARATIVE ASSESSMENT OF ERGONOMIC RISK FACTORS IN UNIVERSITY PERSONNEL USING RULA AND REBA AIMING TO STUDY THE CAUSE AND EFFECT
RELATIONSHIP
A Thesis
Submitted to the Graduate Faculty of the
Louisiana State University and
Agricultural and Mechanical College
in partial fulfillment of the
requirements for the degree of
Master of Science in Industrial Engineering
in
The Department of Mechanical and Industrial Engineering
by
Nabila Chowdhury
B.S., Bangladesh University of Engineering and Technology, 2011
December 2015
ii
ACKNOWLEDGEMENTS
First and foremost, I thank God for blessing me with the proper guidance and support from
mentors, family and friends whose continuous assistance contributed towards the successful
completion of my thesis.
Thank you Dr. Fereydoun Aghazadeh for serving as my major advisor and giving the opportunity
to work on this research. I thank you for all the support that I received from you throughout the course
of the research and my studies, in every aspect. It was a great opportunity to have learnt so much from
you.
I convey special thanks to my thesis committee members Dr. Bhaba R. Sarker and Dr. Craig M.
Harvey for their valuable suggestions to improve the quality and consistency of the research. I would
also like to thank Dr. Brian D. Marx and Dawen Liu from the statistics department for their help in the
statistical analysis.
I would like to express my sincere gratitude to Ms. Diane Morgan for the immeasurable amount
of support she provided throughout my studies.
Last but not the least I want to thank all the participants who took part in the experiment
voluntarily with patience and made my research possible to be carried out.
iii
TABLE OF CONTENTS
ACKNOWLEDGEMENTS .............................................................................................................................................. ii
LIST OF TABLES ........................................................................................................................................................... v
LIST OF FIGURES ........................................................................................................................................................ vi
LIST OF ABBREVIATIONS ........................................................................................................................................... vii
ABSTRACT ................................................................................................................................................................ viii
CHAPTER 2: LITERATURE REVIEW ...............................................................................................................................4
2.1 Risks associated with prolonged work at computer workstation ....................................................................4
2.2 Comparison between different tools for ergonomic assessment ................................................................. 12
CHAPTER 3: RATIONALE AND OBJECTIVE ................................................................................................................ 14
4.3 Tools and equipment ..................................................................................................................................... 27
4.4 Research hypothesis ...................................................................................................................................... 28
APPENDIX A ............................................................................................................................................................. 74
APPENDIX B ............................................................................................................................................................. 76
B4. Rapid Entire Body Assessment (REBA) Worksheet ....................................................................................... 79
APPENDIX C ............................................................................................................................................................. 80
APPENDIX D ............................................................................................................................................................. 83
D1. Proportional Odds Regression Model ........................................................................................................... 83
VITA ......................................................................................................................................................................... 84
Table 3: Parameters to be assessed while evaluating computer workstation design ............................................ 26
Table 4: Demographic data for participants ............................................................................................................ 31
Table 5: Percentage of population reporting pain in different body parts ............................................................. 32
Table 6: Most recurring factors attributed to the symptoms of MSDs in different body region ............................ 35
Table 7: Percentage of males and females reporting MSD symptoms in different body regions .......................... 35
Table 8: Frequency of micro breaks ........................................................................................................................ 36
Table 9: Average RULA and REBA scores ................................................................................................................. 36
Table 16: ANOVA results for the risk factors obtained from RULA and REBA ........................................................ 58
Table 17: P values for significant postural factors ................................................................................................... 60
Table 18: P values for significant design factors ..................................................................................................... 61
Table 19: Variability of RULA and REBA score ......................................................................................................... 64
Table 20: Variability of RULA and REBA (normalized %) ......................................................................................... 64
Figure 12: RULA and REBA scores vs. Age ............................................................................................................... 41
Figure 13: Frequency distribution of RULA scores for female participants ............................................................ 42
Figure 14: Frequency distribution of REBA scores for female participants ............................................................ 42
Figure 15: Frequency distribution of RULA scores for male participants ................................................................ 43
Figure 16: Frequency distribution of REBA scores for male participants ................................................................ 44
Figure 17: Participants with inappropriate workstation design .............................................................................. 45
Figure 18: Monitor angled more than 35⁰ on the right........................................................................................... 46
Figure 19: Viewing angle more than 30⁰ while working on a laptop ...................................................................... 47
Figure 20: Glare on VDT monitor of a participant ................................................................................................... 47
Figure 21: Participant with no wrist or arm support ............................................................................................... 48
Figure 22: Box plot for ANOVA of RULA and REBA scores ....................................................................................... 59
From equation (3) we can predict the probability of having slightly uncomfortable pain in any or all of
the associated body parts = 0.694
From equation (4) we can predict the probability of having moderately uncomfortable pain in any or all
of the associated body parts = 0.263
From equation (5) we can predict the probability of having very uncomfortable pain in any or all of the
associated body parts = 0.043
So we can interpret the results as if the user has postural problem trunk, shoulder and upper
arm, forearm and elbows, wrist and hand and design problem of VDT monitor then the user has 69.4%
probability of having slightly uncomfortable pain, 26.3% probability of having moderately
uncomfortable pain and 4.3% probability of having very uncomfortable pain in any or all of the
associated body parts.
58
5.6 Testing hypothesis
Null hypothesis 1
H0: The risk assessment result will come out the same for Both RULA and REBA.
Alternate hypothesis 1
H1: There will be discrepancies in the scores of two risk assessment scales.
As seen from the analysis of variance (ANOVA) of scores from two risk assessment tools in Table
16, the P value (0.3279) indicates that there is no significant difference between the two groups of
scores.
Table 16: ANOVA results for the risk factors obtained from RULA and REBA
Source Df SS MS F P‐value
Treatments 1 9 9 3.7118 0.3279
Error 142 344.306 2.425
Total 143 353.306
So we can say that we cannot reject the null hypothesis in the favor of the alternative. The level
of significance was set at 0.05. A box‐plot has been drawn below in Figure 22 which provides a
graphical summary of the distribution of scores from both the tools. The box‐plot shows that scores
are normally distributed with no outliers and the variability of the scores is not significant.
Figure 22: Box plot for ANOVA of RULA and REBA scores
Null hypothesis 2
Ho: Worker’s posture will have no adverse effect on workers musculoskeletal system.
Alternate hypothesis
H2: Workers posture will have adverse effects on the musculoskeletal system of the user.
From the cumulative logit regression
Trunk or Torso, Shoulder and Upper arm) factors were significant and one (Wrist and hand) marginally
significant as indicated by the respective P values listed in Table
the null hypothesis in favor of the alternate, which means, workers posture, if inappropriate, might
have adverse effects on the user’s musculoskeletal system. The P values for significant factors are
highlighted in the table below. The level of signi
59
Box plot for ANOVA of RULA and REBA scores
: Worker’s posture will have no adverse effect on workers musculoskeletal system.
have adverse effects on the musculoskeletal system of the user.
From the cumulative logit regression model, we find that three posture (Forearm and Elbows,
Trunk or Torso, Shoulder and Upper arm) factors were significant and one (Wrist and hand) marginally
significant as indicated by the respective P values listed in Table 17. So we can say that we can re
the null hypothesis in favor of the alternate, which means, workers posture, if inappropriate, might
have adverse effects on the user’s musculoskeletal system. The P values for significant factors are
highlighted in the table below. The level of significance was set at 0.05.
: Worker’s posture will have no adverse effect on workers musculoskeletal system.
have adverse effects on the musculoskeletal system of the user.
model, we find that three posture (Forearm and Elbows,
Trunk or Torso, Shoulder and Upper arm) factors were significant and one (Wrist and hand) marginally
. So we can say that we can reject
the null hypothesis in favor of the alternate, which means, workers posture, if inappropriate, might
have adverse effects on the user’s musculoskeletal system. The P values for significant factors are
60
Table 17: P values for significant postural factors
Effect DF Chi-
Square Pr > ChiSq
Forearm and Elbows
1 10.345 0.0013
Trunk 1 5.6621 0.0173
Shoulder and Upper
arm 1 7.9232 0.0049
Wrist and Hand
1 3.1831 0.0744
Null hypothesis 3
Ho: The inappropriate design of computer workstation will have no undesirable effect on the user’s
musculoskeletal system.
Alternate hypothesis
H3: Ergonomic deficiency in the design and organization of workstation will cause WMSDs in the users
working for long hours.
From the cumulative logit regression model, we find that two design factors (monitor and input
device) were significant and one (seating adjustability) marginally significant as indicated by the
respective P values listed in Table 18. So we can say that we can reject the null hypothesis in favor of
the alternate, which means, the workstation design, if inappropriate, might have adverse effects on
the user’s musculoskeletal system. The P values for significant factors are highlighted in Table 18. The
level of significance was set at 0.05.
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Table 18: P values for significant design factors
Effect DF Odds ratio
Pr > ChiSq
Monitors 1 7.255 0.0071
input device
1 2.782 0.0347
Seating 1 3.352 0.0707
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CHAPTER 6: DISCUSSION
This study was conducted using seventy two participants at Louisiana State University with a
view to understanding the major ergonomic issues in their computer workstation. Out of seventy two
participants twenty nine male participants age an average of 35 and forty three female participants age
an average of 37. Both male and female participants worked seven hours each day on their computer
workstation on an average.
As seen from the table 5 and 6 an alarming number of 75.71% participants suffer from
moderately or very uncomfortable upper and lower back pain. 64% of this pain in upper and lower
back can be attributed to awkward posture of torso and poor adjustability of seating arrangement of
computer workstation.
This result can be compared to the results obtained by Holder et al. (1999) while evaluating the
WMSD symptoms of physical therapist (PT) and their assistants (PTA). Thirty‐two percent of the PTs
and 35% of the PTAs reported sustaining a musculoskeletal injury. The highest prevalence of injury was
to the low back (62% of injured PTs and 56% of injured PTAs). The PTs reported the upper back and the
wrist and hand as having the second highest prevalence (23%). The PTAs reported the upper back as
having the second highest prevalence (28%). In the similar study by Sen and Richardson (2007) it was
found that 50% of those with low back pain did not have an adjustable backrest resulting in poor
posture.
Out of 45.71% of participants’ studied suffer from shoulder and upper arm pain, 88.76% of
which can be attributed to awkward posture of shoulder and upper arm and disarrangement of
computer monitor. Similarly, approximately 80% of neck and shoulder pain can be attributed to the
63
incorrect posture of head and neck and the disarrangement of VDT monitor. A user survey by Psihogios
(2001) indicates that monitor positioning was a prime factor in assuring a computer operator’s
comfort.
Out of 42.85% of participants who reported to have wrist pain, 80.95% had been observed to
have wrong postures of wrist and hand and inappropriate input devices like keyboard and mouse.
Participants have exposed blood vessels near the skin at the wrist, which is where the pulse is often
taken. Any pressure in this region will disrupt circulation into the hand and this will increase the risks of
injury. From our study majority of the participants were seen to place their forearm and wrist on the
sharp edge of the working table without any support. It can thus be concluded that the pain of
individual body parts can be attributed to the awkward postures of those parts.
A gender wise comparison has been drawn in Table 7, where it is seen that except for head and
neck, for the same body parts women tend to have more pain suffered compared to that of men. This
result complies with the results from the study by Ekman et al. (2000) .It is also seen that in Table 8
that women tend to take more micro breaks than men. This occurrence can be explained as a
consequence of more pain that they reported to suffer in compared to men.
As explained in Table 19 we can see that for the same person RULA and REBA scored the same
for 33.87% of time. And RULA scored more than REBA approximately 51.61% of time. Only 12.92% of
time REBA scored more than RULA. Even though the average RULA and REBA score from table 5.6
interpret into the same decision, the RULA method has presented a better sensibility to detect prompt
and critical action levels, because, during the analysis using both methods, RULA has detected a bigger
proportion of postures in the risky categories than the proportion detected by the REBA. It can be
64
explained by the fact that the university employees working on VDT station, during a larger part of the
time, using the upper limb of their body which exactly is the evaluation focus of the method RULA.
Table 19: Variability of RULA and REBA score
Cases % of participants
RULA scores = REBA score 33.87%
RULA score > REBA score 51.61%
REBA score > RULA score 12.92%
The same comparison was drawn with the scores normalized as a percentage of the highest
score in Table 20.
Table 20: Variability of RULA and REBA (normalized %)
Cases % of participants
RULA scores = REBA score 35.48%
RULA score > REBA score 52.61%
REBA score > RULA score 11.91%
This result supports the results obtained from the study of comparison of RULA and REBA for
evaluation of postural stress in odonatological services by Diniz et al. (2006). Also, from Figure 10 and
11 we see that, for one score of RULA, the REBA scores vary widely, while for each REBA score the
RULA score varies moderately. Especially for larger values of REBA, RULA tends to give out the same
score, but for larger values of RULA, REBA tends to give out a wide range of scores, which again, means
65
to make RULA a tool with better reliability while evaluating activities of upper limb, as working on
computer workstation.
The average RULA score was obtained 5 and the average REBA score was obtained 4, both of
which mean the average user in the university are at medium risk of WMSDs and prompt action needs
to be taken to investigate further and bring about necessary changes. This is an alarming situation and
from this study we tried to figure out the most recurring factors that contribute to these increasing
symptoms of WMSDs.
Of all the responses 3.41% of the responses were very uncomfortable, 19.84% of the responses
for all body parts were moderately uncomfortable and the rest of the responses were slightly
uncomfortable.
The cumulative logit model was run for all the responses as well as the responses for individual
body part to see if any specific factors contribute towards the WMSD symptom of that part. The most
significant factors that are associated with the moderate and very uncomfortable pain for all the
responses are the arrangement of computer monitors and/or awkward postures of torso, shoulder
upper arm, forearm, elbows, wrist and hand. The significant factors that were found for individual
body part are listed in Table 14. It is observed that the independent variable awkward posture of head
and neck is the most significant parameter for both shoulder and upper back pain. Inadequacy of wrist
support for the input devices has significant effects on wrist pain. The lack of adjustability in seating
arrangements is marginally significant for lower back pain. Since the average population is found to be
at medium risk, due changes are necessary to be brought about regarding these significant factors.
From the correlation between the independent and dependent variables it was observed that
the awkward postures of trunk (torso) and wrist is positively correlated to almost all the parts of upper
66
body, which indicates that the VDT users in the university need ergonomic intervention of correct
postures of wrist and torso. Extensive usage of mouse and keyboard and prolonged sitting on VDT
station is accountable for this correlation. Also, inappropriate postures of forearm and upper arm are
correlated to the WMSD symptoms of shoulder, upper back and wrist. This is to notice that none of the
correlations were very strong.
Predictive probabilities for having slightly, moderately or very uncomfortable pain in any of the
associated body parts can be obtained from equation 3, 4 and 5. Using these equations we can predict
for the probability of user responses at various levels of the independent variables.
67
CHAPTER 7: LIMITATIONS AND FUTURE RESEARCH
Several limitations were recognized before and during the performance of this research. The
limitations of the current study and the future research possibilities are listed below‐
The WMSD symptoms were recorded subjectively thru CMDQ questionnaire. More accurate
results can be obtained by quantitatively measuring the WMSD symptoms. Data would be more
accurate and consistent if they were taken directly using Goniometers, Electrogoniometers or
Electromyography (EMGs).
Also, the WMSD symptoms were recorded if it occurred the previous week of the week the
participant was being experimented. The results might be more reliable with the data taken
over longer period of time.
The cumulative logit model assumes that for the responses, the difference between the lower
categories with the immediate higher category is same for all the categories. But to the
participants, the differences between slightly uncomfortable pain and moderately
uncomfortable pain might not be the same as moderately uncomfortable pain to very
uncomfortable pain.
The three levels of responses for any injury or pain suffered the previous week were‐ Slightly
uncomfortable, moderately uncomfortable and very uncomfortable. Whereas the responses for
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the interruption of work due to this pain were, not at all, slightly interfered and substantially
interfered. So the participants had to choose slightly uncomfortable even if they didn’t suffer
any pain the previous week. The option of answering no pain at all should be incorporated in
any future study with the same questionnaire. However, in the current study only moderately
uncomfortable and very uncomfortable pain were taken into account for the analysis.
Both RULA and REBA scores were measured from photographs taken. Errors might be there due
to unintended mistakes from angles which were calculated from these pictures.
The study was conducted using 72 participants out of which 29 were males and the rest
females. The risk factors for female were higher than that of male. Results might have altered if
the study had more male participants. Number of female participants being more than the male
can be one factor to contribute to the result showing women in a higher risk level of falling to
WMSD.
RULA and REBA tools assess postural loading at a specific moment in the work cycle. It is
important to assess the highest risk posture being adopted. The highest risk posture for analysis
may be chosen based on the duration of the posture (e.g. longest held) or the degree of
postural deviation (e.g. worst posture).Selecting the appropriate stage of the work cycle for
assessment requires long observation. For the current study the participants were observed for
15 minutes to be photographed for their worst posture. Chances lie that the postures analyzed
for RULA and REBA might not be the worst posture adopted by the individual.
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APPENDIX A
A1. Survey Questionnaire
Gender: ☐ female ☐ male Age:
Vision
1)Indicate the type of eye wear you use at work:
1 ☐ None
2 ☐ Contact lenses
3 ☐ Regular glasses
4 ☐ Bifocals glasses
5 ☐ Trifocal glasses
2) How often do you have your eyes examined?
1 ☐ No periodic eye examination
2 ☐ Every 3 or 6 months
3 ☐ Annually
4 ☐ Every two years
5 ☐ every three years or more
3) If you use any type of eye wear at work, is it prescribed specifically for computer use?
1 ☐ Yes
2 ☐ No
4) When was the last time you had your eyes examined?
1 ☐ Less than a year ago
2 ☐ Over a year ago
Work experience/Tasks
5)Job title:
6)Length of time on present job: ______ (yrs)________ (mths) Computer work history: ______ (yrs)________ (mths) Working hrs/day( at workstation): Total working hrs/week:
7) What is your typing style?
1 ☐ Two‐finger typing
2 ☐ Touch typing
8) Do you use a mouse? ☐ No ☐ Yes
If YES, how often?
1 ☐≤ 25% of time
2 ☐ 25‐50% of time
3 ☐ 50‐75% of time
4 ☐ 75‐100% of time
9)Please indicate the major task you perform with computer:
1 ☐ Entering numerical data
2 ☐ Typing e‐mails/ browsing
3☐ programming
4☐ Drawing/Design/CAD
11) How often do you use a keyboard?
1 ☐≤ 25% of time
2 ☐ 25‐50% of time
3 ☐ 50‐75% of time
4 ☐ 75‐100% of time
Habits/Exercises
1) When performing typing tasks, where do you usually place the hard copy?
1 ☐ Clip it on a copy stand
2 ☐ Place it flat on the desk
3 ☐ Hold it by one hand
4☐ Do not use
2)When typing you usually have your wrists supported by:
1 ☐ The desk surface
2 ☐a wrist rest
3 ☐ Desk edge
3 ☐ no support 3) When you need more than 1 hour to do a job with a computer, how do you take breaks?
1 ☐ No breaks till I finish the work
6) Do you do some simple exercises (Wrists/Shoulders exercises) during the breaks?
1 ☐Never
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2 ☐ Some short breaks to alternate the work 4) How often do you take breaks?
1 ☐Once every hour
2 ☐Once in every 2 hours
3 ☐ Once in every 4 hours or greater than 4 hour time interval 5) How long are the breaks?
1 ☐ 5 to 10 minutes
2 ☐ 10 to 15 minutes
3 ☐ 15 to 20 minutes
4 ☐ 30 minutes or greater than 30 minutes
5 ☐> than 30 minutes
2 ☐Sometimes
3 ☐ frequently
7) Do you have the following habits while sitting?
1 ☐ Crossing the legs
2 ☐ Putting the feet on wheels/ supports of the chair
3 ☐ Sitting at the front edge of the chair
4☐Using footrest
5☐ None of above
8) Do you do any type of exercise which lasts 20 min or longer (walk, run, aerobics, etc.)?