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2003:090 CIV
M A S T E R ' S T H E S I S
The Study of Work-Related Musculoskeletal DisordersAmongst Workers in Brick Making Factory
in South Africa
Edith Mufamadi Ndivhudzannyi
Luleå University of Technology
MSc Programmes in Engineering Industrial Ergonomics
Department of Human Work Sciences Division of Industrial ergonomics
2003:090 CIV - ISSN: 1402-1617 - ISRN: LTU-EX--03/090--SE
THE STUDY OF WORK-RELATED MUSCULOSKELETAL DISORDERS
AMONGST WORKERS IN BRICK MAKING FACTORY IN
SOUTH AFRICA
MUFAMADI NDIVHUDZANNYI EDITH
Division of Industrial Ergonomics
Department of Human Work Sciences
Luleå University of Technology
Sweden
Supervisor/s: Professor H Shahnavaz
B Nyantumbu
February 2003
2
ABSTRACT In brick manufacturing industries, studies have been conducted and there has been
a general indication that working with bricks may dispose towards upper limb
disorders. This study investigated work-related musculoskeletal disorders
(WMSDs) in one brick-making factory, concentrating on the sorting section. The
primary objective was to identify specific ergonomic risk factors for WMSDs
among the brick sorters. The Logical Framework Approach method has been used
in the designing of this project because of its simplicity and is objectives oriented,
target group oriented as well as participatory oriented.
Semi-structured interviews were conducted regarding subjective pain/discomfort
on different body regions and psychosocial situations, which brick sorters
perceived as contributing factors to those disorders. Workplace analysis has been
accomplished by observing the employees as they were doing the task. The main
demands of the tasks and the risk factors as to, which may be present, were listed.
Physical exposure to risks for potential WMSDs has been assessed using ovako
working posture analysis method. Lifting indices (LI) based on the 1993 revised
National Institute for Occupational Safety Health lifting (NIOSH) equations were
calculated.
Results of the interviews showed that all of the respondents reported having
experienced pain/discomfort arising from work, with the body parts most
commonly affected being the low back, followed by the wrists/hands, shoulders,
neck and upper back. The respondents consistently identified factors such as
3
frequent twisting and bending of the trunk as the leading cause of the
pain/discomfort. These results were supported by the posture analysis results,
which also recommend that the corrective measures for improving the working
postures are needed immediately. NIOSH results showed the recommended
weight limit ranging from (0.50-0.93 kg) substantially less than the weight of
even a single brick (2. 7 kg). The LI ranged from 2.90-5.4, which exceeds 1.0
indicating the job to be stressful. As a result, the study suggests that the job
should be redesigned ergonomically to eliminate the risk factors that may dispose
towards upper limb disorders.
In conclusion, the results of this study point out a number of important factors that
must be addressed in order to reduce WMSDs among brick sorters. These include
the workplace design necessitating frequent bending and twisting of the trunk,
handling techniques, the way work is organized. Other problems such as
inadequate breaks and high speed of work also need to be addressed.
4
TABLE OF CONTENTS
ABSTRACT…………………………………………………………….………..2
1. INTRODUCTION……………………………………………………………..9
2. LITERATURE REVIEW……………………………………………………..11
2.1. Reported statistics and costs estimate…………………………………….13
3. POTENTIAL RISK FACTORS………………………………………………14
3.1. Workplace risk factors…………………………………………………….14
3.1.1. Job-related risk factors…………………………………………….15
3.1.2. Awkward postures………………………………………………...16
3.2. Personal factors……………………………………………………………17
3.3. Psychosocial factors……………………………………………………….18
4. PROJECT DESIGN…………………………………………………………...21
5. SPECIFIC OBJECTIVES……………………………………………………..22
6. METHODS……………………………………………………………………22
6.1. Subjects……………………………………………………………………22
6.2. Semi-structured Interviews………………………………………………..22
6.3. Workplace analysis………………………………………………………..24
6.4. Use of the 1993 NIOSH guide…………………………………………….24
6.5. Observational method……………………………………………………..26
5
7. RESULTS…………………………………………………………………….27
7.1. Task Description…………………………………………………………27
7.2. Work Organization……………………………………………………….27
7.3. Questionnaire……………………………………………………………..29
7.3.1. Demographic information…………………………………………..29
7.3.2. Self-Reported Discomfort/Pain……………………………………..29
7.3.3. Psychosocial factors…………………………………………………34
7.4. Job Analysis……………………………………………………………..…35
7.5. Postures adopted by workers…………………………………………….36
8. DISCUSSIONS……………………………………………………………….37
9. CONCLUSIONS……………………………………………………………...40
10. RECOMMENDATIONS……………………………………………………40
11. ACKNOWLEDGEMENTS…………………………………………………42
12. REFERENCES………………………………………………………………43
6
LIST OF APPENDICES
13. APPENDIX 1:
POBLEM ANALYSIS…………………………………………………………..52
14. APPENDIX 2:
OBJECTIVE ANALYSIS……………………………………………………….53
15. APPENDIX 3:……………………………………………………………….54
THE BASIC ELEMENTS OF THE PROJECT MATRIX
16. APPENDIX 4:
QUESTIONNAIRE……………………………………………………………..57
17. APPENDIX 5:
A modified version of Norwegian translation of the short Swedish version of the
Job content, Questionnaire (In English)…………………………………………61
18. APPENDIX 6:
CHECKLIST……………………………………………………………………..62
19. APPENDIX 7:
Task variables in the sorting/stacking processes………………………………...64
20. APPENDIX 8:
The procedure for calculating RWL and LI in the sorting/stacking processes…..65
7
LIST OF FIGURES
Figure 1. A global theory of musculoskeletal injury precipitation………………19
Figure 2. Demand and control model……………………………………………20
Figure 3. Percentage of respondents who complained of pain per body region
during the last 12 months lasting at least 24 hours………………………………30
Figure 4. Percentage of respondents who complained of pain per body region
during the last month lasting at least 24 hours…………………………………...31
Figure 5. Percentage of respondents who complained of pain per body region
during the last 7 days lasting at least 24 hours…………………………………...32
Figure 6. Percentage of respondents who have been prevented from doing normal
activities because of pain per body region……………………………………….33
8
LIST OF TABLES
Table 1. The definitions of the multipliers of the revised NIOSH equation and the
variables used for calculations…………………………………………………...25
Table 2. OWAS posture code definitions………………………………………..26
Table 3. An overview of the demographic information of the respondents……..29
Table 4. Description of sorting/stacking tasks and postural analysis……………36
9
1. INTRODUCTION
Work-related Musculoskeletal Disorders (WMSDs) have become a major
problem in many industrialized countries (Hagberg et al., 1995). These disorders
have caused a considerable human suffering and are also economically very
costly because of reduced working capacity and lessened production (Luopajarvi,
1990).
Work-related Muscloskeletal Disorders describe a wide range of inflammatory
and degenerative diseases, and disorders that result in pain and functional
impairment (Kilbom et al., 1996) and may affect the body’s soft tissues, including
damage to the tendons, tendon sheaths, muscles and nerves of the hands, wrists,
elbows, shoulders, neck and back (Saldaňa, 1996). Among such disorders, pain in
the neck and shoulders often causes work disability among employees and are
frequently associated with long periods of disability and sick leave (Westerling
and Johsson, 1980).
According to the World Health Organization, WMSDs arise when exposed to
work activities and work conditions that significantly contribute to their
development or exacerbation but not acting as the sole determinant of causation
(World Health Organization, 1985). These disorders have been found to be
associated with numerous occupational ‘risk factors’, including physical work
load factors such as force, posture, manual handling, repetitive work and vibration
(Gerr et al., 1991); psychosocial stressors (Bongers et al., 1993; Bernard et al.,
10
1994) and individual factors (Armstrong et al., 1993). Ayoub (1990) explained
that these factors become hazardous due to prolonged repetitive, often in a
forceful and awkward manner, without sufficient rest or recovery.
The present study sought to investigate WMSDs within one brick-making factory
in South Africa. This study has focused on the sorting and stacking section, where
bricks were taken from the conveyor belt and stacked in tight packs, ready for
later transportation. The purpose of this study was to identify the specific risk
factors for WMSDs among the brick sorters. The goal is to reduce Work-related
Musculoskeletal complaints among the employees in brick-making factory.
This brick-making factory was based on the South of Johannesburg in South
Africa. The company manufactures bricks that are defined by their strength,
pleasing aesthetics and durability. Their product range includes, clay face bricks
in many colours and textures, clay pavers, plaster bricks and concrete blocks,
pavers and retaining blocks. It markets its products directly to the building trade
as well as through a national distribution structure.
11
2. LITERATURE REVIEW
High incidence rates for WMSDs of the upper extremity have been reported for
workers in office work, manufacturing, and agriculture and numerous materials
handling occupations (Faucet et. al., 2002).
In brick manufacturing industries, studies have been conducted and there has been
a general indication that working with bricks may dispose towards upper limb
disorders. Trevelyen and Haslam (2001) investigated musculoskeletal disorders in
a handmade brick factory, concentrating on the ‘moulding’ department, where
clay is shaped into bricks. Results identified both upper limb and back problems.
Posture and force analysis found poor standing posture and undesirable wrist
positions, accompanied by significant force loadings. An important contributory
factor was considered to be the piecework system.
Basra and Crawford (1995) observed variety of different handling techniques
within the 131 employees in one brick manufacturing plant, of which some of the
techniques were considered potentially harmful although the details of the actual
tasks examined were not given. They identified problems such as poorly designed
workstations, necessitating frequent bending and twisting. Other problems
identified included inadequate rest breaks and effects arising from the employer’s
piecework system.
12
A study investigating brick handling among bricklayers found the primary sites
for work-related musculoskeletal complaints, accounting for most reported lost
time and physician visits, to be the back, neck, and shoulder, followed by the
elbow and wrist/hand (Cook et al., 1996). The survey respondents consistently
identified job factors describing awkward postures of the back and shoulders, and
handling bricks and mortar in these awkward postures, as the loading causes of
their WMSDs.
Also dealing with the bricklayers, Heuer et al. (1996) found that musculoskeletal
complaints decreased with length of employment in their study sample. Further
investigation revealed this was most likely due to a ‘healthy worker effect’ where
individuals’ susceptible to musculoskeletal complaints leave the trade, leaving
their more resilient colleagues in the workforce.
A study evaluating lifting tasks during fire brick manufacturing processes,
concentrating on the forming, heating and packing processes by Chung and Kee
(2002) showed that weight of the load significantly influenced the incidence of
back injuries and that workers who reported to have experienced back injuries
were older than those who did not experience them.
Buckle and Stubbs (1990) identified the industrial classification ‘bricks, pottery,
glass, cement’ as having increased risk of inflammation of tendons of the hand,
forearm, or associated tendon sheaths. In the United States, an analysis of data
13
held by a major insurance company ranked ‘brick or clay product manufacturing’
sixth out of the 10 highest job classification in terms of percentage claims for
cumulative trauma disorders (Brogmus and Marko, 1991).
Ferreira and Tracy (1991) examined a post-kiln brick sorting activity, with high
levels of reported musculoskeletal complaints, performed differently at two sister
locations. Ferreira and Tracy found that one plant had a high level of back
complaints, while the other had an increased frequency of upper limb disorders.
They concluded differences in task performance between the two plants were
influencing the incidence and pattern of disorders, with a large amount of trunk
bending and twisting required at one plant and repetitive handling of several
bricks at a time at the other plant.
2.1. Reported statistics and costs estimate
The Federal Occupational Safety and Health Administration reported as many as
2% of the entire American workforce suffers WMSDs every year and these
disorders account disproportionately for over 1/3 of all worker compensation
costs for medical care and lost wages (Herman, 2000).
In the United Kingdom, Health and Safety Commission (1998) reported that
WMSDs form the largest category of work-related ill health, which estimates for
1995 suggesting 1.2 million individuals experienced a musculoskeletal condition.
In the United States it has been estimated that there are approximately 1.8 million
14
disabling work-related injuries per year, 60 000 of which result in permanent
impairment (Frymoyer, 1997). The Bureau of Labor Statistics reported that
musculoskeletal disorders accounted for the majority of the occupational injuries
and illnesses involving lost days (approximately 705, 800 cases or 32% of the
total cases), are specifically resulting from overexertion or repetitive motion
during manual material handling with an estimated total cost of $13 billion per
year (National institute for Occupational Safety and Health, 1997).
3. POTENTIAL RISK FACTORS
A risk factor is defined as an attribute or exposure that increases the probability of
disease or disorder (Last, 1983).
3.1. Workplace risk factors
Workplace risk factors are considered to be the most important cause for the
majority of the musculoskeletal disorders because they are directly related with
the physical hazards to the worker (Waters and Putz-Anderson, 1997). These
factors include: shift work, heavy physical work, heavy manual material handling,
lifting, bending, repetitive work, frequency and duration of a task and dynamic
workload (Ayoub et. al., 1997).
Manual materials handling and lifting are major causes of work-related low back
pains and impairments (Waters et. al., 1993) with other factors such as bent and/or
twisted position (Riihimaki, 1991; Hagberg, 1992).
15
Manual material handling is the most frequent (36% of all the claims) and costly
(35% of total cost) category of compensable loss (Leamon and Murphy, 1994;
Murphy et. al., 1996) and is associated with the largest proportion (63-70%) of
compensable low back disability (Snook et. al., 1978; Bigos et. al., 1986; Murphy
and Courtney, 2000).
Repetitive and forceful work activities, awkward or static postures and
mechanical pressure associated with work tasks have been cited as important
etiological factors for WMSDs (Bernard et. al., 1993; Hagberg and Wegman,
1987; Silverstein et. al., 1987).
3.1.1. Job-related risk factors
Ayoub et al., (1997) and Garg (1997) mentioned the more important job-related
risk factors and possible reasons for their association with injury risk associated
with manual material handling of loads.
1) Horizontal and vertical location of the load relative to the worker: with an
increase in horizontal distance the external joint loads will increase and
workers will use a large proportion of their strength capacity. Distance
load to be moved: increased travel distance results in reduced strength and
higher energy expenditures.
2) Frequency and duration of the task: as the frequency of lifting increases,
metabolic demands are higher and the onset of physical fatigue is more
rapid.
16
3) Weight and size of the load: the weight of the load can affect the required
strength and postural stress and metabolic demands.
4) Weight and size of the load: the weight of the load can affect the required
strength and postural stress and metabolic demands.
3.1.2. Awkward postures
Awkward posture means a considerable deviation from the neutral position of one
or combination of joints (Pinzke and Kopp, 2001). These postures typically
include reaching behind, twisting, working ahead, wrist bending, kneeling,
stooping, forward and backward bending, and squatting. Such postures are related
to injuries that are incurred during tasks that are static in nature and relatively
long lasting and during tasks that demand exertion of force (Westgaard and Aarås,
1984).
Such strenuous working postures combined with heavy physical workload, they
result in a high frequency of WMSDs (Pinke and Kopp, 2001). It is documented
that there is a relationship between awkward postures and pain, and symptoms
and injuries in the musculoskeletal system (Grandjean and Hünting, 1977). Lifting
with rotated trunk would further increase the risk of back failure (Marras et. al.,
1995).
17
Luopajarvi (1990) indicated the most common and well-known risk factors in
different parts of the body:
- In the neck the most work-related disorders and pains seem to be
associated with sustained positions with a bend or twist of over 20
degrees.
- In the shoulders, the disorders are related to repeated elevation of the arms
to more than 30 degrees from the body.
- In the elbows and hands, the reported causes of disorders were
unaccustomed movements, repetitive movements executed with high
speed, extreme positions of wrist and fingers.
3.2. Personal factors
These factors include level of physical fitness, weight, diet, habits, previous
medical record and lifestyle, may also affect the development of musculoskeletal
disorders (Waters and Putz-Andersson, 1997). Ayoub et al., (1997) listed some
more important personal risk factors and possible reasons for their association
with injury risk:
1) Age: muscle strength appears to be greatest in the late 20’s and early 30’s
and declines thereafter.
2) Gender: women on average are weaker than men. Gender differences are
almost entirely explained by differences in muscle size, as estimated by
either the person’s fat-free body weight or cross sectional area dimensions.
18
3) Anthropometry: body weight and height have been correlated with
muscle static strength.
3.3. Psychosocial factors
The psychosocial work environment constitutes an important part of an
ergonomics evaluation of a workplace. The term “Psychosocial” is commonly
used in the occupational health arena as the general term to describe a very large
number of factors that fall within three separate domains: (Bongers and de
Winter, 1992)
1) Factors associated with the job and work environment,
2) Factors associated with the extra-work environment, and
3) Characteristics of the individual worker.
Interactions among factors within each of these domains constitute what is
referred to as a “stress process,” the results of which are thought to impact upon
both health status and job performance (Bongers and deWinter 1992).
However, it is speculated that an interaction between the relative weighting of the
variables and the extent to which they have been stressed in any individual
determines the final outcomes as depicted in figure 1.
19
Predisposition
Hazards
Vulnerability Stresses
Susceptibility
Response
Tension
Compression
Strain Heightened Probability
Creep
Laxity Progressively Decreasing
Instability Threshold of
Microtrauma Precipitation
Progressively Decreasing
Threshold of Precipitation
Figure 1. A global theory of musculoskeletal injury precipitation (modified from
Kumar, 1991).
Genetic trait
Morphological Characteristics
Psychosocial Profile
Individual
Strain
Structural Biochemical Physiology
Injury Precipitation
Biomechanical Factors
Nociception
Pain
Pain Behaviour
20
Increasing evidence suggests that exposure to adverse work organization
characteristics, such as high performance demands coupled with low levels of job
control and low workplace social support, places individuals at increased risk of
stress and illness (Karasek and Theorell 1990: Johnson and Hall, 1988). It has
been indicated that physical work risk factors acting with psychosocial work risk
factors increases the risk of self-reported back disorders (Devereux, 1998; Linton,
1990).
Karasek (1979) derived a composite measure ‘job strain’ which is assumed to be
experienced by workers facing high psychological demands combined with low
control or low decision latitude in meeting those demands (figure 2).
Psychological Demands
LOW HIGH B
Learning Motivation to Develop HIGH New Behaviour Patterns Decision Latitude (Control)
LOW Risk of Psychological Strain and Physical illness
A
Figure 2. Demand and control model. (Karasek, 1979)
Low-strain Active
Passive High-strain
21
The Karasek and Theorell (1990) job demands-control-support model predicts
that jobs with high mental demand and high degree of decision latitude or control
and social support (called active jobs) lead to learning, motivation and active
workers. The ways in which high ‘job strain’ can be detrimental to individual
health (e.g. musculoskeletal symptoms, psychological distress) have been
reported in several studies (Johansson, 1995; Karasek and Theorell, 1990).
4. PROJECT DESIGN
This project has been designed using the Logical Framework Approach method.
On the basis of available information from previous researches, the major existing
problems among the brick sorters have been identified and the focal problem (i.e.
work-related musculoskeletal complaints) has been selected for the analysis.
Substantial and direct causes of the focal problem were identified (Appendix 1).
Also the substantial and direct effects of the focal problem were identified. In the
objectives analysis, the problem tree was transformed into a tree of objectives
(future solutions of the problems) and analyzed (Appendix 2). The main project
elements were derived from the objectives tree and transferred into the vertical
column of the project matrix (PM) (Appendix 3)
22
5. SPECIFIC OBJECTIVES
i. To determine the prevalence of self-reported musculoskeletal
pain/discomfort among the brick sorters.
ii. To identify the most affected body regions.
iii. To identify specific ergonomic risk factors in the workplace.
iv. To provide the company with advice on how to improve the
work environment.
6. METHODS
6.1. Subjects
Nineteen currently employed male workers performing manual work with
special reference to the process of sorting and stacking of bricks voluntarily
participated in the interviews and signed forms of consent. Each potential
volunteer was informed that participation was on company time at the usual
rate of pay. They were told that their participation in the project was voluntary
and would not influence their employment. The purpose of the study and the
confidentiality of the information provided were also emphasized.
6.2. Semi-structured Interviews
Questionnaires were completed through interviews (Appendix 4). Interviews
were confidential, undertaken in work time but away from the workplace in a
confined office and lasted approximately 15 minutes for each individual.
Frequency and descriptive analysis of data from the questionnaire was
accomplished using Microsoft Excel 2002.
23
The interviews were conducted taking into consideration the following
information:
1) Employees’ work such as job title, hours worked, length of time on
present job and employees’ general health as well as some personal
data like age, gender, weight and height.
2) Subjective pain/discomfort on different body regions, which were
measured using a modified version of Nordic Questionnaire by
Kuorinka et al., (1987).
3) Psychosocial work factors, which were measured using a modified
version of Norwegian translation of the short Swedish version of
the Job content, Questionnaire (Theorell et al., 1991) developed
from the job demand-control-social support model by Karasek and
Theorell (1990) (Appendix 5). Questions were selected because
some questions were interrelated and the checklist already covered
some aspects of the work. Questions were structured and
dichotomized alternative “yes” and “no” was used instead of the
three-point scale ranging from 0 (equivalent to “no”, “never” or
“do not agree” for all items) to 1 (equivalent to “yes”, “often” or
“agree” for all items). The advantage was that it was easy for the
employees to answer and also time saving. Taking into
consideration that the interviews were to be conducted during work
time.
.
24
6.3. Workplace analysis
Work place analysis has been accomplished by observing the tasks, watching the
employees as they were doing the task. Each task has been described according to
how it was performed. This was to note the main demands of the tasks and list the
risk factors as to which may be present (Appendix 6).
6.4. Use of the 1993 NIOSH equation
The revised National Institute for Occupational Safety and Health (NIOSH) lifting
equation by Waters et al., (1993) was used for the calculation of the
Recommended Weight Limits (RWL) of the loads calculated by the following
equation:
RWL = LC x HM x VM x DM x AM x FM x CM
Measurements of the variables were obtained using NC3 Chrome tape (3m x 13
mm) and asymmetry angles were measured using a Protractor square. Table 1
presents the definitions of the multipliers of the equation and the variables behind
them, as well as the values of the variables kept constant in this study.
The Horizontal location (H) and Vertical location (V) at origin of lift were
assumed to remain unchanged at both the lowest and the highest possible
locations. Both the Horizontal and Vertical location at destination of lifts were
changing variables of which the two extreme lifting positions, the lowest and the
highest possible locations of the hands, were included in the calculations. The
25
Frequency Multiplier (FM) was estimated on average of 10 lifts/min and the
average lifting duration per shift of 8 hours. The Coupling Multiplier (CM) was
classified as poor, so the value of the CM was estimated as 0.90.
The procedure for calculating the Lifting Index (LI) was by the formula below:
LI = Object weight
RWL
Table 1. The definitions of the multipliers of the revised NIOSH equation and the
variables used for calculations.
MULTIPLIERS VALUES VARIABLES
Load Constant (LC) 23 23 [ kg ]
Horizontal Multiplier (HM) (25/H) Horizontal location (H) [ cm ]
Vertical Multiplier (VM) 1- (0.003∗ ⎥ V-75⎥ ) Vertical location (V) [cm ]
Distance Multiplier (DM) 0.82 + (4.5/D) Vertical Travel Distance (D) [cm]
Asymmetric Multiplier (AM) 1- (0.0032∗A) Asymmetric Angle (A) [deg]
Frequency Multiplier (FM) FM = 0.13 (F = 10 lifts/min,
T = 8 hrs
26
6.5. Observational method
In this study, an instantaneous observation of the posture and posture recording
were made using Ovako working posture analyzing method (OWAS) by Karhu et
al., (1977). Four-digit code representing the back (four choices), three arm
postures, and seven leg postures. The use of strength or the weight of loads
handled was classified by a three-class scale (as shown in table 2). Postures were
recorded for each of the four work phases during the working session. Posture
recordings for each work phase were done within at least 20 to 30 seconds.
OWAS method was manual and the registrations
Table 2. OWAS posture code definitions __________________________________________________________________ Back Arms __________________________________________________________________ 1= straight 1= both arms below shoulder level
2= bent forward or backward 2= one arm at or above shoulder level
3= twisted or bent sideways 3= both arms at or above shoulder level
4= bent and twisted or bent
forward and sideways
__________________________________________________________________ Legs Load/use of force __________________________________________________________________ 1= sitting
2= standing on both legs straight 1= weight or force needed is 10 kg or less
3= standing on one straight leg 2= weight or force needed exceeds 10 kg
4= standing on both knees bent but is less than 20 kg
5= standing on one knee bent 3= weight or force needed exceeds 20 kg
6= kneeling on one or both legs
7= walking or moving
__________________________________________________________________
27
7. RESULTS
7.1. Task Description
Bricks were manually sorted right from the conveyor belt to the pallet on the
sides, which were more stable and ready for later transportation. The job was
performed while standing. Methods for handling vary from one worker to the
other. Most sorters often hold two bricks, one in each hand and some with five
bricks at a time (held between the hands). As a result of the requirement of
alternating brick faces in each row, the sorters must pay constant attention to brick
orientation. The sorters appears to have a good knowledge of which bricks were
likely to have defects, so that the inspection become rapid and often it was not
necessary to turn the bricks around.
7.2. Work Organization
The work was organized in such a way that sorters share the conveyor belt, but
each of them concentrates on his own daily target. Each brick typically weighs 2.7
kg and each worker ensured that he reached his daily target of 10 500 bricks per
day (i.e. 21 pallets/500 bricks each). Some workers concentrated on 2 to 4 pallets
at a time depending on the colours of the bricks. Each sorter ensured that the
bricks were placed correctly; having alternate layers with faces up and faces
down. They work three days in succession and have three days off the next days.
Work hours were normally between 6.00 am and 6.00 pm but all the sorters leave
early if the daily target has been achieved, which encouraged them to work at a
higher speed of work than may be necessary.
28
Normally, each sorter has 15 minutes tea breaks in the morning at 9.00 am and
4.00 pm in the afternoon. Also lunch break in the afternoon between 12.00 and
12.30 am of which workers have indicated that they prefer to have only one break
of which the team has to agree upon and that would be their lunch for at least 20
to 30 minutes so that they finish their daily target early. They have also indicated
that when they finish early, they have enough time to rest in order to prepare for
the next day. Therefore, each worker had the passion to work as fast as possible
so that he does not remain alone. Sorters at the first stations tend to handle larger
number of bricks, while those at the later stations have a lighter workload,
therefore they allow for flexibility within the team to rotate, then sorters at first
station have to make 13 pallets and rotate and make another 8 pallets at the later
stations and vice versa.
Then once each sorter finishes his daily target, the supervisor has to check if the
bricks were correctly placed then the worker can be released. If the bricks were
not properly placed, they were told to rearrange the pallet until the supervisor was
satisfied.
29
7.3. Questionnaire
7.3.1. Demographic information
The following demographic data was collected from all the 19 male subjects who
participated in the interviews (as shown in table 3). All the subjects used both
hands equally well.
Table 3. An overview of the demographic information of the respondents (n =19).
Mean *S D Range
Age (yrs) 38.7 7.74 28-52
Duration of employment (yrs) 9.4 4.50 2-17
Height (cm) 169.09 6.06 158-183
Weight (kg) 67.75 7.63 51-79
*SD= Standard Deviation
7.3.2. Self-reported discomfort/pain
Workers were asked few questions about perceived pain/discomfort, which lasted,
for at least 24 hrs. Pain was measured at past 12 months, last month and 7 days.
Results are presented in order as mentioned above.
During the last 12 months, 36.8% (7) of the respondents reported pain on low
back and 26.3% (5) on the neck. Of about 21.0% (4) of the employees complained
of upper back problem. And 15.8% (3) of the employees had shoulder and
wrist/hand problems. Concerning elbows and ankles/feet pain, 5.26% (1) of the
30
employees complained. No complaints were reported regarding knees and
hips/thighs (figure 3).
05
10152025303540
Neck
Should
ers
Low Back
Upper
Back
Elbows
Wr/h
ands
Ank/fe
et
Body region
Perc
enta
ge
of r
espo
nden
ts (%
)
Figure 3. Percentage of respondents who complained of pain per body region
during the last 12 months lasted at least 24 hours. (n=19)
During the last month, 26.3% (5) of the employees complained of low back pain,
15.8% (3) of the employees complained of the neck, shoulders and wrist/hand
problems. About 10.5% (2) of the employees suffered from upper back pain and
ankles/feet. Of about 5.26% (1) of the employees suffered from elbows,
hips/thighs and knees pain (figure 4).
31
0
5
10
15
20
25
30
Neck
Should
ers
Low Back
Upper
Back
Elbows
Wr/h
ands
H/thigh
s
Knees
Ank/fe
et
Body re g ion
Perc
enta
geof
res
pond
ents
(%)
Figure 4. Percentage of respondents who complained of pain per body region
during the last month lasted at least 24 hours. (n=19)
For the last 7 days, 21.0% (4) of the employees had an episode of low back pain.
About 10.5% (2) of the employees suffered from upper back. Of about 5.26% (1)
of the employees had an episode of pain on the neck, shoulders, elbows,
wrist/hand, hips/thighs, knees and ankles/feet (figure 5).
32
0
5
10
15
20
25
Neck
Should
ers
Low Back
Upper
Back
Elbows
Wr/h
ands
Ank/fe
et
Body region
Pece
ntag
e of
res
pond
ents
(%)
Figure 5. Percentage of respondents who complained of pain per body region for
the last 7 days lasted at least 24 hours. (n=19)
Workers were also asked if they have been prevented from doing normal activities
because of the pain. 15 of 19 (78.9 %) respondents have been prevented due to
pain from low back. Of about 31.6% (6) of the employees was because of neck
pain. Regarding shoulder pain, 36.8 % (7) of the employees have been prevented.
Of about 26.3% (5) of the employees have been prevented because of upper back
problem. For the elbows, 15.8% (3) and about 47.3% (9) with the wrists/hands of
the employees complained. Also knees and ankles/feet problems were found to be
10.5% (2) and 15.8% (3) of the employees respectively (figure 6).
33
0102030405060708090
Neck
Should
ers
Low Back
Upper
Back
Elbows
Wr/h
ands
Knees
Ank/fe
et
B ody re gion
Perc
enta
ge o
f r
espo
nden
ts (%
)
Figure 6. Percentage of respondents who have been prevented from doing normal
activities because of pain per body region. (n=19)
Of all the complaints reported, low back pain constituted the highest number of
percentage. Workers were also asked if they have seen a doctor because of the
pain. About 73.7% (14) indicated that they have seen a doctor because of the
discomfort/pain and only 31.6% (6) of those have stayed away from work.
According to all the respondents the discomfort/pain was caused by the job.
34
7.3.3. Psychosocial factors
Workers were asked questions regarding their work. All the respondents (19),
described the work as rather ‘very difficult’, ‘monotonous’ and they feel that they
have ‘excessive work’. 18 of 19 (94.7%) employees reported that the working
situation requires that they work ‘very fast’ which forced them to work hard in
order to finish the daily target. About 89.4% (17) of the employees indicated that
they have sufficient time to work whereas only 10.6% showed that the time is not
sufficient, that is why they have to work at high pace. All the employees
emphasized that the job is mentally demanding, since it requires high
concentration, especially that they have to sort different colours at the same time
and they have to ensure that the bricks are correctly placed.
Of about 89.4% (17) of the employees, showed that they are given an opportunity
to voice out their suggestions regarding the work and also that the supervisors are
concerned about their work. Supervisors are responsible of seeing to it that the
work is being performed safely, sometimes advising workers on how to sort well
and also giving good comments if the job has been done perfectly. Of all the
employees, 63.1% (12) indicated that they do not feel like helping their co-
workers, with a reason that, is not possible because they feel that they have a lot
of work to do, whereas only 36.84% (7) of the employees do help friends and
relatives.
With regard to team spirit, 57.9% (11) of the employees explained that they might
like to work in team, because they think that will make the job easier and they can
35
be able to plan together how to work. Of about 42.1% (8) of the employees did
not support the teamwork, because they feel that some may tend to relax since
they do not work at the same pace and that may put more workload on some than
others.
7.4. Job Analysis
Horizontal location (H) at origin of lift was estimated to be always 75 cm and H at
destination was estimated to be 50 cm at lowest hand location; 90 cm at highest
hand location. The minimum and maximum Vertical location (V) were also
measured at the origin and destination of lift. V at origin was estimated to be
always 90 cm, whereas V at destination was estimated 22 cm and 115 cm at
lowest and highest hand location respectively. Thereby in the case of lifting at
lowest hand location, Vertical travel distance (D) was 68 cm and 25 cm at the
highest hand location. Asymmetry angle was approximately 650 both at origin
and destination of the lift except for the destination at the lowest hand location of
1000. Frequency Multiplier (FM) was always 0.13, corresponding to the estimated
average of 10 lifts/min and the average lifting duration per shift of 8 hours. The
quality of coupling between hands and bricks was classified as poor, so the value
of the Coupling Multiplier (CM) was 0.90 (see Appendix 7).
The results of NIOSH equations using normally obtained variables are also shown
in Appendix 7. The total variation of RWL was 0.50 – 0.93 kg. The RWL is less
than the weight of even a single brick. The LI was calculated to be 2.90 – 5.4 as
shown in Appendix 8, which exceeds 1.0 indicating the job to be stressful.
36
7.5. Postures adopted by workers
The scores for the assessment of postural stress in brick sorters were calculated
and found to be 4 for the sub-tasks like lifting of bricks from the conveyor,
carrying bricks to the pallet as well as packing of bricks in the pallet. The score of
3 was found for the sub-task of rearranging the pallet. The scores were obtained
according to OWAS Worksheet. This score 3 indicates that the postures need
corrective measures as soon as possible whereas the score of 4 indicates that the
corrective measures are needed immediately. The scores assessed by OWAS
method in brick sorters are summarized in table 4.
Table 4. Description of sorting/stacking tasks and postural analysis (Postures
classified according to Karhu et. al., 1977).
*OWAS postures codes
Sub-task description Back Arms Legs Force Score
__________________________________________________________________
Lifting bricks from conveyor belt 4 1 5 1 4
Carrying bricks to the pallet 3 1 5 1 4
Packing bricks in the pallet 4 1 5 1 4
Rearranging the pallet 2 1 5 1 3
__________________________________________________________________
*The OWAS posture codes are explained in table 1. e.g. code 4 means
back bent forward and twisted, 3 means back twisted and 2 means back bent
forward. Arms (1) both arms below shoulder level and legs (5) means Standing on
one knee bent and force (1) means weight or force needed is 10 kg or less.
37
8. DISCUSSIONS
Manual materials handling is one of the recognized risk factors for back
problems, with other factors such as bent and/or twisted position (Riihimaki,
1991; Hagberg, 1992). This is specifically evident in industrially developing
countries, where manual materials handling is inherent within industry and where
manual labour involved in physically demanding tasks is a dominant factor (Scott,
1993). In the present study, the job of the brick sorters was described as rather
physically demanding: involving frequent twisting and bending of the trunk. This
type of job was also described as highly repetitive and requires high concentration
as a result of the requirement of alternating brick faces in each row. Therefore,
sorters must pay constant attention to brick orientation and this may impose more
stress and increased mental fatigue.
Brick sorters mainly complained about ‘excessive work’, which encourages them
to work at high pace than is necessary, which appears as a significant source of
stress. Moreover, the workers often explained in the comments that the situations
made them feel frustration and anxiety. It is also seen that workers perceptions
about the job characteristics may differ due to their motivation, emotional state
and work experience level.
However, in this study, pain per body region was measured for the past 12 month,
last month and last 7 days, which lasted for at least 24 hours (Figure, 3, 4, and 5
respectively). The results show that most workers complained of low back pain.
38
Fifteen of nineteen employees (78.95%) indicated that they have been prevented
from doing normal activities because of low back pain followed by wrists/hands,
shoulders, neck and upper back. Pain in other body locations accounted for low
rate. (Figure 6) Similar finding was reported by Chung and Kee (2000), indicating
that 78.5% of the workers performing tasks that require trunk twisting were
reported to have experienced low back pain, while 55.6% performing tasks that do
not require trunk twisting were reported to have experienced low back pain. All
the brick sorters have reported having experienced discomfort arising from work.
A study by Ferreira and Tracy (1991) showed that four workers out of seven
(57.1%) at sorting/packing tasks had sick leave due to upper limb disorders. Back
complaints appear more frequently in sorting processes. It is more likely that the
high incidence in packing processes is more influenced by handling techniques,
the way work is organized and the workplace design than by the age of workers.
Work factors contributing to the development of musculoskeletal disorders were
summarized as follows:
The influence of daily target was to reinforce the fast working pace and encourage
the missing of breaks. A further problem was considered to be the job design,
where the brick sorters single main task was the brick sorting process. This may
lead to high proportion of the brick sorters time spent in repetitive activity. The
other problem that was observed was the handling techniques, where most
workers often lift two bricks, one brick in each hand. This type of technique was
39
alternated with grasping five bricks between both hands. Also that the present
layout of the workplace requires sorters to turn 1000 as they pack bricks to the
pallet. This involves frequent rotation of the trunk and forward bending. Sorters
have to bend down to the floor as they reach to the bottom of the pallet. These
awkward postures could be minimized by simple alterations of the work
environment.
Other aspects of the workplace design were also identified in this workplace.
From NIOSH perspective, the lifting tasks with LI > 1.0 indicates an increased
risk for lifting-related low back pain for some fraction of the workforce (Waters
et. al., 1993). This study found the recommended weight limit substantially lower
than the weight of even a single brick (2.7-kg) with the lifting indices of more
than one. With the lifting indices of this magnitude, the task is always unsafe and
should be totally redesigned to achieve the LI of 1.0 or less.
In Appendix 8, presenting the procedures of calculating RWL and LI of the
sorting/stacking process. It is seen that the smallest multiplier was 0.13 for the
FM, the second 0.27-0.50 for the HM and the third 0.68-0.79 for the AM of,
which must be given an attention. The employees are given a daily production
order of 12 hours shift, and they normally finish the job within 7-8 h to have a
long break for the rest of the day. Such work practices result in high frequencies.
Therefore is of most important to redesign the workplace, which can be presumed
to be safe for most workers.
40
9. CONCLUSIONS
In conclusion, it is likely that the largest number of complaints of work-related
musculoskeletal disorders in sorting/stacking processes is more influenced by the
workplace design necessitating frequent bending and twisting, handling
techniques, the way work is organized. Other problems identified include
inadequate rest breaks and high speed of work.
10. RECOMMENDATIONS
1) Workplace design: positioning the bricks closer to the worker and by
placing the pallet at the right-hand side of the worker in order to reduce
the asymmetric angle.
2) Implement an ongoing training program: to enable each sorter to be aware
of the relevant factors concerning musculoskeletal disorders.
3) Workers should be given education about the types of the work-related
musculoskeletal disorders and causes of these disorders.
4) It is important to address problems related to stress in the workplace as it
may influence the occurrence of the musculoskeletal problems among
employees.
5) Workers should be motivated to adopt working techniques that are
preferable.
6) Encouragement and motivation of all the employees to take rest breaks by
showing its importance.
7) Also by showing the importance of taking physical fitness exercises.
41
8) Work organization: review the “daily target”.
9) If it is possible, alternate strain by changing task (job rotation), especially
for those workers who are much more prone to work-related
musculoskeletal disorders.
42
11. ACKNOWLEDGEMENTS
Firstly, I thank God Almighty for giving me the strength and wisdom to reach this
point in my academic career.
I gratefully acknowledge the STINT Scholarship (The Swedish Foundation for
International Cooperation in Research and Higher Education) for supporting me
financially throughout the whole study period in Luleå University of Technology
I would also like to express my gratitude to all people who have contributed in
significant ways to this work, in particular my supervisor Professor Houshang
Shahnavaz, the head of the Division of Industrial Ergonomics for his guidance
from the beginning of this programme and during my research. Thanks also
extended to Busisiwe Nyantumbu for supervising this work. Also the support,
encouragement and sacrifices made throughout the whole project. Thanks also go
to Dr. Emma-Christin Lönroth who helped me throughout the whole course.
I would also appreciate the help from Dr. Danuta Kilkowski, the head of
Epidemiology Department at National Centre for Occupational Health,
Johannesburg for making this project successful.
This work would have not been possible without the support and strength that I
have gained from my family, to whom I am very grateful.
43
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52
13. APPENDIX 1: PROBLEM ANLYSIS
EFFECTS
CAUSES
Work-related Musculoskeletal Complaints increase amongst workers in Brick
making factory
Inadequate rest pauses
Low payment systems
Monotonous work
Absenteeism increases
Increases costs for productivity
Employees ill health
increases
Decreases productivity
Economic loss for Company
Reduces Working capacity
Insufficient training
Compensation costs increases
Turnover increases
Manual handling of
loads
Awkward working postures
Repetitive work
High job demands
Long working
hours
Low decision latitude
Low social
support
High work pace to meet daily target
53
14. APPENDIX 2: OBJECTIVE ANALYSIS
Work-related Musculoskeletal Complaints reduced amongst workers in Brick making
factory
Absenteeism reduced
Costs for productivity decreased
Employees ill health improved
Productivity increased
Economic loss for Company reduced
Working capacity increased
Compensation costs decreased
Turnover reduced
Manual handling of loads is minimized
Poor working postures are limited
Employees are provided with sufficient training
Adequate rest pauses are provided
Pace of work is minimized
Job rotation is introduced
Repetitive actions
minimized
Recommendations for improvement are provided
Low job demands
High social support from co-workers
Workers have control over the job
54
15. APPENDIX 3: The Basic Elements of the Project Matrix
Goal:
Work-related musculoskeletal complaints
reduced for employees in brick making factory
in South Africa
Indicators:
- Work-related musculoskeletal complaints reduced
among workers in brick making factory within 12
months after the completion of the project.
- 20% reduction is guaranteed as a result of the
implementation of the recommended measures by
the study.
Assumptions
- Management is assumed to agree
and accept the listed risks factors
in order to improve the working
conditions of their employees.
- The process of working is not
changed for further evaluation.
Purpose:
Specific risks factors for work-related
musculoskeletal disorders identified among the
brick sorters in one brick-making factory in
South Africa.
Indicators:
- Specific risks factors for the selected area (i.e.
sorting /stacking section) listed by the end of
January 2003.
Assumptions
-Outside factors do not influence the
results of the study.
55
Outputs:
1) Prevalence of self-reported work-
related musculoskeletal complaints
determined.
2) Most affected body regions identified.
3) Ergonomic risk factors in the
workplace identified.
4) Working postures assessed
5) Results analyzed
6) Written report
7) Recommendations listed
Indicators:
- Among the 19 brick sorters, interviews
regarding subjective pain/discomfort on
different body regions and psychosocial
situations, which brick sorters perceived as
contributing factors to those disorders
conducted by the end of November 2002.
- Workplace analysis: to note the main
demands of the tasks and listing the risk
factors as to which may be present
accomplished by the end of November 2002.
- Assessment of the physical stress by 1993
NIOSH equation completed by the end of
December 2002.
- Among the 19 brick sorters, posture assessed
through instantaneous observation by the end
of December 2002.
- Results analyzed by the end of January 2003.
Assumptions
- The workers who volunteer for
participation will represent the
whole group of brick sorters in this
factory.
- It assumed that workers would not
change the way they perform the
tasks during the observation.
56
Written report completed and recommendations
listed by the 15th of February 2003.
Activities:
1) Talk to employees, to understand the
purpose of the study
2) Give voluntary consent form to sign for
participation.
3) Conducting interviews with employees.
4) Observation of the workplace and
measuring the workstation layout
5) Assessing working postures using OWAS.
Inputs:
- Volunteers for participation in the interviews
- Measuring tape
- Statistical software
- Employees are not forced to
participate in the interviews.
- Subjects always available to
provide information throughout
the whole study.
- The language used during
interviews does not influence
information provided by the
employees.
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16. APPENDIX 4: QUESTIONNAIRE: NUMBER: _____ PART I: GENERAL INFORMATION Gender: What year were you born?
Male Female
What is your job title?
How many years and months have Years + Months you been doing your present type of work? On average, how many hours per shift Hours do you work? Minutes How about the rest breaks? kg How much do you weigh? cm How tall are you? Does your work require the use of both hands?
No Yes
Do you have any health problems? No Yes If yes, explain briefly _____________________________________________________ _______________________________________________________________________
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PART II: This part of the survey is designed to determine the musculoskeletal symptoms
among the workers. Note that the questionnaire is to be answered, even if you have
never had trouble in any part of your body.
1. Have you ever been prevented from doing your normal work activities (at home
or away from home) because of musculoskeletal pain/discomfort?
No Yes
2. Where was this pain/discomfort? Please indicate in the diagram (figure 1 below).
Figure 1. Showing the body regions. 3. Did you see a doctor because of your pain? No Yes 4. Did you stay away from work because of the pain? No Yes 5. What caused the pain? _______________________________________________________________________
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6. Have you at any time during the last 12 months had an episode of pain or discomfort
lasting at least 24 hours?
No Yes If yes, identify area on the body (Identify the areas on the figure above, indicate one or
both sides)
_______________________________________________________________________ 7. Have you at any time during the last month had pain or discomfort, which lasted at
least 24 hours?
No Yes If yes, identify area on the body _____________________________________________ 8. Have you ever at any time during the last 7 days had pain or discomfort, which lasted
at least 24 hours?
No Yes If yes, identify area on the body ____________________________________________ PART III: This part of the questionnaire is to measure the psychosocial aspects of the work. 9. Do you think the job is? Very Fast Fast Normal Slow Very Slow Very Easy Easy Normal Difficult Very Difficult 10. Do you think you have excessive work? No Yes
If yes, elaborate _________________________________________________________
11. Do you think you have sufficient time to work? No Yes
If yes, elaborate _________________________________________________________
12. Does the job require creativity? No Yes
If yes, explain __________________________________________________________
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13. Do you have opportunities to learn new things? No Yes If yes, elaborate _________________________________________________________ 14. Are you given opportunity to voice out regarding suggestions on how to improve the
working conditions?
No Yes If yes, explain ___________________________________________________________ 15.Do you assist each other as fellow-workers? No Yes Explain ________________________________________________________________ 16. Is your Supervisor/s concerned about your work? No Yes Explain ________________________________________________________________ 17. Do you prefer working in groups? No Yes Explain ________________________________________________________________ 18. Please describe how satisfied you are with the health service provided by the company? ______________________________________________________________________________________________________________________________________________ 19. Is there something you want me to know about your working situation? ______________________________________________________________________________________________________________________________________________
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17. APPENDIX 5: A modified version of Norwegian translation of the short
Swedish version of the Job content, Questionnaire (In English)
_______________________________________________________________________
Indices Items
Job demands (5 items)
Working fast
Working hard
Excessive work
Insufficient time to work
Conflicting demands
Job control (decision latitude) (6 items) Learn new things
Requires creativity
High skill level
Repetitive work
Tasks variety-how
Tasks variety-what
Social support (6 items)
Atmosphere in the work
environment
Friendly co-workers
Co-workers helpful
Co-workers interested in me
Supervisor concerned
Team spirit
_______________________________________________________________________
Taken from Morken et. al., (2002)
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18. APPENDIX 6: CHECKLIST
The purpose of this checklist is to increase awareness of potential problems associated
with jobs and their tasks for making effective improvement.
Task Details
1. Task name:…………………………………………………..
Area:…………………………………………………………
Assessor:…………………………………………………….
Date of assessment:……….. ……….………
2. Consultation with employees: (Talk to the people who do the task. Get them to mime
the task actions).
3. Observe the tasks: (Watch the employees doing the task. Describe the manual
handling aspects of the task by writing down its steps).
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
……………………………………………………………………………………………
Task duration (for how long do they perform the same
task):………………………………………………………………………………………
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Hazard Identification 4. The task - does it involve?
Holding load at a distance from trunk?
Unsatisfactory bodily movement or posture,
Especially twisting the trunk?
Stooping?
Excessive movement of load: especially
Excessive lifting or lowering distances?
Excessive carrying distances?
Risk of sudden movement of load?
Frequent or prolonged physical effort?
Handling that goes on for too long without a break?
5. The load- is it:
Lifted manually? Notice factors of importance as:
Periods of repetitive lifting
Weight of the load?
Awkward grasping of the load?
Awkward location of load at onset or end of lifting?
6. The working environment- is there:
Space too limited for work movements or work materials?
Uneven, slippery, or unstable floors?
Variations in level of floors or work surfaces?
Extremes of temperature, humidity or air movement?
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19. APPENDIX 7: Task Variables in the sorting/stacking processes
____________________________________________________________________________________________________________
Hand location (cm)
Origin Destination
____________________________________________________________________________________________________________
Lowest hand location highest hand location lowest hand location highest hand location
_________________ ________________ _________________ ______________
H V H V H V D H V D
75 90 75 90 50 22 68 90 115 25
____________________________________________________________________________________________________________
Coupling Frequency Duration
Asymmetric angle (lifts/min) (hr)
Origin Destination
_________ __________
650 1000 (lowest hand location) 0.90 0.13 8
____________________________________________________________________________________________________________
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20. APPENDIX 8: The procedure for calculating RWL and LI in the sorting/stacking processes.
____________________________________________________________________________________________________________
LC HM VM DM AM FM CM RWL LI ____________________________________________________________________________________________________________
23 0.333 0.955 0.886 0.792 0.13 0.9 0.60 4.5
at origin of lift at the lowest hand location
23 0.333 0.955 1.00 0.792 0.13 0.9 0.67 4.02
at origin of lift at the highest hand location
23 0.50 1.159 0.886 0.68 0.13 0.9 0.93 2.90
at destination of lift at lowest hand location
23 0.27 0.88 1.00 0.792 0.13 0.9 0.50 5.4
at destination of lift at highest hand location
____________________________________________________________________________________________________________
