Ergonomics is the study of human interaction with products, tools, and environments. It aims to optimize human well-being and system performance by taking into account human's physical abilities, limitations, and other characteristics. Key principles of ergonomics include allowing for different postures, using larger muscle groups for tasks, and keeping joints in mid-range positions. Anthropometric data on body sizes must be considered in design. Proper posture and frequent breaks can help prevent repetitive strain injuries.

1. ERGONOMICS
Dr.V.Umasankar
VIT,Chennai

2. Definition of Ergonomics
The word ergonomics comes from two Greek words:
ERGO: meaning work
NOMOS: meaning laws
Ergonomics is a science focused on the study of human fitness,
and decreased fatigue and discomfort through product design.
Ergonomics applied to office furniture design requires that we
take into consideration how the products we design fit the people
that are using them. At work, at school, or at home, when
products fi t the user, the result can be more comfort, higher
productivity, and less stress.

3. “The scientific discipline concerned with understanding of
interactions among humans and other elements of a system,
and the profession that applies theory, principles, methods
and data to design in order to optimize human well-being and
overall system performance”.

6. Repetition
Gripping or Pinching
Bent wrists
Repetition
Gripping or Pinching
Repetition

7. History
• As early as 18th century doctors noted that workers
who required to maintain body positions for long
periods of time developed musculoskeletal problems.
• Within last 20 years research has clearly established
connections between certain job tasks and RSI or
MSD.

8. • A repetitive strain injury (RSI) is an "injury to
the musculoskeletal and nervous system” that may be caused by
repetitive tasks, forceful exertions, vibrations, mechanical
compression, or sustained or awkward positions.
• Musculoskeletal Disorders or MSDs are injuries and disorders
that affect the human body’s movement or musculoskeletal
system (i.e. muscles, tendons, ligaments, nerves, discs, blood
vessels, etc.).

9. Fields of Ergonomics
Physical ergonomics: is concerned with human anatomical, and
some of the anthropometric, physiological and bio mechanical
characteristics as they relate to physical activity.
Cognitive ergonomics: is concerned with mental processes, such
as perception, memory, reasoning, and motor response, as they
affect interactions among humans and other elements of a system.
(Relevant topics include mental workload, decision making,
skilled performance, human-computer interaction, human
reliability, work stress and training as these may relate to human-
system and Human-Computer Interaction design.)

10. Organizational ergonomics: is concerned with the optimization
of socio technical systems, including their organizational
structures, policies, and processes.(Relevant topics include
communication, crew resource management, work design,
design of working times, teamwork, participatory design ,
community ergonomics, cooperative work, new work programs,
virtual organizations, telework, and quality management.)

11. Physical ergonomics is important in the medical field,
particularly to those diagnosed with physiological ailments or
disorders such as arthritis (both chronic and temporary) or carpal
tunnel syndrome.
Pressure that is insignificant or imperceptible to those unaffected
by these disorders may be very painful, or render a device
unusable, for those who are. Many ergonomically designed
products are also used or recommended to treat or prevent such
disorders, and to treat pressure – related chronic pain.
.

13. The carpal tunnel is a narrow passageway in the wrist, about an
inch wide. The floor and sides of the tunnel are formed by small
wrist bones called carpal bones.
The roof of the tunnel is a strong band of connective tissue called
the transverse carpal ligament. Because these boundaries are very
rigid, the carpal tunnel has little capacity to "stretch" or increase
in size.
The nine tendons that bend the fingers and thumb also travel
through the carpal tunnel. These tendons are called flexor
tendons.

14. Carpal tunnel syndrome occurs when the tunnel becomes
narrowed or when tissues surrounding the flexor tendons swell,
putting pressure on the median nerve. These tissues are called the
synovium. Normally, the synovium lubricates the tendons,
making it easier to move your fingers.
When the synovium swells, it takes up space in the carpal tunnel
and, over time, crowds the nerve. This abnormal pressure on the
nerve can result in pain, numbness, tingling, and weakness in the
hand.

17. Human factors issues arise in simple systems and consumer
products as well. Some examples include cellular telephones and
other hand held devices that continue to shrink yet grow more
complex (a phenomenon referred to as "creeping featurism"),
millions of VCRs blinking "12:00" across the world because very
few people can figure out how to program them, or alarm clocks
that allow sleepy users to inadvertently turn off the alarm when
they mean to hit 'snooze'.
A user-centered design (UCD), also known as a systems
approach or the usability engineering life cycle aims to improve
the user -system.

18. 1) Static work: musculoskeletal effort required to hold a certain
position, even a comfortable one.
Example: sit & work at computers; keeping head
and torso upright requires small or great amounts of static
work depending on the efficiency of the body positions we
chose.
What two elements are
at work?

19. Elements at work (cont)
• Force: amount of tension our muscles generate
Example: tilting your head forward or backward from
a neutral, vertical position quadruples the amount of
force acting on your lower neck vertebrae.
• Increased force results in increase in muscular tension
needed to support head in a tilted position.

20. 3 Main Ergonomic Principles:
1. Work activities should permit worker to adopt
several different healthy and safe postures.
2. Muscle forces should be done by the largest
appropriate muscle groups available
3. Work activities should be performed with joints at
about mid-point of their head,trunk,etc.

22. The average person working at a keyboard can
perform 50,000 to 200,000 keystrokes a day
Overexertion, falls & RMI are the most common
cause of workplace injury
An average of 125,000 back injuries due to improper
lifting each year.
Muscles overuse results in tiny tears in the muscles
and scarring; these contribute to inflammation and
muscle stiffness
FACTS

23. Correct & Incorrect Techniques

25. ERGO REMINDERS from
Stretchbreak.com

27. Humanfactors is the term used in the United States and a few
other countries.
The term ergonomics, although used in the United States, is more
prevalent in Europe and the rest of the world. Some people have
tried to distinguish between the two, but we believe that any
distinctions are arbitrary and that, for all practical purposes, the
terms are synonymous. Another term that is occasionally seen
(especially within the U.S. military) is human engineering.
However, this term is less favored by the profession, and its use is
waning.

28. Finally, the term engineering psychology is used by some
psychologists in the United States. Some have distinguished
engineering psychology, as involving basic research on human
capabilities and limitations, from human factors, which is more
concerned with the application of the information to the design of
things.
Suffice it to say, not everyone would agree with such a
distinction.

29. Human factors focuses on human beings and their interaction
with products, equipment, facilities, procedures, and
environments used in work and everyday living.
The emphasis is on human beings (as opposed to engineering,
where the emphasis is more on strictly technical engineering
considerations) and how the design of things influences people.
Human factors, then, seeks to change the things people use and
the environments in which they use these things to better match
the capabilities, limitations, and needs of people.

30. Objectives
To enhance the effectiveness and efficiency
with which work and other activities are carried
out.
Included here would be such things as
increased convenience of use, reduced errors,
and increased productivity.
To enhance certain desirable human values,
including improved safety, reduced fatigue and
stress, increased comfort, greater user
acceptance, increased job satisfaction, and
improved quality of life.

31. Anthropometry
Anthropometry is the science that measures the range of body
sizes in a population. When designing products it is important to
remember that people come in many sizes and shapes.
Anthropometric data varies considerably between regional
populations.
For example, Scandinavian populations tend to be taller, while
Asian and Italian populations tend to be shorter.

33. Anthropometric dimensions for each population are ranked by
size and described as percentiles.
It is common practice to design for the 5th percentile (5th%)
female to the 95th percentile (95th%) male.
The 5th% female value for a particular dimension (e.g. sitting
height) usually represents the smallest measurement for design
in a population.
Conversely, a 95th% male value may represent the largest
dimension for which one is designing.

34. The 5th% to 95th% range accommodates approximately 90% of
the population.
To design for a larger portion of the population, one might use the
range from the 1st% female to the 99th% male.
Figure 1 shows comparisons of percentile males and females.
For a listing of other anthropometric measurements of percentile
humans, see Table.

35. Anthropometric databases
Anthropometric datasets compare people of different ages and
occupations. Data in anthropometric databases may represent
static dimensions, such as “lower leg length” or functional
dimensions such as “reach.”

38. The most commonly referenced database used in design is from
military data collected in the late 1970s and throughout the
1980s, and is known as the Natick studies or ANSUR database.
Other databases exist that were collected using civilian data.
In 2000, the Civilian American and European Surface
Anthropometry Resource (CAESAR) was compiled by the
Society of Automotive Engineers (SAE) to measure civilian
populations.

39. CAESAR contains anthropometric data and 3D body scans of
over 4,000 individuals from North America and Europe.
Business and Institutional Furniture Manufacturer’s Association
(BIFMA) and many ergonomics textbooks reference the Natick
(military) studies for design purposes, but some groups are using
CAESAR data with increasing frequency.

40. When using anthropometric measurements in design, consider
two points:
1. How recently data was collected
2. Type of population measured
First, some data may have been collected over 25 years ago, and
measurements such as height or weight may have changed in the
current population.

41. Anthropometric measurements should be a guide for design.
References :
Indian anthropometric dimensions for design practice by
Debkumar chakrabarti, National Institute of Design, ,1997. ISBN
81- 86199-15-0

42. ABit ofAnatomy
Overuse and small repetitive movements ie: CTD, RSI,
MSD disturb balance of muscles, tendons, ligaments
and nerves
Brachial plexus: nerve group that supply muscles and
skin of UE, course down side of front of neck and
become median, ulnar and radial nerves.
Nerves send signals to muscles to contract
When nerve compressed feel sensation somewhere b/w
point of compression and fingertips

45. Intervertebral Discs
Act as Shock Absorbers
Each disc made up of two parts:
Annulus: Outer part of the disc made of a fibrous ligaments.
Extremely strong and responsible for connecting each vertebrae
to one another. Acts as a coiled spring.
Nucleus Pulposus – a soft jelly like centre. Acts as a ball bearing
that the vertebrae roll over during flexion, extension and lateral
bending.

46. When you lean forward, the front of the vertebrae come closer
together forcing the disc fluid backwards.
When you lean backwards, the back of the vertebrae come closer
together forcing the disc fluid forwards. When you lean to the
right, the disc fluid moves to the left. When you lean to the left,
the disc fluid moves to the right.
This is normal!!

47. Owing to our postures during the day, we tend to mainly move
into a forward (flexed) position for example:- sitting at a
computer, removing items from boxes, driving the car, cleaning
the house, putting on shoes, or relaxing in a sofa.
Therefore the disc fluid is gradually pushed backwards over time.
It eventually places increased pressure on the back wall of the
disc (toothpaste tube)

48. When the disc fluid starts to place more pressure on the rear wall
of the disc, you may start feeling low back pain. The more the
disc fluid moves backwards, the more pressure is placed on the
disc wall which results in the pain being referred further down the
buttocks or down the thigh. The disc wall may bulge and irritate
the nerve causing pain, numbness or weakness down the leg.

50. What causes Nerve Compression or
Entrapment?
1) Repeated motions
2) Tight muscles
3) Inflammation of surrounding tissues
4) Misalignment of the nerve

51. What are 4 Common Nerve injuries?
Thoracic Outlet Syndrome: brachial plexus compression d/t
muscle tightness side of neck from poor head position or slumped
posture.
S/Sx: numbness/tingling in hand, made worse w/overhead
activities or cradling phone b/w ear and shoulder

52. Nerve injuries (cont)
II. Radial tunnel syndrome: compressed radial nerve @
outside of elbow d/t repetitive wrist & finger extension
or turning of forearm
S/Sx: Sensations from elbow to base of thumb w/ wrist
weakness a common sx

53. Nerve injuries (cont)
Cubital tunnel syndrome: ulnar nerve compression inside of
the elbow d/t repetitive bending of elbow or resting your
elbow on a hard surface
S/Sx: numbness or tingling and inside of arm w/
tingling to ring & little fingers

54. Nerve injuries (cont)
IV. Carpal tunnel syndrome: compression of
median nerve at level of carpal tunnel
Where is carpal tunnel? Formed @ wrist by
ligament over the carpal bones in hand
S/Sx: numbness or tingling in thumb, index,
or middle finger & ½ of ring finger; often
awakened @ night by hand “falling asleep”
Sx increased by driving or attempting to hold
objects; dropping objects is a common
complaint

55. Tendons and Tendonitis
• Tendons are connective tissue that attach muscle
to bone; have little stretch or rebound
• Tendon overuse, static or prolonged
position=inflammation or tendonitis
• Tendons of wrist & hand very small; @ high risk
for injury w/ overuse
• “Tennis elbow” or lateral epicondylitis affects
finger extensor tendons outside of elbow
• “Golfer’s elbow” or medical epicondylitis affects
finger flexor tendons inside of elbow

56. What to do ??
a) Warm up & stretch before activities that are repetitive,
static or prolonged
b) Take frequent breaks from ANY sustained posture every
20-30 minutes
c) Respect pain- positions or stop painful activity
d) Recognize early signs of inflammatory process, & tx
early
PREVENT, PREVENT, PREVENT !!!

57. a) Maintain erect position of back
& neck w/ shoulders relaxed
b) Position equipment & work directly in front of and close to
your major tasks
c) Keep upper arms close to the body, elbows 90-100 degrees
d) Keep feet flat on floor, upper body weight resting on “sits
bones”
e) Wrists as neutral as possible; safe zone for wrist movement
is 15 degrees in all directions
Maintain Neutral Posture

58. f) Avoid bending neck forward for prolonged periods of
time (*remember quadruple the force); use a copy
holder
g) Avoid static positions for prolonged time; muscles
fatigue---MOVE to circulation!
You
talking to
me?

59. Modify Tasks:
a) Alternate activities frequently; rotate heavy &/or
repetitive tasks w/ lighter less repetitive ones.
b) If sx become worse REASSESS task setup & look
for alternative methods
c) Avoid repetitive or prolonged grip activities
d) Avoid pinching w/ wrist in flexion or wrist
deviation (bending to side)
e) Take frequent breaks to stretch & rest hands

60. • Use the largest joints & muscles to do the job
• Use 2 hands to lift rather than one, even with light
objects and tasks.
• Avoid lifting w/ the forearm in full pronation (palm
down) or supination (palm up)
• Slide or push & pull objects instead of lifting
• Keep reaching to a minimum
• Carry objects close to body at waist level
Body Mechanics

61. Human Factors
Human factors discovers and applies information about human
behaviour, abilities, limitations, and other characteristics to the
design of tools, machines, systems, tasks, jobs, and environments
for productive, safe, comfortable, and effective human use.

62. Necessity for Human factors analysis
The increased rate of technological development of recent
decades has created the need to consider human factors early in
the design phase, and in asystematic manner. Because of the
complexity of many new and modified
systems it frequently is impractical (or excessively costly) to
make changes after they are actually produced. The cost of
retrofitting frequently is exorbitant.
Thus, the initial designs of many items must be as satisfactory as
possible in terms of human factors considerations.

63. The increased complexities of the things people use (as the
consequence of technology) place a premium on having
assurance that the item in question will fulfil the two objectives
of functional effectiveness and human welfare.

64. Human-Machine Systems
Human-machine system is a combination of one or more human
beings and one or more physical components interacting to bring
about, from given inputs, some desired output.
In this frame of reference, the common concept of machine is too
restricted, and we should rather consider a "machine“ to consist
of virtually any type of physical object, device, equipment,
facility, thing, or what have you that people use in carrying out
some activity that is directed toward achieving some desired
purpose or in performing some function. In a relatively simple
form, a human-machine system (or what we sometimes refer to
simply as a system) can be a person with a hoe, a hammer, or a
hair curler.

65. Going up the scale of complexity, we can regard as systems
the family automobile, an office machine, a lawn mower,
and a roulette wheel, each equipped with its operator. More
complex systems include aircraft, bottling machines,
telephone systems, and automated oil refineries, along with
their personnel.
Some systems are less delineated and more amorphous than
these, such as the servicing systems of gasoline stations and
hospitals and other health services, the operation of an
amusement park or a highway and traffic system, and the
rescue operations for locating an aircraft downed at sea.

66. Industrial Ergonomics
Biomechanics
Anthropometry
Psychology
Physiology
Industrial Engineering
•Work Methods
•Facility Layout
•Work Flow
Methods
Analysis
Workplace
Design
Machine &
Equipment
Design
Tool
Design
Operator
Assignments
& Job Design

67. Two approaches to ergonomics are reactive ergonomics and
proactive ergonomics.
Reactive ergonomics is acting in response to an issue that has
already became a problem while, proactive ergonomics is to
discover potential problems before they take place.

68. •Proactive Ergonomics saves on work injuries,
increases productivity, and individual organization.
•Proactive Ergonomics is the best approach but often
the most forgotten.

69. Ergonomists are usually contacted AFTER a work-related injury
is reported,rather than BEFORE.
Practicing proactive ergonomics will increase the probability that
the benefits exceed the cost in the short and long term.

70. Ergonomics can help
reduce costs by improving
safety. This would decrease the money paid out in workers’
compensation.

71. Workplaces may either take the reactive or proactive approach
when applying ergonomics practices. Reactive ergonomics is
when something needs to be fixed, and corrective action is taken.
Proactive ergonomics is the process of seeking areas that could be
improved and fixing the issues before they become a large
problem.

72. Ergonomics is the study
of the workplace design.
It is important because it
studies and finds ways
to make workers more
comfortable and satisfied
with proper use,
absences are decreased
and productivity
increased.

73. Psychophysiological
Methods
First, the nature of work has largely changed, or at least been
extended, from physical (e.g., measured by muscle force exertion,
addressed in this section) to cognitive (e.g., measured in brain
activity, also covered in this section), a trend that has not reached
ceiling yet.

74. Second, accidents in workplaces of all sorts are
numerous and costly, and they are seemingly ineradicably and in
fact largely attributable to the victims themselves, human beings.
Third, human errors related to mental workload, in the sense of
inadequate information processing, are the major causes of the
majority of accidents.

75. While both low and high mental workload (e.g., as reflected in
heart rate parameters are undoubtedly basic conditions for the
occurrence of errors, an exact relationship between mental
workload and accident causation is not easily established, let
alone measured in practice.

76. De Waard and Brookhuis (1997) discriminated between
underload and overload, the former leading to reduced alertness
and lowered attention (e.g., reflected in eye parameters), the latter
to distraction,
diverted attention, and insufficient time for adequate information
processing.
Both factors have been studied in relationship to operator state;
however, the coupling to error occurrence is not via a direct link.

77. The operator’s working environment and the work itself will only
gain in complexity, at least for the time being, with the rapid
growth in complex electronic applications for control and
management. And last but not least, aging plays a role in the
interest of the measurement.

78. The measurement of mental workload is the specification of that
proportion in terms of the costs of the cognitive processing,
which is also referred to as mental effort.
Mental effort is similar to what is commonly referred to as doing
your best to achieve a certain target level, to even “trying hard” in
case of a strong cognitive processing demand, reflected in several
physiological measures.

79. Computational effort is exerted to keep task
performance at an acceptable level, for instance, when
task complexity level varies or secondary tasks are
added to the primary task. In case of (ominous)
overload, extra computational effort could forestall
safety hazards. Compensatory effort takes care of
performance decrement in case of, for instance, fatigue
up to a certain level. Underload by boredom, affecting
the operator’s capability to deal with the task demands,
might be compensated as well.

80. In case effort is exerted, be it computational or compensatory,
both task difficulty and mental workload will be increased. Effort
is a voluntary process under control by the operator, while mental
workload is determined by the interaction of operator and task.
As an alternative to exerting effort, the operator might decide to
change the (sub)goals of the task.

81. Ergonomic principles in Workplace
(1) Aim at dynamic work, avoid static work (work where there
is no movement). Static work or static loading of the muscles is
inefficient and accelerates fatigue.
Static work can occur when the workplace is too high or too low,
when holding a weight in one's arms for an extended period,
or when there is constant bending of the back to perform a task.
(2) Adjust work surface heights to the size (anthropometry) of
the worker and the type of task performed (precision, light
assembly, or heavy manual).

82. (3) Work within 30 per cent of one's maximum voluntary
contraction (strength). Avoid overloading of the muscular system.
(4) Place primary controls, devices, and workpieces within the
normal working area. Secondary controls should be placed within
the maximum working area so as to reduce extended reaches and
fatigue.
(5) Strive for best mechanical advantage of the skeletal
system.
(6) Work with both hands. Do not use one hand (nonpeferred
hand) as a biological holding device.
(7) Hands should move in symmetrical and opposite directions.
(8) Use the feet as well as the hands.

83. (9) Design knowing the capacity of the fingers. Do not overload
the fingers.
(10) Use gravity. Do not oppose it to dispose of unbreakable
products.
(11) A void unnatural posture. Bend the handle of the tool not the
wrist.
(12) Permit change of posture. Maintain a proper sitting posture.

84. (13)Counter-balance tools when possible to reduce the weight
and forces.
(14)Accommodate the large individual and give him or her
sufficient room.
(15) Use bins with lips for storage and manual retrieval of small
parts instead of boxes. Incline containers so as to reduce awkward
postures of the body.
(16) Train the individual to use the workplace, facility and
equipment properly.

85. Ergonomics Improvement Process: Step 1
The first step in this process is to develop a prioritized list of
departments and jobs to evaluate.
This prioritized list should be developed by the ergonomics
improvement team based on:
1) An initial facility tour and general ergonomic walkthrough
audit. This facility tour will give the team a general sense of the
job demands in each area and allow the team to become familiar
(if not already) and knowledgeable about area operations, work
practices, and potential MSD risk factors.

86. 2) A review of injury and MSD history. Existing injury
information from OSHA logs, safety and medical records,
insurance, and other information sources should be reviewed to
help identify trends and departments or jobs with risk factors that
may be contributing to injuries.
3) Data and information collected from employee surveys.
The real experts for identifying ergonomic risk factors and
improvement opportunities are… (insert drum roll here)… the
people who perform the job each and every day! Employee
surveys are a great way to gain perspective on ergonomic risk in
the workplace.

87. Ergonomic Assessment Tools
Applying a scientific, evidence-based approach to your
ergonomics process is important. The goal is to identify
ergonomic risk factors, quantify then, and then make measurable
improvements to the workplace, ensuring that jobs and tasks are
within workers’ capabilities and limitations.
The best approach for doing that is to make ergonomics an
ongoing process of risk identification and risk reduction based on
objective, scientific analysis of your workplace.

88. Principle 1. Maintain Neutral Posture
Neutral postures are postures where the body is aligned and
balanced while either sitting or standing, placing minimal stress
on the body and keeping joints aligned.
Neutral postures minimize the stress applied to muscles, tendons,
nerves and bones and allows for maximum control and force
production.
The opposite of a neutral posture is an “awkward posture.”
Awkward postures move away from the neutral posture toward
the extremes in range of motion. This puts more stress on the
worker’s musculoskeletal system, is a contributing risk factor for
Musculoskeletal Disorders (MSDs), and should be avoided.

92. Principle 2. Work in the Power / Comfort Zone
• This principle is very similar to maintaining a neutral posture,
but is worth expounding upon here.
• The power zone for lifting is close to the body, between mi-
thigh and mid-chest height. This zone is where the arms and
back can lift the most with the least amount of effort.
• This can also be called the “hand shake zone” or “comfort
zone.” The principle here is that if you can “shake hands with
your work”, you are minimizing excessive reach and
maintaining a neutral posture.

94. Working from the power / comfort / handshake zone ensures that
you are working from proper heights and reaches, which reduces
MSD risk factors and allows for more efficient and pain-free
work.
Now when you notice workers who are working with extended
reaches and at improper heights, you’ll know they are outside
their comfort zone and risk factors are present.

95. Allow for Movement and Stretching
The musculoskeletal system is often referred to as the human
body’s movement system, and it is designed to move.
Working for long periods of time in a static position will cause
your body to fatigue. This is what is known as static load.
For example:
Raise your hands over your head for the next 30 minutes
Remain standing in the same position for the next 8 hours
Write with a pencil for 60 minutes straight

96. If you do those things, you will experience static load. The first
few seconds or minutes don’t seem too bad, but the cumulative
effect of holding these seemingly stress-free positions over time
will cause fatigue and discomfort.
Now, what is the first thing you will naturally do once you when
you are finished with these tasks?
You will stretch.

97. You’ll stretch out your shoulders and back. You’ll stretch out
your legs and maybe do some squats. You’ll stretch out your
fingers and wrist.
Stretching reduces fatigue, improves muscular balance and
posture and improves muscle coordination. Everyone is an athlete
in life, so you need to prepare your body for work by warming up
to improve performance and lower injury risk. A warm-up
stretching regimen is a great way to prepare your body for work.
It is also beneficial to take periodic stretch breaks over the course
of your work day to get your blood moving and restore your
energy.

98. Principle 4. Reduce Excessive Force
• Excessive force is one of the primary ergonomic risk factors.
Many work tasks require high force loads on the human body.
Muscle effort increases in response to high force requirements
which increases fatigue and risk of an MSD.
• There are numerous conditions that affect force, but the idea is
to recognize when a job or task requires excessive force and
then find ways to reduce that force.
• Eliminating excessive force requirements will reduce worker
fatigue and the risk of MSD formation in most workers. Using
mechanical assists, counter balance systems, adjustable height
lift tables and workstations, powered equipment and ergonomic
tools will reduce work effort and muscle exertions.

99. Principle 5. Reduce Excessive Motions
Repetitive motion is another one of the primary ergonomic risk
factors. Many work tasks and cycles are repetitive in nature, and
are frequently controlled by hourly or daily production targets
and work processes. High task repetition, when combined with
other risks factors such high force and/or awkward postures, can
contribute to the formation of MSD. A job is considered highly
repetitive if the cycle time is 30 seconds or less.
Excessive or unnecessary motions should be reduced if at all
possible. In situations where this is not possible, it is important to
eliminate excessive force requirements and awkward postures.
Other control methods to consider are Job enlargement, job
rotation and counteractive stretch breaks.

100. Principle 6. Minimize Contact Stress
According to OSHAS, contact stress results from continuous
contact or rubbing between hard or sharp objects/surfaces and
sensitive body tissue, such as soft tissue of the fingers, palms,
thighs and feet. This contact creates localized pressure for a small
area of the body, which can inhibit blood, nerve function, or
movement of tendons and muscles.
Examples of contact stress include resting wrists on the sharp
edge of a desk or workstation while performing tasks, pressing of
tool handles into the palms, especially when they cannot be put
down, tasks that require hand hammering, and sitting without
adequate space for the knees.

101. Principle 7. Reduce Excessive Vibration
Multiple studies have shown that regular and frequent exposure
to vibration can lead to permanent adverse health effects, which
are most likely to occur when contact with a vibrating tool or
work process is a regular and significant part of a person’s job.
Hand-arm vibration can cause a range of conditions collectively
known as hand-arm vibration syndrome (HAVS), as well as
specific diseases such as white finger or Raynaud’s syndrome,
carpel tunnel syndrome and tendinitis. Vibration syndrome has
adverse circulatory and neural effects in the fingers. The signs
and symptoms include numbness, pain, and blanching (turning
pale and ashen).

102. Principle 8. ProvideAdequate Lighting
Poor lighting is a common problem in the workplace that can
affect a worker’s comfort level and performance. Too much or
too little light makes work difficult – just imagine trying to do
your job without sight!
Dimly lit work areas and glare can cause eye fatigue and
headaches and improperly lit areas put workers at greater risk for
all types of injuries.
Providing workers with adjustable task lighting is often a simple
solution to lighting problems. At a computer workstation, take
steps to control screen glare, and make sure that the monitor is
not placed in front of a window or a bright background

103. Ergonomic Risk Factors
Risk factors related to work activity and ergonomics can make it
more difficult to maintain this balance, and increase the
probability that some individuals may develop a MSD.
The major workplace ergonomic risk factors to consider are:
High Task Repetition
Forceful Exertions
Repetitive/Sustained Awkward Postures

104. 1. High Task Repetition
• Many work tasks and cycles are repetitive in nature, and are
frequently controlled by hourly or daily production targets and
work processes. High task repetition, when combined with other
risks factors such high force and/or awkward postures, can
contribute to the formation of MSD. A job is considered highly
repetitive if the cycle time is 30 seconds or less.

105. Control methods to consider:
Engineering Controls – Eliminating excessive force and
awkward posture requirements will reduce worker fatigue and
allow high repetition tasks to be performed without a significant
increase in MSD risk for most workers.
Work Practice Controls – Providing safe & effective procedures
for completing work tasks can reduce MSD risk. In addition,
workers should be trained on proper work technique and
encouraged to accept their responsibilities for MSD prevention

106. Job Rotation – Job task enlargement is a way to reduce duration,
frequency and severity of MSD risk factors. Workers can rotate
between workstations and tasks to avoid prolonged periods of
performing a single task, thereby reducing fatigue that can lead to
MSD. Counteractive Stretch Breaks – Implement rest or stretch
breks to provide an opportunity for increased circulation needed
for recovery.

107. 2. Forceful Exertions
Many work tasks require high force loads on the human body.
Muscle effort increases in response to high force requirements,
increasing associated fatigue which can lead to MSD.

108. Control methods to consider:
Engineering Controls – Eliminating excessive force
requirements will reduce worker fatigue and the risk of MSD
formation in most workers. Using mechanical assists, counter
balance systems, adjustable height lift tables and workstations,
powered equipment and ergonomic tools will reduce work effort
and muscle exertions.
Work Practice Controls – Work process improvements such as
using carts and dollies to reduce lifting and carrying demands,
sliding objects instead of carrying or lifting, and eliminating any
reaching obstruction to reduce the lever arm required to lift the
object.

109. • Proper Body Mechanics – Workers should be trained to use
proper lifting and work techniques to reduce force
requirements.

110. 3. Repetitive/Sustained Awkward Postures
Awkward postures place excessive force on joints and overload
the muscles and tendons around the effected joint. Joints of the
body are most efficient when they operate closest to the mid-
range motion of the joint. Risk of MSD is increased when joints
are worked outside of this mid-range repetitively or for sustained
periods of time without adequate recovery time.

111. Control methods to consider:
Engineering Controls – Eliminate or reduce awkward postures
with ergonomic modifications that seek to maintain joint range of
motion to accomplish work tasks within the mid-range of motion
positions for vulnerable joints. Proper ergonomic tools should be
utilized that allow workers to maintain optimal joint positions.
Work Practice Controls – Work procedures that consider and
reduce awkward postures should be implemented. In addition,
workers should be trained on proper work technique and
encouraged to accept their responsibility to use their body
properly and to avoid awkward postures whenever possible.

112. Job Rotation – Job rotation and job task enlargement is a way to
reduce repeated and sustained awkward postures that can lead to
MSD. Counteractive Stretch Breaks – Implement rest or stretch
breaks to provide an opportunity to counteract any repeated or
sustained awkward postures and allow for adequate recovery
time.