Introduction to Ergonomics

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Introduction to Ergonomics
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If you have questions about this e-book or any
occupational health safety issue, please
contact EHS by phone at 294-5359 or by e-mail at
ehswwwadm_at_ehsa.adp.iastate.edu.
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What advantages are there in improving ergonomics
in your workplace?
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Improved ergonomics in your workplace will
likely

• Improve employee comfort and job satisfaction
• Reduce turnover
• Reduce human error
• Improve productivity
• Improve quality

Your job should not be a pain in the neck, wrist,
or any other part of your body!
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Whats in a name? That which we call a rose By
any other name would smell as sweet
William Shakespeare
Cumulative Trauma Disorders, or CTDs are known by
many names including Repetitive Strain Injuries,
Occupational Overuse Syndromes and
Musculoskeletal Disorders.
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Cumulative Trauma Disorders
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What are some common cumulative trauma disorder
symptoms?
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While there are exceptions, a rule-of-thumb is
that pain generally indicates damage to muscles,
tendons or ligaments. Numbness, tingling and a
loss of strength and/or coordination may indicate
nerve damage. Cold hands may indicate nerve
and/or circulatory problems.
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What kinds of things can put me at risk for
developing cumulative trauma disorders (CTDs)?

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The term biomechanical describes the body as a
machine. Biomechanical risk factors include
repetitive exertions, posture stresses, contact
stresses, static exertions and forceful
exertions.
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Repetitive exertions include things such as
assembly line work, typing, manual materials
handling and some laboratory procedures. .
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Posture stresses include bending over a
microscope and reaching into biosafety cabinets
with limited or no knee space underneath. If you
experience posture stresses, habit modification
(e.g., keeping hands off the mouse whenever
possible) and new equipment (e.g., stools with
adjustable seats) are things to consider.
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Contact stresses typically involve the upper
extremities and a hard surface. A classic case
involves a person mousing at a square-edged lab
bench, especially when the bench is too high for
mousing. The nerves on the fleshy underside of
the arm are at risk of compression injury where
the arm makes contact with the sharp bench
edge.
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Static exertions can take a toll on our soft
tissues, primarily by reducing blood flow. The
familiar road construction flag-person will
experience pooling of blood in the legs from
standing for long periods. While keying, a typist
will find some muscles in the forearm experience
constant loading (contraction) even though the
fingers are moving rapidly. Lab technicians who
pipette many samples typically experience forearm
static muscle loading.
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Forceful exertions may lead to soft tissue
injury. The risk of cumulative trauma injury due
to force increases as other risk factors
(posture, repetition, etc.) come into play. CTDs
typically take months or years to develop and
months or years to resolve. However, when moving
heavy objects - tissue damage can occur
immediately. Its important to think ahead about
the best method to execute tasks that generate
high force on the body and to ask for assistance.
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In addition to biomechanical risk factors,
environmental risk factors can be important in
some workplaces as well. Vibration and cold
temperatures can impede circulation and lead to
or worsen cumulative trauma disorders. Vibration
associated with use of vortexers may damage
nerves directly. If you have a CTD and your
workplace is cold, you may benefit from warm
clothing or by turning up the heat.
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If physical and biomechanical CTD risk factors
were the only ones to consider, ergonomics would
be a fairly straightforward subject. Of course,
things are not that simple. Other recognized risk
factors include diseases such as arthritis and
Lyme, congenital defects (bone and soft tissue),
pregnancy, caring for small children, obesity,
smoking and alcohol consumption.
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CTDs can be grouped broadly into five categories
muscle, tendon, ligament, circulatory and nerve.

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Muscle pain typically occurs from overuse of
particular muscle groups not accustomed to the
task performed - such as shoveling snow or raking
leaves, etc. Muscle pain may also occur as a
result of chronic overuse. Fortunately, with
rest, symptoms often resolve within a day or two.

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Tendons connect muscle to bone. One tendon type
(involved in tennis elbow, for example) is much
like a bicycle brake cable where it connects to
the brake lever. With overuse, the tendon, like
the brake cable, may fray. Another tendon type
(involved in tenosynovitis of fingers and
thumbs), is similar to a bikes brake cable,
cable housing, and grease. With overuse the
tendon and sheath may be damaged and operate
roughly - like a rusty cable moving through its
housing.
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Ligaments connect bone to bone. Spinal disks
are an example of specialized ligaments that
connect vertebrae together. As with most soft
tissue types, ligaments can suffer acute trauma
(accidents) or cumulative trauma (micro-trauma
over time).
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Nerve damage may occur as a result of disease
(e.g., tumors, infections and metabolic
dysfunction), or by compression. Compression
sources may be internal (e.g., flexed/bulky
muscles, narrow nerve passages, herniated disks)
or external (e.g., elbows resting on hard
surfaces, sleeping on arms).
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Adequate blood circulation is vital to a healthy
nervous system. Circulation can be impaired by
vibration, repetitive motion, static exertions,
awkward postures, contact stresses and low
temperatures. In some cases circulation
deficiency is related to an underlying disease
such as diabetes or hypothyroidism.
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What is Carpal Tunnel Syndrome?
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While the exact disease mechanisms are still
debated, there is general agreement that carpal
tunnel syndrome (CTS) is frequently caused by
compression of the median nerve within the carpal
tunnel (see illustration on next slide). Symptoms
include tingling, burning, numbness, loss of
coordination and muscle loss. Symptoms may occur
in the hand, wrist and forearm.
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Wrist Cross-Section
Carpal Tunnel
Carpal Bone
Radial Nerve
Ulnar Nerve
Median Nerve
Ulnar Artery
Tendon
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In addition to the median nerve, the ulnar and
radial nerves that innervate (supply) the hand
may also be impaired, giving rise to CTS-like
symptoms. These nerves can be impaired anywhere
between the spine and the hand.
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The ulnar, median and radial nerves innervate
(supply) different parts of the arm, wrist and
hand. Knowledge of the distribution patterns
can be used to predict which nerve is impaired
based on where symptoms occur.
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Carpal tunnel syndrome, tendonitis and other
cumulative trauma disorders may cause symptoms
that are difficult to tell apart from one
another. Be sure to get a diagnosis from a
physician.
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Medical Care
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How can I tell if I have a CTD?
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If you suspect you have a CTD, see a physician.
In addition to a medical history, your physician
will likely perform a few simple tests in the
office. You may be asked to bend your wrists in
certain ways, to pull on their finger, and to
allow your nerves to be gently tapped. While
helpful, these simple tests cannot provide
definitive diagnoses.
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Objective tests include X-rays, CAT scans, MRI,
thermography (heat), myelograms (X-rays with
dye), electromyography and nerve conduction
studies. Two of the more common nerve tests are
electromyography and nerve conduction (the gold
standard for CTS diagnosis).
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Normal nerve firing pattern
An electromyogram is a recording of nerve firing
patterns. Neurologists compare patterns to
assess nerve health status.
Pattern indicating nerve dysfunction
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A nerve conduction study shows nerve transmission
velocities at various locations. Transmission
rates that fall below a specified level, or that
are slower between hands or between other nerve
segments, indicate potential nerve impairment.
(R) recording electrode (S) stimulation electrode
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Now that I have a CTD, what can I do to get
better?
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If you suffer from a cumulative trauma disorder,
your physician may suggest analgesics, ice/heat,
splints, steroid injections, physical therapy,
and when other treatments fail, surgery. Keep in
mind that some analgesics have side effects on
the liver, kidneys and/or stomach. Be sure to
consult a physician when using these products to
treat CTDs.
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Some types of nerve and and tendon injuries
respond well to splints. Occasionally, splints
restrict circulation or interfere with daily
activities. If your splint is uncomfortable,
your physician may be able to adjust the splint,
suggest different use patterns (e.g, nights only)
or provide a custom-made splint.
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Health care providers often recommend ergonomic
workplace evaluations for injured employees. EHS
will evaluate work environments for any ISU
employee who requests assistance, whether injured
or simply interested in injury prevention. If you
would like a workplace evaluation, please contact
Environmental Health and Safety at 294-5359.
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