Introduction to Ergonomics. If you have questions about this e-book or any occupational health & safety issue, please contact EH&S by phone at 294-5359 or by e-mail at firstname.lastname@example.org . What advantages are there in improving ergonomics in your workplace?.
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Your job should not be a pain in the neck, wrist, or any other part of your body!
That which we call a rose
By any other name would smell as sweet”
Cumulative Trauma Disorders, or CTDs are known by many names including Repetitive Strain Injuries, Occupational Overuse Syndromes and Musculoskeletal Disorders.
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.
Biomechanical risk factors include repetitive exertions, posture stresses, contact stresses, static exertions and forceful exertions.
Repetitive exertions include things such as assembly line work, typing, manual materials handling and some laboratory procedures.
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.
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.
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.
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.
It’s important to think ahead about the best method to execute tasks that generate high force on the body and to ask for assistance.
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.
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 forsmall children, obesity, smoking and alcohol consumption.
CTDs can be grouped broadly into five categories: muscle, tendon, ligament, circulatory and nerve.
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.
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 bike’s 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.
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).
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).
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.
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.
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.
Dorsal (top) View
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.
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.
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.
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).
An electromyogram is a recording of nerve firing patterns. Neurologists compare patterns to assess nerve health status.
Pattern indicating nerve dysfunction
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
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.
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.
Health care providers often recommend ergonomic workplace evaluations for injured employees.
EH&S 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.