Department of Risk Management & Safety
Ergonomics of Computer Workstations
The office environment has undergone dramatic changes in the last two decades. Some of the changes, including the introduction of computers, have resulted in benefits such as increased efficiency. However, these changes have lead to work habits that are more sedentary than in the past. Previously, an office worker carried out a number of varied tasks including using the typewriter, filing correspondence, looking up documents, and delivering messages to colleagues. During the course of the day, the employee would leave the desk many times. However, in the modern, computerized office it is possible to write and print documents, look up information in files, read electronic mail and participate in interoffice conferences without ever leaving the chair.
One of the results of this new work pattern is an increase in the
number of painful conditions involving the back, neck, wrist and head.
The major factor contributing to these injuries is the long period of
time an employee sits in the chair. Another is the increase in
repetitive motions required with the use of keyboards. The arrangement
of lighting and VDT screens also contributes to the incidence of
For information about Ergonomic
concerns or to schedule a Workstation Evaluation contact Sarah Burnett or phone 656-0738.
Why is sitting bad for you?
Sitting for long periods of time has two important effects on the human body: an increase of muscular tension and a constriction of the spine. Both contribute to pain in the back and neck.
Muscles can be involved in two types of activity: dynamic effort and static effort. Dynamic effort is characterized by movement; the muscle fibers are contracted and relaxed rhythmically. Static effort occurs when a muscle is contracted and held in the contracted position for some time. Bloodflow is restricted in a contracted muscle.
Dynamic effort, such as walking, is easy to sustain for long periods of time because fresh, oxygenated blood flows in a muscle every time it releases. Static effort, however, results in a continual deficit of blood supply to the contracted muscle, so a statically held muscle cannot rid itself of metabolic waste products. It is these waste products which produce the feelings of pain, tenderness and fatigue. Most jobs have a combination of dynamic and static effort tasks. Even individual tasks can have elements of both; for example, typing on a keyboard involves the fingers dynamically and the arms and shoulders statically. It is the statically held muscles that eventually become painful and sore.
A second factor contributing to occupational back pain concerns the orthopaedic aspects of the sitting posture. The human spine has a set of natural curves that become distorted when sitting. The lower back, or lumbar region, which normally curves forward, becomes bowed out. The backward tilting pelvis puts pressure on the intervertebral disks and nerves. The disks are fluid-filled sacs which act as cushions between the vertebrae. If the disks degenerate, then the resulting pressure on the spinal bones and nerves can cause pain.
How is back pain treated?
As the causes of back pain are many, there are many approaches to treatment. Medical doctors are often consulted, as well as orthopaedic specialists. If surgery is not warranted, they will often recommend a regime of rest, painkillers and physical therapy. Physical Therapists are often included to oversee the physical exercises. Many people prefer the services offered by chiropractors for their back pain. For some, this treatment offers immediate relief and has the added benefit of being drug-free. Acupuncture has relieved some people, as well as massage therapy. There is no final consensus as to the best treatment for back pain. Different individuals will find help in a number of different treatments. Nevertheless, most people experience the largest amount of pain relief through a regular exercise plan of walking or swimming. There are many who find a cessation of symptoms through this action alone.
What is Carpal Tunnel Syndrome?
Carpal Tunnel Syndrome (CTS) is associated with many jobs which involve repetitious motion of the wrist. The use of computer keyboards is a potential cause of CTS for many workers. CTS is a painful condition of the wrist and forearm that is a result of repetitive hand motion. Its cause can be traced to a u-shaped cluster of bones at the base of palm which forms the base and sides of the carpal tunnel.
A tough ligament forms the roof of the carpal tunnel. Running through the tunnel are the flexor tendons and the median nerve, which operate the thumb and the first three fingers. CTS occurs when overwork, such as prolonged gripping, repetitive flexing of the fingers, or constant vibration causes the flexor tendons to become inflamed, putting pressure on the median nerve. There are other, non-occupational, causes of pressure on the nerve which can result in CTS, such as the normal aging process, fluid retention (particularly during pregnancy), or a previous bone dislocation or fracture. Irritation resulting from these non-occupational factors can aggravate occupational CTS.
One reason that CTS is often unrecognized as work-related is that the early symptoms usually occur at night. These early signs can be pain, tingling, or numbness in the hand or forearm. As the condition becomes more advanced, there can be a loss of sensation in the hand or stiffness in the hand and fingers, with a gradual loss of grip strength and control of the thumb and first three fingers. Left untreated, CTS can cause permanent nerve damage, with a deterioration of the large muscle of the thumb. Because of the variety of symptoms, CTS can be misdiagnosed, particularly as arthritis. There are several tests used by physicians to diagnose CTS.
How is CTS treated?
In its early stages, CTS can be treated conservatively, without surgery. Relief in mild cases can be provided with stretching exercises. Simply stopping work every hour to gently rotate the wrists and arms to increase circulation and relieve muscle tension can reduce the stress on the carpal tunnel. Further steps include the wearing of a wrist splint at night and, if possible, on the job. Icing the wrist can sometimes reduce the symptoms. Anti-inflammatory drugs such as Motrin and Advil can be used to reduce the tendon inflammation; cortisone shots can also be administered.
In cases where symptoms are so advanced that they do not respond to any of the above treatments, carpal tunnel release surgery may be the only recourse. This surgery divides the transverse ligament to open up the carpal tunnel. Although initially successful, surgery may not be the cure. Continued pain, tenderness, and a perceptibly decreased grip are not unusual. Scarring of the divided ligament may put pressure on the nerve again, causing a re-occurance of symptoms.
Can CTS be prevented?
Obviously, the real key to eliminating CTS is prevention. Workers should make a conscious effort to use proper posturing and grips. The posture of the wrist should be in line with the hand to prevent pinching with the carpal tunnel. Avoid using bent (flexed), extended or twisted wrist positions for long periods of time. Workers using keyboards on a continual basis should change the angle of their chair to properly align the wrists. If the job consists of varied work, switch tasks often. If constant repetition is required, rest the hands periodically.
Early detection of CTS is particularly important since it can be more easily treated in its mild stages. Don't allow the pain to reach intolerable levels before seeking treatment. On-the-job pain that lasts more than an hour should be interpreted as a danger sign. Symptoms that occur at night should also be considered a warning. Always report such pain to a supervisor.
Human eyes were made for most efficient seeing at a distance. But, as you know, VDT use demands using your eyes at a closer range, usually intensely, over long periods of time. This alone can strain your eyes and may cause vision problems to develop or aggravate existing vision conditions. Effects on the eye vary depending on the individual and the work station. Some of the factors influencing this are:
Eye Fatigue: Viewing VDTs at a close range for long periods can be very tiring, and over a long period of time may cause temporary deterioration of vision. VDT operators should take periodic breaks in open areas away from their machines, in addition to alternating an hour or two of screen work with an hour of another kind of work that would allow viewing from a greater distance and more body movement. Two hours is the maximum time that should be spent doing continuous screen work.
Glare: Eyestrain can be caused by improper positioning of the terminal in relation to surrounding office lighting, windows, shiny surfaces and background colors. Glare from a VDT screen that reflects surrounding light can be reduced by using nonreflective glass as well as altering the lighting structures in the vicinity of the screen. Installing blinds or awnings on the nearby windows, relocating the machine for better lighting or relocating the light fixtures can significantly reduce glare from the glass of the VDT.
If a terminal is positioned against a background that makes it difficult for the eyes to adjust to the images on the screen, such as a white wall or a window, strain can also result. In this case, the pupils are adjusting to the bright background rather than to the darker screen, and the images on the screen become difficult to see. The VDT operators often compensate by bending their heads or turning their bodies to block the light, causing muscle strain as well.
Successful solutions include:
But before changes are made in any office, it is important to discuss the proposals with fellow employees, taking into account their preferences. Darker lighting, walls and windows may be more depressing and stressful than the original problem.
Eyeglasses and contacts
Particular problems occur with workers who wear glasses or contact lenses. Glasses overcorrect an operatorÕs eyes for the distance for which they are used with a VDT. Most glasses correct the wearerÕs vision for a reading distance of 10-13 inches, whereas VDT viewing distances tend to be further, usually 16-20 inches. Workers may find it necessary to be fitted with special lenses designed for their normal viewing distance from the screen.
Screen character size and color
The size of the screen and of the characters plays an important part in adding to, or detracting from, the comfort of the operator. A larger screen with a viewing distance of more than two feet, with a character height of at least 3/16 of an inch is optimal.
It is also best to avoid use of terminals where there is a noticeable ÒflickeringÓ of the characters on the screen. All VDTs emit light produced by phosphors which fades rapidly and must be constantly replenished. Unless the rate of replenishment is at least 60 times per second, this flickering may be discernible to operators. Such terminals require more concentration and hence, result in more strain.
What can prevent these VDT problems?
Chairs, keyboards and desks
The most important thing to look for in a chair is adjustability. The second most important thing is to take the time to adjust it to your needs. You should be able to adjust the height so that both feet can rest on the ground. There should be a back rest with good lumbar support for you lower back, which should also be adjustable. Backrests that lean back in a rocking motion are also a good feature, as they give the back muscles a chance to move. The presence of armrests is up to the operator's preference; the best chairs have armrests that are removable and (yes!) adjustable. If you have the opportunity to shop for a new chair, ask the retailer if they will let you take the chair on trial. The only way to really tell if the chair is right for you is to sit in it through the day.
The keyboard should rest at a height that is comfortable for your arms and shoulders. Put your hands on your keyboard as if you were going to type and check your position. You do not want any strong bending or flexing at the wrists, nor do you want to have your shoulders scrunched up high. Sometimes, the keyboard can be lowered by installing an adjustable, sliding tray underneath the workstation. Wrist relief can be sought by having something soft to rest your wrists on in front of the keyboard; a small, rolled towel will often work well. Also, make sure your chair is adjusted properly. If the chair must go up so you can reach the keyboard comfortably, then get a foot rest to go under your feet. Lastly, take a close look at your desk, some of the newer models have adjustable heights.
Your computer should not be placed with the monitor too close in front of your face. Placing it at a distance protects your eyes from strain. If you have a mouse, place it where you can manipulate it without strain on your arm or wrist.
Use proper lighting. It can have a significant impact on your visual comfort and efficiency. The lighting for VDT operation should:
• Be about 20 to 50 foot candles, which is about half the level used in most offices. Lower lighting can be achieved by using fewer bulbs or fluorescent tubes, installing lower intensity tubes, or using dimmer switches.
• Match as closely as possible the brightness of the surroundings with that of the VDT screen for optimum comfort and efficiency. However, the contrast between the characters on the screen and the screen background should be high.
• Minimize reflected glare on VDT screens by keeping them away from windows and other sources of bright light. Use window shades or drapes to block out excessive sunlight. Antiglare screens are also available.
Take a break! Many authorities recommend a 15 minute alternate task break every hour if you are a full time user. If you have any duties that take you away from the computer terminal, divide them up through the day, so as to prevent long stretches of work at the terminal. If you have no alternative duties, take at least ten minutes out of every hour to stand and stretch - movement is good for the body!
It is a good idea to practice a regular schedule of exercise to offset the sedentary lifestyle of the office. Whatever your choice of exercise, remember that a little done regularly is better than a lot done infrequently. Scheduling in twenty minutes a day, or an hour's worth three times a week can have a dramatic effect on your health, and, ultimately, on your work performance.
Where can I read more?
Ergonomics in Computerized Offices, by Etienne Grandjean. 1987. London: Taylor and Francis. 227 pages.
Ergonomics of Workstation Design, edited by Tarald O. Kvalseth. 1983. London: Butterworths & Co. 260 pages.
Computers, Work and Health: A socio-technical approach, by Trevor A. Williams. 1988. London: Taylor and Francis. 142 pages.
Office Hazards: How your job can make you sick, by Joel Makower. 1981. Washington, D.C.: Tilden Press. 233 pages.
Last modified March 04 2010 03:43 PM