Continuing Education Series
IS Continuing Education Series articles allow design practitioners to earn continuing education unit credits through the pages of the magazine. Use the following learning objectives to focus your study while reading this issue's Continuing Education Series article. To receive credit, see the series of questions and follow the instructions.
After reading this article, you should be able to:
- Define ergonomics and explain how it relates to occupational health in office workers.
- Describe how poor seated posture can lead to degenerative joint disease in the spine.
- Describe a "healthy" seated position, including the correct position of the arms, wrists, legs, feet, back and head.
- Identify the attributes of furniture that enables workers to enjoy a healthy, ergonomic work station environment.
As a designer of office work spaces, you have many factors to think about: productivity, work flow, new modes of work, your clients' changing needs, image and aesthetics, standards, costs and much more.
Here's another item to add to your list: ergonomics. A basic understanding of how this science applies to work station design can save your clients huge amounts of money and their employees a great deal of pain and suffering.
Ergonomics is the science of fitting the physical aspects of the work environment to the human body.
That isn't just a matter of making things convenient. It's a vital aspect of workplace health. You may not think of an office as a place where injuries occur: those all happen in areas devoted to manufacturing and warehousing, right? Wrong. Injuries resulting from poor office work station design—or poor use and set-up of its elements—are common and costly.
When the physical environment isn't suited to the physical capacity of the person to perform required tasks, musculoskeletal disorders (MSDs) can result. MSDs are injuries and disorders of the muscles, nerves, tendons, ligaments, joints, cartilage and spinal discs. Examples of MSDs are carpal tunnel syndrome, tendonitis, sciatica, herniated discs and low-back pain. The effects of these conditions have significant impact on worker productivity and cause financial losses to organizations in terms of lost time, employee efficiency and utilization, and insurance and workman's compensation costs.
On the other hand, a solid understanding of applied ergonomics can eliminate most of these injuries and improve worker morale and productivity.
What Ergonomics Really Means
The term ergonomics is in danger of losing its useful meaning. Many products are promoted as "ergonomic" that have little benefit or are even detrimental to the body. The real science of ergonomics is based on anatomy and the merging of man and machine based on the height and size of the body.
The study of workplace ergonomics needs more emphasis on physiology. Most ergonomists are not adequately trained in this field. Physical therapists probably have better training for evaluating work station ergonomics than many of the people who design them. Too many people are led by the norm.
Moreover, a critical aspect of the problem is that workers need to take responsibility for their own health. They need the training and advice to understand what constitutes the right workstation set-up and the motivation to carry it out. My organization, Task Group International, wants people trained and self-sufficient, not dependent on anyone else, so they can make their own decisions on posture and setup.
Designers need to understand how and why the body wears out, why certain postures cause changes in the body—for instance, the head constantly looking down. Bad posture causes a phenomenon called bone remodeling, which leads to osteoarthritis and degenerative joint disease. Even many ergonomists don't understand how bone remodeling works. (Keep reading and you will.) Many are working with incorrect roadmaps, although many doctors are now trying to emphasize anatomy and physiology training in the field. This all needs to be applied to work stations.
The body moves around in the work station. Some furniture manufacturers understand this, yet design a chair that will move or mold into position, but doesn't allow the body to move. After a year, people still have problems; then employers decide this ergonomic stuff doesn't work.
If designed and set up correctly, it will work. My company often works with existing furniture, if it can be adjusted.
Years ago, I realized in my practice as a physician that whatever I was prescribing for a patient spending five hours a week in therapy was counterbalanced by the 40 hours a week he or she spent at work. The big benefits come when we modify the work station to make it work properly.
Spinal Anatomy 101
We need to start with a basic understanding of the spine. When the human embryo is developing in the womb, the spine first grows in a "C" shape, and then straightens out after a few weeks. However, a straight line doesn't bear loads well. A certain amount of curvature provides a lever arm that is far more efficient. This curvature develops in the infant following birth. In the first few months, when lying on its tummy a baby will frequently pick up its head; this repeated movement creates the lordotic (upper) curve in the spine. This is the essential first step, because only after the lordotic curve is developed can the baby roll over, because this curve acts as a lever arm. Then the baby will begin to get up on its hands and knees and crawl. This creates the curve in the lower lumbar region of the spine. Only then is a baby able to stand up.
The spine has 24 vertebrae: seven cervical (neck), 12 thoracic (upper back) and five lumbar (lower back). If you could drop a plumb line from the center mass of the skull it would pass through the back of the neck bones, the front of the thoracic bones and the back of the lumbar in a normal, healthy anatomy. A deviation from the normal curvature of the spine will cause problems.
It is important to understand muscle anatomy, as well. The muscles in the front of your body are called flexors; they are twice as strong as the extensors in the back of the body. This is why people slouch, along with the fact that your upper body mass tends to pull you forward. The extensors are not strong enough to keep the spine upright. Everything is working against you. Many ergonomists say you should sit perfectly erect, your torso at a 90-degree angle to your thighs. I disagree. The upper body should be slightly reclined—at 91 to 112 degrees to the thighs—to take stress off the spine, the extensor muscles and the associated tendons and ligaments. Although theories exist that suggest a closed angle of less than 90 degrees is desirable, most recent research overrules this suggestion.
The purpose of vertebrae is to house and protect the lower portions of the central nervous system—the brainstem and the spinal cord. Damage to central nervous system tissue lasts for life; the central nervous system does not repair itself. Ligaments, cartilage and tendons (soft tissue) between vertebrae will wear out if abused. The key to healthy joints is the discs between the vertebrae.
These intervertebral discs are made of fibro-cartilage that changes from a semi-solid to a semi-liquid and back. The more movement of vertebrae against one another, the healthier—the more liquid and inflated—the discs are. We want discs to be pumped up like water balloons, not deflated and clay-like in consistency. This is because the healthier the disc, the less pressure there is on the connection between the central nervous system and the peripheral nerves that extend from the spinal column into the body's extremities.
In other words, disc health is vital to both the spinal column itself and to protecting the peripheral nervous system from painful and debilitating damage.
This is one reason exercise is important. After age 10, most of the direct blood supply to spinal discs is gone. Instead, discs receive nutrition by osmosis—they absorb it. And they can only absorb nutrition through movement—the more movement the better.
There are three degrees of disc damage.
1. A herniation, in which the disc juts out from the surrounding tissue.
2. A protrusion, in which it sticks out through an abnormal opening.
3. A rupture, in which the disc tissue is torn apart.
How do such injuries occur? In addition to the lack of exercise, putting extreme forces on the discs can cause them to become herniated, protrude or rupture. When we bend over forward (flexion), the front edge of the affected vertebra becomes a fulcrum. When we bend backward (extension) the back edge becomes a fulcrum. In each case, the front or rear edge of the disc is compressed.
Now consider what we know about fulcrums and leverage. With a fulcrum at the center of a lever, as with a seesaw, a weight of 20 pounds on one end is counterbalanced by the same weight on the other end. However, if we move the fulcrum toward one end, the weight needed to counterbalance 20 pounds grows exponentially.
If you hold your elbows at your sides and your forearms extended forward at 90 degrees the fulcrum in your spinal column is about 18 inches from one end of the lever of your forearm and two inches from the other (see Diagram 1). This means that if you are holding a 20-pound weight in your hand, a force of 230 pounds will be needed to counterbalance that weight. That, in turn, means that a total of 250 pounds of pressure will be exerted on the fulcrum in your spinal column, between the fifth lumbar vertebra and the sacrum (L5-S1 disc). If you reach out two more inches, the counterbalancing force increases to 460 pounds. You can see how easy it is to reach the 770 pounds of pressure that will cause a disc to become herniated or protrude—or the 1,440 pounds that will cause it to rupture.
Moreover, repeated stress on discs can cause deterioration. Consider what we put our backs through in an eight- to 12-hour workday—even in an office. Then add the effects of overweight and lack of exercise, and the problem gets worse.
And if all that isn't bad enough, there is another reason why poor work station ergonomics and sitting in forward flexion can cause physiological problems. It's called bone remodeling, and it's a problem that gets worse even when you are sitting still.
Prolonged stresses on bones can cause them to change their matrix in response. Distance runners experience these problems. But so do people who sit still for hours at a time in bad posture.
Scientists have instruments sensitive enough to measure the stress put into a bone. When a bending stress is applied to a bone, a negative charge is measured on the convex side and a positive charge on the concave side. When a bone is broken, the body recognizes the negative force field and lays down calcium and magnesium, two positively charged ions into the area; that is what precipitates the mending of the bone. Essentially, the bone will remodel to the lines of stress. In radiology this is explained as Wolf's Law.
When the body is constantly bent forward, its centerline (weight bearing line) moves forward, in front of the vertebrae rather than behind. In time, this causes bone remodeling in front of the vertebrae, in the body's attempt to stabilize itself. This remodeling causes the cervical curve to straighten. In turn, the loss of the lever of the cervical curve damages discs, ultimately causing vertebrae to fuse in the final stage of degenerative joint disease. (See Diagram 2.)
Designing For Correct Posture
What does all this mean to work station design? It's the reason why we recommend that:
* the angle of the upper body to the thighs be 91 to 112 degrees; and
* the computer monitor is directly in front of the eyes, so that the worker does not have to
look down at it.
These two factors are critical to spinal health for seated workers. Work station design must accommodate these positions. That includes the ability to adjust chair height and configuration to different sizes of people.
Cumulative Trauma Disorders
Of course, correct spinal posture isn't all we have to address in work station design. There is another class of injury that affects the extremities, called cumulative trauma disorders. This includes nerve, tendon and neurovascular problems. Carpal tunnel syndrome is probably the one with which you're most familiar—it's caused by compression of the median nerve in the carpal tunnel and causes pain, numbness or tingling in the hand. Some other common disorders are:
* tendonitis (inflammation of tendons);
* tenosynovitis (inflammation of the tendon sheath);
* thoracic outlet syndrome, a set of neurovascular problems that can cause pain and paresthesia (chronic numbness or tingling) in the neck, shoulders, arms and hands.
These disorders are caused or exacerbated by repeated stress over long periods of time. They can be prevented by proper workstation ergonomics, which allow the worker to operate in neutral, comfortable positions in which tendons, nerves and blood vessels are not subject to repeated stress.
The Basics Of An Ergonomic Work Station
First, let's recognize that there are three zones in the work station:
1. Primary Zone: everything within one's reach when the elbows are at one's side. The keyboard and
mouse should be within this zone to prevent injury.
2. Secondary Zone: everything within arm's reach—planner, telephone, etc.
3. Reference Zone: outside of arm's reach—heavy reference material, files, etc.
Next, let's look at the proper positioning of all the workstation elements relative to the body. In doing so, we'll review what we've already discussed—the correct basic sitting position for good spinal health. We'll also look at primary-zone principals necessary to preventing cumulative trauma disorders.(See Diagram 3, page 57.)
Empowering People To Control Their Work Environment (A Case Study)
By now it has probably become clear that, while there is much designers can do in terms of furniture specification to allow people to reduce their risk of injury, you can't go in and set up every individual's work station.
What you can do, however, is suggest to your client that they train their people in the proper setup and use of their furniture, including putting a page on their company intranet for training and reference. Training employees to set up and use their work stations in ergonomically correct ways will probably be mandated by law in the future. In the meantime, it is very good business.
Our client Merrill Lynch launched such a program several years ago across five campuses for 35,000 employees. The combination of the right furniture and a good training program yielded terrific results.
Merrill Lynch compared their workman's compensation costs for soft-tissue injuries (like carpal tunnel syndrome and tendonitis) before and after implementing their ergonomics program. Below are the reductions in workman's compensation costs over three years.
Designing work stations and specifying furniture with a firm understanding of ergonomics can produce huge benefits. The payoffs come in terms of reduced costs for workman's compensation and insurance, in fewer lost days and greater productivity, in employee morale and retention. Even more important it can help employees avoid injuries that cause pain and debilitation that can last for years or even a lifetime.
Getting the whole job done requires training and motivation programs for workers. But it all starts with providing them with furniture and design that give the proper support and adjusts to meet each individual's physiological needs.
Dr. Mark Vettraino, a consultant working with Teknion, is director of Task Group International, a leading consulting firm in the field of workplace ergonomics. Over the last 20 years he and his company have consulted with scores of clients, including some of the largest corporations in North America, as well as leading furniture manufacturers.