Is An “Ergonomic Chair” Enough?
Posted on Wednesday, December 29, 2004
Adjustability is a key feature that can transform a typical chair into an “ergonomic chair.” But, as many companies have learned the hard way, an adjustable chair is not always enough.
Successful ergonomics requires a systems approach. An office chair is one component in the office system, and the person that sits in it is another. The stapler, telephone, computer, mouse, keyboard, desk, and other work tools are additional components in the system. How the person interacts with those components as he or she performs required work tasks is yet another part of the overall system. Selecting a chair without considering the rest of the system components and work tasks usually leads to a misfit and may introduce new, unforeseen problems into a workstation. In order to fit the broad working population, a computer workstation must have multiple component adjustments, not just chair adjustments. If the chair is the only easily adjustable feature, most people will not be able to achieve their most efficient, productive, safe and comfortable working postures. This problem is not always obvious to the casual observer, and it therefore persists in many companies. Anthropometry, the measurement and study of human body dimensions like height, weight, reach lengths, and eye heights, is one of the most important data sets applied by ergonomists working to fit people with their physical environment. It’s easy to see that people vary in height and weight, but it’s less obvious that we also vary in many other dimensions, such as leg and trunk lengths. For instance, some races have proportionally longer legs than other races, and even within the same race, specific body dimensions vary substantially from person to person. To illustrate, imagine two women of the same height, standing side-by-side. We measure the hip height, which corresponds to leg length, and find that one has legs three inches longer than the other. Next, we measure seated knee height (popliteal height, as the dimension is technically called), and we find yet another difference between them. Finally, we ask each woman to sit in a chair and adjust the chair height so that each may comfortably rest her feet flat on the floor (shoe height introduces yet another variation). Even though they are the same standing height, we’ll find that the seated height may differ substantially, because their leg and their torso lengths are different. Important dimensions like seated eye and elbow heights will also be different, which means each will have different height requirements for their keyboards, mice, and monitors. Contrary to claims otherwise, there is no perfect way to sit, nor is there a perfect way to arrange all workstations, even if the same job is being performed at each. Natural variability in people dictates that the system must be flexible in order to meet the unique needs and dimensions of all the different people that may interact with the system. An adjustable chair provides some of that flexibility, but not enough to accommodate the full, multifactorial spectrum of anthropometric variations. Simply put, the location of the computer keyboard and mouse need adjusting independent of the chair, as may the monitor. The extent to which a system should be adjustable depends upon the nature and diversity of tasks to be performed at the workstation, and whether one individual person or a population of workers is being fitted to the system. If only one person will use the workstation, a one-time set-up and custom adjustment may suffice. If the workstation will be used by different people (e.g., shift work), a system that can be easily adjusted by each worker is recommended. Even without shift work, employee promotions, transfers, and turnover will result in different people using the same system, and adjustment will still be needed, just at a lower frequency. There are several common and relatively inexpensive workstation components designed to accommodate variations in size and preference: footrests, keyboard and mouse platforms, and monitor arms or risers. When work surface or monitor heights are “too high,” a person may benefit from a footrest, allowing her to raise her seat, yet still be able to comfortably rest her feet. When desk height, and therefore the keyboard and mouse that rest on it, is “too high” or “too low,” an adjustable keyboard and mouse platform may help. And when the monitor height is “too high” or “too low,” monitor adjustments may help. Each of these accommodations have strengths and weaknesses. Footrests: Relatively inexpensive and easy to use. Drawbacks include the potential for clutter under a desk, or even a tripping hazard, and may restrict freedom to move and achieve desirable dynamic postures throughout a workday. On the other hand, a footrest is a simple way to accommodate smaller people in particular, who often have difficulty keeping comfortable leg postures. If a footrest is selected, adjustable height and angle are recommended. Keyboard and mouse trays: These are available in a variety of shapes and sizes, and with a variety of adjustments. To be effective, the tray must be large enough to accommodate both the keyboard (and palm rest if desired) and the mouse, side-by-side, and on the same level. Easy height adjustment and positive and negative tilt are recommended so that the user can reduce wrist deviations in a comfortable arm posture. There are drawbacks with such platforms. For example, they usually extend out from under the desk surface, pushing the worker further away from the work surface, and they can present an obstruction under the desk, sometimes hindering leg access and movement and interfering with chair arms. Quality is important when selecting these devices; be sure that the person can type and operate the mouse with stability (i.e., avoid “flimsy” models). Monitor arms and risers: Monitor heights can be raised cheaply by using such things as old phone books. If a more tasteful solution is deired, there are a variety of monitor raising products on the market, including stackable trays or adjustable arms. Lowering a monitor is limited by the work surface height and monitor design, unless a recessed monitor desk is selected. Ergonomists often feel that these types of accommodations are at best a retrofit to a system with deeper problems. Ultimately, the best solution is to provide an easily adjustable work surface, not just adjustable add-ons. In fact, work surfaces that adjust through a height range from seated work to standing work are no longer uncommon. Such systems allow workers to adjust to different heights for different tasks, or to make postural adjustments for comfort and fatigue over the course of the workday. In many cases, cost is the deciding factor when selecting between add-ons or fully adjustable work surfaces. However, more manufacturers are offering fully adjustable systems or work surface adjustment retrofits, and competition is driving prices down. Furthermore, a larger upfront investment can result in significant future savings.