OSH Answers Fact Sheets Easy-to-read, question-and-answer fact sheets covering a wide range of workplace health and safety topics, from hazards to diseases to ergonomics to workplace promotion. What is new in the ergonomics of sitting at an office workstation and office chair design? People sit rather than stand for obvious reasons of comfort; only lying down is more comfortable, but hardly practical for working. The problem arises when we sit for too long at a desk or any workstation for hours and hours, day after day, year after year. The office is one environment where sitting typically takes the highest toll. The most common adverse effects of such prolonged sitting are discussed in the OSH Answers document Working in a Sitting Position - Overview. Despite much research and study over the last few decades, health effects associated with working in a sitting position persist. The number of people suffering postural problems and back pain through excessive sitting is not decreasing.
Even the concept of an ergonomic chair that was developed in the mid 80s, and widely adopted since then, has not contributed to any dramatic improvement in such health problems reported by seated workers. Some experts believe it is time to re-think the entire concept of "proper" sitting and good chair design, but such notions are not entirely new. They go back to the concept of sitting described by A.C. Mandal in The Seated Man: Homo Sedens (Dansk Tidsskriftryk Copenhagen; 3rd edition, 1985). Mandal's core belief is that maintaining the lumbar curve found in the small of the back is absolutely essential to a healthy pain-free back. The majority of guidelines, including our own OSH Answers document (Working in a Sitting Position - Good Body Position, and How to Adjust Office Chairs) however, suggest sitting upright with an angle of approximately 90 degrees between the torso and thighs which actually flattens the lumbar curve. A flattened lumbar curve increases both the mechanical load on your lumbar spine as well as back muscle activity.
As a consequence, sitting upright with the thighs horizontal (i.e., parallel to the floor), may lead in the long run to chronic low back pain (LBP). It was also found that while you lower your body to sit down, the lumbar curve stays unchanged until the last 20 degrees before your thighs become horizontal. In conclusion, without going further into a detailed biomechanical analysis of how the curvature of the spine works, people who need to sit at work could try using a chair with a forward-sloping seat pan as an option (especially if they are experiencing pain with a horizontal (flat) seat pan / 90 degree angle between the thighs and back). Such a chair should allow you to maintain the angle between your torso and thighs at about 105 degrees while keeping your feet flat on the floor or supporting them on a footrest if it is more suitable - see Figure 1. What are benefits of a sloping seat? It decreases the load on your lower back and minimizes the risk for lower back pain (LBP).
Sitting with your thighs in a downward slope increases the activity of your lower leg muscles. As a result return blood flow from the lower legs is improved, and there is less pooling of the blood and pain in the lower legs by the end of the workday. Consequently, in the long run, it can reduce the likelihood of your contracting varicose veins. Much more than a horizontal seat pan, a sloping seat pan not only makes rising from the chair easier, but also allows your leg muscles to recover sooner because any postural changes and shifts are also easier. Once you make the transition from a conventional horizontal seat to one that tilts forward, the next step is to consider using a slanted desk surface, which would reduce bending in the neck and upper torso, thus improving your postural comfort. Yet, of all advantages of the forward sloping chair, it is most beneficial to have more freedom (choices, options) of body positions (or work postures). Frequent changes makes sitting more dynamic rather than static (maintaining fix position) and easiness arising (standing instead of sitting) allows loaded muscles recover faster and postponing fatigue and discomfort.
What are disadvantages of a sloping chair? The major disadvantage reported is the feeling that you have to constantly counteract gravity to avoid sliding off the chair. The seat pan of such a chair has to be curved from front to back to allow sitting on chair without sliding. Nevertheless, you do have do exert some muscular effort in your lower legs to remain seated. This effort is in fact beneficial (providing the slope is not greater than 15 degrees) because it improves the return blood flow from your lower legs. The other disadvantage frequently quoted, of having your clothing ride up your legs can be overcome if the chair is properly designed with a non-slip covering. What is the possible future of seated jobs? Over the last few decades we see more and more sedentary jobs where workers are seated throughout much of their working day. The traditional design of office furniture and poor job design often result in lower back pain. While a forward-slopping chair seat may not be the ultimate remedy, it is one viable option that may be beneficial (and a new chair is much less expensive than the cost and suffering a person experiences with low back pain).
Although every effort is made to ensure the accuracy, currency and completeness of the information, CCOHS does not guarantee, warrant, represent or undertake that the information provided is correct, accurate or current. CCOHS is not liable for any loss, claim, or demand arising directly or indirectly from any use or reliance upon the information.Ramrod Straight Ain't So GreatEverything You Know about Sitting Ergonomically Is WrongIt’s certainly hard on our bodies, which are long and agile and meant to be moved, stretched and used — not crumpled into unnatural postures for hours upon hours each day. It’s also hard intuitively, because most of the time we don’t think about it. We just plop ourselves down in a desk chair and really, honestly think it’s okay — that sitting is sitting, and that nothing bad can come of such a simple act. But according to Alan Hedge, Director of the Human Factors and Ergonomics Laboratory at Cornell University, that line of thinking — that ergonomics don’t matter — is extremely dangerous.
The way you sit, and the chair you sit in, and the desk you sit at, all matters. Even more alarming, Hedge says most of the “knowledge” we hold about the ergonomics of sitting is a sham. Sitting bolt upright with limbs at 90 degrees isn’t just unhelpful, it’s bad for you. Wrist rests don’t help prevent carpal tunnel — they can, in fact, increase the risk of it. Standing all day isn’t the answer — according to Hedge’s research, it decreases fine motor skills and increases risks of atherosclerosis (a dangerous thickening of artery walls) and varicose veins. And those stupid balls people sit on? Yeah, they don’t work either. The scariest part of bad sitting posture isn’t just the threat of carpal tunnel, or obesity, or back pain. It’s all of those put together. So how should you really be sitting? According to Hedge’s research, more like this: 1 Find a good chair. Not all desk chairs were created equally, which is good, because you’re not looking for the same chair as everyone else.
Ergonomics is essentially the science of compatibility. You want a chair that fits your proportions, desk and task. In most cases, assuming you’re working at a computer most of the day, that means you should look for something supportive, dynamic (it’s got to be adjustable) and, if possible, something that looks good doing it. Any of these should work well. 2 Your chair has a back. You’re going to want to sit as far back in your chair as possible, so your back is right up against the back of your chair — which, ideally, will have some kind of lumbar and neck support. Don’t sit on the edge of your chair. Don’t hunch over your computer. Really feel that backrest and let it do most of the work for you. 3 Don’t put your computer at eye level. Put it above eye level, about two or three inches. That’ll help lengthen your body and keep you in the right position (unhunched) as you work. 4 Make sure your monitor is about an arm’s length away, centered in front of you.
This is also conducive to the correct, lengthened sitting position. If you’re going to refer to documents, use a document holder at the same level as the monitor. They’re kind of nerdy looking, but they work. 5 Plant your feet on the floor. It’s like they always told you in hockey drills: plant your feet and your body will stay strong and upright. When you’re sitting, keeping your feet flat on the ground will stabilize you, keep your back up and your body grounded. If you can’t reach, use a footrest. 6 Keep your wrists flat and your arms and elbows relaxed. And if possible, tilt your keyboard downwards, away from you — the opposite of the way most keyboards are set up. The reason, according to Hedge’s research, is that a gentle slope downwards is a more natural position that keeps your arms and wrists more “neutral”. If the keyboard is flat or sloped up, your arms tighten and your wrists have to work to stay upright to meet the keys. 7 If you’re using a laptop… don’t.