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Ergonomic Chairs and Seat Adjustment

Peer Reviewed

Did you know that about 70% of America's workforce sits on the job? Add to that the time most of us spend sitting down doing non-work tasks such as eating, studying, watching television, and driving. Americans today spend a lot of time sitting and it's taking its toll on our bodies.

Affects of Sitting
While most people believe it is relaxing, sitting is actually hard on the back because it transfers the full weight of the upper body onto the buttocks and thighs. Sitting, especially for long periods of time, can also cause increased pressure on the intervertebral discs- the springy, shock-absorbing parts of the spine. It's also hard on the lower extremities since gravity pools blood in the legs and feet and creates a sluggish return of blood to the heart.

In addition, most people do not use good body mechanics while sitting. Improper sitting posture can not only cause physical discomfort but also contributes to serious health problems, including:

  • Back pain
  • Neck pain
  • Eye strain
  • Abdominal pain
  • Leg pain
  • Repetitive movement disorders

Proper seating in a well-constructed ergonomic chair can help reduce fatigue and discomfort, increase blood flow, reduce the risk of injury, and increase productivity.

What is an Ergonomic Chair?
Whether a chair is to be used at a computer workstation or in front of a machine on the factory floor, it must be well suited for the tasks at hand and must fit the worker's size. Many chair manufacturers use the word "ergonomic" to describe their products, but you might need to look further than the label to see if it truly incorporates ergonomic guidelines. The following recommendations can help you choose a chair that will increase comfort and reduce the risk of injury:

Casters
Use a chair with casters (a pivoting roller or wheel attached to the bottom of the chair) and a 5-point base to make movement easier and minimize tipping. Nylon carpet casters are usually standard, but soft wheel casters are available for hard surfaces such as linoleum. Rubber locking casters are useful on stools to prevent tipping. You may also want to choose a chair that swivels easily.

Seat Pan
The seat pan is the part of the chair that supports the majority of the your weight. Choose a chair with a cushion made from dense, small-cell foam padding or spring coils (this usually involves purchasing a chair over $250.00). Inferior cushions that loose shape or compress can cause discomfort, imbalance, and hip and back fatigue.

The seat pan should be at least one inch wider than your hips and thighs on either side. In addition, the front part of the seat should slope down slightly (this is called a waterfall front) and allow a fist size gap between the back of your knees and the front edge of the seat pan to reduce pressure on the back of your thighs.

Also, look for a chair with tilt adjustments that allow for a forward working posture or a reclined posture. A seat pan with a sliding mechanism is also a beneficial feature. This allows small and tall users to adjust the distance of the seat pan from the backrest.

Backrest
Adequate lumbar support is the most crucial element of a backrest. Inadequate lumbar support places excess pressure on the spine. The backrest should either be small enough to fit into the small of the back, clearing the pelvis and back of the rib cage, or curved to provide adequate support. Many chairs come with a built-in lumbar adjustment, which can be adjusted by turning a knob on the side of the chair. This is best if more than one person will be using the chair. You may also want to look for a chair that has back supports that are large enough to provide mid-back and upper back support as well.

Armrests
Adjustable height and width are absolutely necessary when purchasing a chair with armrests. The armrest should be made of a soft material and should be at least 2" wide to provide adequate surface area.

Seat Height
Almost all chairs come with some type of seat height adjustment. This is probably the single most import adjustment mechanism on a chair. It allows you to adjust the chair so your feet can rest properly on the floor while your upper body is properly aligned with your tools such as a computer, display monitor, or keyboard. While hydraulic adjustments are standard on most chairs, pneumatic adjustments are a nice feature as they allow you to adjust the seat height while you are sitting on the chair. Make sure the mechanism to adjust the seat is easy to reach.

Chair Recline or Tilt Adjustability
The chair recline or tilt adjustment changes the angle of the entire seat relative to the floor. As with backrest angle adjustability, a reclined chair transfers some of the upper body weight to the backrest of the chair. Keep in mind that locking the backrest in one position isn't recommended or beneficial.

Other Considerations
Footrest
- in most cases you should not need to use a footrest. However, if you need additional foot support choose a free-standing floor-mounted support that allows you to rest your feet in front of you in a comfortable position.

Fabric - when choosing a chair, keep in mind cleaning and maintenance of the chair when making your choice. Cloth upholstery is the most common covering but may not be easy to keep clean. Vinyl or leather covers are easier to clean but don't breath as well and may make your legs warm.

Safe Sitting
In addition to using a chair that allows you to sit properly, there are other precautions you can take to minimize discomfort and injury while sitting:

  • Don't stay in one position for prolonged periods of time.
  • Alternate between sitting and standing.
  • Make sure your feet are flat on the floor.
  • Sit upright with your back and shoulders against the backrest.
  • Do not use the armrests to slouch. Elbows and lower arms should rest lightly to avoid circulatory problems or nerve pressure.
  • Make sure your shoulders are relaxed and slightly dropped while keyboarding.

Maintain a "neutral" posture:

  • Hips slightly higher than the knees
  • Back fully supported and straight
  • 2-4 inches between the edge of the chair and the back of the knees
  • Equal distribution of weight on the seat cushion

Most importantly, take frequent breaks. Stand up, stretch, and take a few deep breaths. This will help increase your blood flow and reduce fatigue. Be aware of your posture during your sitting time. Correct yourself if you find you are slouching or moving out of the correct position. Small changes like these can go a long way to keeping yourself comfortable and healthy.

Updated on: 04/07/14
Mark R. McLaughlin, MD
This article is a perfect example of how to work smarter and not just harder. Because we spend so much time recumbent in a chair during our working hours, it is imperative that we choose the right chair. The work chair should be considered a piece of equipment at work that will optimize a worker's productivity. Better ergonomics translates into less back pain and better concentration at work. This is one piece of furniture that I would suggest be purchased at the store after sitting in it. Even a good chair purchased on the Internet or by mail order may not be the right fit for a person who is perhaps outside of the standard bell curve with regards to size. Ms. Rodts is to be commended for an excellent summary of the ins and outs of office chairs.
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