Best seat in the house—Jan/Feb print issue

Ergonomic features to consider when purchasing office chairs

March 7, 2013
by By Margo Fraser

Let’s face it, there’s nothing like a good chair. Not only is it comfortable, but it’s an important piece of equipment for proper workstation design. A chair’s adjustability can prevent pain and help employees to adapt to work surfaces that may not be at an ideal height. Below are some of the ergonomic features to consider when purchasing chairs for your organization.

Does it fit the employee?
Many manufacturers are trying to design their chairs to accommodate from the fifth or tenth percentile females on the smaller end to the 90th or 95th percentile males on the tall end. But sometimes the data used is for Caucasians whereas many of our workplaces are made up of individuals from many different ethnic backgrounds, requiring a larger range of adjustability. It’s unlikely an organization will be able to find a single chair to fit everyone, given the range required for a multi-ethnic workforce. Companies should reserve some of their budget to allow for those that don’t fit the standard.

Using international body dimension data, fifth percentile female chair height (floor to top of seat) is roughly 29cm and the 95th percentile male chair height is about 52cm. To accommodate taller people, organizations may need to look for a longer pneumatic cylinder length. As well, it’s worth checking with the vendor up front to determine if this option is available. The range of height adjustability is important when the keyboard and mouse are at a fixed height, as shorter individuals may need to raise their chair to be at the right height for the keyboard (about elbow height) and then use a footrest to support their feet.

Seat pan depth adjustability
If someone sits back in the chair, there should be no pressure on the back of the knees that could cut off circulation to the feet, so the seat pan length should be adjustable. The fifth percentile female dimension for buttock to back of knee length is about 40cm while the 95th percentile male dimension is 61cm. An appropriate seat pan dimension is a few centimetres shorter than these dimensions. Short seat pans are more difficult to find due to the space needed under the seat for the adjustment mechanism.

The chair should have a method to move the lumbar support height to fit a range of torso lengths. Look for chairs with adjustable lumbar support to fit the depth of low back curvature.

Back angle

Generally, a more upright position for computer work is better but people may wish to recline from time to time. But what feels upright can differ between men and women. Although there are always exceptions, women tend to like the back rest in a more vertical position due to being wider through the hips and having a lower centre of mass. Men generally have a higher centre of mass, wider through the shoulders and can feel as if they’re leaning forward while in a chair with a vertical position. They tend to prefer a slight backward recline in the backrest to feel “upright.” Many chairs have backrests that are skewed towards the slightly reclined position, so women can’t move the backrest and therefore don’t use the back support.

Armrest height and width
For those with short torsos and long limbs, there’s little space between their hands and thighs in the 90-degree position and many chairs have armrests that can’t be lowered this far. This forces the person’s shoulders into a shrugged position. It’s often better to remove the armrests so it’s important to look for chairs with this capability.
For those wider through the hips than waist, the support shaft for the armrests must be able to clear the hips, while the armrests must be able to move closer to the body. A telescoping feature, such as pivoting, or a portion that flips over can serve this purpose.

Since the desired height of the armrests and the keyboard/mouse surface are about the same, armrests that extend forward too far prevent employees from pulling in close to the surface, especially for those who are narrower from the front to the back of their torso. This results in reaching forward to the keyboard and mouse, which puts more stress on the shoulder and upper back.

Finally, an adjustable chair won’t help if the person doesn’t know how to use it. Get the most from your purchase by ensuring employees know how to operate the adjustment mechanisms and what the best adjustments are for themselves.

Margo Fraser, M.Sc. is a Canadian Certified Professional Ergonomist and executive director of the Association of Canadian Ergonomists.