What makes an office chair ergonomic?

Ergonomics has been called the science (or art) of fitting the task to the person. So, one chair that can be adjusted to comfortably seat a greater percentage of the population than another chair can be said to be more ergonomic. Can the chair adjust so that both a shorter and taller person can find a comfortable seated position? Some people are thinner and others are at the opposite spectrum. Some weigh less and some weigh more. And, what about body shape? Some people have longer torsos and others have longer legs.

Manufacturers of ergonomic office chairs design for the majority of people somewhere in between the dimensional extremes of the human body. This is accomplished by utilizing a combination of anthropometric statistical data and old school probability tables. Derived from ancient Greek, anthropometric means “the measurement of man.” I’ll use the height of adult males in the U.S. for my illustrative example to keep the data to a minimum, though manufacturers incorporate data that represents both genders and other body dimensions and mechanics.

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The mean height of an adult male in the U.S. is approximately 5’9. The standard deviation is approximately three inches. In the world of statistics and probability, 68% of all sampled values will fall within one standard deviation from the mean, and 95% of all values will fall within two standard deviations from the mean. So, in the U.S., 68% of adult males are between 5’6 and 6’0 and 95% of them are between 5’3 and 6’3.

A chair that adjusts to serve a population subset that is within two standard deviations from the mean will suit the needs of all but 5% of the overall population.

To go one step further, let’s consider all adult males in the U.S. within three standard deviations from the mean. 99.73% of all values fall within three standard deviations, so this really is the overwhelming majority of them. One standard deviation here is three inches; three standard deviations is a total of nine inches from the mean height of 5’9. We can surmise that 99.73% of adult males in the U.S. are between 5’0 and 6’6. If an office chair can successfully suit the needs of all males within that range, then it is a very adjustable chair to say the least.

To design and manufacture a chair that will fit 95% of the population is going to involve some impressive technology and components that will result in a product that isn’t cheap. Aiming for a chair that fits 99.73% of the population will result in an even more impressive and expensive product. At some point the manufacturer has to balance the available human body statistics with development cost and anticipated sales, and so there is no office chair that will fit every single human on the planet.

Obviously, selecting a suitable office chair is very important. More people are working while seated than ever before and this is not good for our spines or our physical health in general. We can’t eliminate every single injury caused by seated office work, but we can do our best to minimize the frequency of these types of injuries and also their severity. If an office chair can adjust to comfortably fit a substantial percentage of the working population, reduce seated discomfort and pain, and minimize the frequency of injuries caused by seated work, then the chair must be truly ergonomic and is functioning as intended; a good fit, you could say.

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