From The Ergoweb® Learning Center

Chairs: what else to consider

While there are some variations in office chair design and style, any chair that might be considered “ergonomic” needs to incorporate some basic features. Before anything else, the chair needs to fit the basic anthropometry of the user. No matter how adjustable the chair might be, if the user cannot fit into it, it is not ergonomic. Chair manufacturers are addressing this by creating sizes of chairs like Small, Medium, Large and XL.

The second necessary feature is adjustability. A chair should be adjustable. Adjustability allows the user, first, to make a more fine tuned fit to their anthropometry, and secondly get postural support in a number of working positions throughout the day. Current manufacturing guidelines provide information on, for example, how high or low the chair needs to go to fit a percentage of the population. Additionally, these guidelines illustrate several acceptable working postures including sitting upright, sitting tilted back, sitting tilted forward and standing. It is encouraged that users change postures often. The chair should continue to provide postural support, particularly lumbar support, throughout these posture changes.

Additional basic adjustments should include back rest height and angle, arm rest height, and tilting of the seat. In addition to these adjustments, many chair manufacturers have added adjustability features such as seat pan depth, lateral arm rest motion, lumbar support firmness, and rocking tension.

Recently, the marketplace has been inundated with a new fad of purported office seating. These seats claim to be at least “ergonomic” and at best can claim to cure injuries, clear the user’s zen and provide everlasting happiness. Examples of these “seats” include exercise balls, kneeling stools, and bar stools on springs. While each of these products may have a place, that place is not throughout the office. These seats may be comfortable and appropriate for some individuals, particularly individuals who may not be able to sit in a traditional chair due to injury, illness, or physical condition. 

These seats are often falsely labeled “ergonomic.” One of the main reason these seats are not ergonomic is a lack of adjustability. A large ball sitting on the floor, or even in a stabilizing cage is not adjustable to the needs of the user. Not only do many of these seats not offer adjustability in areas like seat tilt, or backrest height, but seat pans and back rests are not incorporated in the design of these seats.  Some of these alternative seats, particularly kneeling seats, do not accurately account for body structure function. These seats often claim to reduce back pain through transferring force from the pelvic bones, which were designed for sitting, to the front of the shin area. This area, from a skeletal function standpoint, is not well suited for pressure. A third problem with these types of seating is safety. Having an unstable seat such as a ball, or having the user’s legs wrapped into a kneeling chair can pose additional safety hazards.

This article originally appeared in The Ergonomics Report™ on 2002-12-01.