The chair as a workplace

Seated office workers have many different postures, found PhD researcher Liesbeth Groenesteijn. Current chairs are poorly adapted to that variety.

With a background in physiotherapy and ergonomics (Human Movement Sciences, VU Amsterdam), Groenesteijn became involved in various projects in physical workload and design of work environments at TNO. She started a PhD project within TU’s Faculty of Industrial Engineering and Design in 2007 with seats for knowledge workers. She uses the term knowledge workers to include people who work remote, for example, at a desk at home or at mobile locations with the office workers.

One of her experiments, with ten healthy subjects who were asked to perform various sorts of office work showed how postures and movements of body parts varied with the tasks. While performing correction tasks, persons tend to bend over the paper while keeping the head almost still. In typing, people sit more upright with a little more movement in the trunk and head. When using the mouse, the rest of the body is almost static, while sorting files is the most dynamic task. And on the telephone, people tend to lean back in their chair while keeping the head straight up.

Her professor Peter Vink, “For reading, a backward tilted backrest at 124 degrees is best, for watching television the angle is larger still at 130 degrees. For computer work however, the backrest should be more upright.”

Ideally, seat design facilitates the variety of postures and movements encountered in office work. Sometimes the backrest can be inclined further to accommodate reading instead of desk work. But often, adjustments in seats remain unused since 24-61% of the users don’t touch the controls. Either they don’t know the chair is adjustable or they think it’s too complicated or unlikely to produce the desired outcome.

To illustrate her point, Groenesteijn guided Dori van Rosmalen to design a television chair with a deep seat, an inclined backrest, and a movable armrest. Together with a leg rest, the seat comfortably accommodates a range of different postures.

As for the current office chairs, Groenesteijn concludes they do not optimally support the tasks of knowledge workers. Design of the chairs could be improved in terms of adjustability and usability. Moreover, headrests and low back supports need to be improved to support different positions in various tasks. In the future, she suggests, smart chairs may automatically detect which task is being undertaken, and adapt the supports accordingly.

Liesbeth Groenesteijn, Seat design in the context of knowledge work, PhD supervisor Prof. Peter Vink (IDE), 23 January 2015.

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