Ergonomic study of special seat products for office and VDU workplaces

Status:

completed 12/2007

Aims:

Inquiries have increasingly been received in the recent past from member companies of the institution for statutory accident insurance and prevention in the administrative sector (VBG) regarding the benefits obtained in practice from the use of special ergonomic seat products at office and VDU workplaces. The seat products in question are office chairs with innovative technical elements (such as special spring systems) which, according to the manufacturers' claims, permit or bring about sitting postures and/or movements which are particularly conducive to good health.

In order to demonstrate this effect provided by the special seat products in comparison with a conventional office chair, a comparative study was conducted in the laboratory and in the field, with regard both to ergonomic and biomechanical criteria, and to comfort-related aspects.

Activities/Methods:

Five office chairs (four special seat products labelled A, B, C and E, and a reference office chair D) were selected by the VBG for the purpose of the study.
In order for a comparative cross-sectional study to be performed, laboratory measurements of sitting posture and movement were conducted on ten test subjects (office clerical staff free of disorders). The tests encompassed measurements involving all five models of chair. The survey/measurement parameters were: work task, muscle activity (EMG), body posture and movement, physical well-being, safety, and suitability. The laboratory study was preceded by an accustomization phase on the chairs to be studied, and associated interviews.

A comparative cross-sectional field study was then performed on ten test subjects free of disorders in each of four VBG member companies (a total of 40 office clerical workers of both sexes). Following an accustomization period, the test subjects were interviewed regarding the office chairs. Measurements were conducted on three test subjects from each company in conjunction with three of the five models of chair (one of the three chairs being the reference chair). The survey/measurement parameters were: work task, body posture and movement, physical well-being, safety, and suitability.
The external Dutch body "TNO Work and Employment" assumed the task of drawing up the questionnaires concerning the comfort and acceptance of the special seat products, and of evaluating the results.

Results:

The results of laboratory and field measurements of muscular activity and scale of movement during identical tasks were evaluated. Comparison of the four special chairs with the reference chair yielded for the most part no significant, i.e. statistically verifiable differences. Only for the chair-specific parameters such as forward and lateral tilt of the seat pan and forward tilt of the backrest were differences discernible between the chairs in the statistical evaluation. These results permit the conclusion that although the dynamic characteristics of the chairs differ, they do not directly result in greater physical activity on the part of the seated person.
Conversely, the comparison of different tasks in both the laboratory and field studies revealed generally significant correlations between the movement and sitting posture of the test subjects on the one hand, and the tasks performed on the other. The individual movement patterns of the person whilst seated are thus influenced more by the tasks performed than by the design of the office chairs studied. This underlines the need for a holistic approach to the ergonomic design of VDU and office workplaces, and for measures to be introduced in offices which are conducive to movement, such as the implementation of sit-stand concepts. It is also essential for work to be organized in a manner conducive to greater physical activity at the workplace, in order to counter physical inactivity there.
Statistical evaluation of the questionnaires with regard to comfort, physical well-being and acceptance by the test subjects produced a differentiated picture, with a clear ranking for the different models of chair. The special chairs A and B were rated by the test subjects as being superior to the reference chair in almost all respects. Chair E was rated approximately the same as the reference chair, and chair C as inferior. Overall, the models of chair which possess a facility for lateral tipping of the seat pan appear to be less well accepted than the models with seat pans which feature mobility in the horizontal plane.

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