Design features of an office chair promoting health and performance upon sedentary work

Today there is a large amount of knowledge about appropriate ergonomics postures upon sedentary work. The market offers a large selection of office chairs with numerous possibilities of adjustments for wide-ranged sitting postures. It is often difficult for the users to understand how the various settings should be adjusted to achieve the best individual postures at different occasions. Too many settings, with altered designs and functionality can be confusing. Buttons, knobs and levers can be difficult to understand for the users. This applies to both the purpose of the controls and how they should be handled. It is often difficult to know, without instructions and help, how an optimal setting should be chosen for a single individual. Instructions, both written and oral, and also an introduction given by an ergonomist/physiotherapist are very important in the concept of how an ergonomic office chair should be fully utilized. The objective of this study was to find out how different adjustments of an office chair were perceived, interpreted and used during sedentary work. Well-being, in terms of physical comfort, health effects and working performance was also studied during a longer period of work and related to design features of the chair. In total 48 full-time employed office computer workers in two companies participated in the study. Over a five week period, they changed their existing office chair to another chair with a number of controls for individual adjustments resulting in a variety of possible sitting postures. Each week the participants filled in an questionnaire with estimations of how the chair influenced their work. Among the 48 participants, 28 received an oral introduction with training about ergonomic features of the chair. The results showed that the understanding increased significantly (p<0.01) regarding how to adjust the chair when oral introduction/training was given. Also adjustments were significantly (p<0.05) used more frequently in this group, especially the tilting function. In general this group adjusted their chair 2-3 times per day the first week, while the other group adjusted their chair only 2-3 times during the week. However, when comfortable settings were found the users seldom adjusted the chair again. The number of adjustments decreased after two weeks also for the group who got introductory training.. Sitting height was most often adjusted, followed by seat back angulation. The positions of the neck support and armrests were seldom changed. Few users understood that the length of the seat cushion was changeable. The physical comfort of the chair was generally considered to be at least as good as, or better than in their previous office chairs (p<0.05). A comfort increase of 20 % was experienced by half of the participants while a third graded comfort increase of at least 30%. Half of the participants felt that the physical strain in the neck and shoulders decreased after a few weeks of work in the chair. The chair was the only product that was introduced in their working enviroment, they did not change table hight, hight of screen or mouse location differently than before. After 5 weeks, the perceived load was reduced by 20-25% for the neck and 10-15% for the shoulders (p<0.05). One third of the participants also felt that the load in the lower back decreased during the period. Especially, discomfort in the right part of the body was reduced. The participants who had reported long-term problems in the neck and shoulder regions before the study felt that their symptoms were reduced by 30-40% (p<0.05). To sit in the chair during computer work was estimated by the majority of the participants as beneficial for achieving a good working technique (p