office furniture designers

Abstract: Dynamic-sitting office chairs are usually compared with static sitting rather than with each other, and the contribution of backrest deformability (lateral backrest movement) is unknown. Office work also increasingly spans multiple devices. Twenty healthy adults (10 men, 10 women) completed a 15-minute single-device and a 15-minute multi-device proofreading task on each of three chairs: two commercial dynamic-sitting chairs (T90, Aeron) and a T90 whose backrest lateral movement was mechanically fixed (T90-fixed). We recorded subjective ratings, head and trunk posture (inertial measurement units), upper trapezius and lateral gastrocnemius activity (electromyography), and task performance. Chair effects were largely null: T90 and Aeron did not differ in ratings or performance, posture and muscle activity showed only isolated, direction-inconsistent differences, and preferences were polarized. The standard T90 showed greater trunk movement (mean absolute angular velocity in yaw) than T90-fixed during the multi-device task (p = 0.042), which may indicate that its movable backrest helps accommodate trunk movement under demanding work; no other whole-sample posture, muscle, rating or performance measure differed between these two configurations, and replication is needed. Task effects were large and consistent: the multi-device task elicited greater and faster head, trunk and shoulder movement and higher upper trapezius activity than the single-device task, with lower reading throughput. Multi-device work thus imposes substantially greater movement demands than single-device work, which supports designing chairs that accommodate movement in modern work environments.

Abstract: Adjustability is a core determinant of ergonomic fit in office chairs, but its benefits depend on users being able to operate the controls and, on the chair, continuing to support the body as posture changes during work. We compared two high-end office chairs, the T90 (Sidiz; Chair A) and the Aeron (Herman Miller; Chair B), in two experiments to explore which design features may explain differences between them. In Experiment 1, 20 participants adjusted ten controls common to both chairs and rated perceived adjustment difficulty on four items. Chair A had significantly lower overall difficulty (Wilcoxon signed-rank test, p = 0.008), with control-level advantages for headrest angle, armrest height, armrest rotation angle and lumbar support position; Chair B was easier for seat height, possibly because its side-mounted lever is more visible than Chair A's underside button. The headrest comparisons involved a third-party headrest fitted to Chair B, and control- and item-level tests were not corrected for multiple comparisons. In Experiment 2, the same participants completed a 15-minute multi-device task requiring repeated posture changes, reach and reorientation, then rated body-part discomfort, general comfort and satisfaction with five components. Discomfort and comfort did not differ; Chair A had higher satisfaction for the seat-pan and lumbar support (exploratory, uncorrected). Interviews suggested links to mechanism properties: Chair B's rear lumbar dial was often described as producing little perceptible change, and for controls without significant differences each chair appeared to leave a different aspect of the same need unmet. These findings suggest mechanical and interface properties that designers of adjustable office chairs may consider for dynamic, multi-device work.