Does a dynamic chair increase office workers' movements? – Results from a combined laboratory and field study
Introduction
Sedentary behavior has increased over the past ten years (van der Ploeg et al., 2015, Hagstromer et al., 2015) and sitting itself has been identified as an independent risk factor for several diseases and mortality (Hamilton et al., 2007, Katzmarzyk and Craig, 2002, Wilmot et al., 2012), although the physiological mechanisms modulating these risks are yet not fully understood (van Uffelen et al., 2010). Standing time seems to be positively associated with several positive health outcomes (van der Ploeg et al., 2014, Ebara et al., 2008) and therefore office workers with predominantly desk-based work are recommended to regularly break up their sitting time with standing bouts (Thorp et al., 2014) and light intensity physical activity for up to 2 h/working day (Buckley et al., 2015). However, another way to increase physical activity during desk-based work is to sit in a more “active way”, i.e. on chairs without back support, on dynamic or unstable chairs (Ellegast et al., 2012), on exercise balls (Gregory et al., 2006), or on motor-driven chairs. However, it is not clear to what extent these methods actually increase the workers' movements. In fact, recent studies showed that users of an unstable chair had lower muscle activity levels and fewer body movements compared to sitting on a conventional office (stable) chair (Grooten et al., 2013, O'Sullivan et al., 2012). Another study that compared four dynamic office chairs with a conventional office chair in respect to muscle activity, sitting postures, as well as physical activity intensity (PAI), showed that dynamic chairs did not increase physical activity levels and movements (Ellegast et al., 2012). In contrast, the tasks performed affect more strongly the office workers' movements, totally independent of chair type (Ellegast et al., 2012, Groenesteijn et al., 2012).
Håg Sofi is a dynamic office chair that is equipped with a BalancedMovementMechanism™ below the seat that can be gradually unlocked. The office worker can rotate around the longitudinal and bilateral movement axes, when this mechanism is put in the unlocked mode, and theoretically the worker's movements are stimulated while seated. Positive effects on blood flow in the lower limbs in the unlocked compared to the locked mode has been found (Stranden, 2000). However, to our knowledge no studies have yet evaluated the effects on office workers' movements. The aim of this study was therefore to evaluate the effects of this dynamic chair, compared to a conventional office chair and working at a standing desk, on movements and secondly to investigate its effect on aspects of posture, comfort and task-performance in a combined laboratory and field study. “It was hypothesized that the greatest body movements would occur during the standing conditions, and that the unlocked condition subjects would enhance movement compared to the locked and conventional conditions.”
Section snippets
Material and methods
This study was a combined laboratory and field study. The laboratory study was designed with 3 tasks and 4 chair conditions in a randomized order based on an online randomization program (www.randomization.org). In the field study, professionals with predominantly sedentary desk-based work were studied over three working days using three different conditions in a random order.
Laboratory study– primary outcomes
Table 2A, Table 2B, Table 2CA–CA and Table 3 present the results for the primary and the secondary outcomes.
Main findings
The results of this study on the effects of a dynamic chair on movements in desk-based office work were equivocal. On one hand, in the unlocked mode during the static tasks (and not during the dynamic task), it was found for three out of four variables describing movement and for one variable that described ground reaction forces that the office workers were moving more compared to the conventional condition and less compared to standing, which was in accordance to our hypotheses. However,
Conclusions
Our results indicate that desk-based office workers move more sitting on a dynamic office chair compared to a conventional office chair, but not as much as during standing. However, these results were inconclusive regarding the different measurement parameters used and not verified in a field study. There is a need to develop protocols for studying movements during desk-based office work in laboratory and field studies.
Competing interests
This research was partly funded by the chair company, Scandinavian Business Seating AB, requesting an evaluation of the dynamic chair. Scandinavian Business Seating AB, supplied five chairs used in the study and the transport of the chairs in the field study. However, none of the representatives were involved in the design of the study, the data collection, the data treatment, writing of the manuscript or have in any other way influenced the results.
Acknowledgements
The authors want to thank the ergonomists at the large industrial company in mid-Sweden for their collaboration. Thanks also to all participants.
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