Application of mismatch equations in dynamic seating designs

Highlights

• Office furniture dimensions did not match the sample anthropometrics.

• Adjustability significantly increased cumulative fit while sitting traditionally.

• Dynamic seating although recommended is hard to achieve with some configurations.

• Perching presented the hardest challenge to match within dynamic seating.

• Equations proposed should be tested for subjective and objective measures.

Abstract

Anthropometry is critical for product and workplace design. Highly prevalent, office work is associated with sedentarism and physical discomfort due to prolonged sitting. Dynamic seating (alternating across sitting, perching, and standing) has been suggested as an alternative to overcome those problems. The current study tested a large sample of anthropometric data for mismatch levels against national and international office furniture standards using dynamic seating as a framework with traditional and perching mismatch equations, applied to three recommended dynamic seating components. Dimensions present in the standards used did not match the majority of the sample. For sitting, seat width and depth individually presented the lowest levels of match, as well as under cumulative fit of all office furniture dimensions. However, these were alleviated when incorporating adjustability. Perching was shown to be generally impeded given commercially-available chair height options. Limitations in state-of-the-art perching equations are discussed, and two new models are proposed as design alternatives. Further research should focus on testing the criteria presented in this research through discomfort and objective measures.

Introduction

Anthropometric dimensions are common in designing products and workspaces across highly heterogeneous settings and users, from fire fighters (Hsiao et al., 2014) to highly specific sports equipment for people with disabilities (Bragança et al., 2018). Despite the many unsolved issues still present today, ergonomic standards – which have largely remained unchanged since the 1970's – enjoy more consensus regarding basic product design and user interface principles than ever before (Woo et al., 2016). Unequivocally, every design should focus on the end users, their optimal match, safety, better performance in products and workplaces (Pheasant and Haslegrave, 2006), and overall sustainability (Nadadur and Parkinson, 2013).

Technological advancements have gradually reduced physical labor; this, however, has contributed to sedentary office work. In conjunction with a modern lifestyle, problems associated with sedentary habits are more commonplace. Across greater postural and cardiovascular risks (Brownson et al., 2005; Parry and Straker, 2013; Sowah et al., 2018), spending large portions of the day sitting is associated with cardiovascular ill-health and musculoskeletal disorders, specifically low back pain (LBP) (Corlett, 2008; Kirk and Rhodes, 2011; Parry and Straker, 2013), where workers with especially static sitting behaviors appear more likely to experience chronic LBP compared to their pain-free counterparts (Bontrup et al., 2019).

In preventing low back pain, conventional seating models and standard office chairs generally encourage an upright sitting posture, maintaining right angles at the ankles, knees, hips and elbows; however, working in the same posture or sitting still for prolonged periods may not be healthy or feasible (Woo et al., 2016). Particularly, Zemp et al. (2016) indicated that subjects who suffer from acute low back pain tend to have more static sitting behaviors. Aiming to increase movement and posture alternation while working, office settings have instituted health interventions at the level of individuals (e.g. incidental walking promotion), organizations (e.g. policies for encouraging more movement), and physical workspaces (e.g. treadmill desks, sit to stand workstations, etc.) (Parry et al., 2017).

The traditional sitting posture is based on a 19th century proposal from Staffel, a German doctor, whose “cubist approach” called for hip, knee, and ankle joints to maintain a 90° angle (Dainoff et al., 1994). Since that time, studies have shown that this posture can generate several problems, such as tilting the pelvis backwards (retroversion), rectification of the lumbar spine (Keegan, 1953), increase in intradiscal spinal pressure in the lumbar region (Andersson et al., 1974), overall decreased movement capacity of the spine, and reduced circulation in the legs due to lack of muscular activity (Stranden, 2000). More modern seating posture proposals, like that of Mandal (1982), are based on spinal biomechanics, and recommend an angle between the thighs and trunk closer to 130°; without losing verticality, these proposal has come to be known as astronaut or perching postures. This position presents several advantages over Staffel's, such as tilting the pelvis forwards (anteversion), maintaining lumbar lordosis, and decreasing intradiscal pressure (Noro et al., 2012). Common ergonomic designs that promote these beneficial postures – as well as alternation and movement - have used higher chairs with forward slopes, saddle chairs, and adjustable height desks (Mandal, 1991; Roossien et al., 2017; Kuster et al., 2018; Noguchi et al., 2019; Chambers et al., 2019; Vaucher et al., 2015; Johnston et al., 2019). Demonstrated across different populations - from dentists (Gouvêa et al., 2018) to school children (Castellucci et al., 2016a, Castellucci et al., 2016b) - hybrid sitting interventions incorporate furniture and equipment that allow users to modify their sitting posture according to their preference, work-related use, and comfort. Moreover, they have been shown to be more effective than any single static posture (Noguchi et al., 2019). Based on the above, “new” fundamental design principles to bear under the framework of Dynamic Sitting, i.e., posture changes among sitting, standing, and half-standing positions, also known as semi-sitting or perching, should be included in office settings (Bendix and Bridger, 2004). Several documented principles have addressed Dynamic Sitting, and conclude that height-adjustable desks, a high saddle chair or tilting seat pans, all of them allowing the feet to be placed on the floor, promote higher user comfort levels (Fettweis et al., 2017; Mandal, 1994a). While the design of chair and desk sitting equipment generally imposes specific criteria, these are often extracted from laboratory settings; as such, the resulting sitting design testing equations used to test or match a specific design to an intended population do not generally take posture variability into account (Nadadur and Parkinson, 2013; Pheasant and Haslegrave, 2006). This creates a challenge in defining standards aimed at larger populations (Dainoff et al., 1994).

In accommodating larger populations, there is a tendency toward either stratified fixed designs, or adjustable designs (Underwood and Sims, 2019). On one side, even when adjustable designs are used, economic constraints from final production costs may jeopardize product viability. On the other side, accommodating less than 90% of the population can have an impact on sustainability and users’ safety (Nadadur and Parkinson, 2013; Pheasant and Haslegrave, 2006). Therefore, there is as yet no consensus among ergonomics specialists in recommending “proper” sitting designs that fit the majority of a given population, especially when considering office furniture that allows sitting, standing, and perching postures. The aim of the current paper is thus to assess sitting, perching and standing design equations using a recent anthropometric database of Chilean workers on the level of mismatch using available standards and products for three common sitting designs: a) traditional seating, with fixed desk and adjustable chair; b) traditional seating, with adjustable chair and desk; and c) hybrid sitting, with adjustable chair and desk. Additionally, the paper discusses hybrid sitting criteria and presents novel equations that can be applied in order to design and test accommodation in any population.