Hard Facts About Soft Machines

The Ergonomics Of Seating

Rani Lueder, Kageyu Noro, Rani Lueder, Kageyu Noro

• Publisher: CRC Press
• Year: 2020
• ISBN:
  9781000162929
• Edition: 1
• Topic: Technologie et ingénierie
• Subtopic: Santé et sécurité au travail

Although work furniture has had so much more attention recently there is a long way to go before this is translated into action in the wider world. Increased international concern for the health and safety of people at work is one of the driving forces behind this book.; The Science of Seating brings together researchers in ergonomics and posture with industrial designers, to review and assess the current state of chair design, with implications for cultural, behavioural and occupational aspects of health. The contributions are a significant step in the science of seating and should lead to a better understanding of the mechanics, dynamics and the effects of seating on the sitter.; They point to ways in which seats might become easier-to-use and adjust, offering both comfort and postural support without compromising freedom of movement: and in the not-too-distant furture, "the intelligent chair" will "remember" the sitter's preferences for position, cushiness and so on.; Topics covered include: Adjustability, Anthropometics, Posture, Back Pain, Biomechanics, Seat Pressure Distributions, School children, Special Needs of Users, Design Applications, Industry Perspectives, VDT Standards.; It is aimed at researchers and practising seating designers, ergonomists, design engineers, occupational health workers and physiotherapists and furniture manufacturers.

PART I

Introduction

Introduction

Kageyu Noro

Rani Lueder

The genesis of chairs and sitting is not known. A primitive version of the chair was discovered in the Toro ruins in Japan, circa 100 AD. During the Middle Ages, chairs were also used by high-level samurai who commanded field operations, and by priests during religious ceremonies.

Given this, it is surprising that chairs did not predominate until recently. In Japan, citizens began to use chairs during the Meiji era (1868–1912). In the West, seats were primarily used by royalty, and only gradually infiltrating the upper classes. Stewart (1986) describes a 1458 painting, in which robed justices of the French high court sprawled across the floor in session. Chairs became available to the emerging leisure classes during the reign of Louis XIV. ‘Commoners’ reconciled themselves to sitting on baskets, benches, and such.

Over time, technological innovations, first directed towards the achievement of specific ends, were incorporated into general purpose seating. For example, swivel-tilt seat capabilities were probably developed to facilitate navigation at sea. Today, the evolution of chair design is frequently driven by specialized requirements, such as to accommodate car driving or the disabilities.

Recent advances in the variety, complexity, and rapid pace of change of the materials and related sciences continue to accelerate innovations for all the various stages, associated with product design, manufacture, assessment and (ultimately) recycling. For example, intelligent computer systems, using computer-aided design and large-scale databases, are extending our ability to take advantage of the almost infinite variety of materials and composites now available to allow chairs to perform in new ways.

These advances continue to promise breakthroughs that allow seats to become more comfortable, yet easier to use and adjust. Some models can already flex in new ways, improving both postural support and freedom of movement. Cushioning composites may impart both firm support and ‘cushy’ comfort; features that have historically been at odds. Seat tensioning and contours may respond to the specific user, and absorb shocks. Chairs are increasingly becoming lighter, safer, stronger, and more stable, and at less cost and with less waste. Some chairs have become ‘intelligent’, and impart ‘memories’ to accommodate different users, tasks, and positions.^¶

These possibilities arrive not a moment too soon. Never before has there been such a recognition of the health consequences that may accompany seated work. A review of research over the last decade underscores the prevalence of physical discomforts experienced by computer users, as well as general office workers (Kroemer, 1988; Lueder, 1992; National Research Council, 1983; Sauter and Schleifer, 1991).^*

An increasing recognition of the health hazards incurred from lack of movement (Kilbom, 1987; Lueder, 1992) has accentuated concerns regarding the future impact of a technology-driven work processs that systematically reduces the potential for movement – to a greater extent every year.

In Japan, attention to seating has also been heightened by a shortfall of workers since 1990. Employers have become increasingly focused on how to attract good workers with ergonomic seating. Concurrently, greater employee expectations in ‘quality of work life’ extended to their expectations of seating comfort.

Within Japan, this demand became so acute that there arose a severe shortage of ergonomic seats during 1990 and 1991. It also provided the impetus for ‘The New Office Campaign’ project by Japan’s Ministry of International Trade and Industry, which accelerated corporate interest in ergonomic seating.

Zaken (a Japanese abbreviation of ‘Posture and Chair Study Committee’) was established in April of 1991 through financial support from the Japan Institute of Posture Research. The objectives of this committee are: to help organizations evaluate chairs; to provide users with information to improve their seated comfort; and, to promote an exchange of information between users and manufacturers.

This book is an outgrowth of this initiative. Originally based on the Proceedings of the 1989 Second International Symposium on the Science of Seating (Tokyo), it included fifteen papers from participants in seven countries^†. This was the first such symposium since the 1968 International Symposium on Sitting Posture, organized by Dr Etienne Grandjean, and held at the Swiss Federal Institute of Technology.

The Symposium’s objective was to address a few of the myriad of questions that remain regarding how to design ergonomic seats. Although a vast body of research on seating in recent years has greatly advanced our understanding, we are left with many gaps in how to address users’ discomforts and support their activities. The answers that we have gleaned have only underscored how much remains to be discovered.

•  Some issues are ignored, because little research attention has been directed to them. Such gaps may result, for example, from the difficulty of performing this research or an absence of sources of research funding. A sampling of such issues may include:

What is the relationship between comfort and physiologic well-being?

Do users have an intuitive sense of how they should sit?

How does posture affect our emotions and awareness?

How does one reconcile the various trade-offs implicit in designing a seat (e.g., the interaction of seat elements; the benefits of increasing support at the cost of promoting movement)?

How can tomorrow’s technologies, such as artificial intelligence, be applied to address seating requirements?

•  Some issues have ‘fallen through the cracks’, between the questions commonly investigated by ergonomists, and the answers needed by manufacturers and users. Such gaps may result, for example, from dogma (which besets all disciplines), resistance to paradigm shifts, or a limited understanding of the holistic interplay among seat considerations. A sampling of such subjects may include:

How does one begin to prioritize the costs and benefits associated with different seat features?

How does one compare highly adjustable seats with ‘dynamic’ versions, which ostensibly reduces the need for user intervention?

What kinds of chair do special populations need (e.g., pregnant women, school children)?

What user, task, and seat factors affect the kind and level of seat tention?

What are the implications of the wide variability in the population in the symmetry and shape of the spine (particularly the degree of lumbar lordosis), and other individual factors on seating design?

•  Frequently, research has been fragmented, and reflected national orientations. Correspondingly, our attention is often limited to the perspectives imparted by our society.

The contributions we offer here, all fully revised and updated, cannot provide conclusive answers to many of the broad spectrum of questions that need to be answered, but we believe that they can stimulate new areas of research, new design applications, and further the international exchange of information.

Kageyu Noro
and Rani Lueder

Editors
Tokyo/Los Angeles
August 1994

References

Kilbom, A., (1987), Short-and long-term effects of extreme physical inactivity: a brief review, in Knave, B., Wideback, P. G.,(eds.) Work with Display Units, Amsterdam, Elsevier Science, 219–28.

Kroemer, K. H. E., (1988), VDT work station design, in Helander, M. (ed.) Handbook of Human–Computer Interaction, Amsterdam: Elsevier Science, 521–39.

Lueder, R., (1992), Seating, posture, and ergonomics, in Sweere, J. (ed.) Chiropractic Family Practice: A clinical manual, Gaithersburg, Maryland: Aspen Publishing. Section 21.

National Research Council, (1983), Video displays, work and vision, Washington, DC: National Academy Press.

Sauter, S. L. and Schleifer, L. M., (1991), Work posture, workstation design, and musculoskeletal discomfort in a VDT data entry task, Human Factors, 33(2), 151–67.

Stewart, D., (1986), Modern designers still can’t make the perfect chair, Smithsonian. March, 97–105.

*  It should be noted that this attention is presently centered in the West. The frequency and types of physical problem of computer users in countries such as Japan are not well understood, but appear less pronounced at this time.

†  This symposium was jointly sponsored by Waseda University and the Japan Society for the Promotion of Science. It was conceived and organized by Professor Noro, with the collaboration of Rani Lueder, MS (US).

¶  My thanks to Mr Bill Marks, Dupont, for his insightful comments. (RL)

PART II

Adjustability

1

Sashaku : a user-oriented approach for seating

K. Noro

Creating an information loop for seating

Introduction

This chapter describes a model for chair adjustability. First, sashaku, as used traditionally in Japan, is introduced and sashaku for workstations using VDT (called VDT sashaku) is described. Second a parametric model which includes VDT sashaku is introduced and ‘Foot overplus posture’ and ‘Foot float posture’ are defined. Third, the mathematical interpretation of those postures is described. Finally, as only adjustment by anthropometric dimensions is known to date, a new adjustment method is proposed.

Information required by users to adjust their chairs

Chair guidelines are available from many sources; These include the Labour Standards Bureau, Ministry of Japan (1985), Human Factors Society of the United States (1988), Personnel Department of Waseda University (1987), and other organizations. These guidelines often refer to the need for adjustability. The Occu...