123
8
Driving Posture and
Healthy Design
Diane Elizabeth Gyi
Loughborough University, UK
8.1 INTRODUCTION
So, why is driving sometimes a pain? Driving as a task involves prolonged sit-
ting, a static and constrained posture, vibration and muscular effort (from steering,
braking, reversing etc.), all loading the spine to varying degrees and any of which
individually could lead to musculoskeletal symptoms. For successful vehicle seat
design and good ergonomics, some knowledge of the anatomy, physiology and bio-
mechanics of the human seated posture is required. In the view of the author, it is
important to understand ‘the human body’ and the impact that design decisions
will have on behaviours that affect driver comfort and health. As a contribution
to this goal, this chapter provides an overview of ‘the basicsof the human seated
posture, why driving is a pain, and principles of good ergonomics in the driving
task. Although it mainly focuses on car driving, some items are of relevance to
other vehicles.
8.2 THE SEATED POSTURE AND DRIVING
Traditional human factors texts clearly document the anatomical and physiological
factors involved in sitting. The efciency of any posture from a simple biomechan-
ics viewpoint can be determined by the degree to which it loads the skeleton and
postural muscles. Postural stress is a result of gravitational (and other forces) acting
CONTENTS
8.1 Introduction ..................................................................................................123
8.2 The Seated Posture and Driving ...................................................................123
8.3 Driving and Musculoskeletal Health ............................................................126
8.4 The Older Driver ........................................................................................... 127
8.5 Design Ergonomics, Comfort and Driving ...................................................128
8.6 Summary ......................................................................................................129
Acknowledgment ................................................................................................... 129
References ..............................................................................................................130
124 Automotive Ergonomics: Driver–Vehicle Interaction
on the body and the forces required by muscle activity to maintain any particu-
lar posture (Troup, 1978). In fact, the muscular effort required for sitting is greater
than that for standing as shown by Nachemson, Andersson, and Schultz (1986) in
an experimental study using electromyography. In another early study, Andersson et
al. (1974), using a transducer mounted in a hypodermic needle also found that intra-
discal pressure in the spine was 40% higher in sitting than in standing. These early
studies have implications for the modern driving task.
When changing from standing to a seated posture, backwards rotation of the pel-
vis attens the curve of the lumbar spine and changes its shape (Figure8.1). This
increases pressure on the posterior part of the inter-vertebral discs and within the
nucleus itself making it vulnerable to damage (Figure8.2).
The lumbar curve could be actively maintained by contraction of the muscles in
the back (e.g., latissimus dorsi and the sacrospinalis) but this is very tiring. So, when
sitting on a seat with a backrest, the pelvis will rotate backwards until the persons
back comes into contact with the support. In a well designed seat, the weight of the
trunk is taken by the backrest, the muscles are then relaxed and the curve of the
lumbar spine is supported. Conversely, in a poorly designed seat, the lumbar curve is
attened (a loss of lordosis) increasing pressure within the discs (Figure8.2), strain-
ing the spinal ligaments and gluteal muscles and increasing the thoracic c-shaped
curve in the upper spine (increase in kyphosis). In a car, this slouched posture could
be exacerbated by design elements, such as low headroom space or a seat cushion
length, which is too long. So, although this slouching reduces the need for muscular
effort in the trunk, it increases disc loading.
Lumbar
curve
Backw ards
rotation
Femur
Femur
Standing posture
Seated posture
Pelvis
Pelvis
FIGURE 8.1 Rotation of the pelvis when changing from standing to a seated posture.

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