PRINCIPLE 1. Equitable Use
6.1 INTRODUCTION
6 Wheelchair Ambulation:
Biomechanics and Ergonomic Considerations *
Lucas H. V. van der Woude, Sonja de Groot, Dirkjan H. E. J. Veeger, Stefan van Drongelen, and Thomas W. J. Janssen
CONTENTS
States and Europe may be extrapolated to, respectively, a rough 2.6 and 3.9 million—on average elderly—people. The majority of these people will use a or assistant-propelled manual wheelchair. This chapter will focus on the self-propelled wheelchair. By nature, the use of the upper-body and arms, a limited (age-related) fi tness, and the impairment itself, a wheelchair-confi ned lifestyle will hamper individual mobility and participation. Simmons et al. [152] conclude their study “Wheelchairs as mobility restraints…” with: “Improving wheelchair skills with targeted intervention programs, along with making wheelchairs more ‘user friendly’ … could result in more wheelchair propulsion with resultant improve-ments in the resident’s independence, freedom of movement and quality of life.”
This statement, evidently coming from the heart, seemingly sets the scene for a straightforward research agenda. However, this puts the complexity of wheeled mobility into a somewhat too simplifi ed perspective. Wheeled mobility is indeed a complex issue both in theory and practice and its study requires a systematic approach that can do well with a clear conceptual framework.
Although mobility is an essential element in daily life, its importance is usually only then recognized when it is for some reason (temporarily) limited, as is the case in those who are wheelchair dependent. Mobility is a multilayered concept. One can speak of joint mobility, but also of mobility as an element of daily activities and of course within the context of participation we use the term mobility (social range of action, freedom of movement). All three mentioned connotations of mobility substantiate the main objectives of an integral (often lifelong) rehabilitation process. As such, mobility can be positioned at each of the three domains of functioning within the International Classifi cation of Functioning, Disability, and Health (ICF) model [198]. This model is exemplifi ed for (the rehabilitation of) persons with a spinal cord injury (SCI) in Figure 6.1. It is in many ways the conceptual starting point of the different aspects
ICF, 2001
Lesion characteristics secondary impairments,
comorbidity
Hand and arm functionality, basic and complex (wheelchair)
skills, ADL and functional independence Cardiovascular and
respiratory functions; motor, autonomic and sensory
functions
Work, school, sports, family,
friends
Rehabilitation, strategy, treatment intensity and form, exercise, training
Age, cultural background, socioeconomic
status, fitness, gender
FIGURE 6.1 ICF model, as applied to persons with a SCI. (From WHO, International Classifi cation of Functioning, Disability and Health, Geneva, World Health Organisation, 2001. With permission.)
of (biomechanics and ergonomics) research in rehabilitation and in the related issues of restoration of (wheeled) mobility, activities of daily living, and sports for those with a disability.
Within the context of a chronic impairment, rehabilitation focuses on restoration of mobility in its widest sense. Continuing to be a mobile individual and having an optimal social and physical range of action are key objectives in rehabilitation of those with lower-limb impairments. In today’s rehabilitation fi eld, this goes beyond the mere restoration, compensation, and (technology-based) adaptation of sensomotor function, functional capacity, activities of daily living (ADL), functional capacity, and independence. A physically active lifestyle, including sports, during and after reha-bilitation is becoming an increasingly important issue on the rehareha-bilitation research agenda [37,58,65,138]. Understanding the underlying mechanisms and processes of adaptation and/or the compensation of function and functioning, with or without the use of optimal assistive technology, is the core of biomechanics and ergonomics-based rehabilitation research and knowledge. The underlying multicausal and multilayered rehabilitation paradigm is “To restore function and functionality, and to stimulate optimal activity and participation.”
Wheelchairs are assistive devices crucial for daily functioning of those with lower-limb impairments. The interaction between assistive technology and the (disabled) human system is complex by defi nition and requires a detailed research approach from a combined ergonomics and biophysical rehabilitation perspective.
As an example, the long-term use of assistive technology* and its consequences on the musculoskeletal system have become an important issue in manual wheel-chair research, where the continued imbalance between the task stresses, physical strain, and overall mechanical and physiological work capacity leads to overuse injuries in the upper extremities [13]. In general when assistive technology for (wheeled) mobility and the biological system do not optimally match and func-tion, a debilitative cycle may start that can lead to an inactive lifestyle [88,98], leading to disuse and even nonuse of assistive technology, and consequently to an increased risk for secondary health complications. This stresses the impor-tant preventive role of an integrative ergonomics approach within the fi eld of rehabilitation and assistive technology, as is clearly exemplifi ed in the Human-Activity-Assistive-Technology (HAAT) model of Cook and Hussey [32] (Figure 6.2). This model emphasized the, not too often explicitly recognized in the sci-entifi c literature [25,103,111,116,151,155,201], ergonomics basis of assistive and rehabilitation technology, and of the rehabilitation approach in a broader context [92,111,121].
Optimal functioning of the human movement system in the context of (wheeled) mobility restoration can be conceptualized as a continued effort of the biological system to maintain a proper balance between external stresses, internal strain, and the (physical) work capacity. As such, the stress–strain–work capacity model of
* For example, “…a broad range of devices, services, strategies and practices that are conceived and applied to ameliorate the problems faced by individuals who have disabilities…”
van Dijk et al. [57] expresses the interdependency of these domains in a fl ow diagram (Figure 6.3), applicable also in rehabilitation and indeed useful in the context of assistive technology research and practice. “Overall work capacity” must be inter-preted here as the total sum of maximum physical, cognitive, mental, and social aspects of the human capacity in every day functioning.
Although the individual is by defi nition viewed as a biopsychosocial entity, the issues addressed in the following will primarily have a biophysical perspective.
Context
Human
Human–technology interface
Processor
Environmental interface Activity
output Activity
Assistive technology
FIGURE 6.2 The HAAT model. (From Cook, A. and Hussey, S., Assistive Technologies:
Principles and Practice, Mosby Year Book Inc., St Louis, MO, 2002. With permission.)
Stress:
External load and personal
control
Strain:
Short-term effects
strain
Strain: Long- term and permanent
effects
Overall work capacity
FIGURE 6.3 The stress–strain–work capacity model of van Dijk et al. (From van Dijk et al., TSG, 68, 3, 1990. With permission.)
From an ergonomics perspective, the external stresses in the context of wheeled mobility for instance are a consequence of (1) the combined effect of mechanical wheelchair characteristics and environmental conditions and (2) from the fi ne-tuning of the wheelchair–user interface [6,112,120,160,175]. Beyond that, (3) physical work capacity is defi ned by the overall functional capacity of the cardiovascular, respira-tory, and the neuromuscular systems, and clearly is dependent on such individual characteristics as impairment, age, gender, training status, genetics, and expertise.
In manual wheelchair use, the optimal level of, and interplay among, these three dif-ferent domains are crucial for a maximum range of mobility, as it would be for any other assistive devices for ambulation, as indeed can be represented with Cook and Hussey’s “ergonomics” model for assistive technology [31] (Figure 6.2).
Having the different conceptual models at the background of our mind, the current chapter will address important practical and research issues of a mobile and physically active lifestyle for those in rehabilitation, especially in those who are wheelchair dependent. In addition, it will provide a framework of biophysical and ergonomics considerations for manual wheelchair practice and research.