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 Table of Contents  
Year : 2019  |  Volume : 2  |  Issue : 2  |  Page : 8-12

1.1 Basic Concepts, Definitions and Models

Department of Health Sciences and Health Policy, University of Lucerne, Lucerne; Swiss Paraplegic Research; ICF Research Branch, A Cooperation Partner within the WHO Collaborating Centre for the Family of International Classifications in Germany (at DIMDI), Nottwil, Switzerland

Date of Web Publication11-Jun-2019

Correspondence Address:
Prof. Gerold Stucki
Department of Health Sciences and Health Policy, University of Lucerne, Lucerne, Switzerland. Swiss Paraplegic Research, Nottwil, Switzerland. ICF Research Branch, a Cooperation Partner within the WHO Collaborating Centre for the Family of International Classifications in Germany (at DIMDI), Nottwil
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jisprm.jisprm_5_19

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How to cite this article:
Stucki G, Bickenbach J. 1.1 Basic Concepts, Definitions and Models. J Int Soc Phys Rehabil Med 2019;2, Suppl S1:8-12

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Stucki G, Bickenbach J. 1.1 Basic Concepts, Definitions and Models. J Int Soc Phys Rehabil Med [serial online] 2019 [cited 2019 Aug 20];2, Suppl S1:8-12. Available from: http://www.jisprm.org/text.asp?2019/2/2/8/259366

  Introduction Top

In the groundbreaking 1978 World Health Organization's (WHO's) Declaration of Alma Ata,[1] four healthcare strategies were recognized: promotion, prevention, cure or treatment, and rehabilitation. Of these, the rehabilitative health strategy has received the least attention, both in the public's mind and among health policy makers. However, this is changing. As the world's population is rapidly aging because of better health care and increased survival,[2] and as noncommunicable chronic diseases are becoming the primary source of mortality,[3] people are living longer but with considerably more disability.

In the future, in addition to maintaining the effectiveness of prevention and continuing progress toward cures, the social challenge will be to respond effectively to this rapidly increasing prevalence of disability. This is where rehabilitation and Physical and Rehabilitation Medicine (PRM) come in.

The focus of rehabilitation has always been on improving the lives of people who are living with a health condition, whether it is acute, chronic or progressively debilitating. In addition, the objective of rehabilitation interventions in general, and PRM specifically, is to optimize people's intrinsic health capacity, including strengthening psychological resources, facilitating the person's immediate environment and so translating these improvements in a better lived experience of their state of health.[4],[5],[6] As the WHO has recently concluded, demographic and epidemiological trends are in the process of transforming rehabilitation into the key health strategy of the 21st century.[7],[8]

Understanding this fundamental healthcare transition – and developing both research agenda and the clinical tools and policy strategies to respond to it – has required some important conceptual shifts, primarily in the notion of functioning that is the focus of rehabilitation interventions and in the rationale of rehabilitation as a health strategy. Although rehabilitation practitioners intuitively understood the notion of functioning, the first attempt to formally and scientifically conceptualize it was WHO's 2001 International Classification of Functioning, Disability and Health (ICF).[9]

  The International Classification of Functioning, Disability and Health: Functioning and Rehabilitation Top

Since its endorsement, the ICF has proven to be a robust and widely applicable conceptual framework for documenting functioning information for rehabilitation and more generally, the international common language of functioning and disability across the spectrum of the health sciences.[10],[11] The ICF is a conceptual framework and practical lens for describing the lived experience of health in a meaningful and useful manner. It has provided the scientific foundations for rehabilitation practitioners aiming to optimize functioning, for policy makers shaping health systems to effectively respond to the functioning needs of the population, and finally, for researchers seeking to explain functioning and disability and their determinants.[12] In the end, the ICF provides the basis for understanding the on-going significance of rehabilitation as a health strategy.[6]

In the ICF, the notion of functioning denotes the complete set of human body functions and structures, as well as all human behaviors, actions, tasks and social roles, simple to complex. Functioning, in other words, is comprised of all the functions of the human body and mind as well as the actions that people perform in their real-life situations. In the ICF classification, functioning is operationalized in terms of functioning domains, and these are partitioned into the dimensions of body functions and structures, activities, and participation. These are further organized in a standard genus-specific classification structure in terms of a spectrum from simple to complex: in other words, from basic body functions such as seeing, hearing and doing housework to highly complex and socially determined areas of participation such as engaging in family relationships, working, and participating in community life.

Moreover, each domain of functioning is itself understood as a continuum from complete functioning, to mild and moderate problems with functioning, to complete loss or absence of functioning. As a classification, the ICF is designed to be comprehensive yet flexible, providing the clinician or researcher with a complete international standard language of functioning while at the same time allowing for expansion by the specification of additional domains as required.

Since each of the ICF functioning domains is understood on a continuum, from total absence of functioning to full functioning, at every point in time, everyone's level of functioning in every domain can in principle be described, and depending on the intended research or clinical purpose, a slice-in-time (a cross-section) comprehensive portrait of a person's overall functioning can also be described. In addition, as a person's overall functioning varies over the lifespan, the ICF provides a reference language for longitudinal description as well. In general, while functioning increases during a person's early years, it tends to decrease with the gradual occurrence of injuries, diseases and other health conditions, major and minor, and with the process of aging. This suggests that, in terms of functioning, it is possible to create functioning trajectories both at individual and through aggregation at population level that have important research and policy planning applications.

In the ICF, the notion of disability is derived from that of functioning, in the sense that a domain of disability is some level of less-than-optimal functioning in that domain. In the case of body functions and structures, these limitations are more commonly called impairments. Significantly, the ICF does not set out for each domain where, on the continuum of extent of functioning, the threshold between disability and nondisability lies. The continuum is a continuum of functioning, and disability is some, undefined, range of that continuum, intuitively at the problematic end of total loss or mild or moderate loss. The ICF does not determine where the threshold line is since that decision needs to be empirically based and fit for purpose. The ICF is a classification, not an assessment instrument although it forms the classificatory framework for all assessment tools purporting to measure extent of functioning by domain.

  International Classification of Functioning, Disability and Health and the Model of Functioning and Disability Top

The ICF notion of functioning is at the heart of a conceptual model that defines the full ICF conceptualization of functioning, disability and health [Figure 1]. Termed the “biopsychosocial” model, it is interactional in the sense that it identifies two essential classes of determinants of levels of functioning – namely health conditions and contextual factors. Health conditions are broadly characterized as diseases (acute or chronic), disorders, injuries, trauma, or any other “natural” circumstance such as pregnancy, aging, stress, congenital anomaly, or genetic predisposition. Contextual factors include both environmental and personal factors. The former, which include all aspects of the person's environment, may have a positive or negative impact on functioning. This ranges from climate, air quality, and other physical conditions, to the human-built environment and products, human relationships, attitudes, and complex services, systems and policies across several social domains (e.g., housing, communications, transportation, media, economic, social security, health, education, labor, and political). Personal factors such as coping style and a sense of optimism have been left undeveloped in the ICF.
Figure 1: The ICF framework

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The ICF model characterizes functioning as the outcome of complex interactions between the health state of an individual – determined by health conditions and body functions and structures – and the physical, interpersonal, and social environment. Implicit in this model is the notion of universality − that functioning and disability are universally applicable to all human beings. This means that the ICF is a universal health classification, grounded in the concept of functioning, that is applicable to human beings as such, not to some specific subgroup of people (e.g., “the disabled”).

The ICF is also etiologically neutral in the sense that it does not imply that the relationships between dimensions are either causal or linear. Specific health conditions are not presumed to uniquely cause specific impairments or problems in activities and participation domains. No assumption is made that some problem in a functioning domain is always or even more likely to be caused by a specific health condition.

  Capacity and Performance Top

At the heart of the ICF conceptual framework is a fundamental distinction that transforms the interactional or “person-environment” model of functioning into a powerful scientific and clinical tool. This is the distinction between capacity and performance. Formally, this distinction is represented by the two severity qualifiers found in the activities and participation classification, but its significance goes to the heart of the ICF model.[13]

The ICF notion of capacity is a theoretical construct that in practice typically is a clinical inference based on information about a person's underlying health conditions and observations of what people can do given impairments and their severity. Capacity constitutes the intrinsic health state of a person, wholly independent of the environment. Capacity is comprised of all physiological, psychological functions, and anatomical structures of the body, and by virtue of these functions in various combinations, results in the “capacity” of the person to perform all human activities, from the very simple to the very complex. A person's capacity is independent of the external, environmental determinants that may facilitate or hinder the actual execution of these activities. Inasmuch as people do not conduct actions outside of an environment, capacity is invariably the result of an inference based on observations – including from clinical standardized tests – of what the person can do.

Performance, on the other hand, describes the extent to which a person actually performs or executes activities, simple or complex, fully in the context of, and in interaction with, all aspects of that person's environment. Performance can be understood both quantitatively – the extent of performance against some standard – and qualitatively – the nature or characteristics of the performance, e.g., too slow, out of sequence, or erratic.

Unlike capacity, performance is not a theoretical construct, but a full factual description of what actually takes place. The nature and extent of a person's performance in some domain will always be a function of the level of capacity in that domain but also will depend on features of the person's environment, as shaped by what people do in their daily lives and by extension, what complex social roles they perform (be it spouse, father, student, or employee). Environmental factors may make it harder to perform activities (e.g., because of poor air quality, inaccessible and nonaccommodating physical environments, or stigma and discrimination, and social exclusion) or make it easier to perform activities (e.g., because of assistive technology, accessible buildings, supportive attitudes, and social arrangements). In short, the intrinsic capacity of a person to read a page of print may be limited by an impairment of visual acuity; yet with reading glasses, an environmental facilitator, the performance of reading may no longer be restricted.

  International Classification of Functioning, Disability and Health and the Lived Experience of Health Top

Keeping this distinction in mind, it is important to notice that, from the perspective of rehabilitation, the ICF provides the language for the description of how our health state plays out in the real world, where our intrinsic health state or capacity has an impact, but so too does many environmental factors. This has been termed the “lived experience of health” – not merely our biological state of health, but health as it is lived, fully within the context of our lives and environments. It is the lived experience of health – functioning as it plays out in our lives – that is the focus of the rehabilitation health strategy, and optimizing this experience is the objective of rehabilitation interventions.

As a scientific tool, the ICF provides an international standard language that ensures comparability across data collecting and reporting methods, across health and health-related disciplines, across settings and countries. Information about functioning across domains is the essential information for rehabilitation practice. Collecting functioning information about relatively simple activities such as grasping, standing or walking might require nothing more than direct observation and standardize tests. Information about the performance of complex activities, such as making friends, going to school, or participating in cultural activities, is far more intricate, socially constructed, and difficult to collect, and here, a reliance on self-report questions and interviews is probably unavoidable since direct observation would be wholly impractical. All of this information, however, is relevant to the experience of living with a health condition.

  International Classification of Functioning, Disability and Health: Disability and Health Top

The ICF notion of functioning helps us to characterize the domain and rationale of rehabilitation. It also offers a practical conceptualization of disability that not only fits with rehabilitation practice but also avoids the pitfalls and misunderstanding associated with this contentious term. In terms of performance of activities in real-life situations, ICF notion of disability is not a theoretical or political issue, it is a matter of how one gets along in one's actual world. Disability is not identical to biological health, but biological health is a key determinant of disability. Moreover, disability is very much a matter of the environmental barriers and facilitators that a person experiences in real-life situations. Many of these barriers are artificial and morally objectionable (stigma, negative stereotypes, discrimination), others can be remedied by social interventions (providing accessible public space, and employment accommodations) and still others can be compensated by health and social interventions. Finally, the ICF makes it clear that disability is a health issue since disability does not occur without an underlying health problem or associated limitations in capacity; but at the same time, disability is also very much a matter of how a person's physical and social environments impact on their lives.

While the ICF does not explicitly define or provide a theory of health, it does something more useful: it provides us with a practical operationalization of health. The health of an individual, and by extension a population, can be understood as the actual experience of living with a health condition, and that experience can be operationalized in terms of the two constructs of functioning, the pure biomedical, expressed in terms of the functions and structures of the body, and the resulting intrinsic capacity of a person to perform, as well as the actual performance of those activities in interaction with features of the person's physical, human-built, and social environment.

The pragmatic test of the validity of an operationalization of health is that it explains why health matters to us and thus why we spend social resources designing health systems that are responsive to the health needs of a population. The ICF operationalization clearly passes this test: when we experience pain, anxiety, weakness, tight joints, or skins sores and the rest, it impacts our lives. We do not seek healthcare because we become aware of diagnostic signs and symptoms in themselves; rather, we experience impairments that interfere with what we want to do. We notice changes, not only in what we can do but how: we find it difficult to climb stairs, walk as far as we used to, clean or dress themselves as quickly as we need to, read a book, make and keep friends, do all the housework we have to, or perform our job to expectations. When these limitations are linked to how our bodies and minds function, health matters to us.

  International Classification of Functioning, Disability and Health Functioning and Prm Top

The ICF and specifically the notion of functioning offers a representation of how PRM doctors themselves organize rehabilitation.[4],[13] The ICF model and classification framework includes components familiar to PRM specialists although perhaps not in the terms the ICF uses. PRM practitioners daily encounter patients with perceived restrictions in the performance in important life activities such as work, recreation, moving from place to place, and independence in self-care. Presented with these complaints, they seek to determine the impairments that contribute to the restrictions and seek information regarding physiological, pathophysiological, and psychological body functions and anatomic structures, and their impact on the ability of the patient to perform life activities.

Typically, the PRM specialist first focuses on the patient's capacity to perform activities in a neutral or clinical environment and collect information regarding the health conditions and impairments associated with these limitations. PRM specialists are well aware of the impact of physical barriers, both natural and person-made, social attitudes and other social restrictions, and how these seriously impact the successful performance of life activities of those with limitations in functioning. They also recognize the impact of life experiences, age, and overall approaches to life on the extent of a person's recovery of functioning. In short, the PRM specialist takes into account all of the ICF components when developing, usually with the patient and other rehabilitation professionals, the treatment plan designed to optimize patient functioning and enhancing their performance of activities in fundamental life experiences.

As the ICF suggests, PRM interventions seek to optimize functioning through treatment of both the intrinsic health aspects of functioning, or capacity, and by means of enabling changes to the patient's environment to optimize the actual performance. Ultimately, PRM's goal is to translate a person's intrinsic capacity or biological health into actual performance in interaction with the environment and personal factors, that is, the person's lived health. In short for rehabilitation in general and PRM in particular, functioning is the starting point of clinical assessment, the anticipated outcome of intervention, and the basis for quality management of interventions.

The future challenge of rehabilitation as the key health strategy of this century and PRM in particular as “the medicine of functioning” is to strengthen rehabilitation services within the health system. In the social and political context of increased burden of care, increased costs of health and social care and greater social expectations of good health will be needed to create complex intervention strategies that respond to the entire experience of functioning and disability, involving several, diverse, domains of functioning. Equally important will be the evaluation of the outcomes of these interventions, to ensure quality and contain costs. The ICF is fundamental to both of these endeavors and can further serve as the basis for the classification of rehabilitation services, the conceptualization and organization of functioning and rehabilitation research, the role of rehabilitation as a health strategy, and the basis for an information reference system for collecting functioning information relevant, not merely to rehabilitation service delivery and assessment but across the healthcare system.

  Conclusion Top

The WHO 2001 International ICF provides a key concept, named functioning, that not only accounts for the primary aim of the PRM specialist but also helps to explain why rehabilitation will become increasingly important in the future. Functioning in the ICF denotes the complete set of human body functions and structures, as well as all human behaviors, actions, tasks, and social roles, from the very simple (looking, housework) to the increasingly more complex and socially constructed (engaging in family life, education, and work). Rehabilitation as a health strategy is primary aimed at optimizing a person's functioning that has been compromised by an underlying, often chronic health condition. The ICF provides a distinction between the underlying capacity to perform actions – capacity – and the actual performance of the action, in light of both the level of capacity and environmental facilitators and barriers. The PRM specialist will focus on the patient's capacity to perform activities in a neutral or clinical environment, be aware of the impact of physical barriers, both natural and person-made, social attitudes and other social restrictions, and through planned interventions, seek to optimize the patient's performance. Given population aging and increasing chronic, noncommunicable diseases, an increase in population prevalence of disability is expected. Although the health strategies of prevention, promotion, and cure will always be important, the role of rehabilitation in optimizing functioning will likely become increasingly key to the effectiveness of health systems.

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Conflicts of interest

There are no conflicts of interest.

  References Top

World Health Organization. Declaration of Alma-Ata. International Conference on Primary Health Care, Alma-Ata, USSR, 6–12 September 1978. World Health Organization; 1978. Available from: http://www.who.int/publications/almaata_declaration_en.pdf?ua=1. [Last accessed on 2019 Feb 28].  Back to cited text no. 1
World Health Organization. World Report on Ageing and Health. Geneva: World Health Organization; 2015.  Back to cited text no. 2
World Health Organization. Global Status Report on Noncommunicable Diseases, 2014. Geneva: World Health Organization; 2014. Available from: http://www.apps.who.int/iris/bitstream/10665/148114/1/9789241564854_eng.pdf?ua=1. [Last accessed on 2019 Feb 28].  Back to cited text no. 3
Gutenbrunner C, Meyer T, Melvin J, Stucki G. Towards a conceptual description of physical and rehabilitation medicine. J Rehabil Med 2011;43:760-4.  Back to cited text no. 4
Meyer T, Gutenbrunner C, Bickenbach J, Cieza A, Melvin J, Stucki G, et al. Towards a conceptual description of rehabilitation as a health strategy. J Rehabil Med 2011;43:765-9.  Back to cited text no. 5
Stucki G, Bickenbach J, Melvin J. Strengthening rehabilitation in health systems worldwide by integrating information on functioning in national health information systems. Am J Phys Med Rehabil 2017;96:677-81.  Back to cited text no. 6
World Health Organization. Rehabilitation: Key for Health in the 21st Strategy. World Health Organization; 2017 Available from: http://www.who.int/disabilities/care/KeyForHealth21stCentury.pdf?ua=1. [Last accessed on 2018 Jan 22].  Back to cited text no. 7
Stucki G, Bickenbach J, Gutenbrunner C, Melvin J. Rehabilitation: The health strategy of the 21st century. J Rehabil Med 2018;50:309-16.  Back to cited text no. 8
World Health Organization. The International Classification of Functioning, Disability and Health (ICF). Geneva: World Health Organization; 2001.  Back to cited text no. 9
Stucki G, Cieza A, Melvin J. The international classification of functioning, disability and health (ICF): A unifying model for the conceptual description of the rehabilitation strategy. J Rehabil Med 2007;39:279-85.  Back to cited text no. 10
Stucki G, Rubinelli S, Reinhardt JD, Bickenbach JE. Towards a common understanding of the health sciences. Gesundheitswesen 2016;78:e80-4.  Back to cited text no. 11
Stucki G. Olle Höök Lectureship 2015: The World Health Organization's paradigm shift and implementation of the International Classification of Functioning, Disability and Health in Rehabilitation. J Rehabil Med 2016;48:486-93.  Back to cited text no. 12
Stucki G, Bickenbach J, Selb M, Melvin J. The international classification of functioning, disability and health. In: Frontera W, editors. DeLisa's Physical Medicine and Rehabilitation, Principles and Practice. 6th ed. Philadelphia: Wolters Kluwer.  Back to cited text no. 13


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