1. Top of page
  2. Introduction
  3. Major Disability Models
  4. The International Classification of Functioning, Disability, and Health (ICF)
  5. Disability and Participation Concepts Viewed in a Sociocultural Context
  6. Exercise and Physical Activity Interventions Within a Disablement Perspective

Walking across a room, opening jars, and performing personal and social role activities are often painful and difficult for people with chronic arthritis conditions. Indeed, arthritis is the leading cause of activity limitations and disability among adults (1–4). Exercise and physical activity are promoted as effective, noninvasive intervention strategies to enhance health and function among people with arthritis. There are, however, some important questions that need to be considered when developing and evaluating exercise and physical activity intervention programs. What are the desired outcomes of exercise and physical activity? Is the primary outcome of interest to increase strength, function, or performance of personal and social role activities? What factors and processes are related to performance of basic tasks, such as walking, or more complex tasks, such as participating in social role activities, and how do exercise and physical activity influence task performance? This article aims to provide the reader with a conceptual foundation to facilitate discussions of the role of exercise and physical activity in health promotion and the prevention of disability for individuals with arthritis. To do so, we focus on several tasks: Presenting a review of some of contemporary definitions of disability; discussing these definitions in the context of several major disability models; and discussing the implications of these models for exercise interventions designed to promote health and prevent disability of individuals with arthritis.

Major Disability Models

  1. Top of page
  2. Introduction
  3. Major Disability Models
  4. The International Classification of Functioning, Disability, and Health (ICF)
  5. Disability and Participation Concepts Viewed in a Sociocultural Context
  6. Exercise and Physical Activity Interventions Within a Disablement Perspective

There are several schools of thought that have defined disability and related concepts. We will focus our discussion on the Disablement Model developed by Nagi (5), the International Classification of Impairments, Disabilities and Handicaps (ICIDH-1) (6), and its current revision, International Classification of Functioning, Disability and Health (ICF) (7). The Nagi Disablement Model, ICIDH, and ICF frameworks have in common the view that overall disablement represents a series of related concepts that describe the consequences or impact of a health condition like arthritis on a person's body, on a person's activities, and on the wider participation of that person in society. We will compare and contrast the 2 major models along with their major derivatives and explore implications for exercise interventions.

Saad Nagi's concept of disability.

According to the conceptual framework of disability developed by sociologist Saad Nagi (5), disability is the expression of a physical or a mental limitation in a social context. Nagi specifically views the concept of disability as representing the gap between a person's capabilities and the demands created by the social and physical environment—a product of the interaction of the individual with the environment (5, 8, 9). This is a fundamental distinction of critical importance to scholarly discussion and research related to disability phenomena.

According to Nagi's own words (9):

[Disability is a] limitation in performing socially defined roles and tasks expected of an individual within a sociocultural and physical environment. These roles and tasks are organized in spheres of life activities such as those of the family or other interpersonal relations; work, employment, and other economic pursuits; and education, recreation, and self-care. Not all impairments or functional limitations precipitate disability, and similar patterns of disability may result from different types of impairments and limitations in function. Furthermore, identical types of impairments and similar functional limitations may result in different patterns of disability. Several other factors contribute to shaping the dimensions and severity of disability. These include (a) the individual's definition of the situation and reactions, which at times compound the limitations; (b) the definition of the situation by others, and their reactions and expectations—especially those who are significant in the lives of the person with the disabling condition (e.g., family members, friends and associates, employers and co-workers, and organizations and professions that provide services and benefits); and (c) characteristics of the environment and the degree to which it is free from, or encumbered with, physical and sociocultural barriers.

Nagi's definition stipulates that a disability may or may not result from the interaction of an individual's physical or mental limitations with the social and physical factors in the individual's environment. In Nagi's terms, for an individual with arthritis, his or her physical and mental limitations would not invariably lead to a disability. Furthermore, similar patterns of disability may result from different types of health conditions, and identical arthritic disease patterns may result in different patterns of disability.

Nagi's Disablement Model has its origins in the early 1960s. As part of a study for the US Social Security Administration, Nagi constructed a framework that differentiated disability from 3 other distinct, yet interrelated, concepts: active pathology, impairment, and functional limitation (10). This conceptual framework has come to be referred to as Nagi's Disablement Model.

For Nagi, active pathology involves the interruption of normal cellular processes and the simultaneous homeostatic efforts of the organism to regain a normal state. He notes that active pathology can result from infection, trauma, metabolic imbalance, degenerative disease processes, or other etiologies. Examples of active pathology are the cellular disturbances consistent with the onset of disease processes such as osteoarthritis, cardiomyopathy, and cerebrovascular accidents.

For Nagi, impairment refers to a loss or abnormality at the tissue, organ, and body system level. Active pathology usually results in some type of impairment, but not all impairments are associated with active pathology (e.g., congenital loss or residual impairments resulting from trauma). Impairments can occur in the primary locale of the underlying pathology (e.g., muscle weakness around an osteoarthritic knee joint), but they may also occur in secondary locales (e.g., cardiopulmonary deconditioning secondary to inactivity).

To describe the distinct consequences of pathology at the level of the individual, Nagi uses the term functional limitations that represent restrictions in the basic performance of the person. An example of basic functional limitations that might result from arthritis could include limitations in the performance of locomotor tasks, such as the person's gait, and basic mobility, such as transfers. Such functional limitations might or might not be related to specific impairments secondary to arthritis and thus are seen as distinct from organ or body system disturbances.

An example will illustrate the distinctions being drawn between the various concepts within Nagi's Disablement Model. Two patients with rheumatoid arthritis may present with a very similar clinical profile. Both may have moderate impairments, such as restricted range of motion and muscle weakness. Their pattern of function may also be similar with a slow, painful gait and difficulty grasping objects. Their disability profile, however, may be radically different. One individual may restrict or eliminate his or her outside activities, require help with all self-care activities, spend most of the time indoors watching television, and is unemployed and depressed. The other may fully engage in his or her social life, receive some assistance from a spouse in performing daily activities when needed, is driven to work, and through workplace modification is able to maintain full time employment. The 2 patients present very different disability profiles yet have very similar underlying pathology, impairment, and functional limitation profiles.

Elaboration of Nagi's basic disablement model.

In their work on the disablement process, Verbrugge and Jette (11) maintained the original Nagi concepts but extended his model by specifying dimensions of disability and including in the model relationships among sociocultural factors (e.g., physical or social environments) and personal factors (e.g., lifestyle behaviors and attitudes) with the core disablement concepts. Verbrugge and Jette's elaboration of Nagi's model was an attempt to attain a full sociomedical framework of disablement that they defined as the “impact that chronic and acute conditions have on functioning of specific body systems and on people's abilities to act in necessary, usual, expected and personally desired ways in their society” (11). The term process is described as “the dynamics of disablement, that is, the trajectory of functional consequences over time and the factors that affect their direction, pace, and pattern of change” (11).

Nagi's definition of disability and the elaboration by Verbrugge and Jette operationalizes disability as a broad range of role behaviors that are relevant in most people's daily lives. Five commonly applied dimensions of disability evolved from this line of scientific inquiry: basic activities of daily living include behaviors such as basic personal care; instrumental activities of daily living include activities such as preparing meals, doing housework, managing finances, using the telephone, and shopping; paid and unpaid role activities include occupation, parenting, grandparenting, and student roles; social activities include attending church and other group activities and socializing with friends and relatives; and leisure activities include sport and physical recreation, reading, distinct trips, etc. This important conceptualization of disability highlights the varied nature of role task behavior from fairly basic self-care activities to advanced and complex social, work, and leisure activities.

Verbrugge and Jette attempted to clearly differentiate the “main pathways” of the disablement process (i.e., Nagi's original concepts) from factors hypothesized or known to influence the ongoing process of disablement (see Figure 1).

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Figure 1. The disablement process. Adapted from Verbrugge and Jette, 1994 (1).

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From a social epidemiologic perspective, Verbrugge and Jette argued that one might analyze and explain disablement relative to 3 sets of variables: predisposing risk factors, intraindividual factors, and extraindividual factors. These categories of variables, which are external to the main disablement pathway, can be defined as follows.

Risk factors are predisposing phenomena that are present prior to the onset of the disabling event that can affect the presence and/or severity of the disablement process. Examples include sociodemographic background, lifestyle, and biologic factors.

Intraindividual factors are those that operate within a person, such as lifestyle and behavioral changes, psychosocial attributes and coping skills, and accommodations made by the individual following onset of a disabling condition.

Extraindividual factors are those that perform outside or external to the person. They pertain to the physical as well as the social context in which the disablement process occurs. Environmental factors relate to the social and the physical environmental factors that bear on the disablement process. These can include medical and rehabilitation services, medications and other therapeutic regimens (such as exercise or physical activity), external supports available in the person's social network, and the physical environment.

These factors may mediate or moderate the relations between pathology, impairment, functional limitation, and disability. The intricate interrelations of these factors with the disablement process, however, are not well understood.

A further elaboration of Nagi's conceptual view of disability is contained in Pope and Tarlov's Disability in America (12). The 1991 Institute of Medicine (IOM) report uses the original main disablement pathways put forth by Nagi with minor modification of his original definitions. The IOM report adds 2 important additions to the Disablement Model: the concept of secondary conditions and quality of life. Both of these concepts are discussed elsewhere in this article. In a more recent IOM report entitled Enabling America: Assessing the Role of Rehabilitation Science and Engineering (13), Nagi's person-environment interaction is emphasized with the explicit notion that disability is not inherent in the individual but rather is a product of the interaction of the individual with the environment. Furthermore, the 1997 IOM report (13) proposed an “enabling-disabling process,” which was an attempt to acknowledge within the disablement framework itself that disabling conditions not only develop and progress but they can be reversed through the application of rehabilitation and other forms of explicit intervention.

The International Classification of Functioning, Disability, and Health (ICF)

  1. Top of page
  2. Introduction
  3. Major Disability Models
  4. The International Classification of Functioning, Disability, and Health (ICF)
  5. Disability and Participation Concepts Viewed in a Sociocultural Context
  6. Exercise and Physical Activity Interventions Within a Disablement Perspective

Independent of Nagi's work in the early 1970s, another group in Europe developed the first draft of what later became the WHO International Classification of Impairments, Disabilities, and Handicap (6). Like Nagi's, this model differentiates a series of related concepts: health conditions, impairments, disabilities, and handicaps that we refer to as the ICIDH-1 concepts (6, 14). We will not review the ICIDH-1 classification as such, except to note that in principle this original system was designed as a model for coding and manipulating data on the consequences of health conditions. This classification system has been revised, giving rise to the ICF.

The ICF has 2 parts, each with 2 components (see Table 1). Part 1 is entitled Functioning and Disability, which includes body functions and structures and activities and participation. Part 2 is entitled Contextual Factors, which includes environmental factors and personal factors. Unlike the Nagi model, each component of the ICF can be expressed in both positive and negative terminology. Each component consists of various domains and, within each domain, categories that are the units of classification.

Table 1. An overview of ICF*
ComponentPart 1: Functioning and DisabilityPart 2: Contextual Factors
Body functions and structuresActivities and participationEnvironmental factorsPersonal factors
  • *

    ICF = International Classification of Functioning, Disability and Health. Adapted from ICF Introduction, An Overview of ICF (7).

DomainsBody functions Body structuresLife areas (tasks, actions)External influences on functioning and disabilityInternal influences on functioning and disability
ConstructsChange in body functions (physiological) Change in body structures (anatomical)Capacity: executing tasks in a standard environment Performance: executing tasks in the current environmentFacilitating or hindering impact of features of the physical, social, and attitudinal worldImpact of attributes of the person
Positive aspectFunctional and structural integrityActivities ParticipationFacilitatorsNot applicable
Negative aspectImpairmentActivity limitation Participation restrictionBarriers/hindrancesNot applicable

The first component of the ICF model is Body Functions and Structures, which is defined as follows: Body functions are the physiological functions of body systems (including psychological functions). Body structures are anatomical parts of the body such as organs, limbs, and their components. Impairments are problems in body function or structure such as a significant deviation or loss.

This first element of the ICF is similar to Nagi's concept of impairment, but it also includes positive terms and some of Nagi's notions of pathology (see Figure 2).

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Figure 2. International Classification of Functioning, Disability and Health (ICF) and Disablement Model frameworks.

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The second component of the ICF model is Activity and Participation, which is defined as follows: Activity is the execution of a task or action by an individual. Activities may be limited, defined as difficulties an individual may have in executing activities. Participation is involvement in a life situation. Participation restrictions are problems an individual may experience in involvement in life situations.

The domains of life areas of Activity and Participation include the following: learning and applying knowledge; general tasks and demands; communication; mobility; self care; domestic life; interpersonal interactions and relationships; major life areas; and community, social, and civic life. The second element is similar to Nagi's concepts of functional limitations and disability, but it also includes positive terms and applies both concepts to similar life domains. Although the ICF model does not clearly distinguish “activities” and “participation” as separate domains, it does acknowledge that users of the classification system may wish to differentiate the terms (7). Therefore, they provide methods to distinguish the terms, which more closely corresponds to Nagi's Disablement Model and the elaboration by Verbrugge and Jette.

At the activity and participation level, the ICF classification system incorporates qualifiers of performance and capacity. Performance describes what an individual does in his or her current environment and capacity describes an individual's ability to execute a task or an action. The gap between capacity and performance reflects the difference between the impacts of current and uniform environments as well as personal factors, the second part of the ICF framework. Environmental factors are defined in the framework as the physical, social, and attitudinal environment in which people live and conduct their lives. Personal factors are the particular background of an individual's life and living, and are composed of features of the individual that are not part of a health condition or health states. Personal factors can include gender, race, age, or other health conditions, fitness, lifestyle, habits, upbringing, coping styles, social background, past and current experience, character style, as well as other psychological assets.

Disability and Participation Concepts Viewed in a Sociocultural Context

  1. Top of page
  2. Introduction
  3. Major Disability Models
  4. The International Classification of Functioning, Disability, and Health (ICF)
  5. Disability and Participation Concepts Viewed in a Sociocultural Context
  6. Exercise and Physical Activity Interventions Within a Disablement Perspective

To understand fully Nagi's concept of disability and the ICF concept of participation, it is helpful to review the sociological concept of social roles and tasks. Social roles—such as being a parent, a construction worker, or a university professor—are basically organized according to how individuals participate in a social system.

To Parsons (15), “… role is the organized system of participation of an individual in a social system.” Tasks are specific activities through which the individual carries out his or her social roles. Social roles are made up of many different tasks, which may be modifiable and interchangeable. For Nagi, the concept of disability is firmly rooted in the context of health. Thus, for Nagi (9), health-related limitations in the performance of specific social roles are what constitute specific areas of disability. Roles can be disrupted by a variety of factors other than those that are health related. A change in the economic climate or technological changes, for example, may lead to unemployment totally unrelated to health conditions. These would not represent work disability in the way that Nagi defines this term.

As Parsons (15) clarifies:

Roles, looked at that way, constitute the primary focus of the articulation and hence interpenetration between personalities and social systems. Tasks on the other hand, are both more differentiated and more highly specified than roles, one role capable of being analyzed into a plurality of different tasks. … A task, then, may be regarded as that subsystem of role which is defined by a definite set of physical operations which perform some function or functions in relation to a role.

Are there limits of this concept of disability from the perspective of role performance? Nagi argues that components of roles—expectations or specific tasks that are learned, organized, and purposeful patterns of behavior—are part of the disability concept. They are more than isolated functions or muscle responses (9, 16). Some tasks are role specific, whereas others are common to the enactment of several roles. For Nagi, to the extent that these tasks are learned, organized, and purposeful patterns of behavior, they are part of the disability concept. It is for this reason that Nagi views the concept of disability as ranging from very basic tasks of daily life (the basic activities of daily living) to the exquisitely complex social roles, such as one's occupation. Because activities of daily living such as dressing, bathing, and eating, are part of a set of expectations inherent in a variety of other social roles, Nagi sees deviations or limitations in the performance of even such basic social roles as components of the concept of disability (9). For Nagi, disability as a heuristic concept is inclusive of all socially defined roles and tasks. In contrast, within the ICF, overall role performance mainly falls into the domain of participation. The boundary between activity limitation and participation, however, is not clearly delineated within the ICF.

Fundamental to differentiating the concept of disability from those of pathology, impairment, and functional limitation, is to consider the difference between concepts of attributes or properties on the one hand and relational concepts on the other (17).

As Nagi describes it (9):

Concepts of attributes and properties refer to the individual characteristics of an object or person, such as height, weight, or intelligence. Indicators of these concepts can all be found within the characteristics of the individual. Pathology, impairment, and functional limitations are concepts of attributes or properties. … Disability is a relational concept; its indicators include individuals' capacities and limitations, in relation to role and task expectations, and the environmental conditions within which they are to be performed.

Take the example of limitation in the performance of one's work role—a work disability. Work disability typically begins with the onset of 1 or more health conditions that may limit the individual's performance in specific tasks through which an individual would typically perform his or her job. The onset of a specific health condition, say osteoarthritis, may or may not lead to actual limitation in performing the work role—a work disability. The development of work disability will depend, in part, on the extent to which the health condition limits the individual's ability to perform specific tasks that are part of one's occupation, and alternatively, the degree of work disability may depend on external factors, for example, work place attitudes, say flexible working hours, that may restrict employment opportunities for persons with specific health-related limitations. Or, work disability might be affected by accessible modes of transportation to the work place, environmental barriers in the work place, or willingness to modify the individual workstation to accommodate a health condition. Viewed from the perspective of role performance, degree of work disability could be reduced by improving the individual's capacity to accomplish functional activities, for example, through an exercise intervention or by manipulating the physical or social environment in which work occurs.

The fundamental conceptual issue of concern is that a health-related restriction in participation in work may not be solely or even primarily related to the health condition itself or its severity. In other words, although the presence of a health condition is a prerequisite, “work disability” may be caused by factors external to the health condition's impact on the structure and functioning of a person's body or the person's accomplishment of a range of activities.

Disablement models such as Nagi's (5, 9) or the ICIDH-1 formulation (6) present the disablement process as more or less a simple linear progression of response to illness or consequence of disease. One consequence of this traditional view is that disabling conditions have been viewed as static entities (18). This traditional, early view of disablement failed to recognize that disablement is more often a dynamic process that can fluctuate in breadth and severity across the life course. It is anything but static or unidirectional.

More recent disablement formulations or elaborations of earlier models have explicitly acknowledged that the disablement process is far more complex (11, 13, 19–22). These more recent authors all note that a given disablement process may lead to further downward spiraling consequences. These feedback consequences, which may involve pathology, impairments, or further limitations in function or disability, have been explicitly incorporated into the graphic illustrations of more recent disablement formulations. Pope and Tarlov (19) use the term secondary conditions to describe any type of secondary consequence of a primary disabling condition. Commonly reported secondary conditions include pressure sores, contractures, depression, and urinary tract infections (18), but it should be understood that they can be either a pathology, an impairment, a functional limitation, or an additional disability. Longitudinal analytic techniques now exist to incorporate secondary conditions into research models and are beginning to be used in disablement epidemiologic investigations (23).

Exercise and Physical Activity Interventions Within a Disablement Perspective

  1. Top of page
  2. Introduction
  3. Major Disability Models
  4. The International Classification of Functioning, Disability, and Health (ICF)
  5. Disability and Participation Concepts Viewed in a Sociocultural Context
  6. Exercise and Physical Activity Interventions Within a Disablement Perspective

Disablement models, as described in this article, provide a conceptual map of causal pathways from a disease, such as arthritis, to the ensuing health-related consequences. This framework may be useful in examining the potential of different interventions on various disablement outcomes (22, 24, 25). Which factors of the disablement process are amenable to change and how may they be modified through health intervention? What outcomes of disablement should be targeted by different interventions? How do dimensions of disablement relate to one another and what implications do these associations have for interventions, such as exercise and physical activity?

Within contemporary clinical practice, exercise and physical activity interventions are promoted as effective, noninvasive intervention strategies to manage arthritis and promote patient health and function. Using a disablement framework, the theoretical rationale for exercise and physical activity interventions might be hypothesized to work through direct effects on minimizing impairments and functional limitations, thereby reducing subsequent disability. Exercise or physical activity, when performed in a manner that minimizes damaging joint forces, may minimize or prevent musculoskeletal impairments secondary to the arthritic disease process. For example, an individual with osteoarthritis may engage in exercise or physical activity programs with the aim to strengthen musculature that has been weakened by restricted activity due to joint pain. Furthermore, engaging in exercise or physical activity that is closely related to daily tasks and activities, such as walking, may improve locomotor characteristics, such as gait speed, step length, and walking endurance, thus minimizing restrictions in personal and instrumental activities of daily life. The implicit theoretical assumption inherent in most exercise and disability research is that improvements in musculoskeletal impairments or functional limitations will positively impact subsequent performance of personal and social role behaviors, i.e., decrease disability.

A comprehensive review of whether or not scientific evidence supports this theoretical assumption is beyond the scope of this article. However, recent reviews of randomized controlled studies show some evidence that aerobic and/or resistance training programs have achieved improved disablement outcomes among adults with arthritis, i.e., improvements in strength and aerobic capacity, enhanced gait characteristics, and decreased physical disability (26, 27). The magnitude of the effect of exercise on impairment outcomes, such as strength and range of motion, has been shown to be moderate to strong, whereas the effect on functional limitations, such as walking and stair climbing, has been shown to be less consistent and moderate. The beneficial effect of exercise, however, on physical disability has been shown to be inconsistent and of modest magnitude.

Exercise interventions appear to have many different beneficial health effects. If, however, we are interested in designing interventions that enhance people's ability to perform in personal and social role behaviors, i.e., minimize or prevent disability, then we may need to expand our theoretical thinking and design of future interventions. One explanation of the lack of strong and consistent evidence supporting a beneficial effect of exercise on disability may be due to an over simplified theoretical rationale. For example, an individual with bilateral knee osteoarthritis and subsequent pain, poor aerobic capacity, and muscle weakness around the involved joints, as well as distally and proximally, may be instructed in an exercise program to increase strength, flexibility, and aerobic capacity, i.e., target impairment outcomes as a means of minimizing future disability. The assumption inherent in such an intervention approach is that improvements in impairments will result in improved ability to negotiate his or her physical environment and participate in social role activities; yet this approach does not take into account the theoretical knowledge that complex personal and social behaviors are embedded in and influenced by an individual's cultural, social, and psychological context. Adequate muscle strength and aerobic capacity indeed may be important components of role behaviors, such as running errands, shopping, visiting friends and family members, or performing personal care and homemaking activities. However, additional skills or resources, such as modifying physical or social environments or enhancing one's perceptions of self efficacy to safely perform the behaviors, may be necessary for the completion of these kinds of activities within daily life. Self efficacy is a component of Bandura's Social Cognitive Theory (28, 29) and “refers to beliefs in one's capabilities to organize and execute the courses of action required to produce given attainments.”

An example of such an approach in the arthritis literature is Lorig's work on arthritis self management. The Arthritis Self-Management Program developed by Lorig and colleagues (30–33) uses a social cognitive approach to optimize individual-level management of arthritis conditions. A significant component of her program is the enhancement of self efficacy. The Arthritis Self-Management Program is designed to enhance people's confidence in their ability to manage pain, fatigue, social relations, and physical functioning. The program has been found to be cost effective, resulting in decreased medical service utilization as well as pain (33, 34). The effects of this program on minimizing or preventing disability, however, are not clear (33). Perhaps integrating sound, scientifically designed physical activity and exercise interventions with arthritis self management programs into a combined intervention that emphasizes behavior change in regard to physical activity and self care practices would enhance disability outcomes for people with arthritis.

One of the challenges we see in the field of arthritis exercise and disability research is to achieve a clearer understanding of how noninvasive, cost effective interventions, such as exercise and physical activity, can achieve even greater positive impacts on function and disability by applying theoretical insights provided by the models of disablement. Given the high prevalence of arthritis conditions and the high prevalence of activity restrictions and disability among people with arthritis, developing effective, noninvasive, cost effective interventions to enhance function and decrease disability is imperative. The use of exercise and physical activity to promote health and minimize disability among people with arthritis is promising. Using a disablement-enablement framework to further develop and enhance exercise and physical activity interventions may result in improved disability outcomes for the estimated 60 million people in the United States who will be living with arthritis by the year 2020 (35).


  1. Top of page
  2. Introduction
  3. Major Disability Models
  4. The International Classification of Functioning, Disability, and Health (ICF)
  5. Disability and Participation Concepts Viewed in a Sociocultural Context
  6. Exercise and Physical Activity Interventions Within a Disablement Perspective
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