Mobility is fundamental to active aging and is intimately linked to health status and quality of life. Although there is widespread acceptance regarding the importance of mobility in older adults, there have been few attempts to comprehensively portray mobility, and research has to a large extent been discipline specific. In this article, a new theoretical framework for mobility is presented with the goals of raising awareness of the complexity of factors that influence mobility and stimulating new integrative and interdisciplinary research ideas. Mobility is broadly defined as the ability to move oneself (e.g., by walking, by using assistive devices, or by using transportation) within community environments that expand from one’s home, to the neighborhood, and to regions beyond. The concept of mobility is portrayed through 5 fundamental categories of determinants (cognitive, psychosocial, physical, environmental, and financial), with gender, culture, and biography (personal life history) conceptualized as critical crosscutting influences. Each category of determinants consists of an increasing number of factors, demonstrating greater complexity, as the mobility environment expands farther from the home. The framework illustrates how mobility impairments can lead to limitations in accessing different life-spaces and stresses the associations among determinants that influence mobility. By bridging disciplines and representing mobility in an inclusive manner, the model suggests that research needs to be more interdisciplinary and current mobility findings should be interpreted more comprehensively, and new more complex strategies should be developed to address mobility concerns.
The maintenance of mobility is thought to be fundamental to active aging, allowing older adults to continue to lead dynamic and independent lives (World Health Organization [WHO], 2007). Loss of mobility may occur, for example, when an older adult is no longer able to safely drive a vehicle and/or when physical disabilities interfere with walking. Because activity restriction is associated with numerous consequences related to physical deconditioning and reduced levels of social participation, mobility is intimately linked to health status and quality of life (Groessl et al., 2007; Metz, 2000; Yeom, Fleury, & Keller, 2008). Impaired mobility has been shown to be an early predictor of physical disability (Hirvensalo, Rantanen, & Heikkinen, 2000) and, ultimately, to be associated with falling, loss of independence, institutionalization, and death (Hirvensalo et al.; Rubenstein, Powers, & MacLean, 2001; von Bonsdorff, Rantanen, Laukkanen, Suutama, & Heikkinen, 2006). For these reasons, researchers and older adults themselves are keenly interested in determining factors that influence mobility and ways to maximize mobility as people age.
Despite the importance of mobility for older adults, a comprehensive theoretical framework that describes mobility in an inclusive manner is lacking, and research and social programs targeting issues related to mobility in later life have been largely discipline specific. For example, rehabilitation-related studies concerned with the biomechanical and physiological aspects of gait typically have not been linked to driving-related research, and efforts to promote the use of public transportation systems have not been coordinated with programs designed to improve functional walking tolerance. Models developed to date have focused on specific components of mobility (e.g., life-spaces relevant to older adults and environmental factors that influence physical aspects of mobility) but have not defined mobility in a broad or inclusive way (e.g., incorporating movement on foot and in vehicle; recognizing biographical, psychosocial, cognitive, and financial influences). Our purpose was to develop a comprehensive new framework by examining the concept of mobility, along with its primary predictors and modifiers, from a variety of points of view. In doing so, it was not our intention to review all aspects of the pertinent literature in detail, but rather to highlight the key determinants of mobility and demonstrate interrelated factors that influence mobility in different environments. We propose that this interdisciplinary model for mobility will challenge researchers, clinicians, and policy makers to consider mobility from a number of different perspectives, which will increase awareness of the different contexts of mobility issues relevant to older adults. Demonstrating linkages among the various areas of mobility may guide future research to be more holistic and contribute to the development of more extensive and effective intervention programs.
In this article, we briefly discuss some of the perspectives taken by different disciplines and bodies of research in defining and measuring mobility. Conceptual frameworks that have contributed to our understanding of mobility are then described, and components are used to generate a new more comprehensive model.
Defining and Measuring Mobility
Self-reported mobility limitation is common in older people. The prevalence of mobility impairment depends on the definition used to identify restrictions. Approximately one third to one half of individuals 65 years of age or older report difficulties related to walking or climbing stairs (Shumway-Cook, Ciol, Yorkston, Hoffman, & Chan, 2005; Statistics Canada, 2007), which are common tests used to quantify mobility capabilities (Guralnik, Ferrucci, Simonsick, Salive, & Wallace, 1995; Shumway-Cook et al., 2005; Simonsick et al., 2008). However, when mobility is defined more broadly, the concept also includes movement outdoors and beyond the home, which frequently entails the use of some form of transportation (Myers, Cyarto, & Blanchard, 2005; Stalvey, Owsley, Sloane, & Ball, 1999). Stalvey and colleagues referred to mobility as “the spatial extent of one’s travel within the environment,” encompassing “travel in, around, and outside the home as one conducts the business and social aspects of everyday life” (p. 461). The WHO’s International Classification of Functioning, Disability and Health also recognizes a broad description of mobility, including both indoor and outdoor movement as well as the use of assistive devices and transportation (WHO, 2001).
In this article, mobility has been defined as the ability to move oneself (either independently or by using assistive devices or transportation) within environments that expand from one’s home to the neighborhood and to regions beyond. For research purposes, mobility within and beyond one’s home has frequently been defined and measured in terms of life-space (Baker, Bodner, & Allman, 2003; May, Nayak, & Isaacs, 1985; Peel et al., 2005; Stalvey et al., 1999). Life-space “estimates the magnitude or extent of travel into the environment, regardless of how one gets there” (Stalvey et al., p. 472).
Research has also focused on the effects of the built environment on community mobility (Clarke, Ailshire, Bader, Morenoff, & House, 2008; Nagel, Carlson, Bosworth, & Michael, 2008). Vehicles and other forms of transportation are required in order for older adults to maintain access to essential services, activities, and people (Oxley & Whelan, 2008). There is a large body of literature that deals specifically with mobility issues related to transportation options for older adults. For example, the majority of older adults still rely on the personal automobile as their primary form of transportation. Much research is therefore focused on maintaining and improving safety in older drivers to keep them behind the wheel as long as possible (Dickerson et al., 2007; O’Neill, 2000) because driving cessation is associated with numerous negative consequences, including increased dependency, social isolation, depression, and increased mortality risk (Edwards, Perkins, Ross, & Reynolds, 2009; Fonda, Wallace, & Herzog, 2001; Marottoli, 2000; Marottoli et al., 1997).
Conceptual Frameworks Relevant to Mobility in Older Adults
Over the past 40 years, a number of conceptual frameworks have been developed that relate directly or indirectly to mobility issues relevant to older adults. Early work related to mobility in older adults was largely focused on the environment and the role of the person–environment fit (Lawton & Nahemow, 1973; Rowles, 1983). Rowles explored locations that had meaning and were frequently visited by older adults. Lawton and Nahemow developed an ecological model of adaptation in older age, which laid the theoretical foundation for examining an individual’s ability to interact successfully with the demands of the environment. According to their model, matching levels of competence with the demands of the environment engenders well-being and fosters independence. Carp (1988) further conceptualized mobility itself as being central to well-being and independence in later life. In this model, mobility is portrayed as being fundamental to determining whether life-maintenance needs (e.g., food, clothing, health care) are met independently, and whether higher order needs (e.g., social relationships, recreational activities) are fulfilled to promote well-being.
Patla and Shumway-Cook (1999) introduced a mobility continuum that portrayed the positive relationship between independent walking tolerance and ability to access the community. They also presented a framework centered around physical and environmental factors and their influence on walking. Minimum walking distance, time constraints, ambient conditions, terrain characteristics, external physical loads, demands on attention, postural transitions, and traffic levels were conceptualized as eight spokes on a mobility wheel. Although this framework focused on factors relevant to accessing the community on foot, many factors would apply equally well to using wheelchairs or other forms of transportation.
Rose (2005) also proposed a theoretical framework for balance and mobility relevant to older adults. This framework included consideration of the interrelationships among individual capabilities, environmental constraints, and task demands. Similar factors were included in the theory of driver behavior proposed by Fuller (2005), which involves driving task demands and driver capabilities (e.g., physical, cognitive, and psychological characteristics) and recognizes that environmental factors, compensatory strategies, and driver perceptions influence driver action.
In order to conceptualize mobility more coherently, a framework that links factors relevant to walking, wheeling, driving, and taking alternate forms of transportation within different life-spaces is required. Much of the research to date has been relatively compartmentalized, focusing heavily on physical aspects related to the person and/or the environment. Existing theoretical frameworks have successfully portrayed specific aspects of mobility, but a new model capable of illustrating more comprehensively interrelated factors relevant to mobility in different contexts is necessary to bridge disciplines, drive new research questions, and inform at the societal and political level.
A New Theoretical Framework for Mobility
In order to conceptualize mobility in a more holistic fashion, it is necessary to consider multiple determinants that influence mobility, for those living independently and for those requiring care, and extending from the home into the larger community. For the new theoretical framework, it is assumed that mobility may take many forms, including, but not limited to, walking, using a wheelchair, driving, and using alternate forms of transportation.
Life-Spaces Portrayed in the Framework
As portrayed in the life-space literature (May et al., 1985; Peel et al., 2005) and the mobility continuum (Patla & Shumway-Cook, 1999), the framework includes concentric areas of expanding locations from home with increasing requirements for independent mobility. Included as mobility zones are the room where one sleeps, the home (e.g., house, apartment, institution), the outdoor area surrounding the home (e.g., yard, parking lot), the neighborhood (e.g., nearby streets or parks), the service community (e.g., shops, banks, health care facilities), the surrounding area (e.g., within one’s country), and the world (see Figure 1). Each life-space portrayed in the vertical order may be represented by a cross section made up of five categories of determinants that influence mobility at all life-space levels. The total cross-sectional area increases with expanding life-spaces, suggesting that a greater number of factors contribute to each determinant category as one moves farther from home.
Gender, Culture, and Biography Influence Mobility
The model recognizes that gender, culture, and biography (personal life history) each fundamentally shapes individuals’ experiences, opportunities, and behaviors and therefore acts as crosscutting influences on mobility (Commission on the Social Determinants of Health, 2008; WHO, 2002). For example, mobility limitations in older adults are not equally distributed, with women demonstrating greater limitations and greater risk of mobility disability compared to men (Leveille, Penninx, Melzer, Izmirlian, & Guralnik, 2000; Murtagh & Hubert, 2004; Shumway-Cook et al., 2005; Statistics Canada, 2007). Culture also influences mobility through its effect on social relationships, educational and occupational opportunities, and physical activity habits (Golant, 1984; Mollenkopf et al., 1997). Because gender, culture, and biography indirectly affect mobility through their influence on the five key determinants, they are depicted as encircling the entire mobility cone (Figure 1).
Key Determinants of Mobility
The key determinants of mobility illustrated in Figure 1 include cognitive, psychosocial, physical, environmental, and financial influences. Cognitive determinants include a broad range of factors such as mental status, memory, speed of processing, and executive functioning, whereas psychosocial determinants include factors like self-efficacy, coping behaviors, depression, fear, and relationships with others that affect interest and/or motivation to be mobile. The relative importance of different factors depends on the specific mobility context for an individual. For example, speed of information processing and visual attention are important for safe driving (Owsley et al., 1998). However, an individual with low self-efficacy beliefs may not even attempt to be mobile beyond the home, despite his or her actual driving or walking capabilities (McAuley et al., 2006; Perkins, Multhaup, Perkins, & Barton, 2008). Older individuals also sometimes self-restrict mobility due to depression (Gayman, Turner, & Cui, 2008) or in response to opinions voiced by friends, family, and physicians (Rudman, Friedland, Chipman, & Sciortino, 2006). Older adults who have had a previous fall (Tinetti, Richman, & Powell, 1990), as well as those who have never fallen (Friedman, Munoz, West, Rubin, & Fried, 2002; Howland et al., 1993; Maki, Holliday, & Topper, 1991), may demonstrate fear of falling to the degree that it may interfere with mobility choices. Diagnoses such as mild cognitive impairment and dementia also have the potential to seriously challenge mobility outside the home. Problems related to driving safety, wandering, and getting lost (in vehicle and on foot) are common (Adler & Silverstein, 2008; Cotter, 2007).
Interrelationships Among Mobility Determinants
Inherent to the mobility framework is the notion that mobility determinants are interrelated. For example, age-related changes such as impairments in vision and/or reaction time may be incongruent with specific challenges presented by environmental conditions, making mobility hazardous in certain circumstances (e.g., driving at night or in poor weather conditions, walking on a slippery surface with limited lighting). Because dimensions are linked (e.g., self-efficacy affects physical function), a change in one dimension (e.g., a fractured ankle that affects physical capabilities) may also result in an altered ability to meet specific requirements in other determinant categories (e.g., stairs and outdoor terrain in the environment may become obstacles to someone using a walker). In this example, mobility may be enhanced by providing aids or assistance to deal with environmental challenges (e.g., crutches to use on stairs, a scooter for short-distance outdoor travel, and handi-transit or friends to provide transportation). Improving physical status by increasing stamina for using walking aids and maximizing bone healing may also prove beneficial.
Financial factors also directly influence mobility and interact with other key determinants to affect overall mobility status. Research indicates that people with lower incomes are at greater risk for mobility disability (Shumway-Cook et al., 2005). Economic resources dictate activity options away from home and accessible modes of transportation. In this way, financial factors have the potential to influence psychosocial factors (e.g., relationships that are maintained), physical factors (e.g., access to fitness classes), and environmental factors (e.g., income may be a primary factor in determining the location of one’s home).
The inclusion of factors within each of the determinant categories is meant to be broad and inclusive. It is recognized that factors will have different levels of relevance depending on individual living situations. The mobility cone used to illustrate this new framework would be “built up” as one moves from childhood to adulthood and acquires greater physical capabilities and financial resources, as well as knowledge, experience, and confidence in being active beyond the home. However, community mobility generally declines at older ages (Cannon Hendrickson & Mann, 2005), and the cone may erode from the top down, with different determinant wedge stacks remaining. Some life events (e.g., fracturing a hip, losing a spouse who was the driver for the couple, changing the location of one’s residence) have the potential to change one’s mobility profile suddenly and substantially.
It should not be assumed that all individuals will, at some time during their lifetime, have the ability to deal with all factors in all mobility dimensions to allow travel to distant parts of the world or even to areas surrounding the community. For some, financial constraints, cognitive limitations, and/or psychosocial factors may preclude this type of travel. As well, it should be noted that mobility portrayed on this three-dimensional cone is meant to represent one’s capacity to be mobile. What is most important is having the capability to handle increasingly complex mobility factors (i.e., the “ability to be mobile”) for it is these capabilities that define mobility potential (Metz, 2000). In this way, the mobility model may be used to predict impairment and guide the design and interpretation of research studies. Consider, for example, an older woman who restricts her driving to the neighborhood during the winter because she does not feel comfortable driving in cold and snowy weather. The framework would predict that her mobility would be more impaired in the winter because of environmental and psychosocial (self-efficacy) factors, but only in terms of accessing larger life-spaces; no differences would be expected within her home. These kinds of predictions have a number of implications for research; for example, the need to measure all important contextual factors relating to mobility (i.e., potentially at different times of the year) and all types of mobility in order to gain a true picture of overall mobility status.
Also intrinsic in the model is the concept that deficits affecting mobility at a particular life-space may be compensated for by altering other determinants affecting mobility at that level. This is in accordance with the competence-press model (Lawton & Nahemow, 1973), which suggests that people will adapt within a range of environmental demands in attempts to maintain control and independence. Backman and Dixon (1992) have suggested that people compensate for real or perceived mismatches in skills and environmental demands by investing more time or effort to improve abilities, by drawing on latent skills, and/or by acquiring new skills. Certain adaptations to driving which may be implemented voluntarily or imposed by license restrictions may also require learning new skills (e.g., to make use of vehicle adaptations or implement driver training recommendations) and/or changing driving habits to compensate for declining capabilities (e.g., driving only during the day or on roads with lower speed limits; Eberhard et al., 2006; Marshall, Man-Son-Hing, Molnar, Wilson, & Blair, 2007). Advances in technology also continue to provide options that allow older adults to compensate for various mobility-related deficits (e.g., robotic walkers, driving assistance and vehicle control devices, visions aids, global positioning system [GPS] devices, “kneeling” buses).
Directions for the New Theoretical Framework for Mobility
Previous research has substantiated that older individuals restrict their walking and/or driving behaviors because of cognitive, psychosocial, physical, environmental, and financial influences, which supports the inclusion of these determinants in the mobility model (Rudman et al., 2006; Shumway-Cook et al., 2003; Shumway-Cook et al., 2005). This theoretical framework is presented in the hopes that it will encourage researchers and clinicians to consider broadly the determinants of mobility and the interactions among determinants in order to truly appreciate reasons for mobility impairments in particular life-space locations and possible compensatory strategies. The model may drive new research to establish the relative importance of mobility determinants in different mobility contexts and lead to the development of further integrative instruments similar to the Mobility Questionnaire, a tool which includes questions about accessing different levels of life-space and driving habits (Ball et al., 1998; Owsley, Stalvey, Wells, & Sloane, 1999; Stalvey et al., 1999). Further to this, in order to better understand associations among determinants and their influences on indoor and outdoor mobility, new relationships need to be forged among disciplines (e.g., engineers, psychologists, and researchers who use physical activity monitors and GPS devices) to determine more effective ways to deal with challenges in the built environment and psychosocial factors that affect walking and driving habits.
From an applied perspective, the conceptual model suggests that a more holistic approach is required for mobility assessment and treatment, and broader consideration is required for development of related policies and programs. As portrayed in the framework, mobility becomes more complex as one moves away from the home and neighborhood region; yet, health care professionals and society in general often do not consider the resources required to enable older adults to maintain independence in the larger life-spaces. Efforts may target discharge from hospital; yet, older adults may then be left relatively isolated in their homes. The development of comprehensive mobility teams, including, for example, geriatricians, rehabilitation professionals, ophthalmologists, licensing authorities, and social workers, could provide more integrative assessment and treatment recommendations to target issues related to transfers, indoor and outdoor walking, driving, and options for alternate forms of transportation.
Given that mobility is fundamentally important to older adults being able to maintain their physical and psychological health (Groessl et al., 2007; Yeom, et al., 2008), it is important that we are able to conceptualize mobility in a broad fashion that applies to all older adults, regardless of living situation or functional ability. The new theoretical framework recognizes that all forms of movement are important and that many interrelated determinants influence mobility. This conceptualization of mobility may drive new interdisciplinary research that recognizes the complex interactions between determinants of mobility in different mobility contexts. From a clinical perspective, it provides a more holistic view of mobility and may, thus, promote more effective assessment and treatment practices. Lastly, the framework may help shape program delivery and policy in order to enable older adults to live independently by maintaining their mobility for as long as possible.
Sandra C. Webber is supported by a Canadian Institutes of Health Research (CIHR) Institute of Aging fellowship. Verena H. Menec holds a Canada Research Chair in Healthy Aging.
We would like to acknowledge the technical assistance of Andre Worms and Trevor Kosowan in constructing the figure in this article.