Physical Activity, Physical Fitness, and Quality of Life
Summary and Keywords
Health-related quality of life (HRQL) is a multidimensional subcomponent of quality of life involving subjective appraisal of various dimensions of one’s life that can be affected by health or health-related interventions. There is considerable evidence demonstrating that exercise consistently results in meaningful improvements in an array of HRQL outcomes. Advances in the conceptualization of HRQL and recent evidence identifying select moderators and mediators of the effects of upon HRQL outcomes have important implications for the design and delivery of exercise interventions. Taken collectively, contemporary findings support the utility of adopting a hierarchical, bottom-up approach to the investigation of the effects of exercise upon HRQL.
It is well established that regular exercise results in numerous health benefits. Compelling evidence has emerged in the contemporary physical activity literature clearly linking inactivity and a sedentary lifestyle with increased risk for mortality and morbidity (Blair, LaMonte, & Nichamon, 2004). Across the past 30 years, accumulating epidemiological evidence has demonstrated that regular physical activity is inversely related to all-cause mortality (Pate et al., 1995) and to risk for developing a variety of the most prevalent forms of chronic disease, including cardiovascular disease, type 2 diabetes, hypertension, obesity, stroke, and select forms of cancer (Haskell et al., 2007). In light of this evidence, the beneficial role of physical activity in the prevention of and rehabilitation from many prevalent chronic diseases is widely recognized.
Assessing quality of life has been proposed to be instrumental in obtaining a comprehensive understanding of both the disease process and the efficacy of clinical interventions to prevent or treat chronic disease (Buffart et al., 2017; Focht, 2014; Latimer-Cheung et al., 2013) Consistent with this position, measures of quality of life are now advocated as important indicators of treatment efficacy, and the National Institutes of Health in the United States mandate the inclusion of indices of quality of life in most clinical studies examining the efficacy of therapeutic interventions (Kaplan & Bush, 1982; Pavot & Diener, 1993; Shumaker, Anderson, & Czajkowski, 1990). Accordingly, there is a growing consensus among clinicians and researchers that subjective, patient-based evaluations of functional status and well-being are integral to developing a comprehensive understanding of chronic disease processes and treatment efficacy (Ware, Kosinski, & Keller, 1997).
As exercise becomes increasingly advocated as an integral behavioral intervention in disease-prevention and health-promotion efforts, there is growing interest in the delineating the role of physical activity and exercise behavior in enhancing quality of life. Evidence from the physical activity literature suggests that exercise results in meaningful improvements in quality-of-life outcomes when implemented in the treatment of a variety of populations with or at risk for disease and disability. Notably, there is empirical evidence that physical activity is associated with improvements in select dimensions of quality of life among cancer survivors (Courneya, Campbell, Karvinen, & Ladha, 2006; Winters-Stone & Schwartz, 2006); patients with cardiovascular disease (Tai, Meininger, & Frazier, 2008), osteoarthritis (OA; Focht, 2006; Rejeski, Brawley, & Shumaker, 1996), chronic obstructive pulmonary disease (COPD; Berry, 2007), and multiple sclerosis (Motl & Gosney, 2008); older adults (McAuley & Katula, 1998; Rejeski & Mihalko, 2001); and overweight or obese individuals (Bouchard, 2001; Wing, 1999).
In spite of the interest in the quality-of-life benefits of exercise, there is considerable heterogeneity in the conceptualization and measurement of quality-of-life outcomes across various behavioral sciences disciplines. A consensus regarding the definition of the terms “quality of life” and “health-related quality of life” and the core dimensions that make up these constructs remains elusive and detracts from what can be concluded about the effects of exercise on quality-of-life outcomes (Rejeski et al., 1996; Rejeski & Mihalko, 2001). Additionally, a comprehensive understanding of the variables that may moderate or mediate the exercise–quality of life relationship have yet to be adequately delineated.
Consistent with the increased recognition of the importance of health-related quality-of-life outcomes within the context of disease-prevention and health-promotion intervention efforts, the primary purpose of this article it to provide an updated summary of extant findings from reviews addressing the effects of exercise on health-related quality of life (Focht, 2012, 2014; Latimer-Cheung et al., 2013; Mishra, Scherer, Snyder, Geigle, & Gotay, 2014). In this regard, particular emphasis will be placed upon (1) the definition and structure of health-related quality of life, (2) providing a brief updated synopsis of the current evidence of the effects of exercise upon health-related quality of life, (3) identifying potential mediator and moderator variables that consistently influence the relationship between exercise and health-related quality of life, and (4) addressing areas of future inquiry that can advance progress in delineating the effects of exercise on health-related quality-of-life outcomes.
The Definition, Structure, and Measurement of Health-Related Quality of Life
There is considerable heterogeneity in the definition of quality of life and health-related quality of life (HRQL) across behavioral science disciplines addressing exercise research. Accordingly, in the absence of a widely accepted conceptualization of the terms, discipline-specific definitions of the constructs have emerged. In the psychology literature, quality of life is often conceptualized and measured as an index of overall life satisfaction (Diener, 2000; Diener, Oishi, & Lucas, 2003; Pavot & Diener, 1993; Rejeski & Mihalko, 2001).
Conversely, other disciplines have espoused a multidimensional perspective on quality-of-life outcomes (Focht, 2012, 2014; Mayou & Bryant, 1993). For example, the World Health Organization Group (1995) defines quality of life as a multidimensional construct reflecting an individual’s perception of his or her position in life based on an appraisal of key life components such as physical health, psychological well-being, social relationships, and level of independence. In this context, quality of life has frequently been viewed as being synonymous with constructs such as subjective well-being, life satisfaction, or satisfaction with functional domains that influence individuals’ evaluation of their lives (Berger & Tobar, 2007).
In the aging and medical literature, the term “quality of life” has frequently been replaced with the terms “health status” or “health-related quality of life.” This conceptualization views HRQL as a multidimensional, umbrella concept that constitutes broad categories of well-being and functioning (Stewart & King, 1991) and more discrete, specific aspects reflecting core dimensions of those generic categories (Lox, Martin Ginis, & Petruzzello, 2006; Rejeski & Mihalko, 2001). Thus quality of life and HRQL represent related but not isomorphic constructs (Motl & McAuley, 2010). Emerging evidence from the behavioral medicine literature also suggests that quality-of-life and HRQL outcomes are hierarchically organized, with change in proximal HRQL constructs predicting change in distal, global quality-of-life outcomes (Elavsky et al., 2005; Motl & McAuley, 2010). Collectively, it is clear that there remains considerable heterogeneity in the conceptualization and definition of quality-of-life outcomes across medical, social, and behavioral science disciplines (Focht, 2012, 2014).
Similar variability is evident in the methods used to measure HRQL. Measures used to assess quality-of-life and HRQL outcomes can be generally classified into two broad categories: objective and subjective. Objective measures of quality of life or HRQL involve a quantitative rating made by an external observer rather than the individual person or patient. These measures, such as quality-adjusted life-years, are frequently used by health economists to determine the cost-effectiveness of treatments (Kaplan & Bush, 1982). Because these measures fail to account for individuals’ perceptions of health, function, and well-being, this assessment approach has been viewed as controversial (Lox et al., 2006).
By contrast, subjective measures of quality of life and HRQL involve patient-defined evaluations of life satisfaction and functioning in core dimensions of well-being. As noted, provided that quality of life is viewed as a cognitive evaluation of one’s overall life satisfaction in this context, it is assessed using global life satisfaction measures such as the Satisfaction with Life Scale (Diener, 2000; Pavot & Diener, 1993) or Cantril’s Life Ladder (Cantril, 1965). Generic measures of HRQL tap broad dimensions of HRQL that are posited to be relevant across populations. The Short-Form 36 (SF-36) from the Medical Outcomes Study is one of the scales most widely employed to assess generic HRQL (Ware et al., 1997). Conversely, targeted HRQL instruments are designed to tap HRQL information specific to a particular disease or population (or both) that may not be adequately captured by broad, generic measures. For example, the Functional Assessment of Cancer Therapy has both a general version and disease-specific versions that are designed to assess concerns that may be specific to particular subgroups of cancer patients and survivors (Courneya, Campbell, Karvinen, & Ladha, 2006).
Quality of life is now well established as an important indicant of treatment efficacy across a wide variety of therapeutic interventions and populations. The divergence in the conceptualization and definition of quality-of-life and HRQL terms across disciplines, as well as the breadth of measures used to assess these outcomes, presents a considerable challenge to effectively synthesizing knowledge of the effects of exercise on quality-of-life outcomes. In the present chapter, HRQL is operationally defined as a subcomponent of quality of life that involves the subjective appraisal of various dimensions of one’s life that can be affected by health or health-related interventions. Within this context, HRQL is an umbrella construct representing both broad domains of functioning and well-being and more specific core dimensions of HRQL including, but not limited to, perceptions of physical function, emotional well-being, social functioning, health states, and physical symptoms and states (Focht, 2012, 2014).
The Effects of Exercise Interventions on HRQL Outcomes
There is now considerable evidence that exercise consistently results in small to moderate, yet clinically meaningful, effect size improvements in multiple QOL outcomes ranging from global indices of life satisfaction to disease-specific measures of QOL dimensions. Collectively, these findings provide compelling evidence of the QOL benefits of exercise across a variety of populations. Indeed, there are numerous prior comprehensive reviews of the effects of exercise on quality of life and HRQL (Berger & Tobar, 2007; Courneya et al., 2006; Eshah & Bond, 2009; Gillison, Skevington, Sato, Standage, & Evangelidou, 2009; Schmitz et al., 2005; Speed-Andrews & Courneya, 2009) and specific dimensions of HRQL in select chronic disease populations (Focht, 2006; Lawlor & Hopker, 2001; Linden, Stossel, & Maurice, 1996; Winters-Stone & Schwartz, 2006) documenting such benefits. In the next section a brief summary of the effects of exercise on HRQL updated from our prior recent narrative reviews of this area of inquiry is provided (Focht, 2012, 2014).
Findings from the extant exercise–HRQL literature demonstrate that exercise interventions consistently result in significant, clinically meaningful improvements in an array of HRQL outcomes. For example, exercise yields improvements in global, generic, disease-specific HRQL outcomes. Exercise is typically associated with small-to-moderate improvements in the HRQL outcomes. Nonetheless, it should be noted that substantial variability in the magnitude of the effects of exercise has been observed across studies and measures of HRQL (Focht, 2012, 2014).
The HRQL benefits accompanying exercise do not appear to be limited to any particular population subgroup, to be strongly linked with improvements in physical fitness, or to vary systematically as a function of any specific exercise intervention characteristics such as exercise mode, frequency, duration, or intensity (Berger & Tobar, 2007; Focht, 2012, 2014; Rejeski & Mihalko, 2001; Rejeski et al., 1996). Although aerobic forms of exercise have been the most frequently studied mode of exercise across studies, emerging evidence underscores the utility of resistance exercise to elicit beneficial effects on HRQL in cancer patients. Indeed, findings from a recent systematic review demonstrate that resistance exercise results in significant, clinically meaningful improvements in an array of HRQL outcomes (Fairman, Focht, Lucas, & Lustberg, 2016; Focht et al., 2013).
In light of the strong empirical evidence supporting the beneficial effect of exercise on HRQL, there is growing interest in identifying the factors that may influence the strength of the exercise–HRQL relationship or serve as intermediate variables that account for the favorable effect of exercise on HRQL outcomes. Therefore, the following section will address the role of potential moderator and mediator variables that may influence the effects of exercise on HRQL outcomes.
Moderators and Mediators of the Effects of Exercise on HRQL
In the context of the exercise–HRQL relationship, a moderator is a variable that influences the strength of the effect of exercise on HRQL outcomes. A mediator is an intermediate variable that serves as an underlying mechanism for the effect of exercise on HRQL outcomes. A mediator variable essentially represents a proximal outcome that, when positively affected by exercise, subsequently contributes to improvements on more distal HRQL outcomes.
One of the most frequently observed moderators of the exercise–HRQL relationship is initial level of HRQL. Baseline HRQL values have consistently been found to serve as independent predictors of subsequent change in HRQL outcomes (Focht, Brawley, Rejeski, & Ambrosius, 2004; Gillison et al., 2009; Rejeski et al., 1996; Rejeski, Focht, et al., 2002; Rejeski & Mihalko, 2001). This effect has been documented across population subgroups (both healthy and various chronic disease samples) and for multiple HRQL outcomes, including global ratings of life satisfaction, generic HRQL, and disease- or population-specific measures of perceived physical function and psychological well-being (Berger & Tobar, 2007; Focht, 2006; Focht et al., 2004; Gillison et al., 2009; Rejeski et al., 1996; Rejeski & Mihalko, 2001). Consequently, there is strong empirical support for the position that, from a quality-of-life perspective, those who have the most to gain at the outset of exercise interventions derive the greatest benefit across an array of HRQL outcomes.
Although less compelling than the evidence supporting the influence of initial HRQL status, some recent findings from randomized controlled trials suggest that gender may moderate the effects of exercise on select HRQL outcomes. For example, findings from the REACT trial demonstrated that while men exhibited significant improvements in multiple aspects of disease-specific HRQL following long-term exercise training, women did not obtain similar added benefits beyond those conferred by a short-term exercise intervention (Foy, Rejeski, Berry, Zaccaro, & Woodard, 2001). Furthermore, in the CHAMP trial, men reported more favorable improvements than women in a generic index of HRQL and in perceived physical functioning (Focht et al., 2004; Rejeski et al., 2003; Rejeski, Foy, et al., 2002). Two important points should be considered when interpreting these findings. First, gender differences have not been observed in the majority of studies addressing changes in HRQL accompanying exercise interventions. Additionally, many randomized trials examining exercise have not been stratified by gender and have lacked the statistical power to detect potentially meaningful gender differences in treatment responsivity (Focht et al., 2004). Moreover, recent meta-analytic demonstrated the effects of exercise upon quality-of-life outcomes in cancer patients were not systematically moderated by any demographic, clinical, or exercise characteristics (Buffart et al., 2017). Consequently, it is possible that gender may be an important individual difference that moderates exercise-induced changes in HRQL outcomes among select chronic disease samples (i.e., patients with COPD and cardiovascular disease).
The importance or value one places on a particular dimension of functioning has also been proposed to impact the strength of the exercise–HRQL relationship. Importance or value appears to be particularly relevant when HRQL is assessed as an index of satisfaction with life or satisfaction with a specific HRQL domain. For example, Rejeski and colleagues found that knee OA and COPD patients who had the greatest difficulty completing valued functional tasks reported the least satisfaction with their physical function (Katula, Rejeski, Wickley, & Berry, 2004; Rejeski, Martin, Miller, Ettinger, & Rapp, 1998). Individuals who appear to adapt to disease and compromised levels of functioning by cognitively devaluing physical function have also been found to report less physical activity participation, placing them at greater risk for the onset of functional limitations and subsequent progression toward disability (Martin et al., 1999; Rejeski & Focht, 2002). Together, these findings suggest that the value one places on particular dimensions of HRQL may affect satisfaction with one’s function, well-being, and capabilities related to that domain. Thus, when assessed as an index of satisfaction, overall or domain-specific aspects of HRQL may be influenced by the importance ascribed to this aspect of quality of life. These evaluations also appear to have meaningful consequences for the perception of and participation in exercise behavior.
Findings from several recent randomized controlled trials have also expanded knowledge pertaining to potential mediators of the effects of exercise on HRQL. Within the context of the exercise–HRQL relationship, mediation is observed when each of the following criteria is satisfied: (1) exercise has a significant effect on HRQL; (2) exercise significantly influences a targeted potential mediator variable; (3) change in the potential mediator variable is significantly related to change in the HRQL outcome; and (4) the effects of exercise on the HRQL outcome become nonsignificant after the effects of the mediator have been controlled for in a composite model.
It should be acknowledged that from a conceptual perspective, study of mediators of the effects of exercise on HRQL outcomes have adopted either top-down or bottom-up perspectives (Focht et al., 2014). Top-down perspectives suggest that more global ratings of overall quality of life and/or well-being determine judgments of satisfaction with specific domains of life, functioning, and/or well-being. Hence, individuals reporting favorable ratings of global life satisfaction or well-being evaluate specific dimensions of life in a similarly positive manner. By contrast, bottom-up perspectives propose that judgments of specific life domains influence global ratings of QOL. Although it can be argued that both top-down and bottom-up models have conceptual merit, findings from the exercise-HRQL literature have yielded consistent support for the bottom-up perspective but little, if any, evidence supporting the top-down conceptualization (Focht et al., 2014).
Consistent with the bottom-up perspective, there is evidence that self-related psychological variables can serve as mediators of the effects of exercise on HRQL. For example, within a large sample of knee OA patients, self-efficacy beliefs relating to mobility (specifically, confidence in one’s ability to complete incrementally more challenging amounts of a stair climb task) and knee pain symptoms were found to mediate the beneficial effect of exercise on a measure of functional performance (Rejeski, Ettinger, Martin, & Morgan, 1998). Knee pain mediated the effects of exercise on a generic index of HRQL. Evidence of similar meditational pathways was observed in the ADAPT trial (Rejeski, Focht, et al., 2002). Satisfaction with physical function and pain ratings were shown to be independent mediators of the effect of the lifestyle intervention involving exercise and dietary weight loss on the Physical Health summary scale of the SF-36. Mobility-related self-efficacy and knee pain were also shown to be significant, independent partial mediators of the effect of the combined exercise and diet intervention on select performance measures of physical function (Focht, Rejeski, Katula, Ambrosius, & Messier, 2005).
Furthermore, select psychological constructs such as self-efficacy beliefs, satisfaction with physical function, perceptions of physical symptoms, and affective responses have been observed to act as mediators of the effects of exercise on HRQL in a variety of population subgroups. Notably, self-efficacy and satisfaction with physical function and appearance served as independent mediators of the effects of exercise on life satisfaction in the Activity Counseling Trial (Rejeski et al., 2001). Recent evidence has also demonstrated that the effects of exercise on global quality of life were mediated by changes in intermediate psychological constructs within samples of community-dwelling older adults. More specifically, improvements in ratings of overall life satisfaction were mediated in part by the positive effects of exercise on affective responses, self-efficacy, and perceptions of social support among older adults at risk for functional decline (Elavsky et al., 2005; McAuley et al., 2006).
Largely consistent with these findings, results of multiple studies among multiple sclerosis patients also provides support for the assertion that the effects of exercise on global quality-of-life and generic HRQL constructs are mediated by its influence on intermediate psychological variables. Results of path analyses demonstrated that exercise positively influenced self-efficacy, disease symptoms, and select indicants of psychological well-being. In turn, changes in these intermediate outcomes were linked with more favorable ratings of global quality of life (Motl & McAuley, 2009; Motl, McAuley, Snook, & Gliottoni, 2009; Motl & Snook, 2008).
More recent findings from exercise intervention trials also support the mediational role of select psychological and fitness outcomes in breast and prostate cancer patients/survivors, cancer survivors, and older adults. Notably, Buffart et al. (2015) demonstrated that the beneficial effects of a supervised aerobic and resistance exercise intervention upon HRQL was mediated by change in lower body function performance. Consistent with the bottom-up conceptualization, results from a recent trial examining the effects of exercise in cancer survivors following chemotherapy completion revealed that improvements in global quality of life were mediated by the effects of exercise upon change in fatigue and aerobic fitness (Kalter et al., 2016). Additionally, recent findings in breast cancer patients and survivors reveal that the improvements in HRQL accompanying exercise or physical activity are mediated by self-efficacy beliefs and health status (Phillips & McAuley, 2014) as well as enjoyment and improvements in sleep dysfunction (Rogers et al., 2014).
Collectively, the majority of findings in this line of inquiry suggest that exercise has little direct effect upon enhancing global quality of life, rather that exercise has direct effects upon subdomain indices of HRQL, which, in turn, influence change in global quality-of-life measures. However, in contrast to this position, recent findings from a randomized controlled trial targeting 179 sedentary older adults revealed that a walking intervention resulted in significant improvements in both the mental health component of HRQL and global quality of life (Awick et al., 2015). These findings suggest that it is possible that exercise may yield improvements in global quality of life as well. Nonetheless, given the preponderance of findings in the extant literature documenting that exercise has little effect, at least directly, upon changes in global quality of life, further research delineating the nature of the influence of exercise upon HRQL and global quality of life warrants further investigation.
Overall, these updated findings since the publication of prior similar reviews (Focht, 2012, 2014) remain consistent with previous conclusions suggesting that the effects of exercise on generic indices of HRQL and global ratings of life satisfaction are consistently mediated in part by changes in intermediate psychological outcomes. The recent evidence demonstrating the indirect effect of exercise on HRQL and quality of life suggests that these potential mediators should be targeted and assessed in future exercise intervention trials. These findings also have important implications for the conceptualization of quality-of-life outcomes. The results indicate a hierarchical organization of quality-of-life outcomes in which change in proximal HRQL constructs predicts change in more distal, global indices of quality of life. Consequently, exercise may influence proximal HRQL dimensions assessed by measures of generic core dimensions of HRQL and disease- or population-specific symptoms. In turn, favorable changes in these proximal intermediate HRQL outcomes subsequently contribute to improvements in overall ratings of life satisfaction. Clearly, these findings have important implications for the design and delivery of exercise interventions as well as for the way in which HRQL and quality of life should be measured in future exercise trials.
Exercise and HRQL: Overall Summary
As noted in prior systematic reviews of the exercise–quality of life relationship (Berger & Tobar, 2007; Rejeski et al., 1996; Rejeski & Mihalko, 2001), heterogeneity in the conceptualization and measurement of salient quality-of-life constructs makes attempts to synthesize the effects of exercise on HRQL particularly challenging. The exercise–quality of life relationship is unquestionably complex. Nonetheless, findings from the contemporary exercise psychology, medical, and behavioral medicine literature clearly demonstrate that exercise consistently results in statistically significant, clinically meaningful improvements in a variety of quality-of-life outcomes, including global measures of overall life satisfaction, generic domains of HRQL, and targeted measures of specific HRQL dimensions and physical symptoms relevant to particular diseases or populations.
Although the wide array of HRQL benefits can be generally characterized as small to moderate in magnitude, not all dimensions of HRQL are equally responsive to exercise. There is sufficient evidence to conclude that certain dimensions of HRQL, such as perceptions of physical function and select physical symptoms and aspects of psychological well-being, are more sensitive to change with exercise interventions than others that are not as readily tied to the stimulus properties of exercise (e.g., social function). Current findings also suggest that improvements in HRQL do not appear to be limited to any particular population subgroup. Both healthy individuals and those with or at increased risk for chronic disease exhibit favorable changes in HRQL outcomes following exercise training interventions (Focht, 2006; Gillison et al., 2009; Lacasse, Martin, Lasserson, & Goldstein, 2007; Rejeski et al., 1996). However, initial perceptions of health status are consistently independent predictors of the magnitude of improvement observed. Those individuals with the worst level of or the least satisfaction with a particular quality-of-life outcome at baseline report the most favorable improvement following exercise. This effect has been observed across numerous HRQL outcomes and population subgroups (Focht et al., 2004; Rejeski et al., 1996; Rejeski, Focht, et al., 2002). Additionally, the development and application of targeted measures of HRQL has led some to conclude that individuals with disease benefit more from exercise training than do healthy individuals (Gillison et al., 2009). Nonetheless, whereas the magnitude of the benefit may differ based on one’s initial HRQL status, improvements in HRQL do not appear to systematically vary as a function of demographic variables or exercise intervention characteristics such as exercise mode, duration, intensity, or frequency.
With regard to exercise characteristics, it is particularly important to acknowledge that the effects of different amounts or “doses” of exercise on quality of life remain poorly understood. Accordingly, the minimum amount of exercise training required to produce improvements in various HRQL outcomes is not known. This dearth of information detracts from the ability to develop accurate guidelines for the recommended amount of exercise for enhancing and maintaining HRQL. There is emerging evidence that individuals meeting or exceeding public health recommendations for physical activity participation report superior HRQL relative to those failing to accrue this amount of activity (Blanchard, Stein, & Courneya, 2010). Accordingly, adhering to public health recommendations for physical activity and exercise may hasten improvements in HRQL (Speed-Andrews & Courneya, 2009). It has also been proposed that moderate-intensity exercise can facilitate superior changes in select dimensions of HRQL compared with more demanding or less demanding amounts of activity (Berger & Tobar, 2007).
There is certainly sufficient empirical evidence to warrant advancing such intuitively appealing proposals. However, current recommendations for physical activity and exercise prescription are largely based on the amounts of activity associated with physical health promotion and disease prevention benefits. Compelling arguments have been forwarded that these recommendations are based on a passive stimulus–response paradigm that erroneously assumes that any prescribed dose of activity will yield a uniform response across both physiological and psychological domains (Rejeski, 1994; Rejeski & Focht, 2002). Although accruing recommended amounts of physical activity and exercise may elicit a specific physiological adaptation, participants’ tolerance for and perception of a given exercise prescription is shaped in part by the cognitive appraisals of and affective responses to that prescription that they experience directly or that they perceive to be related to the prescription (Ekkekakis, Parfitt, & Petruzzello, 2011, Focht, 2014). Given that HRQL inherently involves an individual’s perception of a variety of dimensions of function and well-being, any single dose of exercise is unlikely to affect all valued aspects of HRQL equally. Additionally, improvements in HRQL outcomes are influenced by perceptions of initial health status and functional value. Hence, while it seems prudent to suggest that achieving current public health recommendations for exercise participation will be sufficient to enhance HRQL, this amount of activity may not be appropriate for all people or elicit favorable changes in all relevant HRQL outcomes. As such, when a primary objective of the exercise prescription is to enhance HRQL, flexible prescriptions tailored to individuals’ deficits, values, and preferences with respect to function and well-being would be preferable to advocating any single dose.
Directions for Future Research
A considerable body of empirical evidence supporting the position that exercise represents an efficacious behavioral intervention for enhancing HRQL. Despite these findings, advances in knowledge of the exercise–HRQL relationship can be characterized as incremental in recent years. Indeed key areas of inquiry identified nearly 20 years ago (Rejeski et al., 1996) have yet to be systematically addressed in contemporary exercise–HRQL literature (Focht, 2012). We have highlighted these considerations in our recent reviews of the literature (Focht, 2012, 2014) and provide a brief updated overview of select directions for future inquiry to conclude this chapter.
Rejeski and colleagues (Rejeski et al., 1996; Rejeski & Mihalko, 2001) convincingly argued that one of the primary barriers to synthesizing and advancing knowledge of the effects of exercise on quality-of-life outcomes is inconsistency in the definition and measurement of quality-of-life and HRQL constructs (Berger & Tobar, 2007; Lox et al., 2006; Rejeski et al., 1996; Rejeski & Mihalko, 2001). However, findings from the physical activity literature provide advances in this area as well as strong support for the assertion that quality of life and HRQL are related yet conceptually distinct constructs (Awick et al., 2015; Elavsky et al., 2005; McAuley et al., 2006; Motl & Snook, 2008; Motl et al., 2009). There is also emerging evidence that quality-of-life outcomes may be hierarchically organized. Within the proposed hierarchical model of quality of life, exercise is purported to influence global quality of life indirectly through its effect on both generic domains and specific indices of HRQL as well as self-related psychological constructs such as self-efficacy beliefs, satisfaction with select aspects of function and well-being, affect, and social support (Elavsky et al., 2005; McAuley et al., 2006; Motl et al., 2009).
The proposed hierarchical structure of quality of life and findings supporting the bottom-up conceptualization indicating that exercise positively influences higher-order quality-of-life and HRQL outcomes indirectly have important implications for exercise interventions (Focht, 2012). It suggests that quality of life and HRQL should be viewed and measured as distinct constructs. The consistent integration of a multilevel assessment approach that includes global indices of life satisfaction, generic measures of HRQL, and targeted measures of disease- or population-specific assessments of HRQL will be critical to advancing toward a more comprehensive understanding of the effects of exercise on quality-of-life outcomes. Additionally, measurement of select, conceptually relevant intermediate psychological constructs that may serve as mediator variables of the effect of exercise on quality of life and HRQL will aid in elucidating the mechanisms underlying the beneficial effect of exercise on HRQL (Focht, 2014).
Adoption of a hierarchical model of quality of life, inclusion of a multilevel measurement approaches, and investigation of bottom-up effects will also aid in addressing other important research issues. Rejeski et al. (1996) proposed that many researchers mistakenly equate change in a core dimension of HRQL with improvements in more broad indices of function and well-being or overall quality of life. Given that quality of life and HRQL are not isomorphic constructs, it is erroneous to assume that improvements in a core dimension of HRQL, such as physical function, will also produce concomitant improvements in perceived physical health status or overall life satisfaction. The effects of exercise on HRQL are not consistent across all outcomes. Consequently, change in one particular index of HRQL cannot be used to infer change in separate measures of HRQL. Provided that HRQL is seen as an umbrella construct comprising numerous core dimensions and disease- or population-specific symptoms, acknowledging that exercise may have unique influences on those outcomes is both practically and conceptually relevant for future inquiry.
It is important to acknowledge that there is considerable heterogeneity observed in exercise-induced improvements in HRQL (Rejeski et al., 1996; Rejeski & Focht, 2002). Individuals with normative levels of perceived function or well-being will not demonstrate as much improvement as those who exhibit compromised levels of these outcomes prior to exercise. Initial values are consistent, reliable predictors of HRQL responses to exercise and must be carefully considered when interpreting the efficacy of any exercise intervention. Individuals vary considerably in the importance they place on various aspects of HRQL. The beneficence of exercise for HRQL is partially determined by the extent to which an individual values a particular aspect of HRQL. Furthermore, the extent to which change in a lower-order HRQL outcome will facilitate improvements in global ratings of quality of life would be expected to be influenced by the value ascribed to that dimension of HRQL. That is, exercise-related improvements in highly valued aspects of functioning and well-being should have more pronounced effects on global quality of life, as these personally meaningful aspects of HRQL are most likely to be to be sufficiently relevant to alter perceptions of overall life satisfaction. Because few investigations have directly addressed the role of perceptions of initial health status or of the importance and value attached to particular domains of HRQL, evidence supporting these relationships remains sparse.
Finally, to develop appropriate exercise recommendations for enhancing HRQL, it is obviously critical to more fully explicate the range of exercise program characteristics that facilitate favorable changes in HRQL. The heterogeneity of exercise program factors (exercise mode, intervention length, intensity, frequency, and duration) that have been used in investigations of the exercise–HRQL relationship considerably restricts the ability to synthesize exercise recommendations for optimizing HRQL benefits. Efforts to determine a single optimal prescription reflect a passive stimulus–response paradigm that ultimately lacks utility or generalizability (Rejeski, 1994; Rejeski & Focht, 2002). No single exercise prescription will be equally efficacious in producing improvements in all facets of HRQL for all participants. In progressing toward the development of appropriate exercise guidelines, it must be recognized that the impact of exercise on HRQL outcomes is due not only to the physiological dynamics of the exercise stimulus but also to the social and behavioral characteristics of the exercise intervention.
Findings from the CHAMP trial illustrated that exercise combined with a cognitive behavioral intervention produced superior changes in HRQL compared with exercise alone (Focht et al., 2004). Determining the “dose” of exercise that facilitates the most favorable changes in HRQL involves more than simply quantifying the exercise stimulus characteristics. Consequently, while identifying more precise ranges of exercise characteristics through the implementation of flexible, individually tailored prescriptive approaches seems prudent, the social, environmental, and behavioral factors that influence perceptions of health status are also critical considerations in enhancing treatment efficacy. The emerging evidence that exercise influences higher-order quality-of-life constructs through improvements in intermediate, self-related psychological variables underscores the potential importance of integrating behavioral intervention components that enhance self-efficacy beliefs, tolerance for and affective responses to exercise, and perceptions of social support (Ekkekakis, Hall, & Petruzzello, 2008; Ekkekakis et al., 2011) Expanding the conceptualization of the aspects of exercise interventions that comprise a given dose of exercise is a necessary step in facilitating meaningful advances in understanding the psychosocial mechanisms through which exercise results in HRQL benefits.
In summary, there is sufficient evidence to conclude that exercise is an efficacious intervention for promoting enhanced HRQL. Exercise has been linked with small-to-moderate improvements in numerous HRQL outcomes. Although exercise does not influence all HRQL outcomes equally, these benefits do not at present appear to systematically vary as a function of population subgroup or exercise intervention characteristics. However, the initial levels of HRQL prior to exposure to the exercise intervention and the amount of importance one places on a particular dimension of HRQL have been shown to influence the magnitude of the exercise effect. Individuals with compromised perceptions of function and well-being will demonstrate more pronounced changes in those specific aspects of HRQL than will individuals exhibiting higher levels of function.
Exercise also has great potential to positively influence value dimensions of HRQL that change in response to exercise participation. In turn, within the context of a hierarchical model of quality of life, exercise-related improvements in aspects of HRQL that are personally important have the greatest potential to contribute to enhancing subjective evaluations of generic HRQL domains and appraisals of overall satisfaction with life. This suggests that the beneficial effect of exercise on quality of life may be indirect, operating through its favorable influence on intermediate psychological and HRQL constructs. Given the clear value of exercise as a public health intervention and the relevance of HRQL as an indicant of treatment efficacy, further inquiry designed to provide a more comprehensive understanding of the complex exercise–HRQL relationship is warranted. In conclusion, as more consistent conceptualizations of HRQL are adopted, the likelihood of meaningful progress toward designing and delivering exercise interventions that are effective in enhancing HRQL is likely to be realized.
Brian Focht and Ciaran Fairman are supported by grant 1R01 AG050725-01 from the National Institutes on Aging.
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