Quality of life (QOL) assessments are instrumental in developing a more comprehensive understanding of the efficacy of disease prevention and health promotion interventions. There is growing interest in delineating the role of exercise in enhancing QOL outcomes. Indeed, findings from multiple reviews on the effect of exercise on QOL reveal that exercise consistently results in small to moderate, yet clinically meaningful, 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.
Given the well-established QOL benefits of exercise, determining factors that influence the exercise–QOL relationship is a focal point of contemporary exercise psychology research. Therefore, among the objectives of this entry are to identify: (a) considerations in the conceptualization and structure of QOL and (b) potential moderators and mediators of the exercise–QOL relationship.
Definition and Structure of Quality of Life
Definitions of QOL vary across studies examining the exercise–QOL relationship. In the psychology literature, QOL is conceptualized as an index of overall life satisfaction. Conversely, medical and behavioral science disciplines have espoused multidimensional perspectives of QOL outcomes reflecting one’s appraisal of key life components including physical health, psychological well-being, social relationships, and level of independence. In select medical disciplines, QOL is conceptualized as health-related quality of life (HRQOL), a multidimensional, umbrella concept that comprises broad categories of well-being and functioning and more discrete, specific aspects reflecting core dimensions of function and wellbeing. Subjective well-being (SWB), a related yet distinct outcome, is comprised of life satisfaction (the cognitive evaluation of the overall quality of one’s life) and positive and negative affect (the frequency and intensity of pleasant and unpleasant feelings experienced in one’s life).
Variability in the conceptualization of QOL across disciplines presents a challenge to synthesizing knowledge of the QOL benefits of exercise. Nonetheless, it can be concluded that QOL, HRQOL, and SWB are related, though not isomorphic, constructs and that exercise consistently elicits improvements of similar magnitude across these outcomes. Emerging evidence also suggests that QOL outcomes are hierarchically organized and exercise-related improvements in proximal QOL subdomains predict favorable change in more distal global QOL outcomes. Consistent with this proposed hierarchical structure, QOL can be viewed as an umbrella term involving the subjective appraisal of various dimensions of one’s life, encompassing global ratings of life satisfaction, broad dimensions of functioning and well-being, and perceptions of specific domains of functioning and well-being.
Moderators and Mediators of the Effects of Exercise on Quality of Life
With regard to moderator variables, baseline QOL values consistently act as independent predictors of improvements in QOL following exercise across multiple population subgroups and QOL outcomes. These findings provide compelling evidence for the position that those who have the most to gain in terms of improvement of QOL (e.g., those presenting with the least favorable QOL profile at baseline) prior to initiating exercise derive the greatest benefit from exercise interventions across an array of QOL outcomes. Although gender has been proposed to moderate the effects of exercise on QOL, evidence of consistent gender differences in the QOL responses to exercise interventions remains equivocal and warrants further inquiry.
Investigations addressing mediators of the QOL benefits of exercise have adopted top-down or bottom-up perspectives. Top-down perspectives propose that judgments of satisfaction with specific domains of life, functioning, and/or well-being are determined by ratings of overall QOL and wellbeing. Thus, those reporting favorable ratings of global life satisfaction or well-being evaluate specific dimensions of life in a similarly positive manner. Conversely, bottom-up perspectives propose that judgments of specific life domains influence global ratings of QOL. Although both top-down and bottom-up models have merit, findings from the exercise–QOL literature have yielded consistent support for the bottom-up perspective and little evidence of the utility of the top-down approach.
Consistent with the bottom-up perspective, recent studies in multiple sclerosis patients 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 QOL. Similar mediational pathways were observed with exercise interventions targeting arthritis patients. For example, mobility-related self-efficacy beliefs and knee pain symptoms, both domain-specific QOL measures, mediated the beneficial effect of exercise upon functional performance and ratings of generic HRQOL.
Additionally, satisfaction with physical function, knee pain ratings, and mobility-related self-efficacy has been identified as independent mediators of the effect an exercise and dietary interventions on QOL in arthritis patients. Studies also demonstrated that the favorable effects of exercise on global QOL were partially mediated by improvements in affective responses, self-efficacy, and perceptions of social support among older adults at risk for functional decline.
Thus, the effects of exercise on global indices of QOL can be mediated by changes in proximal QOL domains. The indirect effect of exercise upon global QOL suggests that these potential mediators should be targeted within future exercise intervention trials. It also provides support for the hierarchical structure of QOL outcomes whereby improvements in proximal QOL constructs lead to improvements in distal global QOL outcomes. Thus, exercise may influence proximal QOL dimensions assessed by measures of generic core domains of QOL and disease or population-specific symptoms. In turn, favorable changes in these proximal QOL outcomes subsequently contribute to improvements in overall, global ratings of QOL.
Directions for Research in the Exercise–Quality of Life Relationship
Select areas of future inquiry may be particularly integral to advancing knowledge of the exercise– QOL relationship. It is critical for researchers to acknowledge that QOL, HRQOL, and SWB represent related yet conceptually distinct constructs. Additionally, emerging evidence supports the position that QOL outcomes are hierarchically organized and that a bottom-up model accounts for the direct effects of exercise on QOL domain outcomes and indirect effects upon global QOL.
Implementation of a hierarchical, bottom-up conceptualization of the exercise–QOL relationship has important implications for designing exercise interventions. This approach suggests that multilevel assessments integrating global indices of life satisfaction, generic measures of QOL, and targeted measures of domain-level QOL outcomes should be included as a standard part of theoretically driven assessment batteries. Augmenting this approach through the measurement of conceptually relevant and evidence-based mediators will also expand understanding of the mechanisms underlying the QOL benefits of exercise. Adoption of the hierarchical model could have ancillary benefits in advancing knowledge of the role of exercise in enhancing QOL. For example, exercise-induced increases in specific QOL domains are mistakenly interpreted as reflecting improvement in other QOL domains or global QOL. In a hierarchical model of QOL, improvements in QOL domains should not be assumed to be indicants of change in global QOL. Consequently, improvement in one QOL measure should not be used as a proxy for inferring change in different QOL outcomes.
In summary, exercise is valuable for enhancing and sustaining QOL. Despite the well-established QOL benefits of exercise, advances in the conceptualization of QOL outcomes and the mechanisms underlying improvements in QOL have been limited. Adopting a hierarchical, bottom-up approach to the study of exercise-related QOL benefits is an important step in augmenting the incremental progress that has been observed in the investigation of the exercise–QOL relationship.
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