The current study examined the longitudinal changes in PA that influenced HRQoL in middle age and early old age over 8 years of follow-up. The results showed that elderly participants who continued to be inactive or became inactive, compared with their PA during middle age, had increased likelihood of worsened quality of life.
PA improves the HRQoL by improving physical function and lowering the risk of chronic diseases such as obesity and various diseases, thereby inducing fundamental health benefits , as reported in earlier studies. An analysis of older adults 65 years and older in Korea showed that the physically active group had lower pain, pain interference, and fatigue than the inactive group . HRQoL decreased linearly with decreasing PA, with participants showing weakened physical and mental health such as bodily pain, physical role limitation, and emotional role limitation . Consistent with the findings of enhanced HRQoL with PA [11, 27], the current study observed a positive effect of PA on the quality of life in old age while re-emphasizing the importance of being physically active throughout life.
A strength of this study is that it considered the changes in the PA level of the elderly in a period of 8 years. In a similar study  with a large sample of middle-aged and older Australian adults, the group that reported any PA or vigorous activity had associated risk reductions in mortality as well as positive effect of PA on health. In a large study in England , both becoming and remaining active were associated with healthy aging, compared with remaining inactive, over an 8-year follow-up, and its impact was higher in the group that remained active than in the group that became active. This requires the attention of practitioners in terms of achieving the goal of extension of healthy life rather than simply extending life expectancy in an aging society. The recommended amount of PA for the adult population should be more actively accepted from the viewpoint of not only preventing chronic diseases but also preparing for a healthy life in the elderly. Extending a healthy lifespan without the burden of disease has become a health goal for many countries; hence, the benefits of physically active life from adulthood should be emphasized in terms of preparing for a healthy quality of life in old age.
The phenomenon of the rapidly increased aging population led health researchers to give more attention on frailty, which is one of the determinants of HRQoL. The high prevalence of frailty, a dynamic state of experiencing declines in least one of the human function domains (physical, psychological, and social) , is among the major problems of older adults, and earlier studies showed the negative influence of frailty on the HRQoL of older adults [29, 30]. Importantly, PA is considered an important component that can help prevent or improve frailty of older adults, with the evidence of 19 interventional studies . In this study, the effect of changes in PA with frailty as an outcome variable was not analyzed, but in light of the relationship with HRQoL, the changes in PA from middle age to old age can have a possible relationship with frailty. Hence, the state of frailty according to the stages of PA is suggested to examine in future research.
Despite the benefits of PA, most people find it difficult to start and maintain PA [32, 33]. Health behavior is not easy to modify because of long-term habits; furthermore, it is difficult to influence simply by value judgment and norms that say PA is beneficial to health . A step-by-step intervention program is important to improve motivation, intention, and practice. A 12-week intervention study with older Korean-Americans showed that PA, walking endurance, and flexibility were higher in the group that received PA motivational intervention that incorporated social support, empowering education, and motivational education. A systematic literature review of motivational studies for PA using behavior change techniques (BCTs) showed the effectivity of BCT in improving PA. Therefore, we recommend a motivational method through BCT for a PA intervention in older adults.
Similar to the results of the earlier studies, the current study revaled the influence of social economic status on HQoRL among older adults. It seems that the strategy of physical activity intervention or the priority of the population group should be different by the education level, which is among most commonly operationalized social economics status variables, Recent literature shows that a lower level of education was strongly related to reported a lower level of physical functioning  and daily life activities , and a decrease in quality of life [35, 36, 37]. According to the Korea National Health and Nutrition Examination Survey published recently , older adults with a higher level of education showed higher walking adherence to “more than 5 days a week and more than 30 minutes a day,” whereas older adults with a low educational level (did not graduate from elementary school) did not practice recommended walking. This suggests that interventions aimed at changing individuals' behavior to increase physical activity should be prioritized for populations with lower socioeconomic status to reduce existing health inequalities.
Since these secondary data were obtained from people at home, excluding members from branch or dead households at the time of the survey, there is a possibility that the group with low quality of life and high probability of dying from severe illness may have been excluded. Most of the HRQoL responses were concentrated in ≥0.9 in the range of 0–1; therefore, the logistic regression value was estimated by dividing the 10% lower cutoff point. In future research, we recommend comparing the amount of PA according to the five dimensions of the EuroQol quality-of-life system or analyzing the quality of life more discriminatively through other research tools. In addition to analyzing the effect of PA frequency and intensity analysis on quality of life in more detail, future studies should analyze both aerobic PA and strength exercise because they have a positive effect on health in older adults.
Explanatory variables for the association between PA and quality of life through mediators such as self-efficacy and social support should be identified. In the survey data of this study, the responses regarding PA were subjective and memory-dependent; thus, recall bias may occur. Thus, we recommend that more objective data be collected through wearable devices and that experimental research be conducted to supplement the evidence for PA and quality of life.
All data from which the conclusion of this study can be made are included in this manuscript and no data is deposited in any public data repository.