Zhou, Chuyi; (2025) Associations Between Physical Activity and Frailty in Chinese and English Middle-aged and Older Adults: Evidence from the China Health and Retirement Longitudinal Study (CHARLS) and the English Longitudinal Study of Ageing (ELSA). Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Background: Frailty is an important indicator of health status for older adults and is closely linked with physical activity (PA). Existing evidence shows that performing PA can delay the progression of frailty in older adults. However, the associations between different aspects of PA (total PA level, total volume of PA, and PA intensity pattern) and frailty are still unclear. The role of age in this relationship is also inconclusive, especially in longitudinal studies. Moreover, the comparative study on the rural-urban difference in the association between PA and frailty in Chinese and English populations is lacking. Aims: The aims of this thesis are to examine the associations between PA and frailty and compare the similarities and differences in these associations between older Chinese and English adults. Methods: Data from the China Health and Retirement Longitudinal Study (CHARLS; 2011 to 2018) and the English Longitudinal Study of Ageing (ELSA; 2010 to 2018) were used in this study. Frailty was measured by the frailty index (FI), which contains physical, physiological and cognitive aspects of frailty. PA was assessed using the total PA level, total volume of PA, and PA intensity pattern. Wave 1 of CHARLS (n=5,136) and Wave 5 of ELSA (n=9,535) were considered baseline waves for this study. Changes in PA were assessed using waves 1 and 3 (2011 to 2015) in CHARLS, wave 5 and wave 8 (2010 to 2016) in ELSA. Multivariable linear regression models were used to analyse the cross-sectional relationships between PA and frailty at baseline and the association between changes in PA and subsequent frailty. Multivariate mixed-effect regression models were applied to explore the longitudinal relationships between baseline PAs and frailty during follow-up. Predative fitted values were used to plot the trajectory of frailty. Results: In cross-sectional analyses, higher total PA levels, higher PA volume levels, and higher PA intensity patterns were associated with lower FI scores in CHARLS. In longitudinal analyses, Chinese middle-aged and older adults who engaged in higher total PA levels, the highest total PA volume, and moderate to vigorous PA intensity patterns had lower trajectory of frailty over time. Similar results were found in ELSA. Additionally, age was an effect modifier in the longitudinal association between three aspects of PA and frailty in Chinese participants. The magnitude of frailty reduction after performing PA was greater among Chinese adults of older age than those of younger age, though this result was not observed in English participants. Moreover, changes in PA over time were not associated with subsequent frailty in Chinese participants, while this association was statistically significant in their English counterparts: those who increased their PA intensity pattern or maintained a high PA intensity pattern over time had a lower FI score later on compared to those who maintained inactivity or only walking. Furthermore, in Chinese urban areas, the effect of walking on reducing frailty was comparable to moderate and vigorous PA, while in rural areas, vigorous PA was the most effective intensity for reducing frailty. In ELSA, no differences were observed in the association between PA intensity pattern and frailty between rural and urban areas. Conclusions: This study will provide a deeper understanding of the association between PA and frailty by examining the association between three aspects of PA and frailty, exploring the role of age in this association, and comparing the differences in this association across and within countries. The findings can offer valuable suggestions for developing PA guidelines for frailty prevention and management in Chinese middle-aged and older adults and provide profound implications for future research, practices, and policymaking.

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