Association between physical activity and handgrip strength among older adults in the Korean longitudinal study of ageing.

Population ageing is progressing rapidly worldwide, with Korea experiencing one of the fastest rates. Handgrip strength is used as a marker for physical capability and has potential as a biomarker of vitality. Among various influencing factors such as socioeconomic status, health behaviors, and genetics, physical activity stands out as a key modifiable lifestyle factor that may help preserve muscle strength in older adults. However, most prior studies have employed cross-sectional designs, which provide only a limited snapshot of this relationship. Longitudinal evidence based on repeated measures is scarce, especially in Asian populations, leaving it unclear whether physical activity maintains a consistent association with muscle strength over time. To examine the longitudinal effect of physical activity on handgrip strength among older Korean adults, we analyzed 50,584 person-wave observations from 9,835 older adults who participated in up to 8 waves of Korean Longitudinal Study of Ageing (KLoSA) over 14 years. A linear mixed model was employed to examine the relationship between physical activity and handgrip strength among older adults. Both variables were assessed biannually in each wave over 14 years. Analyses were stratified by sex, and sensitivity analyses were conducted by levels of baseline physical activity. The dose-response relationship was assessed using a generalized additive mixed model. Engaging in ≥ 30 min of physical activity per day (self-reported) was associated with higher handgrip strength over time in men (coefficient [coef]: 0.51, confidence interval [CI]: 0.35, 0.66) and women (coef: 0.19, CI: 0.07, 0.31), after adjusting for confounders. Additionally, in a separate analysis modeling physical activity as a continuous variable, we observed a moderate dose-response relationship, which was stronger in women and remained robust after accounting for changes over time during the follow-up period in both physical activity levels and handgrip strength. Physical activity was positively associated with handgrip strength, with a moderate dose-response relationship. These findings suggest that engaging in regular physical activity, even of moderate duration, may help preserve muscle strength in older adults.