Relationships between physical activity dimensions and frailty incidence and progression in middle-aged and older adults: A 7-year cohort study.

Objective: Physical activity (PA) is well-established as a key factor in frailty prevention. However, existing evidence relies predominantly on cross-sectional studies, creating a gap in understanding the long-term impact of PA on frailty progression. This study therefore aimed to investigate the longitudinal associations of multiple PA dimensions with both the incidence and trajectory of frailty in middle-aged and older adults in China. Methods: This 7-year cohort study included 5916 initially non-frail participants (frailty index, FI < 0.25) from the China Health and Retirement Longitudinal Study. PA was assessed using the International Physical Activity Questionnaire and quantified in terms of frequency, duration, and volume. Frailty was assessed with a validated 40-item FI. The study employed discrete-time survival models to estimate hazard ratios (HRs) for incident frailty (FI ≥ 0.25) and linear mixed-effects models to evaluate the FI trajectory over time. Results: During the 7-year follow-up, 22.9 % of participants developed frailty. In fully adjusted models, most dimensions of PA (frequency, duration, and volume) demonstrated inverse associations with frailty risk. A clear dose-response relationship was observed, whereby engaging in vigorous-intensity physical activity (VPA) for 1-2 days per week was associated with a 63 % lower risk (Adjusted HR = 0.37). Similarly, even as little as 10-29 min of VPA per day was associated with a 75 % risk reduction (Adjusted HR = 0.25). Higher levels of PA were also significantly associated with a slower annual increase in the FI score (e.g., Adjusted β = -0.0025 for VPA 6-7 days/week). Gender-stratified analyses revealed that the protective association of VPA was more pronounced in men, whereas moderate-intensity physical activity (MPA) was more consistently associated with reduced frailty risk in women. Conclusion: The findings suggest that regular PA, particularly VPA, is associated with a lower incidence and slower progression of frailty, showing a clear dose-response relationship. Notably, even modest amounts of VPA were associated with substantial protection. The associations appeared to be gender-specific, with the protective association of VPA appearing more pronounced in men and MPA more consistent for women. These findings underscore the critical importance of promoting tailored PA for frailty prevention in aging populations.