Abstract Body: Introduction: Current physical activity (PA) recommendations support replacing time spent sedentary with PA of any intensity. There is ample evidence that moderate/vigorous intensity PA is beneficially associated with physical function. Light intensity PA may provide an additional opportunity to improve physical function in inactive individuals. However, the longitudinal associations of replacing sedentary time with light intensity PA and physical function are not clear.
Hypothesis: We hypothesized that replacing sedentary time with light intensity PA is associated with better physical function.
Methods: Participants in the CARDIA study with accelerometer data at the Years 20 ([Y20] 2005-06) and 35 ([Y35] 2020-22) exams and physical performance at Y35 (n=996) were included. Measures of balance, endurance, gait speed, grip strength, and lower extremity strength Y35 were used to create a composite physical performance (CAPP) score; higher scores represent better physical function. We used compositional isotemporal substitution models to estimate predicted differences in CAPP resulting from hypothetical replacement of sedentary time with light intensity PA and whether associations varied by initial time spent sedentary, in moderate/vigorous intensity PA, or age. Secondary analyses evaluated associations with individual CAPP components. Multiple imputation was used to address missing data.
Results: Across midlife (mean 45±SD 3.5 [Y20] to 60± 3.6 [Y35] years old), 26% of participants increased daily time in light intensity PA. Mean CAPP score at Y35 was 13.1±SD 3.9. Hypothetical replacement of 3 hours of daily sedentary time with light intensity PA from Y20 to Y35 was associated with 1.0 unit greater CAPP score at Y35 (95% CI: 0.6,1.4) (Figure). This association was similar across initial time spent sedentary, in moderate/vigorous intensity PA, and age. By subcomponent, hypothetical replacement of 3 hours of daily sedentary time with light intensity PA was associated with better balance (6 seconds; 95% CI: 4,8), endurance (86 feet; 95% CI: 49,123), gait speed (0.04 m/s, 95% CI: 0.01,0.06), and lower extremity strength (0.7 sit-stands; 95% CI: 0.2,1.2), but not grip strength (0.6 kg/lbs of force; 95% CI: -0.3,1.4).
Conclusions: Replacement of sedentary time with light intensity PA across midlife was associated with better physical function. Interventions to increase light intensity PA may help improve physical function in midlife in active and inactive individuals.