Reallocating accelerometer-assessed sedentary time to light or moderate- to vigorous-intensity physical activity reduces frailty levels in older adults: An isotemporal substitution approach in the TSHA Study

Introduction: The effects of replacing sedentary time with light or moderate- to vigorous-intensity physical activity on frailty are not well known. Aim: To examine the mutually independent associations of sedentary time (ST), light-intensity physical activity (LPA), and moderate- to vigorous-intensity physical activity (MVPA) with frailty status in older adults. Methods: A total of 628 people aged ≥65 years from the Toledo Study of Healthy Aging (TSHA) participated in this cross-sectional study. Frailty was measured using the Frailty Trait Scale. Hip-worn accelerometers were used to capture objective measurements of ST, LPA, and MVPA. Linear regression and isotemporal substitution analyses were used to examine associations of ST, LPA, and MVPA with frailty status. Analyses were also stratified by comorbidity. Results: In single and partition models, LPA and MVPA were negatively associated with frailty. Time in sedentary behavior was not associated with frailty in these models. In the isotemporal substitution models, replacing 30 minutes/d of ST with MVPA was associated with a decrease in frailty [β −2.460; 95% confidence interval (CI): −3.782, −1.139]. In contrast, replacing ST with LPA was not associated with favorable effects on this outcome. However, when the models were stratified by comorbidity, replacing ST with MVPA had the greatest effect on frailty in both the comorbidity (β −2.556; 95% CI: −4.451, −0.661) and the no comorbidity group (β −2.535; 95% CI: −4.343, −0.726). Moreover, the favorable effects of LPA in people with comorbidities was found when replacing 30 minutes/d of ST with LPA (β −0.568; 95% CI: −1.050, −0.086). Conclusions: Substituting ST with MVPA is associated with theoretical positive effects on frailty. People with comorbidity may also benefit from replacing ST with LPA, which may have important clinical implications in order to decrease the levels of physical frailty.