Relationship Between Sarcopenia and Intensity-Specific Physical Activity in Older Adults Living in a Rural Area: An Isotemporal Substitution Analysis from the NEIGE Study

Background and Purpose: This study examined the relation between sarcopenia and the replacement of sedentary behavior (SB) with physical activity (PA) of varying intensities using the isotemporal substitution (IS) model. We explored effective intensities and time substitution patterns that may contribute to the prevention of sarcopenia through increased PA and reduced SB. Methods: A total of 527 community-dwelling adults aged 65-84 years in Tokamachi city, Niigata, wore accelerometers for 7 consecutive days to measure time spent in SB, light PA (LPA), and moderate-to-vigorous PA (MVPA). Sarcopenia was assessed based on the criteria of the Asian Working Group for Sarcopenia, using skeletal muscle mass index, gait speed, and grip strength. Three analytical approaches were applied: the single-factor model, partition model, and IS model. The IS model specifically evaluated the effects of reallocating time among SB, LPA, and MVPA. Results and Discussion: The prevalence of sarcopenia in this population was 6.3%. The IS model revealed that reallocating 10 minutes per day of either SB or LPA to MVPA was significantly associated with improved gait speed. Furthermore, replacing SB with MVPA was linked to a reduced prevalence of sarcopenia. Conclusion: These findings suggest that preventing sarcopenia requires not only reducing SB but also replacing sitting or lying time with MVPA. Physical therapists should therefore encourage older adults to decrease prolonged sitting and engage in more active movements, such as brisk walking or structured exercise.