Muscle Mitochondrial Function And Objective Physical Activity Patterns In Older Adults

Abstract

PURPOSE: Although age-related declines in mitochondrial function affect physical function, the association between mitochondrial function and accelerometry-derived physical activity—a measurement that summarizes biological, phenotypic, functional, and environmental effects on mobility—remains unclear. This study aimed to characterize the degree to which mitochondrial function is linked to free-living, objectively measured daily physical activity across features of intensity, amount, endurance, and accumulation patterning. METHODS: Data are from 449 participants (mean age 71 years; 55% women) in the Baltimore Longitudinal Study of Aging. Mitochondrial function was measured as skeletal muscle oxidative capacity via post-exercise phosphocreatine recovery rate (τPCr) in the vastus lateralis muscle of the left thigh, using 31P magnetic resonance spectroscopy. Accelerometry was collected by a 7-day, 24-hour wrist-worn protocol. Accelerometer metrics extracted include total activity counts/d (intensity), overall active minutes/d (amount), active minutes/d spent in 5 different bout lengths (endurance; ≥10, ≥20, ≥30, ≥40, ≥50, and ≥ 60 min/day lengths) and activity fragmentation (patterning). Linear regression models were used to estimate the association between τPCr and outcomes of total activity counts, overall minutes spent active, and activity fragmentation. For each bout outcome model, tobit regression was used to account for right skewness. RESULTS: After covariate adjustment, higher τPCr (or slower recovery) was associated with lower total activity counts/d (β = -7118.8, SE = 2394.0; p = 0.003). Conversely, τPCr was not associated with daily active minutes/d (p = 0.11) nor activity fragmentation (p = 0.10). In the bout analysis additionally adjusted for # bouts, τPCr was only associated with time spent in activity bouts lasting ≥60 minutes/d (β = -24.0, SE = 0.12; p = 0.04), which can be considered a biomarker of endurance. CONCLUSIONS: Our results suggest that mitochondrial function is associated with features of intensity and endurance to perform activities lasting ≥60 minutes during everyday physical activity engagement. Our findings help define the connection between laboratory-measured mitochondrial function and real-world physical activity behaviors in older adults.