Associations of accelerometry-measured and self-reported physical activity and sedentary behavior with skeletal muscle energetics: The Study of Muscle, Mobility and Aging (SOMMA)

Skeletal muscle energetics decline with age, and physical activity (PA) has been shown to offset these declines in older adults. Yet, many studies reporting these effects were based on self-reported PA or structured exercise interventions. Therefore, we examined the associations of accelerometry-measured and self-reported PA and sedentary behavior (SB) with skeletal muscle energetics and explored the extent to which PA and SB would attenuate the associations of age with muscle energetics. As part of the Study of Muscle, Mobility and Aging (SOMMA), enrolled older adults (n = 879), 810 (mean ± SD age = 76 ± 5 years old; 58% women) had maximal muscle oxidative capacity measured ex vivo via high-resolution respirometry of permeabilized myofibers (maximal oxidative phosphorylation (maxOXPHOS)) and in vivo by 31Phosphorus magnetic resonance spectroscopy (maximal adenosine triphosphate (ATPmax)). Accelerometry-measured SB, light activity, and moderate-to-vigorous PA (MVPA) were assessed using a wrist-worn ActiGraph GT9X over 7 days. Self-reported SB, MVPA, and all physical activity were assessed with the Community Healthy Activities Model Program for Seniors (CHAMPS) questionnaire. Linear regression models with progressive covariate adjustments evaluated the associations of SB and PA with muscle energetics as well as the attenuation of the age/muscle energetics association by MVPA and SB. As a sensitivity analysis, we also examined activPAL-measured daily step count and time spent in SB and their associations with muscle energetics. Every 30 min/day more of ActiGraph-measured MVPA was associated with 0.65 pmol/s × mg higher maxOXPHOS and 0.012 mM/s higher ATPmax after adjusting for age, site/technician, and sex (p < 0.05). Light activity was not associated with maxOXPHOS or ATPmax. Meanwhile, every 30 min/day spent in ActiGraph-measured SB was associated with 0.39 pmol/s × mg lower maxOXPHOS and 0.006 mM/s lower ATPmax (p < 0.05). Only associations with ATPmax held after further adjusting for socioeconomic status, body mass index, lifestyle factors, and multimorbidity. CHAMPS MVPA and all physical activity yielded similar associations with maxOXPHOS and ATPmax (p < 0.05), but SB did not. Higher activPAL step count was associated with higher maxOXHPOS and ATPmax (p < 0.05), but time spent in SB was not. Additionally, age was significantly associated with muscle energetics for men only (P < 0.05); adjusting for time spent in ActiGraph-measured MVPA attenuated the age association with ATPmax by 58% in men. More time spent in accelerometry-measured or self-reported daily PA, especially MVPA, was associated with higher skeletal muscle energetics. Interventions aimed specifically at increasing higher intensity activity might offer potential therapeutic interventions to slow age-related decline in muscle energetics. Our work also emphasizes the importance of taking PA into consideration when evaluating associations related to skeletal muscle energetics.