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Background: This study aims to describe the relationships between physical activity (PA), body composition, and multimorbidity over 10 years.Method: Participants (N = 373; 49% women; average age 61.3 ± 6.7 years) were followed for 10 years. Multimorbidity was defined by self-report as the presence of 2 or more of 12 listed chronic conditions. PA (steps per day) at baseline was assessed by pedometer, handgrip strength (HGS) by dynamometer, and appendicular lean mass (ALM) and total body fat mass by dual-energy x-ray absorptiometry. Relative HGS and ALM were calculated by dividing each body mass index (BMI). Regression cubic splines were used to assess evidence for a nonlinear relationship.Results: After 10 years, 45% participants had multimorbidity. There was a nonlinear relationship between PA and multimorbidity-PA was associated with lower multimorbidity risk among individuals who engaged in <10 000 steps/d (relative risk [RR] = 0.91, 95% CI: 0.85, 0.97, per 1 000 steps/d), but not among those who participated in ≥10 000 steps/d (RR = 1.04, 95% CI: 0.93, 1.09, per 1 000 steps/d). Higher BMI (RR = 1.05, 95% CI: 1.02, 1.08, per kg/m2) and fat mass (RR = 1.03, 95% CI: 1.01, 1.04, per kg), and lower relative HGS (RR = 0.85, 95% CI: 0.77, 0.94, per 0.1 psi/kg/m2) and ALM (RR = 0.93, 95% CI: 0.88, 0.98, per 0.1 kg/kg/m2) were linearly associated with a higher risk of multimorbidity. Absolute HGS and ALM were not significantly associated with multimorbidity.Discussion: These findings highlight the potential clinical importance of maintaining adequate levels of PA and of reducing adiposity and maintaining muscle function for minimizing the risk of multimorbidity in older adults. [ABSTRACT FROM AUTHOR]

Aim: To describe the associations of between-person and within-person variability in serum 25-hydroxyvitamin D (25(OH)D), physical activity (PA), and knee pain and dysfunction with muscle mass, strength, and muscle quality over 10 years in community-dwelling older adults.Method: Participants (N = 1033; 51% women; mean age 63 ± 7.4 years) were measured at baseline, 2.5, 5, and 10 years. Lower limb lean mass (LLM) was assessed using dual energy X-ray absorptiometry, lower limb muscle strength (LMS) using a dynamometer, and lower limb muscle quality (LMQ) calculated as LMS/LLM. Knee pain and dysfunction were assessed using the Western Ontario and McMaster Universities Osteoarthritis (WOMAC) index. PA was measured using pedometers. Linear-mixed effect regression models, with adjustment for confounders, were used to estimate the association of within-person and between-person variability in PA, 25(OH)D, and WOMAC scores with muscle mass, strength, and muscle quality.Results: Both between-person and within-person increases in PA were associated with LLM, LMS, and LMQ (all P < 0.05). Within-person and between-person increases in knee pain and dysfunction were associated with LLS and LMQ, but not with LLM (all P < 0.05). Between-person effects showed that higher average 25(OH)D was associated with a higher 10-year average LLM, LMS, and LMQ (all P < 0.05), whereas within-person increases in average 25(OH)D were associated with a higher LMS and LMQ, but not with LLM.Conclusions: Variability in 25(OH)D, pain, and dysfunction within an individual over time is related to muscle changes in that individual. Increasing one's own PA level further increases muscle mass, strength, and quality supporting the clinical recommendation of promoting PA to reduce age-related muscle loss. [ABSTRACT FROM AUTHOR]