Background and aims: There are no data showing whether or not age-related declines in physical function are related to in vitro properties of human skeletal muscle. The purpose of this study was to determine whether physical function is independently associated with histologic and metabolic properties of skeletal muscle in elderly adults.
Methods: The study was a cross-sectional observational study of 39 sedentary, older (60-85 yrs) men and women. A needle biopsy of the vastus lateralis for assessment of muscle fiber type, fiber area, capillary density and citrate synthase and aldolase activities was performed. Physical function tests included the Short Physical Performance Battery (balance, walking speed, and chair rise time), as well as self-reported disability.
Results: Total fiber area (R=-0.41, p=0.02), number of Type II fibers (R=-0.33, p=0.05), and aldolase activity (R=-0.54, p=0.01) were inversely related to age. Persons who reported greater difficulty with daily activities had lower capillary density (R=-0.51, p=0.03) and lower citrate synthase activity (R=-0.66, p=0.03). Walking speed was directly related to fiber area (R=0.40, p=0.02), capillary density (R=0.39, p=0.03), citrate synthase (R=0.45, p=0.03) and aldolase (R=0.55, p<0.01) activities, even after adjustment for age, BMI and disease status.
Conclusions: In older adults, skeletal muscle capillary density and metabolic enzymatic activity are independent predictors of lower extremity physical function.