Increased Intramyocellular Lipid and Capacity for Fat Oxidation with Exercise Training

Abstract

2260 The association between intramyocellular lipid (IMCL) and insulin resistance may be modulated by the capacity for fatty acid oxidation by muscle. PURPOSE: We examined whether exercise training would increase both IMCL and skeletal muscle's capacity for oxidative fat metabolism in older, previously sedentary individuals. METHODS: Thirteen elderly subjects (5 men; 8 women) participated in a 12 week exercise training intervention. Before and after the intervention, IMCL and oxidative enzyme capacity was determined by quantitative histochemical analysis of vastus lateralis biopsies. Fat oxidation induced by one hour of cycle exercise at 45% of of VO2max was determined with indirect calorimetry. RESULTS: Maximal aerobic capacity (VO2max) increased from 1.65 ± 0.12 to 1.85 ± 0.14 L•min-1 (p<0.05), and systemic fat oxidation increased from 15.03 ± 40 to 19.29 ± 0.80 (μmol•min-1•kg FFM- 1. IMCL increased (p<0.05) from 22.9 ± 1.9 to 25.9 ± 2.6 Arbitrary Units (AU). The oxidative capacity of muscle, determined by SDH staining intensity, increased (p<0.05) from 75.2 ± 5.2 to 83.9 ± 3.6 AU. Finally, the percentage of type I fibers determined by anti-myosin immunohistochemistry significantly increased (p<0.05) from 35.4 ± 2.1 to 40.1 ± 2.3%. CONCLUSIONS: Exercise training increases both the capacity for oxidative fat metabolism and IMCL in older persons. These data suggest that an enhanced capacity for triglyceride within skeletal muscle may represent a positive adaptation to chronic exercise in the context of augmented fat oxidation.