LIPID METABOLISM IN CHRONICALLY STIMULATED AND ENDURANCE-TRAINED MUSCLES OF HUMAN SUBJECTS 444

Abstract

The purpose of the present study was to investigate the changes in the skeletal muscle lipid metabolism of subjects submitted to 4 weeks of chronic low-frequency electrical stimulation (LFES). LFES was delivered to the knee extensor muscles of 9 subjects at a frequency of 8Hz, 8 hrs/d, 6 days/wk. Vastus lateralis samples were taken before and after the stimulation protocol and were analyzed for β-hydroxyacyl CoA dehydrogenase (HADH) and carnitine palmitoyl transferase (CPT) activities, and cytosolic fatty acid-binding protein (FABP). Levels (mean±SE) of these markers of lipid metabolism were compared to those of 10 highly trained cyclists (VO2max of 68±2 ml O2·kg-1·min-1). LFES induced significant increases in CPT (0.10±0.01 vs 0.13±0.01 U/g ww, p<0.001) and HADH (15.4±0.5 vs 18.3±0.6 U/g ww, p<0.002) activities as well as in FABP content (6.5±1.5 vs 9.0±1.8 R.U./g ww, p<0.01). Values of HADH and CPT activities in stimulated muscles were similar to those in muscles of highly trained cyclists(HADH: 19.7±0.8 U/g ww, CPT: 0.13±0.01 U/g ww), whereas the FABP content (15.7±3.0 R.U./g ww) tended (p=0.08) to be higher than that of stimulated muscles. These results indicate that 4 weeks of chronic LFES induced significant increases in the skeletal muscle lipid metabolism. They also revealed that HADH and CPT activities, but seemingly not the FABP content, of endurance-trained muscles can be reached by increasing muscle contractile activity with the use of chronic LFES.