AIM: Whereas the impact of ES strength training on skeletal muscle mass and function has been described in detail, no data are available on the plastic muscular adaptations at the level of single muscle fibers and the molecular mechanisms underlying such adaptations. Thus, the present study aimed to investigate single fibers functional and structural changes and whole muscle proteome adaptation to bilateral ES of the quadriceps muscle in young subjects. METHODS: 14 young (18-30 years of age), healthy, male subjects were subjected to 24, 18-min sessions of isometric (bilateral) ES over a period of 8 weeks with 3 sessions per week. Needles biopsies were taken from the vastus lateralis muscle pre- and post-training. Single fibres were dissected from bioptic samples and chemically skinned. Isometric specific tension (Po/CSA) and maximal shortening velocity (Vo) were estimated at pCa 4.6. MHC composition of the fibre segments and bulk muscles were analysed by SDS-PAGE followed by computerized gel electrophoresis. Changes in MHC mRNA expression were quantified by real-time PCR analysis. 2D gel electrophoresis was used to examine the overall protein pattern before and after ES and spot identification was confirmed by Western Blot. RESULTS: Maximum voluntary contraction (MVC) and neural activation were found to be significantly higher post-training (+20% and +9% respectively). MHC isoform distribution showed a significant shift from MHC-2X towards MHC-2A and MHC-1, i.e. a fast to slow transition. Real-time PCR analysis of changes in MHC expression showed the same pattern. -cardiac, embrional and perinatal MyHC isoforms, considered as transitional isoforms, were expressed at the levels of mRNA but not at the level of protein. Significant increases in Po/CSA in type 1 and 2A fibers (range +8-30%) and Vo in type 1 and 2A and hybrid fibers 1-2A and 2A-2X (range +11-40%) were observed. Fluorescently stained proteome maps showing 600 spots were identified and subdivided in different categories. A significant increased expression of oxidative and antioxidant enzyme expression was observed following ES. CONCLUSION: ES strength training exerts a profound change in function and structure at the level of single muscle fibers and in protein expression pattern of bulk muscle. These changes highlight a peculiar muscular plastic response to ES strength training in comparison with voluntary training. ACKNOWLEDGEMENT: This study was supported by PRIN2007 to GD.
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