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J Appl Physiol (January 27, 2005). doi:10.1152/japplphysiol.01103.2004
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Submitted on October 1, 2004
Accepted on January 23, 2005

THE EFFECTS OF RESISTANCE-TRAINING ON MYOSIN FUNCTION STUDIED USING THE "IN VITRO MOTILITY ASSAY" IN YOUNG AND OLDER MEN

M. Canepari1*, R. Rossi2, M. A. Pellegrino1, R. W. Orrell3, M. Cobbold4, S. Harridge4, and R. Bottinelli1

1 Department of Experimental Medicine Human Physiology Unit, University of Pavia, Pavia, Italy; Interuniversity Institute of Myology, Italy
2 Department of Experimental Medicine Human Physiology Unit, University of Pavia, Pavia, Italy
3 Department of Clinical Neurosciences, Royal Free & University College Medical School, London, United Kingdom
4 Department of Physiology, Royal Free & University College Medical School, London, United Kingdom

* To whom correspondence should be addressed. E-mail: Canepari{at}unipv.it.

It is generally believed that the maximum shortening velocity (Vo) of a skeletal muscle fiber type does not vary unless a change in myosin heavy chain (MHC) isoform composition occurs. However, recent findings have shown that Vo of a given fiber type can change following training, suggesting the hypothesis that the function of myosin can vary without a change in isoform. The present study addressed the latter hypothesis by studying the function of isolated myosin isoforms by the use of the in vitro motility assay (IVMA) technique. Four young (age 23-29 YEARS, YO) and four elderly men (age 68-82 YEARS, EL) underwent a 12-wk progressive resistance training program of the knee extensor muscles and to one pre- and one post-training biopsy of the vastus lateralis muscle. The significant increase in 1-RM maximum post-training in both YO and EL indicated that training was effective. Following training, MHC isoform composition showed a shift from MHC-2X towards MHC-2A in YO and no shift in EL. The velocity of sliding (Vf) of actin filaments on pure myosin isoforms extracted from single fibers was studied in IVMA. 160 IVMA samples were prepared from 480 single fibres and at least 50 filaments were analysed in each experiment. Whereas no traininginduced change was observed in Vf of myosin isoform 1 either in YO or in EL, a significant increase in Vf of myosin isoform 2A following training was observed in both YO (18%) and EL (19%). The results indicate that resistance training can change the velocity of the myosin molecule.




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