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J Appl Physiol 98: 2390-2395, 2005. First published January 27, 2005; doi:10.1152/japplphysiol.01103.2004
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HIGHLIGHTED TOPICS
Biomechanics and Mechanotransduction in Cells and Tissues

Effects of resistance training on myosin function studied by the in vitro motility assay in young and older men

M. Canepari,1,4 R. Rossi,1 M. A. Pellegrino,1,4 R. W. Orrell,3 M. Cobbold,2 S. Harridge,2 and R. Bottinelli1,4

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

Submitted 1 October 2004 ; accepted in final form 23 January 2005

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 after 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 yr, YO) and four elderly men (age 68–82 yr, EL) underwent a 12-wk progressive resistance training program of the knee extensor muscles and to one pre- and one posttraining biopsy of the vastus lateralis muscle. The significant increase in one-repetition maximum posttraining in both YO and EL indicated that training was effective. After training, MHC isoform composition showed a shift from MHC2X toward MHC2A 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. One hundred sixty IVMA samples were prepared from 480 single fibers, and at least 50 filaments were analyzed in each experiment. Whereas no training-induced change was observed in Vf of myosin isoform 1 either in YO or in EL, a significant increase in Vf of myosin isoform 2A after training was observed in both YO (18%) and EL (19%). The results indicate that resistance training can change the velocity of the myosin molecule.

myosin isoforms; velocity of shortening


Address for reprint requests and other correspondence: M. Canepari, Dept. of Experimental Medicine, Human Physiology Unit, Univ. of Pavia, Via Forlanini 6, 27200 Pavia, Italy (E-mail: canepari{at}unipv.it)




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