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This Article Full Text Full Text (PDF) Data Supplement All Versions of this Article: 570/3/611    most recent jphysiol.2005.101642v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by D'Antona, G. Articles by Bottinelli, R. Search for Related Content PubMed PubMed Citation Articles by D'Antona, G. Articles by Bottinelli, R. Related Collections Skeletal Muscle and Exercise

¹ Department of Experimental Medicine, Human Physiology Unit, University of Pavia, Pavia, Italy
² Department of Sciences and Biomedical Technologies, University of Milano, Milano, Italy
³ Fondazione Salvatore Maugeri (IRCCS), Scientific Institute of Pavia, Pavia, Italy
⁴ Interuniversitary Institute of Miology, University of Pavia, Pavia, Italy

Needle biopsy samples were taken from vastus lateralis muscle (VL) of five male body builders (BB, age 27.4 ± 0.93 years; mean ±S.E.M.), who had being performing hypertrophic heavy resistance exercise (HHRE) for at least 2 years, and from five male active, but untrained control subjects (CTRL, age 29.9 ± 2.01 years). The following determinations were performed: anatomical cross-sectional area and volume of the quadriceps and VL muscles in vivo by magnetic resonance imaging (MRI); myosin heavy chain isoform (MHC) distribution of the whole biopsy samples by SDS-PAGE; cross-sectional area (CSA), force (P_o), specific force (P_o/CSA) and maximum shortening velocity (V_o) of a large population (n= 524) of single skinned muscle fibres classified on the basis of MHC isoform composition by SDS-PAGE; actin sliding velocity (V_f) on pure myosin isoforms by in vitro motility assays. In BB a preferential hypertrophy of fast and especially type 2X fibres was observed. The very large hypertrophy of VL in vivo could not be fully accounted for by single muscle fibre hypertrophy. CSA of VL in vivo was, in fact, 54% larger in BB than in CTRL, whereas mean fibre area was only 14% larger in BB than in CTRL. MHC isoform distribution was shifted towards 2X fibres in BB. P_o/CSA was significantly lower in type 1 fibres from BB than in type 1 fibres from CTRL whereas both type 2A and type 2X fibres were significantly stronger in BB than in CTRL. V_o of type 1 fibres and V_f of myosin 1 were significantly lower in BB than in CTRL, whereas no difference was observed among fast fibres and myosin 2A. The findings indicate that skeletal muscle of BB was markedly adapted to HHRE through extreme hypertrophy, a shift towards the stronger and more powerful fibre types and an increase in specific force of muscle fibres. Such adaptations could not be fully accounted for by well known mechanisms of muscle plasticity, i.e. by the hypertrophy of single muscle fibre (quantitative mechanism) and by a regulation of contractile properties of muscle fibres based on MHC isoform content (qualitative mechanism). Two BB subjects took anabolic steroids and three BB subjects did not. The former BB differed from the latter BB mostly for the size of their muscles and muscle fibres.

(Received 10 November 2005; accepted after revision 5 December 2005; first published online 8 December 2005)
Corresponding author G. D'Antona: Department of Experimental Medicine, Human Physiology unit, University of Pavia, Via Forlanini 6, 27100 Pavia, Italy. Email: giuseppe.dantona{at}unipv.it

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