title: Myosin heavy chain IIX overshoot in human skeletal muscle.
abstract: The distribution of myosin heavy chain (MHC) isoforms, fiber type composition, and fiber size of the vastus lateralis muscle were analyzed by sodium dodecylsulfate polymerase gel electrophoresis (SDS-PAGE), ATPase histochemistry, and immunocytochemistry in a group of adult sedentary men before and after 3 months of heavy-load resistance training and, subsequently, after 3 months of detraining. Following the period of resistance training, MHC IIX content decreased from 9.3 +/- 2.1% to 2.0 +/- 0.8% (P < 0.01), with a corresponding increase in MHC IIA (42.4 +/- 3.9% vs. 49.6 +/- 4.0% [P < 0.05]). Following detraining the amount of MHC IIX reached values that were higher than before and after resistance training (17.2 +/- 3.2% [P < 0.01]). Changes in fiber type composition resembled the changes observed in MHC isoform content. Significant hypertrophy was observed for the type II fibers after resistance training. Maximal isometric quadriceps strength increased after resistance training, but returned to pretraining levels after detraining. The present results suggest that heavy-load resistance training decreases the amount of MHC IIX while reciprocally increasing MHC IIA content. Furthermore, detraining following heavy-load resistance training seems to evoke an overshoot in the amount of MHC IIX to values markedly higher than those observed prior to resistance training.
authors.affiliation: Copenhagen Muscle Research Centre, Department of Molecular Muscle Biology, Rigshospitalet Section 9312, Juliane Mariesvej 20, First Floor, DK-2100 Copenhagen, Denmark. jla@rh.dk
authors.forename: J L
authors.initials: JL
authors.lastname: Andersen
authors.forename: P
authors.initials: P
authors.lastname: Aagaard
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000328:Adult; D004591:Electrophoresis, Polyacrylamide Gel; D004734:Energy Metabolism / Q000502:physiology; D006801:Humans; D007536:Isomerism; D007537:Isometric Contraction / Q000502:physiology; D050356:Lipid Metabolism; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000201:enzymology / Q000502:physiology / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism* / Q000502:physiology; D009213:Myography; D018995:Myosin Heavy Chains / Q000096:biosynthesis*; D010084:Oxidation-Reduction; D014891:Weight Lifting / Q000502:physiology
chemical_list: D000251:Adenosine Triphosphatases; D018995:Myosin Heavy Chains