title: Progressive resistance training reduces myosin heavy chain coexpression in single muscle fibers from older men.
abstract: The purpose of this study was to examine myosin heavy chain (MHC) and myosin light chain (MLC) isoforms following 12 wk of progressive resistance training (PRT). A needle biopsy was taken from the vastus lateralis to determine fiber-type expression [ATPase (pH 4.54) and MHC/MLC] in seven healthy men (age = 74.0 +/- 1.8 yr). Subjects were also tested for 1-repetition maximum (1-RM), pre- and posttraining. The progressive knee extensor protocol consisted of three sets at 80% of 1-RM 3 days/wk for 12 wk. Freeze-dried, single muscle fibers were dissected for MHC and MLC analysis and then subjected to SDS-PAGE and silver staining, pre- and posttraining. MHC expression increased in the I (10.4%; P < 0.05) and decreased in I/IIa (9.0%; P < 0.05), I/IIa/x (0.9%; P < 0.05), and IIa/x (8.9%; P < 0.05) isoforms, with no change in the IIa and IIx isoforms, pre- vs. posttraining (total fibers = 3,059). The MLC(3f)-to-MLC(2) ratio did not change with the PRT in either the MHC I or MHC IIa isoforms (total fibers = 902), pre- to posttraining. ATPase fiber distribution did not significantly differ following training (I: 50. 4 +/- 6.7 vs. 51.9 +/- 7.9, IIa: 36.8 +/- 5.3 vs. 41.1 +/- 7.0, IIb: 12.8 +/- 5.6 vs. 7.0 +/- 4.0%; pre- vs. posttraining, respectively). 1-RM increased (51.9%; P < 0.05) from pre- to posttraining. The PRT provide a stimulus for alterations in MHC isoforms, which demonstrated a decrease in all hybrid isoforms and an increase in MHC I expression (not found in the ATPase results), unlike the MLC ratio (3:2), which was not altered with training.
authors.affiliation: Human Performance Laboratory, Ball State University, Muncie, Indiana 47306, USA.
authors.forename: D L
authors.initials: DL
authors.lastname: Williamson
authors.forename: M P
authors.initials: MP
authors.lastname: Godard
authors.forename: D A
authors.initials: DA
authors.lastname: Porter
authors.forename: D L
authors.initials: DL
authors.lastname: Costill
authors.forename: S W
authors.initials: SW
authors.lastname: Trappe
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000368:Aged / Q000502:physiology*; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000201:enzymology / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000096:biosynthesis*; D018994:Myosin Light Chains / Q000096:biosynthesis; D005082:Physical Exertion / Q000502:physiology*; D020033:Protein Isoforms / Q000096:biosynthesis
chemical_list: D018994:Myosin Light Chains; D020033:Protein Isoforms; D000251:Adenosine Triphosphatases; D018995:Myosin Heavy Chains