Progressive resistance training reduces myosin heavy chain coexpression insingle muscle fibers from older men

The purpose of this study was to examine myosin heavy chain (MHC) and myosi n light chain (MLC) isoforms following 12 wk of progressive resistance trai ning (PRT). A needle biopsy was taken from the vastus lateralis to determin e 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 maximu m (I-RM), pre- and posttraining. The progressive knee extensor protocol con sisted of three sets at 80% of 1-RM 3 days/wk for 12 wk. Freeze-dried, sing le muscle fibers were dissected for MHC and MLC analysis and then subjected to SDS-PAGE and silver staining, pre- and posttraining. MHC expression inc reased 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 MLC3f-to-MLC2 ratio did not change with the PRT in either the MHC I or MHC IIa isoforms (total fibers = 902), pre- to posttraining. ATPase fiber d istribution 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 v s. 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 alte rations in MHC isoforms, which demonstrated a decrease in all hybrid isofor ms and an increase in MHC I expression (not found in the ATPase results), u nlike the MLC ratio (3:2), which was not altered with training.