Different effects on human skeletal myosin heavy chain isoform expression: strength vs. combination training

Myosin heavy chain (MHC) isoform expression changes with physical training. This may be one of the mechanisms for muscular adaptation to exercise. We aimed to investigate the effects of different strength-training protocols on MHC isoform expression, bearing in mind that alpha-MHCslow ( newly identified MHC isoform) mRNA may be upregulated in response to training. Twelve volunteers performed a 6-wk strength training with maximum contractions (Max group), and another 12 of similar age performed combination training of maximum contractions and ballistic and stretch-shortening movements (Combi group). Muscle samples were taken from triceps brachii before and after training. MHC isoform composition was determined by SDS-PAGE silver staining, and mRNA levels of MHC isoforms were determined by RT-PCR. In Max group, there was an increase in MHC2A (49.4 to 66.7%, P <0.01) and a decrease in MHC2X (33.4 to 19.5%, P < 0.01) after training, although there was no significant change in MHCslow. In Combi group, there was also an increase in MHC2A (47.7 to 62.7%, P < 0.05) and a decrease in MHCslow (18.2 to 9.2%, P < 0.05) but no significant change in MHC2X. An upregulation of alpha-MHCslow mRNA was, therefore, found in both groups as a result of training. The strength training with maximum contractions led to a shift in MHC isoform composition from 2X to 2A, whereas the combined strength training produced an MHC isoform composition shift from slow to 2A.