Effects of low- and high-intensity resistance exercise on skeletal muscle specific transcription factor activity and myosin heavy chain gene expression in males.

A single bout of resistance training is capable of activating the expression of many diverse groups of genes including myosin heavy chain (MHC) isoforms and the myogenic regulatory factors (MRF). However, the role of exercise intensity in regards to the effects on transcription and protein synthesis are not well defined. Therefore, the purpose of this study was to investigate the effects of exercise intensity on MRF mRNA and protein and MHC mRNA isoforms. Thirteen male participants (21.5 ± 2.9 yrs, 86.1 ± 19.5 kg, 69.7 ± 2.7in) completed two bouts [low-intensity (LI = 65% 1-RM) and high-intensity (HI = 85% 1-RM)] of single-legged resistance exercise. The resistance exercise bout consisted of four sets of leg press and leg extension. Muscle biopsies were obtained from each leg immediately before exercise (PRE), and at 30 minutes (30MPST), 2 hours (2HRPST), and 6 hours (6HRPST) following each resistance exercise bout. Data were analyzed using RT-PCR for mRNA expression and ELISA for protein expression. Statistical analyses were performed by utilizing a 2 x 4 MANOVA (level of significance was set at p < 0.05). Results indicated that MHC I, IIb, and IIx all significantly increased in response to resistance exercise (p < 0.001). Furthermore, exercise intensity/volume played a role with LI high volume exercise stimulating a more positive response in MHC I (p < 0.001) and HI eliciting a greater response in MHC IIb and IIx (p < 0.001). In regards to the MRF, resistance exercise significantly increased the expression of Myogenin, Myf5, and MRF-4 mRNA (p < 0.05). Furthermore, LI high volume exercise stimulated a more positive response in MyoD, Myogenin, and Myf5 mRNA (p < 0.05), as well as MyoD, Myogenin, and MRF-4 protein (p < 0.05). MRF-4 protein significantly increased at 6HRPST over the baseline values (p < 0.05). Changes in MyoD and Myogenin mRNA were also found to be significantly correlated (p < 0.05) to changes in MHC I, IIa, IIb, and IIx mRNA. We can conclude from the findings of this study that both the MHC mRNA and MRF mRNA respond very quickly and positively in response to resistance exercise, in addition to LI high volume exercise eliciting a more positive response in most MRF mRNA and protein.