Impact of repeated bouts of eccentric exercise on myogenic gene expression

Evidence indicates that repeated-bouts of eccentric exercise (EE) do not exacerbate the extent of muscle damage indices, as compared to a single-bout. We hypothesized that molecular adaptations, under repeated-bouts of EE, would include suppression of muscle repair inhibitory factors such as myostatin and up-regulation of muscle repair positive regulatory factors such as myogenic regulatory factors (MRFs). Fifteen males were recruited for this study. The exercise group (n=9) successfully completed six sets of 15 reps of maximum voluntary eccentric contractions, for six consecutive days, using a dynamometer (Multicont-II). Blood and muscle biopsy samples were obtained from each subject 1 week prior to exercise, 2 days post the first training session, and 24 h after the last training session. Gene expression levels were determined using real-time RT-PCR. Blood samples were analyzed for creatine kinase (CK) and lactate-dehydrogenase (LDH) activity. Repeated-bouts of EE induced a large down-regulation of myostatin mRNA (-73%) which persisted throughout the study. The responses of MRFs were mild. At day 3 only myogenin increased significantly (1.9 fold) while MyoD decreased by 45%. Surprisingly, at day 7, despite the presence of muscle damage indices, all MRFs returned to the pre-exercise levels. The results of the present study showed that repeated-bouts of EE, for six consecutive days, dramatically decreased Myostatin mRNA expression but impaired the expression patterns of MRFs such that, with the exception of myogenin that showed a moderate non-sustained increase, MyoD and MYf5 response was minimal.