Impact of repeated bouts of eccentric exercise on myogenic gene expression

Abstract

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.

Effects of pre-exercise feeding on serum hormone concentrations and biomarkers of myostatin and ubiquitin proteasome pathway activity

“…Due to the large variance commonly attributed to molecular variables, the Shapiro-Wilk statistic was performed for each dependent variable to ensure a normality in distribution existed. If data exhibited a non-normal distribution (i.e., skewness and/or kurtosis [1.96, or Shapiro-Wilk statistic p value\0.05) and standard transformation approaches were not possible, a nonparametric approach, as has been previously reported [37,38], was used to analyzed changes in gene expression. The Kruskal-Wallis statistic was employed to detect between-condition differences at each time point.…”

Role of MyoD in denervated, disused, and exercised muscle

“…18 MyoD has been suggested to be an important regulator involved in the adaptation of the skeletal muscle to mechanical stress such as exercise. The influence exercise has on MyoD regulation remains unclear, as both an increase 9,43,65,89,114 and decrease 22 in MyoD expression after exercise as well as no change at all 58,60,68,98 have been found. These discrepant results might be due partly to the different exercise protocols used as well as to the metabolic status of the muscle prior to the intervention or the time at which muscle specimens were taken.…”

“…Twenty-four hours after 6 consecutive days of exercise, MyoD expression returned to the pre-training levels despite evidence of muscle damage, such as elevated serum creatine kinase and lactate dehydrogenase activity. 22 Since MyoD expression varies over time, multiple sampling is essential to avoid missing a MyoD response postexercise (Fig. 4).…”

Myogenic satellite cels: a brief review

“…In order to occurs muscular fibre hypertrophy, the addition of new myonuclei to fibers is essential, and this can be facilitated by the proliferation of satellite cells and the differentiation of their progeny into new myonuclei that fuse with existing fibres (Snijders et al, 2009). With this exercises, myogenic regulatory factors mRNA expression appears to increase following the resistance exercise in both young and older subjects (Costa et al, 2007). In addition, the literature is precise about impaired aged Notch pathway.…”