Myostatin expression during human muscle hypertrophy and subsequent atrophy: increased myostatin with detraining

Journal Title (Medline/Pubmed accepted abbreviation): Scand. J. Med. Sci. Sports
Year: 2011
Volume: 21
Page numbers:215-223
doi (if applicable): 10.1111/j.1600-0838.2009.01044.x

Summary of background and research design

Background: Myostatin is an enzyme that negatively regulates muscle mass; high amounts of myostatin will lead to muscle atrophy (breakdown).

Hypothesis: Myostatin expression at the level of the gene (mRNA) and the protein will decrease while participants partake in a 90-day resistance training protocol (leading to muscle hypertrophy) and then myostatin will increase in the 90 days following exercise, while the participants do not train.

Subjects: Fifteen healthy men who had not been involved in sports activities or had done resistance training in the previous year, age 24 ± 0.8 y

Experimental design: Repeated measures
Protocol: The participants completed a 90-day progressive resistance training program.  They went to the gym 3x/wk, lifting progressively heavier weights.  Exercises included leg press, knee extensions, hamstring curl, and various upper body exercises.  After the 90 days, they were asked to not partake in resistance or endurance exercise (“detraining period”) for an additional 90 days.  A total of 8 muscle biopsies were acquired from the outer quadriceps muscle: before resistance training (PRE), after 30 and 90 days of training (T), and after 3, 10, 30, 60, and 90 days of detraining (D).  Cross-sectional areas (CSA) of the quadriceps muscle fibers were measured using magnetic resonance imaging (MRI).  Total mRNA and protein concentrations were assessed for myostatin and GADPH as a control. 

Summary of research findings
  • The 90-day training protocol increased the CSA of the whole muscle from 77.4 ± 2.5 to 85.2 ± 2.8 cm2 (p < 0.001).  The 90 day detraining period brought the CSA down to pre-training levels (77.1 ± 2.1 cm2).  The CSA of the individual muscle fibers increased accordingly.
  • As expected, myostatin mRNA was downregulated at T30 and T90, and still slightly lower at D3 compared to PRE.  Participants showed induced myostatin mRNA levels from D10-D90.
  • The 10 kDa myostatin protein appeared to increase with resistance training and then decrease back to baseline.  The authors proposed that this protein is the mature protein or a newly discovered form of myostatin.
  • There was not a clear trend in myostatin protein (28 kDa).

Interpretation of findings/Key practice applications

Resistance training decreases myostatin mRNA concentrations, which may lead to the ability to build more muscle mass. On the other hand, stopping a resistance training protocol will cause myostatin mRNA concentrations to increase above pre-training concentrations. However, there are still some questions regarding the quantification of the myostatin protein itself and more research is necessary to confirm that actual protein concentrations reflect the mRNA concentrations.

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