Men's Fitness


We all have had those training partners who seem to grow just by touching a weight. We’ve also had those training partners who can’t seem to grow any decent muscle no matter how hard they train. Although it’s tough to say precisely what separates someone who grows like crazy from weight training and someone who barely grows at all, it is safe to say that it resides somewhere in the genes. When you lift weights you activate genes located on the DNA in the nuclei of your muscle cells. These genes encode for certain proteins that make up the structure of the muscle fibers. When a gene is activated, a copy of it is made in the form of messenger RNA (mRNA). The mRNA is used to build the protein one amino acid at a time via the process known as protein synthesis. Of course, there are many actions along the way that allow lifting a weight to turn on muscle protein synthesis. But scientists believe they are getting closer to understanding why some people have greater muscle protein synthesis and therefore better muscle growth than others. MicroRNAs (miRNAs) may be involved. These are small RNA molecules that bind to mRNA molecules and stop them from generating proteins. So guys who do not build muscle as easily as others may have more of certain miRNAs.


In collaboration, researchers from McMaster University in Canada, the University of Copenhagen in Denmark, and the University of London, placed subjects on a 12-week weight-training program. Those who gained about two pounds or less of lean mass were grouped in the “low-responders” group; those who gained 10 pounds or more were placed in the “high-responders” group. The scientists analyzed specific miRNAs in the subjects’ muscles to see if any differed between the groups.


They reported in the Journal of Applied Physiology that the miRNA known as miR-378 was lower in the low-responders than the high-responders. Lower levels of this miRNA were associated with lower levels of mRNA for the muscle growth factor insulin-like growth factor-1 (IGF-1). They also found that the lower the levels of miR-378, the less muscle mass the subjects gained. It was also discovered that the low-responders had higher levels of the miRNA known as miR-451.


Since miRNAs usually inhibit mRNAs from doing their job to produce proteins, having lower levels of certain miRNAs would benefit muscle growth. This appears to be the case for miR-451, although it is uncertain at this point, which mRNA it targets in muscle cells to inhibit muscle growth. However, in the case of miR-378, having lower levels of this miRNA appears to interfere with the production of the important muscle growth factor IGF-1 and ultimately lowers muscle growth.


Although it is still way too early in the process, and more research needs to be done on these specific miRNAs, the future of bodybuilding may be in finding training programs and/or supplements that decrease miR-451 and increase miR-378 in an effort to better stimulate muscle growth. Only time will tell, but you can count on FLEX to keep you updated on it.

Reference: R. Simão et al., J Strength Cond Res., 26(5):1389–95; 2012.