The Biochemistry on How Muscle Grows
How muscle grows could be a challenge to construe, largely because of its physiological complexity. Very few fitness professionals are as well advised in how muscles grow and adapt due to the increasing amounts of health propaganda. Believe it or not, skeletal muscle is actually the most adaptable tissues in the human body.
Contusion to the Muscle Activating Satellite cells
As muscles go through high levels of intense exercise, as in resistance training, they cause tiny microtears in our muscle fibers, which helps with the expansion of our muscles. This obstruction to the muscle cell organelles activates our satellite cells (precursors to skeletal muscle cells), which are located on the outside of our muscle fibers to proliferate to the site of injury. Essentially, a biological effort to repair or restore damaged muscle fibers starts with the satellite cells merging together and to the muscle fibers, often leading to muscle hypertrophy (muscle enlargement). As these satellite cells multiply the majority of them differentiate and merge to muscle fibers to create new muscle protein strands (myofibrils) and repair damaged muscle fibers. Hence, this will allow muscle cell protein strands to increase in thickness and size. It’s also compelling to note that elevated numbers of satellite cells are found to be linked with slow-twitch muscle fibers as compared to fast-twitch muscle fibers within the same muscle, as they are normally going through cell maintenance repair and recovery from it’s daily heavy load.
Muscle Growth Factors
Growth factors are hormone-like compounds that activate satellite cells to assemble the gains in the muscle fiber size. These growth factors have shown to affect muscle growth by regulating satellite cell activity. One of the growth factors, the hepatocyte growth factor is a key regulator of satellite cell activity. This is the activating factor when muscle cells are damaged and research has shown they may also be responsible for causing satellite cells to migrate to the site of injury of the muscle area. The Fibroblast growth factor (FGF) is another growth factor that plays a key role in muscle repair following intense exercise. Research has shown that the role of FGF may be in the revascularization (creating new blood capillaries) process during muscle regeneration. Our third and most critical growth factor, insulin-like growth factor (IGF) plays a critical role in regulating the amount of muscle mass growth, promoting changes occurring in the DNA for protein synthesis, and promoting muscle cell repair. There are two IGFs: IGF-1 and IGF-2. These two factors are distinguishable in terms of the roles they play on tissues because they bind to and activate different receptors. The major action of IGF’s is on cell growth.
Insulin also contributes to the stimulation of muscle growth by promoting protein synthesis and facilitating the entry of glucose into cells. The satellite cells utilize glucose as a fuel substrate, allowing for their growth activities.
Growth hormones stimulate tissues, mainly the liver, to synthesize and secrete IGF-1, which in turn stimulates hypertrophy (enlargement of cell) and hyperplasia (Increase in cell number) of most tissues, including bone.
Lastly, our steroid hormone testosterone may affect our muscle hypertrophy. Testosterone has the ability to produce growth hormone responses in the pituitary, which can enhance cellular amino acid uptake and protein synthesis in the skeletal muscle. In addition, by also interacting with nuclear receptors on the DNA, it results into protein synthesis.
Overview of Muscle Growth: Conclusion
In closing, as you can see muscle growth has its biological complexities and involves the interplay of numerous cellular organelles and growth factors. It’s important to note that the best way to understand how muscle grows is whenever the rate of protein synthesis is greater than the rate of muscle protein breakdown. Muscle protein synthesis and muscle protein breakdown are controlled by complimentary cellular mechanisms.
Through resistance training, nutrition, rest/recovery and sleep optimization will yield you the best results when it comes to maximizing muscle growth. All 4 of these pillars work synergistically to help you obtain optimal performance. Our body is continuously going through a remarkable remodeling process, trying to carefully design the perfect structure based off the healthy physiological habits you feed it.
- Foss, M.L. and Keteyian, S.J. (1998).
Fox’s Physiological Basis for Exercise and Sport. WCB McGraw-Hill.
- Rasmussen, R.B., and Phillips, S.M. (2003). Contractile and Nutritional Regulation of Human Muscle Growth. Exercise and Sport Science Reviews. 31(3):127-131.