What causes muscle hypertrophy?
What causes muscle hypertrophy on the cellular level?
This is a very complicated question that most people get wrong and give false answers to. One reason for that is the fact that new research tend to not get out to the general population that fast. I believe most people reading this will have heard the following regarding muscle hypertrophy, that if you just train hard, and break down the muscle fibers the body will repair itself and grow stronger and biggger than before. It's a common saying and a very popular belief amongst the general population and gym goer. This general principle is called muscle damage and is just one of the three hypothesis behind how hypertrophy occur.
Although muscle hypertrophy is one of the mechanisms we’ve longed believed to be responsible for our muscles growing after exercising, recent studies the past decade has shown some conflicting results. Firstly hypertrophy have been proven in studies without markers of muscle damage, as well as studies conducing a lot of muscle damage have shown both none and negative results in hypertrophy, potentially hindering it by increasing resting and recover demands. So if this popular belief probably isn't responsible for hypertrophy, what is?
On to the next hypothesized mechanism of the three, metabolic stress, or the infamous ¨¨pump¨¨ that Arnold Schwarzenegger loved so deeply. The pump is refered to the increased lactic acid and metabolic waste in the muscle as well as an increase of blood. It’s hypothesized that this swelling of the muscle leads to an enlargements of the muscle cells over time and specifically the sarcoplastic fluid that holds all the organells in the body, which is called sarcoplastic hypertrophy. A theory that has yet to be proven by research, however in rodent studies there have been observations and findings that hyperplasia is occuring as a result of metabolic stress. Hyperplasia means that instead of an increased of the fibres, the amount of cells in the muscle increases, especially satelite cells and mitocondria which theoretically should increase the hypertrophic potential. This is all still just speculations regarding us humans at the moment.
however, the last of the three is mechanical tension, which is just the tension that your muscle fibers get put on under an exercise, for an example when you’re curling a weight up your muscle fibres in your biceps generates a force to move the object up, that force or tension is then stimulating signals for hypertrophy.
So the mechanical tension creates a stimuli which sensors presumably in your muscle cells takes up and send forward by molecules, what molecules are still in question, although there are theories. Then that signal reaches another molecule called Mtor that is responsible for a lot of actions in your body, cell growth for one. The Mtor is then sent to the nucleus to create a mRna copy of the Dna string, which is sent to the ribosomes that in turn creates amino acids based off of that mRNA. This whole process is called translation, and this is what we mean when we say ¨protein synthesis¨ . Here are proteins synthesized, and in this case myofibrillar proteins. If this process of creating new proteins is higher than the breakdown of proteins then we are in a positive protein balance and new contractile proteins are sent to the muscle fibres and we have myofibrillar hypertrophy.
Another way of achieving this is through amino acids, the proteins that we eat. The proteins are transported to the cell and activates the Mtor molecule and the same process occurs. This is probably why we need higher amounts of protein when our goal is maximizing muscle. However this stimuli from eating is weaker than the stimuli from training, which is why we need both to optimize hypertrophy.
And when talking about stimulating protein synthesis we can’t look past the importance of testosterone, one of the reasons men tend to have about 30% more muscle mass than women. The reason being is that testosterone binds to androgen receptors in the muscle cell or is turned into DHT which binds to these receptors which is then sent to the ribosomes directly to start the protein synthesis. So more testosterone stimulates more protein synthesis.
Hopefully that explains it somewhat well, it’s a very advanced process which we have yet to uncover every single detail, however the broader picture is quite clear.
I will lists the studies I’ve used for this article down below.