Thanks, I will read up on the periodization links you included, I see they have a list of references for further reading at the end which hopefully should address most of my questions.
Uh, very little fiber type change (type IIb to type IIx does occur some), NO quantifyable hyperplasia in humans.
While I was mentioning that just in passing under the umbrella of protein expression changes (which includes a lot more things of course), I did want to make a point about
muscle fiber type changes, because I thought it was a well established scientific fact that you can and will have switching between any and all types of fibers (1, 2a and 2x or 2b for human/animal).
The distinction itself is a bit artificial as muscle fibers transition say between slow oxidative typeI and fast twitch typeII fibers in a more gradual way from one set of characteristics to another, so it's a bit arbitrary to decide in those cases when a myotube can now be fully called one way or another (this is very common in cell biology actually whenever you have numerous transitions between cell types like in immunology or stem cell differentiation sequences). Every characteristic of their working definition, like protein expression (myosin chain types), number of mitochondria, vascularization and metabolism is subject to turnover, adaptation and change in response to exercise. This has been demonstrated in humans as well as in animal models.
If I had to put it in those intuitive-sounding analogies that I don't usually like to hear as the only explanation, that's why people are not strictly born marathon runners or sprint runners but can actually transition from one to the other and do ok, while showing a marked change in proportion and number of fiber types of one type or another (e.g., you are not just born with say 30% of one and 70% of the other and able to only change the respective size of each, rather you can also change their proportional number through exercise by causing some of those fibers to switch type to whatever you need).
However I wouldn't say this just because of a hand-wavy analogy. Rather I would say this is a well-established scientific fact because of the extensive amount of studies that demonstrated and measured these changes in humans and animals, and even figured out the molecular mechanisms for each of the changes that occur in these transitions.
As a bit of an overview, see for example
Training effects on the contractile apparatusOr for more specific details on exercise-induced increase in mitochondria numbers
Contractile activity-induced mitochondrial biogenesis in skeletal muscleAnd for an example of an inducible repeatable switch from type II to type I (this one in mice since they used gene manipulation directly)
Regulation of Muscle Fiber Type and Running Endurance by PPARδor in Rats (where early studies had some trouble showing transition from type II to type I but later were able to demonstrate it):
Fast-to-slow transformation in stimulated rat muscleThat's why I would say fiber type switches between any of the 3 forms is a well established fact with a known and clear mechanism. If you have any evidence, literature, studies or reasoning that suggests otherwise I would be of course very interested in examining them.
In terms of your comment on
hyperplasia and hypertrophy, I wanted to make sure we did not have a misunderstanding on the nomenclature.
The examples I given of myoblasts from satellite cells traveling to the site of myotrauma and fusing with the damaged myotube is not hyperplasia, it's still hypertrophy (as the number of muscle fibers does not increase when myoblasts fuse to existing myotubes), and it is again a well established mechanism occurring often in humans in response to exercise.
The word hypertrophy is a bit problematic because it's one of those vague descriptive terms, it doesn't say if the muscle increased in size because of water retention, blood volume, increased in contractile protein (from more transient increases in protein expression), or a more permanent adaptation like the increase in nuclei and organelles like mitochondria and ribosomes from entire myoblasts fusions.
At some point in my post I also mentioned in passing hyperplasia next to hypertrophy just because it can happen through the same mechanism under the right conditions, basically if the myoblasts arrive at a site of muscle injury and they happen to be in much larger number with less myotubes to fuse to and enough empty space, they will tend to align to each other, fuse with each other and differentiate to new myotubes. If you every tried growing myoblasts in cultures that happens a lot even spontaneously. That's the only reason why I mentioned them together really, although the end result is quite different (in terms of number of fibers).
On hyperplasia I would agree that it's a lot easier to demonstrate in animals, since you can do studies like injecting them directy with IGF or tying a big weight on one limb for weeks/months and then count the increased number of fibers directly, that's how we know for sure it can and does happen in animals. For humans I would still strongly believe that it can happen as well but again we are talking about a more severe stimulus and precision in measurement that is hard to replicate/produce in humans without getting in trouble with some ethics board
The question about fiber number increase in humans in response to exercise is a bit complicated by the fact that fiber numbers are estimated. Even studies that have been used in the past to suggest that hypertrophy is unlikely to happen from normal exercise in humans actually are careful to point out that they did see muscle fiber numbers increase after training in a subset of their test subjects (some of the college men):
from
"Muscle fiber hypertrophy, hyperplasia, and capillary density in college men after resistance training"With respect to fiber number estimates, exclusion of the two GH subjects whose fiber numbers were estimated resulted in a significant increase in the estimated fiber number (from 279.8 ± 65.5 × 10^3 pretraining to 306.2 ± 75.6 × 10^3 posttraining) in the remaining six subjects. Therefore, although muscle fiber hypertrophy was a determinant of overall muscle enlargement for all subjects, the contribution of muscle fiber hyperplasia may have been dependent on the magnitude of type II fiber hypertrophy. These contrasting results suggest there may be differences in how individuals achieve similar degrees of muscle hypertrophy.
Although our subject population was not homogenous for pretraining variables, the degree of muscle fiber hypertrophy and/or hyperplasia after training did not appear to be dependent on the pretraining values for muscle fiber area(s), biceps brachii CSA, or 1-RM strength.
On this point again if you have any specific study etc that you think would contradict any of this please let me know.
Sorry if any of this might seem a bit confrontational (just because we seem to have different background premises on a few things), it's not intended to. I just want to make sure I understand and share these more fundamental technical aspects with people that know way more than me about parkour and use training that clearly served them well, so I can better understand these various training strategies.
On a final note on your example of volume, I understand the point you are making and I will definitely try to keep it in mind when training, especially in regards to performance-based variables like strength. It still leaves me with some dissatisfaction because by using more descriptive terms like volume, work, fatigue etc rather than well established phisiological responses and mechanisms, it is hard for me to really be able to compare and contrast the expected outcome and being able to say whether this couldn't be optimized even further.
I have of course your very welcome and convincing personal anecdotal experience (and that of I am sure many many others including various sources you pointed to), and some reasonable explanation of the principles behind it and why it works well, which is enough from a practical perspective.
But in terms of curiosity and intellectual pursuit, as you know what happens often is that various slightly suboptimal training philosophies have done fairly well in the past, and yet something newer and better often comes up, maybe because they focused too much on just one aspect or neglected another. That's why it's nice to know the exact mechanisms suggested, the supporting evidence and the unanswered questions or unproven assumptions, so it's easier to integrate new ideas rather than just remaining a proponent for one philosophy or another.
So anyways I'll keep reading up the links you pointed out to me and I will try to put in practice your suggestions knowing they served you very well in training parkour, and I will try to also find answers to some of the extra questions I have from overthinking things on my own, without necessarily bothering you too much hehe
