Does Training CAUSE Hyperplasia?

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[@benjaminlair]

Great video ! I think that one of the most overlooked methodoligical bias in this study is the way of estimating fiber number. The way they do it implies that fiber size and hypertrophy is similar between all muscle fibers so that the fibers analyzed from msucle biopsy are truly representative of the rest of the muscle. I do not think that this premise is true, at least from my experience in mice, which shows a great effect of muscle fiber area variability and regionalization. This could lead to a significant oversestimation of fiber number in trained individuals in my opinion. I do believe that this is even a bigger bias that study design unless some literature can show that fiber size is homogenous throughout the muscle in humans.

[@datadrivenstrength]

It's a good point! I focused on the philosophical aspects of study design purely because I have limited experience in methods used to estimate fiber number - though I agree that some of the assumptions seemed a bit tough to justify. Mainly just wanted to discuss that, even if you grant the measurement as a accurate representation of the construct it aims to quantify, without putting forward a causal model that aims to elucidate confounders/colliders etc., the effect can't be interpreted causally imo

[@winstonshinya982]

There're studies on animals where they train one side of the subject and then count muscle fibers of both side after training, which discovered causality. e.g., W. Gonyea et al. 1977. For research purpose, It's not rigorous to say that this also works for human, but I guess the evidence is strong enough for coaching purpose

[@ericrhelms]

this is excellent

[@EvanZamir]

I totally get the causality argument but either way it’s a super interesting result. I mean either resistance training does indeed cause significant hyperplasia or if it doesn’t there’s some really wild selection bias going on. I wouldn’t have believed that if you told me. If it is true, then think about the consequences. You could take untrained individuals, count their fiber density and predict whether they will respond better to resistance training. That’s amazing! My guess is because that sounds even more farfetched than the original hypothesis, that the simpler explanation ala Occam’s Razor is actually hyperplasia. Just a thought from a failed academician. 😂