This is an interesting vid and corresponding article. Again it is hardly definitive as the studies cited are far from exhaustive with tons of limiting factors. It seems to be a well researched bit of info.
There are several interesting factoids I came away with (tho still not sure how to apply them in any sort of day to day).
One is that myofibrillar density actually seems to
consistently decrease in trained athletes. And this is apparently true of powerlifters
and BBers.
However, this
decrease accompanies increases in overall size. IDK at what point myofibrillar density would increase as you shrink, but the trade-off is not going to be worth it!
The
force produced by a muscle fiber is a function of its diameter and not its cross section, so as muscle size goes up, overall force projection will increase as well but is not linear. This is likely related to the above observation re myofibrillar density as it was consistent with both BBers and (to lesser extent but still evident) powerlifters.
The good news - even if inefficient, an increase is muscle size will pretty much always result in an increase in strength above baseline relative to bodyweight.
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About 40% of the typical male’s mass is skeletal muscle. Let’s say he weighs 100kg, and has 40kg of skeletal muscle, and totals 600kg (nice rough numbers just to make the math easy). That’s 15kg per kg of muscle, and a Wilks score of 365. If he increases his muscle mass by 25%, but that extra muscle mass is only 80% as strong, then he’s adding 10kg of muscle and 12kg on his total per kg of muscle added – another 120kg. So, weighing 110kg, he’d have a total of 720, for a Wilks score of 423. He’d only need a total of 620-625 to keep the same Wilks score while added an extra 10kg of muscle, or in other words, the extra muscle he added would need to be only 20% as strong as his original muscle to reach the break-even point.
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Most studies show that strength trained people’s whole muscles have higher specific tensions than those of untrained people. However, this study (to the best of my knowledge) is the only one that compared whole muscle specific tension (force/CSA) to single fiber specific tension pre- and post-training. They found that specific tension for single fibers was unchanged, but specific tension for the whole muscle increased. They posited that lateral force transmission (muscle fibers side-by-side linking up with each other to aid in force transmission) was the most likely cause for the increase in whole-muscle specific tension, and that myofibrillar density within the individual fibers themselves was unchanged since single fiber specific tension didn’t change.
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A last one I thought was very interesting:
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A recent meta-analysis by Schoenfeld et al looking at the effects of training load on hypertrophy, dynamic strength, and isometric strength helps counter one of the main arguments people use to contend that light, high rep training causes sarcoplasmic hypertrophy. People claim that since strength gains are larger with heavier training, heavy training must be adding more contractile proteins (myofibrillar hypertrophy), while lighter training must be expanding muscle size without adding as many contractile proteins (sarcoplasmic hypertrophy). Earlier in this article I discussed why that’s not an entirely logical argument, but this meta-analysis provides us with some direct evidence to refute it.
Unsurprisingly, heavy training was better for dynamic strength. However, there’s a skill component to dynamic strength, and heavier training helps to train that skill. On the other hand, there was no significant difference between high load and low load training for gains in isometric strength (i.e. force output with virtually no skill required). This suggests that low load training is still adding contractile proteins just as effectively as high load training; it’s just not great for training you to use them effectively for maximal dynamic contractions (i.e. 1RMs).
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As mentioned, I still don't know what to make of this in terms of applicability or how many of the conclusions are accurate, but sure is an interesting read if you haven't already stumbled across it.
Sarcoplasmic Hypertrophy: The Bros Were Probably Right