Fast Talk: 293: Beyond the Basics: Everything You Need to Know About Muscle Fibers

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The more there is about muscle fibers the better! Any thing going deep into physiology is good.

So yeah. I enjoyed that episode very-very-very much.

I’ve been sitting on a draft of post bringing up additional notes. I have my other leg on strength sport side, which in my opinion does complement point-of-view of endurance sports because often question or answer endurance folk can think of is only half of the picture.

Like being strong and powerful which are not the same thing and one can be VERY strong without speed/power component.

Mehdi Kordi, Dutch track cycling coach, has interesting things to say about power production on bike. And maybe one could ask if track cycling is more about ability to produce force rather than power.

Or that there in only one animal with more slow twitch fibers. That animal is sloth and it only does have slow twitch fibers.

Or that distance running at least on track, maybe even marathon, actually is demanding more and more type II fibers because they are necessary for developing enough running speed to be competitive.

Or that Crosscountry skiers does have huge type II fibers in their tricpes because those fiber shave to develop both big force output and endurance capabilities. Most of the additional volume when compared to type I fibers comes from extra capillaries, end result being that type I and Type II fibers have same capillary density. Same wasn’t observed in legs in where fibers remained more typical to their role. But i wonder if this is true for cyclists that type II fibers develop far more aerobic adaptations and basically they can produce same amount of work than type I fibers. But not from fats.

One thing in that study was that leg muscles are much more capable of using fat as fuel and it doesn’t get explained away only by muscle fiber typology. There is difference in upper body and lower body (or rather arms) in this regard.

But i should find all references for my points which i’ve gathered over years so my post will probably remain draft for rest of eternity.

HI @antti.hankonen,

Thanks for the feedback! I’m glad you liked the episode.

Loved reading all the extra complexity you’re bringing to the subject. As Rob said at the end of the episode, we could do another 10 shows to cover everything about muscle fibers. If you find those studies, please share! I’d love to read them. I’ve never seen that about triceps in CX skiers.

I have seen what you’re talking about with track racers - especially short event track. While power is important, it’s almost more important for them to look at torque. Your ability to turn over a big gear quickly off the start is critical.


Hi @trevor

Here’s few.

Crosscountry skier study is this:

Most of it goes way over my head so i have to rely on conclusions they draw. And it’s been years since i’ve read it, so i might be that i summarized things wrong. Hopefully it’s worth the read!

Here’s one recap of muscle fiber types in strength stuff:

Quite broad article on muscle fiber type and how it should, if it should, affect one’s strength training. I think one key take away here is that people with more type IIA fibers might not be more powerful, it might just mean that this person has transformed one’s Type IIX fiber away by being physically active. Even Endurance athletes supposedy would fit this bill because type IIX fiber are being converted into something: Type IIAs. So looking at how little Type I fibers one has is more helpful here to determine anything.

In strength sports it’s bit tricky, or rather stupid, because you have sport named ‘Powerlifting’ which actually measures maximal amount of force one can put out, while (olympic) Weightlifting is sport of power production. i’ve seen one study on international level powerlifters and they had quite regular amount of type I fibers when compared to regular people, which might be the same Stronger by Science article refers as well. So they reached high levels of strength by not being type II dominant. Or rather Type I deficient.

Andy Galpin’s study on (olympic) Weightlifters: Extraordinary fast-twitch fiber abundance in elite weightlifters - PubMed

Things turn bit different, remember that these are considered power athletes. Unlike powerlifters. (It’s so stupid). They have lots of Type IIA fibers, even around 70% (so they might have had around 20-30% of type I fibers). They display no Type IIX fibers. With one exception, superheavy weights. They had Type IIX fibers. But Galpin’s lab doesn’t dare to speculate why these people have X fibers left while lighter weightclass athletes had transformed them into type IIAs.

I think that Galpin said same about track and field sprinters in some podcast, they had high amount of Type IIX fibers. Again question is how and why? Weightlifters produce one of the highest watts in any sport, rivaled only by shotputers to my knowledge. Sprinting is quite measily in this sense. So maybe type IIX fibers should not be considered powerful, but more as fastest fibertype?

I’m used to think of strength-power-speed continuum, powerlifters are strong, weightlifters are powerful and (running) sprinters are fast.

My brain is too fried to try to summarize anything relevant to cyclists, and even if i would be fresh i’d dare not to. Mehdi Kordi seemed to think that for sprint capability muscle mass is more important than muscle fiber distribution, this is because cyclists can manipulate their gearing to fit their strengths and weaknesses, unlike in pretty much any other sport where cadence is set into tight limits.

I suppose main takeaway is that you can gain muscle to improve sprint power as endurance cyclist, but the next question is: Is 10kg/22lbs of muscle worth the 200-300 watt increase in sprint? You get to sprint line just more tired and more unable to out your maximal sprint power.

I’m trying to loose that amount of weight so i suppose that answers the question at least for me.

Maybe following example helps someone to picture this thinking in more “whole” way: I was strong guy, had worldclass deadlift around 270kg/600lbs range at 78kg weight. My squat numbers weren’t as stellar, around 190/420lbs. So national level. My vertical jump or weightlifting movements (snatch and power snatch) were around average hobbyist level which should be reached with few months of training. I was unable to improve them practically at all during year and half i did them. I suppose my muscles were so capped with endurance and strength training that there is no room for power. I did train 800 hours yearly, mainly cycling, at that time.

On bike i was/am able to put out 1000-1100 watts which is around 14w/kg. In Training Peaks i think i get into best 10% of users with my 5 sec power, which i take to be good. Thou it’s been long while last time i checked how i’d rank with other users. And that’s on indoor trainer (race indoors= practice sprints indoors).

So i’d say that my power on bike is more along my deadlift and squat numbers rather than power movements such as vertical jump or power snatch. It probably is not 100% correlation, either.

Maybe this is something which is unique to me and serves no purpose to anyone else as example. I dunno.