Can You Change A Muscle's Fiber Type?

[@Marco_My_Words]

And then also type 2a fibers are convertible too. I mean, that's part of their normal function, they can do both resistance training and endurance training, but they kind of shift more to the one or more to the other depending on how you train your muscle. They can be balanced if you do both cardio and resistance training and they can be more on the strength side if you do less or no endurance training and a lot of resistance training.

[@foxdogs1st]

For Clarity- can you change slow twitch to fast twitch ? If so, is there a reason to train slow twitch if your focus is in pure Strength ? Or will training slow twitch interfere with your strength goals ?

[@brenogandini1605]

Thanks for taking the time to explain science even when people want short answers that may lead to misunderstandings (to say the least)

[@davidfillary]

So what would happen for an athlete that trained for both - would their profile stay the same?

[@Telagioth2]

I think it'd be tough to look at something like that because how can one equivilate resistance training and endurance focused activities?

[@greglnuckols]

Not sure. I don't think there's data on that

[@adgcih1689]

Does that have to also do with energy systems (atp)? So theoretically i should avoid all exercise that last more than 10seconds if i want to be as explosive as possible? So instead train low reps 1-3 and for cardio do some type of hiit.

[@Telagioth2]

That does make sense and it's what a lot of high level athletes do already. Principle of specificity being the focus here. Although I think that for health and performance you shoulddo polarized forms of training so that you are training all forms of energy synthesis pathways well. For example you can be a powerlifter and never train aerobic capacity but then your rest times will be like 5-10 minutes since your aerobic capacity and general conditioning sucks.

[@Telagioth2]

Also gotta think about fatigue and what not. Basically it's more nuanced. I feel this talk of fiber conversion is one of the things that feeds into the principal of specificity and the repeated bout effect.

[@adgcih1689]

@@Telagioth2 yea nice reply thanks! Also from lets say 10 training sessions 9 is max strenght/explosiveness and 1 is high rep endurance (10-20) do you think this 1session gonna stop a part of the conversion to fast twitch fibers?

[@Telagioth2]

@@adgcih1689 I think you might be missing the overarching theme of the vid lw. You're gonna get the type 2 fibers from resistance training, all kinds of it. Be it in the 1-30 rep range. The type 1 fibers are coming from like running or cycling. So if you lift 10 times, you will get the fast twitch fibers from each of the 10 times. If for one of the tries you run some amount sure you won't get type 2 growth from that but you probably won't have fiber conversion either since you mostly lift.

[@Telagioth2]

Think about it like this. If you can get maximally strong in a rep range (1-5) or can achieve muscular hypertrophy in a rep range (1-30) then you are most likely getting fast twitch fibers. The reason is only the fast twitch fibers grow and respond well to hypertrophy training. Second is that by the very nature of moving heavy weight you will gain the more explosive fast twitch fibers.

[@lastsonofkrypton3918]

What is the biological mechanism that initiates the conversion process of the fiber type change? Is it epigenetic? Is there a magic powder I can take to make it happen faster? thanks grog

[@greglnuckols]

I'm not sure of the upstream mechanisms, but gene expression ultimately shows up somewhere. At the most basic level, it's just an upregulation of the production of some MHC proteins and a downregulation of the production of other MHC proteins.

[@matthewbeeler3354]

@@greglnuckols If we really do have the ability to shift these hybrid muscle fibers from one MHC isoform to another, that would mean that we can freely replace the MHC subunits on the myosin molecule and that type I isoforms can freely be replaced by type II isoforms on the same myosin protein? As I understand, there can be up to 300 MHC subunits per myosin molecule and they are freely replaced as they are turned over or damaged. The paper "Thick filament-associated myosin undergoes frequent replacement at the tip of the thick filament" shows these MHC subunits are rapidly changed. Does this mean that if you do aerobic exercise and activate downstream pathways that the gene expression will be upregulated to replace the MHC on the myosin of these hybrid fibers with the MHC isoform for type I fibers? This is all very confusing, lol.

[@greglnuckols]

@@matthewbeeler3354 probably so

[@kaganas_edits7551]

Isnt that a question of yes or know😐 why 10 mins

[@ronalcott3449]

This was actually pretty concise for a Greg answer. 😂