The difference between fast-twitch and slow-twitch muscles | Peter Attia and Andy Galpin

let's make sure people understand what the difference is between a fast and a slow twitch fiber let's Y and we'll come I want to come right back to where we are but I just want to make sure we haven't lost that thread yeah in general there's a lot of ways to describe it but the easiest way is to describe it by the name so fast twitch means that the twitch or the speed of contraction is higher and so those these fibers can contract and squeeze together with through the mechanisms we haven't got to yet we'll get there Mas in Acton um and a much rate having said that the fast R fibers tend to be larger though not always and certainly not in endurance training individuals um and definitely not with aging um that they tend to be almost they almost always are more glycolytically driven and so they're going to have more the enzymes responsible for anerobic glycolysis they're going to have more glucose in the cell they're going to have less intramuscular triglycerides and they're going to be having that generally have more phosphocreatine slow twitch f are fatigue resistant which means these are the ones that they can contract kind of all day long because they don't use as much glucose so they do use quite a bit still they are much better at using fat as a fuel they are uh they tend to have more and larger mitochondria and the downside is they don't contract with as much velocity in general so that's the the functional that's why we call them twitch and and just to be clear the force difference between them is it doesn't matter it's just velocity or is there a force difference as well so the yeah no well so a couple of things um in in large part Force production from muscle fibers is determined mostly by size cross-sectional area so getting the fiber bigger is the play to get it faster having said that power is markedly different and so if you're talking because power is based on velocity as well that's yeah you times the multiply the force um by the velocity so if you use this metric that we'll use in single fiber experiments called specific tension which is sort of like relative strength so you you take the size portion out of the equation um what you're going to see is a true slow twitch so these are also called type one fibers um if you compare those to a type 2A so that's a fast twitch muscle fiber um you're going to see something like five to 6X power between these two so it's not when you normalize for size Norm for cross if you go if you go to the 2x fibers which is a special class of fast fibers now you're talking 20x that power curve and that is mostly explained by more metabolic apparatus what's enabling the speed why does the 2x fiber go faster yeah it's all has to in fact the way that we differentiate muscle fibers in the laboratory is we measure What's called the meas and heavy chain and so to to kind of actually come back to micro Anatomy here so the way the muscle fibers work is this is all in a 3D sequence right so you can imagine that cylinder I'm going to explain it to you in 2D just so you understand but this is actually occurring in 3D and so what happens is you've got two of these microfilaments called actin and myosin all right now what happens is they're overlap so they're not touching each other and you've got mein um kind of laying in the middle and it's this big thick tube and it's got these heads that flick off the top of it all right now these heads reach up and they extend again in 3D but if just think about 2D they reach up and grab on what's called actin all right and so the idea when you contract the muscle is the myosin will reach up and they're going to reach out sort of outward so if you're watching this video you're seeing my hands kind of reach up and away from my body like I'm stretching my arms like I'm doing a big T if you will and my hands would then grab onto the actin and then if I I were to squeeze my hands and bring my hands closer to my face that's the myosin is actually then pulling the actin closer together so what actually happens in real life is those start stacking on top of each other and that's why when you squeeze your bicep it actually glows larger vertically because those muscle fibers are stacking on top of each other and that's actually elevating the sides and so what determines Force production versus velocity is what we call cross Bridges so the amount of time that these meas and heads grab onto that little place of connection is called a crossbridge the more those cross Bridges you have the more effectively you can pull the AC in closer to each other the the more effective you do that the faster the contraction the more forceful the contraction is going to be so primary thing explaining Force production is the amount of cross Bridges so the thicker your myosin the more likely you are to grab actin the faster the stronger the hold if you will so the better connection your hand has to that thing it's grabbing on to rather than you can imagine like a couple of fingertips on it and trying to pull something closer to you versus having your whole hand wrapped around it a strap on it chalk on it and like you're gonna be able to rip that thing down quickly now there are six actin that surround in a circle each meas in human skeleton muscle so again a picture that 3D structure so you can imagine if I'm standing up in a room and I'm my and six people are forming a circle around me like they're going to jump me or celebrate me or whatever that's what it looks like and my arms can sort of reach out and no matter where my arms are there's going to be somebody that I can grab and you only have two arms still in this you only have two masas and filaments you have a ton okay okay you so you have one masas in F I'm sorry you only have um two heads or how many heads do you have theil okay so you have billions of heads to grab on to six potential targets so you're always going to grab a Target you're you're going to grabb one right now you can't increase the amount of those actin that are around you but we do see that in other animals so this is one of the reasons that explains why like fruit flies spiders and things like that can contract with so much more Force relative to humans is they might have eight or 10 or 12 or 20 mice or acting per mice and ants which we always think of as like for their size being insanely strong totally they'll do that so so Evolution's tool to make things stronger is give more actin because you already have an infinite number of Myas and heads the more things I can give you to grab on to the stronger you are the stronger you're gonna be yeah you you realize there's somebody out there using crisper right now trying to figure out how to double the number of these things in humans right so I'm not going to say this officially All I'm gonna say is well officially the world knows about the bare muscle studies that we've worked on so there have been be tissue come through and under my microscope put it that way um bear tissue is actually quite unique so they actually have a so humans have that 2 a and they have that 2x which is formerly 2B right incorrectly identified as 2B that's correct most other animals do actually have in fact 2B and the 2B is even faster than the 2X and bears have a lot of them so this is one of the other reasons why not only do you have that they simply have a simp a fiber type that is much faster than any of the fastest ones we have a cheetahs yeah and um other cats like that have like 20 to 60% of these two B fibers just extraordinarily high amounts and they and in those do they have more actin targets I think actually I think cats are are pretty close to Six to1 but we could fact check that one but I'm pretty sure that part of it's fairly it tends to be fairly similar on similar kind of manal mammals it's when you get to the insects and things like that I think where that number jumps off but my comparative physiology is not the sharpest so don't trust me there so um yeah that's a great description of the micro anatomy and I want to remember let me finish the speed thing this what actually happens so what determines the speed so on those little mein there were kind of connects to the ACT it's called the mein head okay now a part of that is a bunch of stuff that you guys don't need to know about but a part of that is is called the heavy chain so there's a light chain portion and a heavy chain all right now on the tip there the way that we could get a muscle to contract is ATP so what happens is the mein are kind of loosely connected to the Acton at all times but in order for it to grab and pull you need a strong connection and for that connection to happen and for that to be able able to pull it together it requires energy so pardon the the somewhat crude analogy but the way that it kind of works is if you imagine cocking a pistol so in order to actually the pistol versus fire the the trigger the squeezing the trigger actually produces it takes a lot less energy than cocking it back if you've ever cocked a thing like it actually you have to pull pretty hard so the energy that we need actually for muscle contraction is not the pulling together that's actually almost passive it is the cocking back part that takes energy right and so that energy comes from ATP so on the little tip of that mein head is an enzyme called ATP Ace as you know you hear Ace you think kise like you think like something enzyme that's going to work that's the molecule that hydrolyzes ATP uh splits ATP rather right so um to make that simple so what you have to do is actually invest in ATP that gives you energy use that energy to that mein back into place and now it's kind of sitting there but it can't bind strongly until calcium comes into the picture it gets released from the sarcoplasmic reticulum that has to come to the equation it has to cause this confirmational change and act in and move these T tubules or that comes from T tubules move some other things around once those things get moved around by the calcium theasin is like oh boom it connects something and then it just almost subconsciously snaps as hard as it possibly can and that's why you can't regulate Force production it's like it's just going to catch and snap catch and snap in order for that to go back you actually have to invest more ATP this is also side note what explains riom mortis so this happens it gets contracted you don't have the energy to then pull it back in so then you stay in this locked sort of skeletal muscle contraction position so now the speed at which you can do that that atpa thing that's what determines single muscle fiber contracto speed that's also that M and heavy chain is what we measure in the lab and that's how we determine fast switch versus slow switch so if you were to use a technique that we use called gel electropheresis basically you put a gel between two pieces of glass and you just pour gel in there and it gets like solidified just like hair gel like a little bit thicker and then you put each individual muscle fiber in its own vertical lane and then you put a little bit of positive charge on the top end a little bit of negative charge in the bottom end or inverse doesn't matter and then you actually put a little bit of chemical bath around the muscle fiber that has a charge you turn the electricity on positive goes to negative Etc and so those fibers run down vertically through the Gill we hit stop at a certain time point and the smaller ones have gone further because smaller molecular are will go through the gel faster and so we stop basically we put it we develop it like you would develop a picture like like old school photography stuff literally the same silver nitrate Etc that you use and we can see the ones that have gone further down are slow twitch the ones that on say up higher are fast twitch and of course we use molecular weight markers to to confirm all that but that's effective we're looking at so what that means is the Myas and heavy chain molecular weight determines fiber type and that regulates its twitch ability the the more of those the faster those heavy chains work the faster atpa can operate the faster the whole thing can contract the faster the muscle fiber contracts and there you go and that's why muscle fiber typ is not predicated on signs it is specific to either metabolic abilities in the olden days or now more specifically twitch [Music] velocity

Channel: Peter Attia MD

Views: 17,230

Keywords: Peter Attia MD, Dr. Peter Attia, Early Medical, The Drive Podcast, The Drive, Longevity, Zone 2, andy galpin, fast twitch, slow twitch, muscle

Id: XV2Wf2U75eU

Length: 12min 49sec (769 seconds)

Published: Fri Mar 15 2024