let's go into the next one the second one now the second one's really cool all right and this is the type we're going to have this one be the type 2 x muscle fiber okay so this one is going to be specifically the type two x muscle fiber now again type 2x muscle fibers are special because we can also call them a another type of name we can call these ones fast glycolytic okay so these are the fast glycolytic ones but let's actually you know so we can keep it consistent let's come back to this one because this one's going to be make the most sense after we finish up this next one so let's actually come back to this one in a second we're going to do this one because this one's actually going to go along with what we did over here okay so this last one we're going to talk about is specifically called the type 2 a muscle fibers so this one is actually called the type 2 a muscle fibers and the type 2A muscle fibers are really special the reason why is that these are fast oxidative muscle fibers okay now fast oxidative now some of you guys who are out there and you guys lift or you're you know you enjoy learning about muscle physiology you've probably heard the term fast twitch muscle fibers and you've probably heard of the term slow twitch muscle fibers so your slow ttch slow twitch muscle fibers are your type one fibers your fast twitch fibers are your type 2X and type 2A fibers now what really differs between the type 2 a and the type 2x that's what we're going to talk about here I want to do this one first so it's going to make more sense okay think about this fast oxidative okay let's go back to the structure now with type 2A let's look at this again look at this in just an overall view this is the smallest this must be kind of like intermediate and this is the big boy so this is the largest of all the skeletal muscle fibers so this is the largest of all the skeletal muscle fibers so this is the largest diameter fiber okay now some of you might be like oh Zach I don't know that's that's weird why would why would that be you know I always thought that the fast glycolytic ones were the ones that for powerlifting and all that kind of stuff like that that's true but in humans type 2A fibers are bigger than the type 2x fibers okay in other animal studies they found that the type 2x fibers which they also refer to as the type B fibers are bigger than the type 2A but not in humans so in humans the type 2x is intermediate fiber diameter and the type 2 a is actually the largest fiber diameter next thing I want you guys to correlate oxidative oxidative means that it depends upon a lot of oxygen now that means that there must be a lot of blood going to that area so this muscle fiber must also have a decent amount of capillary density and that is true so if we show again here let's say here I'm just going to show this capillary Network here here's this capillary Network and again the whole concept here is that this is going to have a lot of blood flowing through this actual muscle tissue if it has a lot of blood flowing through this muscle tissue what does that mean then it's going to be able to drop off a significant amounts of oxygen to the tissue not only that but what color is our blood normally if it's delivering it to this actual muscle tissue arterial wise it's going to be a nice reddish color right so this is going to have a high capillary density but I want you guys to go back to that concept I explained it before it can have a high capillary density but such a large muscle fiber that even though it has a large uh capillary density it's not going to produce the full reddish color because it would take so much capillary density so much blood flow through this muscle for it to produce a perfect reddish Hue it is still red but it's not as red because of its large diameter so it would take tons and tons of capillaries to make it red it's more of a reddish pinkish color okay so again when we describe this structurally we say it has a high capillary density but because the muscle fiber is so big even though there's a decent amount of capillary supplying it it would take so much for it to cause the whole muscle to produce a nice reddish color so it's more of like a reddish pink Hue okay next thing we're already going to throw this down it has lots of mitochondria and this should make sense and why should this make sense guys because there's the word oxidative and again if it has lots of mitochondria let's draw a couple mitochondria here if it has lots of mitochondria what does that mean that it depends upon well that means oh Zach said if it has a lot of mitochondria it's probably going to depend upon a lot of you know oxygen that is right so it is depending upon primarily aerobic cellular respiration because of the word oxidative so again when you think about this one it's going to be using glucose primarily right and it's going to be utilizing oxygen and when it UTI utiliz this oxygen it's going to convert this glucose right through these processes what is it going to do it's going to lead to the formation of ATP so it primarily performs this action by aerobic cellular respiration so it is depending upon aerobic conditions but you know what's special about this muscle he has the ability to switch in between aerobic and anerobic all right now the type one a muscle the type one sorry the type one muscle fibers do have a tiny bit of this molecule called glycogen but the type 2A are going to have a lot of glycogen okay they have a decent amount of glycogen okay so we'll say like if it comparing type 2 a versus type 2x type 2A actually has kind of like in between intermediate or moderate amounts of glycogen what is glycogen so let's say I have a glucose molecule here and I taken out another glucose and another glucose and another glucose and another glucose and eventually it starts kind of just looking like this it's a big big polymer of glucose this right here is called glycogen glycogen is plentiful in moderate amounts inside of this inside of these vesicles though our muscles they store it inside of these granules so I'm going to draw these dots here and these dots are representing our glycogen okay this structure here is called glyco soms and we have a moderate amount inside of the skeletal muscle fiber but whenever our body needs you know certain types of ATP and we don't have as much oxygen available guess what this muscle can do it can break down some of this glycogen into glucose and where can this go this can go into being oxidized and eventually used to produce ATP okay all right now there's another mechanism that kind so again there's going to be this glycosome so they do have a moderate amount of glycogen so we've already gone over the structural Co Concepts metabolically we already said that they depend upon aerobic conditions but they can do anerobic conditions okay but to be even more specific you know whenever glucose under goes a specific pathway there's a specific pathway where it uh actually gets split because glucose is six carbons it gets split into two three carbon molecules called pyruvate and during that process you know what happens to the pyruvate we produce 2 ATP what is this process here called this process is specifically called glycolysis this is really what's happening during this Anor robic pathway so glycolysis is one of the main things that is occurring during the anerobic process and this can come from glycogen but in the same way some of this gly gen can get broken down into glucose and then go to crab cycle electron transport chain but it also can go through glycolysis to produce pyruvate and a little bit of ATP you know what else is really cool skeleton muscles are really cool because they have a special enzyme inside of them a special enzyme look at this enzyme this enzyme is really cool because it helps us to produce a little bit of ATP very quickly doesn't last very long but it helps to produce a little bit of ATP if we need it you know there's a molecule that's very plentiful within your skeletal muscles that molecule is called creatine phosphate but I'm just going to denote it as CP so there we have one molecule and that again what does CP stand for it stands for creatine phosphate this is very plentiful in your skeletal muscles and even in your cardiac muscle too what happens is creatine phosphate is going to bind onto this enzyme what is this big blue enzyme here called this enzyme right here this blue enzyme is called creatine kinas and what creatine kisee does is you know it can bind into this pocket so one pocket the creatine phosphates binding the other pocket is going to be ADP ADP let's do this in a different color let's put this in blue a DP you know what this creatine kisee does he binds both of these guys and smushes that phosphate off on the on the creatine onto the ADP that's pretty cool right so what is he doing he takes this phosphate here from the creatine and adds it onto the ADP and as a result what would you get from that reaction I would get ATP right so I'm going to get ATP when I produce ATP it's not very plentiful amounts of ATP but what's coming out of this reaction I'm also getting creatine and creatine will get acted on by another enzyme to get converted back into creatine phosphate but this is one way that our muscle cells this muscle fiber can also produce ATP and again this is through the creatine phosphate pathway so the creatine phosphate pathway but again being very very specific this cell mainly depends upon aerobic it's more specifically depending upon aerobic but it can undergo anerobic processes okay next thing think about it metabolically since it's a large diameter muscle fiber this is where it's a little tricky that's a little tricky on this one because it's a large diameter muscle fiber it does have oh think about the word first before this fast what is this contractile speed fast it contracts very fast so if that's the case then it's going to have a fast contractility right so it contracts very fast this guy here here's our mein here's the mein and then again what do you have over here you have actin so here's the actin cups right and again what do we say was binding to this ATP what was the name of that enzyme that was cutting the ATP mein ATP a if it cuts it fast what would that say then for this whole crossbridge and sliding filament theory that's going to occur faster if that's occurring at a faster rate won't the actual contraction speed increase too yes so this fast contractility is due to fast or high amounts of myin atpa activity okay so fast or high amounts of mein atpa activity now not only is there fast contractility not only is there fast M and atpa let's think about the word oxidative that means it produces a decent amount of ATP so because it produces a decent amount of ATP okay it's it's it's pretty good at being fatigue resistant but if it contracts really really fast wouldn't it burn out pretty quick yes so it doesn't last hours but it can last a decent amount of time within minutes so specifically this one is fatigue resistant moderately I'd say it's moderately Fe fatigue resistant right so it's moderate fatigue resistant but because it has a moderate fatigue resistance so you know and I like I said it can last for maybe a little bit less than 30 minutes so this muscle fiber can continuously carry out its contractile activity for a little bit less than 30 minutes but it it can generate a decent amount of power so I can say I would say it generates a moderate amount of power but not as much power as the type 2x muscle fibers okay so again recapping this metabolically it carries out aerobic cellular respiration it can do Anor robic via glycolysis and the creatine phosphate pathway it contracts very fast because it has a high amount of myosin ATP activity remember this enzyme that we showed you here this enzyme that was connected with the mein here's the myosin right here it has a high amount of myosin atps activity what does that mean it's good at breaking down ATP into ADP and inorganic phosphate very fast and also we said that because it contracts very fast but it does produce decent amounts of oxygen I'm sorry it does produce decent amounts of ATP by aerobic cellular respiration it kind of Falls within the middle there and has a moderate fatigue resistance it might about less than 30 minutes and it doesn't generate a sign it doesn't generate large amounts of power but it does generate a decent or moderate amount of power so if that the case then again thinking about lifting something if I want to lift something which muscle fiber is going to get recruited first it'll be the type one then after that if I want to recruit some other muscle fibers that help to generate a little bit more power a little bit more power not significant but a decent amount more power which one would you want to recruit next this muscle fiber so this would be the second recruitment so this one is actually going to have a second recruitment order so this muscle fiber is recruited second okay so this recruitment order for this one is a second recruitment order so the motor neurons will go and stimulate the first one okay the motor units will stimulate that first muscle fiber type one first but as we try to carry a heavier load what are you going to engage you're going to G your engage your type 2 a muscle fibers who can generate a little bit more power okay now what kind of activities would this be good for this is good for very you know short burst of energy okay but they can last a decent amount of time about 30 minutes now I don't know anyone who can Sprint along 30 minutes that that distance but it can go you know a decent amount of time so for this case if someone is actually having uh this type 2A muscle fibers and you're trying to figure out the main activities that it's involved in it's involved in walking so a lot of the muscles that are involved in Walking as well as sprinting okay as well as sprinting so walking and sprinting are going to be two big activities that are uh going to be dependent upon this muscle fiber so walking and sprinting utilizes these muscle fibers and again I I'm not saying that every person Sprints you know 30 minutes it's just anything less than 30 minutes but nothing less than a minute okay because if it's less than a minute it's not going to be utilizing this muscle fiber it's going to be utilizing this muscle fiber so it has to be at least greater than a minute but less than 30 minutes for it to be classified under the activity of this muscle fiber okay that's our type 2 a now we'll talk about the last one here which is type 2x type 2x muscle fibers are your fast glycolytic muscle fibers are very interesting so let's go back to the Structural Concepts of it okay well the first thing that we should understand is let's look at it first okay that one's the smallest we already said that that one was intermediate or decent I'm sorry this one was actually the smallest this one was the largest diameter muscle fiber we said that this one is the right in between so it's intermediate diameter muscle fiber so we're going to say that this one is intermediate fiber diameter okay and again I told you um in certain animal studies they found that the type 2x is bigger than the type 2 a but in humans it is not okay so as intermediate fiber diameter now another name for this type of fiber so again we said that these are your red slow oxidative that is your fast and technically those are your fast fast red oxidative muscle fibers these are your fast white glycolytic let's put that word up here this is the white fibers and we'll explain why they're white now okay so if you think about it and we shouldn't even really say white we should say even uh palish Pink let's even add on to this let's say let's say say palish pink so palish pink okay just not a lot of uh you know reddish Hue to it okay now why is that look at the actual capillary density here very little look at this okay very little capillary density going into this muscle fiber so there's not as much capillar supplying this muscle fiber then what can we say is it going to be delivering a lot of oxygen to this actual tissue cells this muscle cell no so very little oxygen is being dropped off at this tissue as compared to these tissues okay well that's interesting so again we said intermediate fiber diameter we set a um you know we said very low capillary density and again if it has a very low capillary density what color would you expect it to be well it's not carrying a lot of red blood to it are right it's not it's not carrying a lot of blood to it if it's not carrying a lot of blood to it and it's a decent diameter muscle fiber it's not going to produce very much red or pink at all so it's going to be very white or like we said palish pink because there's not a lot of blood going to that area Okay and then mitochondria I'm going to put down for right now very little okay so very little mitochondria and we're going to understand here why well there's very little oxygen being delivered to this area so what would be the need for having significant amounts of mitochondria so if there is very little mitochondria then this isn't going to be usually utilizing a lot of oxygen so the amount of aerobic Pathways that are occurring here are almost none so very little aerobic cellular respiration if any is actually occurring within this muscle cell so if there's very little oxygen if there's very little mitochondria then aerobic cellular respiration is almost null okay almost no aerobic cellular respiration so it must be depending primarily upon anerobic and anerobic we already know okay same thing with this guy metabolically remember how we said that there was a lot of glycogen granules in that guy there's a lot of glycogen granules in this guy too so this one's also going to have a significant amount of glycogen granules and again what are those glycogen granules called they're called glycosomes and what are they going to have in them they're going to have Polymers of glucose which we refer to as glycogen and what's it going to do to that gly it's going to break that glycogen down into glucose right that's called glycogenolysis but then what can happen to that glucose it can be converted into pyruvate what happens in that step you produce a little bit of ATP right so you can produce a little bit of ATP but not a significant amount of ATP but you're going to be carrying out these activities you know very fast because it's a fast glycolytic fiber what was the other mechanism that we could produce ATP anerobic remember this enzyme here it was utilizing the creatine phosphate which we denoted as CP and it was transferring the phosphate from the CP or the creatin phosphate to who it was transferring it to ADP and whenever these two reacted what did we get we got ATP but it doesn't produce a significant amount of ATP it only produces a little bit of ATP right and again what was the name of this enzyme this was the creatine kinas enzyme okay so now if it's utilizing this creatin kinas enzyme so this creatin kinas enzyme is involved in this muscle fiber and also glycolysis is involved in this muscle fiber so there's going to be glycolysis and there's also going to be this creatine kise pathway so okay what two pathways are involved in this one okay well first off is it undergoing aerobic Cellar respiration no it's primarily anerobic conditions so it's primarily anerobic and by what type of Anor robic process creatine I'm going to put CP pathway and glycolysis okay glycolysis and the reason why is because it's doing this because there's very little mitochondria and very little oxygen okay oh real quickly I didn't even think about this I'm sorry what about the myob content in this guy what about the little myoglobin dudes what about those proteins this one has a decent amount of myoglobin also okay you know another thing about myoglobin that we could also say is that myoglobin is also has a heem pigment in it and so because it has a nice amount of uh heem pigment in it if it's bound to oxygen what can that also do it can also produce a reddish Hue so myoglobin also contributes a little bit to the actual reddish Hue of the actual muscle fiber okay as well as the cap AR density but in this guy this type 2x it has very very little myoglobin look he's crying because he doesn't have a lot of myoglobin dudes to hang out with so there is very little myoglobin present in this actual muscle fiber so very little myoglobin present within this muscle fiber and so that again that also contributes to the very little oxygen as well as it also contributes to the very uh whitish palish pinkish color of the actal muscle cell okay now another thing this muscle fiber is intermediate in diameter right okay also this pathway anerobic pathways anerobic through the crean phosphate pathway and the glycolysis pathway they C at a pretty fast rate so because they occur at a pretty fast rate they're also going to produce ATP very fast but is not enough of it okay what about the mice and ATP activity in this one the my ATP activity is off the charge it's insane so the my and atpa activity I'm not going to draw that whole thing again because we should already know but this enzyme who's doing what breaking down ATP into ADP and inorganic phosphate which is again connected to the myosin protein his activity is going to be very very fast so if he has a very fast myin atps activity and we're producing ATP very fast wouldn't this produce a very fast contractility yes okay so what do we say here there's going to be very fast contractility actually the fastest contractility right and then there's going to be the highest amount of Myas and ATP activity activity right and then what else did we say okay we said it has fast contractility high amounts of mice and ATP activity it's also producing ATP very fast because it has to under only undergo anerobic which is a shorter pathway another thing because it's Contracting so fast and it's undergoing anerobic conditions so it doesn't have a lot of oxygen it's Contracting really fast so it's going to wear out really fast what do you think about these actual fatigue resistant with respect to this muscle very very low so very low fatigue resistance this is the one that lasts for maybe about less than a minute so about less than one minute okay but this is the one that can produce the largest amount of power okay so because it is anerobic doesn't produce a lot of oxygen but it produces very quick it's going to contract fast also it's going to contract fast because it has a high amount of M ATP activity it has a very low fatigue resistance okay very very low and the reason why is is because it's not producing a lot of oxygen I mean it doesn't have lot of oxygen so it can't produce lots of lots of ATP also it's Contracting really fast so it's going to wear itself out really fast now it can produce the largest amount of power though so whenever you're carrying a load that's extremely extremely heavy and you're trying to be able to move that load this would be the last type of muscle fiber that you would recruit so this has the third recruitment order so this is recruited last or in this case recruited third so when whenever you're looking at muscle fiber types you recruit first muscle fiber is going to be type one this is the first one that you're going to recruit the second one that you're going to recruit is type two a and the last muscle fiber that you recruit is the type 2 x because this can generate the most power least amount of power the moderate amount of power Now function for this muscle fiber again it's going to be carrying out very very uh trying to lift heavy loads or put or or generate a lots of power very quickly so this would be for example you know hitting a baseball or you know trying to get your gains on you know doing bench press and stuff like that lifting weights okay so lifting weights is a good one for this one and also like I said hitting you know hitting a baseball I'm just giving an example but it's just very quick and burst of power okay these muscles will be utilized now one last thing I got to talk about and then we're done in this video I'm sorry that it's long I know I appreciate you guys hanging in there with me but I want to talk about these muscle fibers because what can happen is that in one muscle that bundle right there this fasle right I might have different types all right or amounts so for example let's say that in my muscle fibers versus whoever is watching this video I might have a little bit more of the type 2x in the type 2A where whereas compared to someone out there who runs marathons and is very very active in endurance activities they're going to have more type one now there's two reasons why that person who has a marathon runner will have more type ones and as compared to me first off I don't like to run at all so I'm not going to have a lot of type one muscle fibers but that's just because these things are contributed by two concepts one is genetics so your genetics determines the uh abundancy or the amount of type one type two and type 2x but also Environmental stress what do I mean by that okay let's let's make this as simple as possible let's say that I I decide to become a runner for whatever reason which would never happen but anyway if I decided to I'm going to start running a lot and as I start running a lot what's going to happen to these actual muscles well the first thing that's going to happen is if I'm running a lot my muscles are going to lead need a lot more oxygen because I'm carrying out a long activity if I need a lot more oxygen what will I need to make more of I need to make more blood vessels so the first thing that's going to happen here is I need more blood vessels so if I'm trying to do endurance let's say I'm trying to do endurance activities for whatever reason um I'm going to make more blood vessels so more capillaries why would I make more blood vessels so that I can bring more oxygen to the muscle tissue second thing I want more I want my mitochondria to be big birth the size okay I want to have a lot of mitochondria and I want to have big amounts of mitochondria so I want my mitochondria because if they're bigger they're going to be able to carry out more activity so I want my mitochondria to increase in number and to hypertrophy hypertrophy and the last thing I want what is the purpose of these actual myoglobins to hold on to oxygen to deliver as much oxygen to the tissue as possible so when blood is coming by what is the actual blood do it drops off oxygen to the myoglobin so that whenever the muscle is relaxing it can drop that oxygen off produce ATP right and whenever the ATP is produced this muscle will be able to contract very heavily right or carry out a long activity so for this case I'd want to produce more myoglobin that's what happens in these individuals now if you think about it for a second if I make more blood vessels I have my mitochondria get bigger and I have more myoglobin aren't aren't I really all I'm doing is really switching from a fast oxidative to a slow oxidative because that has a lot of capillaries but this one has a decent amount also that that has a lot of mitochondria and the mitochondria you know decent size but they're bigger and there's more mitochondria this one has about decent amount of myoglobin this one has more myoglobin that's all I'm doing is I'm switching so whenever you go from endurance exercises you're switching from type 2A to some of the type ones that's it okay by making more blood vessels making more mitochondria having hypertrophy and having more myoglobin now let's take the contrast let's take the opposite so let's do that down here now let's say that we're do the good stuff you're trying to join the gain train all right you're trying to go from a puny human to a you know fing Hulk so if that's the case then I want to do start doing resistance exercise if I'm going to start doing resistance exercises I'm going to start trying to lift heavy loads as I try to lift heavier loads than normal I put a lot of stress on my muscles and three things happen when you put a lot of stress onto the muscle your muscle fibers actually split let's say here I have a muscle fiber I'm looking at it like this right let's say here's this muscle fiber and this muscle fiber what can happen is I can split this muscle fiber longitudinally from excessive amounts of weight load when it splits something really crazy happens you have these cells they're called myos satellite cells myo satellite cells what these myosatellite cells do is they come in and they plug and proliferate and fuse into that little longitudinal split and grow into it as they grow into it guess what happens to the size of this actual muscle fiber it gets bigger and as it gets bigger it starts what is that called when a muscle fiber gets bigger it's called hypertrophy so that's one thing that's going to happen is whenever the muscle cells have a longitudinal split the myosatellite cells proliferate and plug into that and fuse in there and develop a larger muscle size that's one Theory the second theory is what is making up a muscle fiber what did I tell you was one of the main components of this muscle fiber if I were to pull one of these muscle fibers out I told you there's thousands upon thousands of these things called myofibrils I want you guys to just think for a second if I make more myof fibros isn't that going to myof fibers are actually occupying 80% of the cell volume that's a that's a lot so if these guys if you make more of these or you make them bigger what's going to happen to the actual cell volume it's going to get bigger if the cell gets bigger what's going to happen to the overall size it's going to hypertrophy okay that's one thing as well as think about mitochondria if I have more if my mitochondria get bigger or I have more mitochondria that'll also make the cell bigger also another thing is those glycosomes if I have more glycosomes I'm going to have more glycogen if I have more glycogen the muscle cell is going to even get bigger and the last thing that they believe is can happen with a resistance exercise besides the myos satellite cells fusing this longitudinal split and making the muscle bigger as well as increasing the number of myof fibral as well as increasing the number of glycogen as well as increasing the number of mitochondria they also believe that you can switch some of your fibers particularly you can switch some of the type 2A fibers into the type 2 x fibers and those are for more of the actual heavier resistance exercises that should make sense all right so the last thing I want to mention guys is disuse atrophy it's really simple think about it whenever you're actually not utilizing a muscle what happens it starts actually decreasing in size because if you don't use it you lose it that's the whole concept so what can happen is if you do resistance exercise think about a bodybuilder who's been Lifting for a while spent years and years working hard to get those big nice muscles right and he switched a lot of the type 2 a to a lot of the type 2x if he let's say that for some reason he's like I'm done bodybuilding I don't want to do this anymore what will start happen to that person's muscles they'll start decreasing in size when they start decreasing in size what is that called that's called atrophy and sometimes that can happen due to an injury or sometimes it could just due to not doing not wanting to do anything but that's one of the important things is that if you do not utilize a muscle enough the actual muscle fiber can switch back from type 2x to type 2 a and then again uh whenever the muscle atrophies it becomes weaker and if the muscle becomes weaker that can actually be a bad thing okay so overall guys I I really want to say thank you guys for sticking in there with me if you guys watch this whole video I appreciate it I hope it all made sense that's our goal here at engineered Sciences to make it make sense and I hope it did if you guys did like this video please hit the like button subscribe put some comments down in the comment section all right Engineers until next time