How Your Muscles Change With Exercise

muscles are some of the most amazing dynamic and adaptable structures in the human body i mean think about this we beat the crap out of muscle tissue at the gym or when we work out and then a day or two later those muscles are ready for more so in today's video we're going to talk about how muscles respond to the many beatings that they take as well as these amazing adaptations that come from exercise and yes one of those adaptations that we'll discuss is how muscles get bigger and stronger but is that the only way that muscles adapt not even close and we're going to talk about how and why so let's do this [Music] so in order for us to understand how muscles adapt we need to know a little bit about how they're put together and how they function now keep in mind we're going to be focusing on skeletal muscle tissue throughout this video which the name implies the majority of these skeletal muscles attach to and move the skeleton but there's actually two other types of muscle tissue throughout the body and that's our video quiz question of the day can you name those other two types of muscle tissue if you can post them in the comments below and we'll pin the correct answer at the top of the comment section but back to skeletal muscles let's take a look at this cadaver dissection as an example this is a right upper arm and a muscle that we're all pretty familiar with called the biceps brachii now the muscles of the body are made up of hundreds to thousands of muscle cells and if you look closely you can probably make out string like or fiber like cells making up that whole muscle now muscle cells muscle fibers can be used interchangeably so they're the same thing and forgive me i may do that throughout the video but if i save muscle cells same thing as muscle fibers but these muscle fibers have this amazing ability to contract and you can see the tendons attaching the muscle belly or those muscle fibers up to the skeleton and even down here and so when they contract generally one of the attachments is going to be more mobile and one's going to be more of an anchor like in the case of the biceps that anchor point is more up here and when those fibers contract poof we move the skeleton so now think of the last time that you exercised and if it's been a small season since you exercised last imagine yourself exercising so what did you or your imaginary self do maybe some of you participated in a long endurance run or went to a yoga class or played a sport or maybe did some heavy weight training now the reason why this is important and why i'm having us think about this is that depending on the activity that you participated in you are likely to engage a different percentage of certain types of muscle fibers as compared to participating in other activities think about how cool this is yes we know that a whole muscle is made up of hundreds to thousands of muscle fibers but of those total muscle fibers some of them are going to be classified as slow twitch and another percentage of them are going to be classified as fast twitch muscle fibers yes i will acknowledge to all of us anatomy and physiology geeks that there is an intermediate type but we're going to mostly focus on those fast and slow twitch and this is really important also because the slow twitch will adapt differently than the fast twitch will adapt and you have some level of control over this depending on the activities or the sports or the types of exercise that you choose to participate in now exercising and stimulating the muscle fibers is one thing but the other side of this is making sure that your muscles and body have all the nutrients vitamins and minerals needed to have the energy to perform as well as recover after engaging all these wonderful muscle fibers and that's why i'm excited to take a minute to discuss ag-1 by athletic greens ag-1 by athletic greens is a daily supplement that has certainly helped me simplify my health routine i used to open up 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packets with your first purchase the link is in the description below so back to muscle fibers and let's start with slow twitch muscle fibers slow twitch muscle fibers are actually known as slow oxidative or type 1 fibers and that name slow oxidative implies the amazing aerobic capacity of these muscle fibers and that's because they utilize oxygen to break down carbohydrates fats and sometimes proteins in order to synthesize the energy currency of our cells called atp or adenosine triphosphate now our muscle cells burn through a ton of atp especially when we're exercising so it seems like it would be a good idea to create a situation where a muscle fiber could effectively make high quantities or high amounts of atp and these slow twitch fibers are set up to do this slow twitch fibers have a high number of capillaries which means they have a great blood supply in order to receive a lot of oxygen and nutrients they also have a high number of these iron containing proteins called myoglobin myoglobin helps to bind and store oxygen within the muscle fiber so that that can be utilized to synthesize atp and for those of you who loved learning about the powerhouse of the cell the mitochondria these slow twitch fibers are packed with a high number of these mitochondria and if you haven't learned about mitochondria before that's okay think of these as little organelles or tiny little organs inside the cell that help synthesize atp and they use oxygen in order to do that so as you can see because of their great blood supply their myoglobin content and the number of mitochondria that they have these slow twitch fibers are really set up to utilize oxygen well in order to make atp now why is oxygen so important well let me give you an idea here when our cells utilize oxygen to make atp they can make about 18 times more atp per molecule of glucose as compared to in a situation where the cells are making atp without oxygen we generally say that per glucose molecule we can make 36 atp about that with oxygen but only 2 atp in situations without oxygen now 36 atp compared to 2 sounds great but there's always pros and cons or trade-offs in the land of biology for example slow twitch fibers tend to have a smaller diameter and so therefore contract with less force and they are called slow twitch fibers because their speed of contraction is relatively slow when compared to the fast twitch fibers and part of that has to do with the time it takes to make that much atp as compared to how fast the fast twitch fibers make their atp but during lower intensity activity when there's enough time to synthesize these high amounts of atp aerobically these muscle fibers are extremely resistant to fatigue they can take you 26 miles during a marathon they can help you sit in a chair or pose for an extended period of time during yoga they can help with low weight high repetition weight training and they can help keep you upright all day long as the majority of your postural muscles are packed with high percentage high percentages of slow twitch fibers so think of these muscle fibers at excelling in muscular endurance and they definitely will adapt to consistent exercise and training at certain intensities and how they adapt you can kind of think about that list of characteristics of these muscle fibers changing so in other words we'll increase the number of capillaries to these muscle fibers so we can deliver more oxygen and nutrients the myoglobin content will go up we can bind more oxygen within that muscle fiber and the mitochondria will even increase in number as well as size so we can process that oxygen and make more atp one other thing that's really really cool is that the transporters on the outside of the muscle fiber membrane or and even on the mitochondrial membrane will increase in number so you can exchange things through the inside and outside of the cell as well as in and out of the mitochondria so you've essentially created this ability to get nutrients and utilize oxygen to make even more atp in these slow twitch muscle fibers and that means more muscular endurance but what about those fast twitch muscle fibers are they great at endurance or are they great at something else fast twitch muscle fibers are known as fast glycolytic or type 2b fibers and for us to understand these fast twitch fibers we could almost reverse the facts that we learned about the slow twitch muscle fibers because the fast twitch fibers have fewer capillaries lower amounts of myoglobin and fewer mitochondria so these fast twitch fibers are not going to be known for their endurance or their ability to resist fatigue but they are larger in diameter tend to store more glycogen which is the storage form of glucose and contract with more force and velocity hence the name fast twitch or fast glycolytic and let me address that name fast glycolytic they're referred to as such because they undergo or typically utilize this process called glycolysis to synthesize their atp and glycolysis is the breakdown of glucose and in the case of doing it anaerobically or without oxygen we get that two atp that we mentioned and a byproduct of lactic acid and that only takes about 18 steps so the benefit of that is we can get those atp quickly but eventually we're going to run out and you know that when you go for a full-fledged sprint and engage those fast twitch fibers you know that you can only go so far before you run out of gas or run out of atp so to speak but i have to be clear your slow twitch muscle fibers can also utilize glycolysis they can also utilize fats to synthesize atp and that's a whole other video which is going to be awesome we'll do that soon but if they utilize glycolysis the big difference is there's oxygen and what will happen is that those end products of glycolysis will get funneled into different pathways in the presence of oxygen something called the krebs cycle which you may have heard about and then going through this process of oxide oxidative phosphorylation and that process yields 36 atp but it takes about 124 steps so you can see how much time that takes and that's why it can only be done in lower intensities of activity like jogging but jogging or running compared to sprinting in those jogs you can go for mile after mile after mile in the presence of oxygen so again we're kind of drilling this point home of the pros and cons of oxygen versus not having oxygen and fast twitch versus slow twitch but let's finally get to this idea how do these fast twitch muscle fibers adapt so in order for your fast twitch muscle fibers to even adapt you first have to tap into them or engage them and so let's use this example moving this adorable three pound weight or curling it and engaging my biceps let me ask you a question to move this three pound weight am i engaging all of the muscle fibers of my biceps and the answer is no because if every time when i engaged my biceps to curl this weight if i engaged every single muscle fiber it would look more like this coming up and i'd have to dodge it because i'd almost hit myself in the face with the weight and so we need to be able to modulate the amount of muscle fibers we recruit in order to lift weights appropriately if you will and what's really really cool is again if we go back to this whole muscle that we know as the biceps as our example yes it's made up of multiple muscle fibers but those muscle fibers are organized into groups or units so just for example say maybe there's a unit of muscle fibers here and another unit there and another unit there but they're kind of organized and bundled into units or groups called motor units now the textbook definition of a motor unit is the motor neuron or the nerve cell and the muscle fibers that it controls now something also that's important to note with motor units is they will only contain a certain fiber type so one motor unit would be slow twitch and another motor unit would only include fast twitch fibers you're never going to have motor units that include both fast twitch and slow twitch fibers so back to this example with the weight when i'm lifting this weight or only when a weak contraction is necessary to lift a light weight your body is going to recruit recruit motor units that only include the slow twitch fibers first and so as i increase the weight say i go from 3 to 10 pounds i'll need to recruit more muscle fibers and so therefore motor units and i may engage a couple more slow twitch containing units but eventually when the weight or the intensity increases to a certain point i'll start recruiting motor units that include the fast twitch fibers so you can see you have to get to some level of intensity to engage those fast twitch fibers and therefore even get an adaptation and the two ways that we really increase intensity most the time is one we just increase the weight or two we increase the speed say from going from like a jog to a sprint or maybe something like an explosive jump and finally now that we've tapped into these fibers how will they specifically adapt physiologically well they tend to adapt by getting larger or undergoing a process called hypertrophy and that is the muscle fibers that you have will increase in size and in order for them to increase in size you need protein to make more protein contractile units and that's why you hear a lot about people getting protein supplements when trying to build muscle or at least having enough protein in your diet and a muscle with a larger cross-sectional area will produce more force now they also tend to be able to store more glycogen as an adaptation and so therefore you have more glucose stores in there to create more atp even though you only create a few amounts or those two hp that we talked about you'll at least have more glucose to funnel that into glycolysis and bringing this all together i think it's important to discuss that these different fiber types do not exist in a vacuum and neither do you the majority of athletic activities or different exercise routines that we participate in tend to engage both fiber types granted you're going to engage one more than the other based on your activity of choice and we've brought up endurance runners multiple times throughout the video so yes an endurance athlete or like a marathon runner is primarily going to engage their slow twitch fibers but there will be times where they have to increase their speed maybe they have to pass somebody during a race or they really push it towards the end of the race and start recruiting some of those fast twitch fibers a sprinter turning that sprint fast twitch dominant but after maybe doing a recovery run around the track or a light jog around the track going to go more into those slow twitch fibers and what's also interesting to note is that we have percentages of fast versus slow in any given muscle i gave the example that yes the postural muscles in general and all of us have a higher percentage of slow versus fast so they can hold us up and endure throughout the day but if you were to take two people and analyze say like their cat gastroc medius or their calf muscle gas i was trying to mix calf and gastroc there but if you were to analyze that muscle one person might have a higher percentage of fast versus slow as compared to the other person but what i still think is so amazing about this depending on the activity that you like or tend to participate in whether it's fast twitch dominant or slow twitch dominant that will influence these amazing adaptations that your skeletal muscles can undergo based on this wonderful thing that we call exercise and luckily we have jeffrey the skeleton here to continually remind us of our manners and to remind us to say thank you to you all for watching all of our crazy anatomy videos it really does help support the channels and so we really are grateful for that support jeffrey also does want to say that you don't get a stomach forever as he is portraying here and that you may want to take advantage of that by maybe supplementation like ag-1 by athletic greens if you're interested in that go ahead and check out that link in the description below if you feel the need like subscribe leave some comments with the answers to those quiz questions from earlier and also let us know about maybe any other future fitness athletics or health and wellness videos that you guys might want to see in the future and we'll see you next time [Music] you

Channel: Institute of Human Anatomy

Views: 2,932,966

Keywords: human body, how to build muscle, muscle fibers, muscle fiber types, fast twitch vs slow twitch, fast twitch muscle fibers, slow twitch muscle fibers, muscles, anatomy, human anatomy, motor neuron, motor unit, biceps, fast twitch muscle training, slow twitch muscle training, mitochondria, glycolysis, glycogen, krebs cycle, workout, endurance training, marathon training, ATP, adenosine triphosphate, aerobic exercise, anaerobic exercise

Id: 2vXOq-aRtYY

Length: 16min 39sec (999 seconds)

Published: Fri Apr 08 2022