Muscle Shape: The Hidden Factor in Performance

if you look closely at the muscles here on the cadaver you'll notice that while they're all made of the same stuff so various proteins blood vessels Etc they have distinct shapes to them but if you look for long enough you'll start to notice that despite their differences they each fall into a specific category of muscle architecture meaning we can actually group them together based off of the shape they take now these differences in muscle shape come with their own unique consequences in regards to how strong or mobile the muscle is so in today's video with the help of the cadavers here in the lab we're going to investigate the various skeletal muscle architectures and see exactly what it is they do for the surrounding joints as well as for the overall function of the human body it's going to be a really fun one let's do this you are looking at a horizontal or transverse cross section around the mid to upper thigh area of a right lower limb so you can see the femur that's this gigantic bone here and then you can also see a bunch of muscle tissue as well as some vasculature and what I'm going to do is I'm going to kind of peel it apart a little bit and you're going to see that as soon as I do this those muscles are made up of a lot of different muscle fibers now to understand what those fibers are we need to like say like we could zoom in and zoom in and zoom in and get very microscopic what you'd see is a lot of multi-nucleated skeletal muscle cells you could think of those as just really long cells kind of like a string that are going to have multiple nuclei and the reason why that's important is because you're going to need multiple nuclei to just help this really long muscle cells survive and thrive but also if one of those nuclei gets damaged let's say through some kind of trauma event the other nuclei will be able to still maintain that cell so you're not going to get cellular death which is extremely important because essentially for the most part you're born with as much skeletal muscles you're ever going to have I mean there are some circumstances with which that changes but for the most part that is true but real quick I want to say thank you to the sponsor of today's video let's get checked let's get checked offers private convenient testing in the comfort of your own home they offer routine blood work STI tests and even hormone tests such as a test test all you have to do is go online pick a test such as the testosterone test and they'll ship it to you with detailed instructions so that you can gather the specimen and then ship it back to them with their prepaid label they even have medical staff on hand so that you can discuss your test results with them so if you're having libido issues or erectile dysfunction or maybe you're just curious where your levels are at go ahead and visit try lgc.com Institute and they'll give our viewers 25 off their very own home test kit if they use the promo code Institute 25 link is in the description below all right let's get back to it now what will happen is you take those individual muscle cells and then you wrap them in a loose connective tissue that we call endomysium now loose connective tissue just means there's going to be collagen proteins that are scattered in various directions but they're not going to be densely packed and that's important because that allows blood vessels to go to and from the skeletal muscle cell as well as you know it allows for movement because inside of those skeletal muscle cells are going to be the proteins for contraction so it makes sense that you don't want to have a lot of tight collagen around the area because there's going to be a lot of friction now if you take as little as 10 of those muscle cells or maybe somewhere around 100 of them and you bundle them together into you know like just I like to think of as like a bundle of firewood but you bundle them together and then what you'll do is you wrap them in a more dense connective tissue that we call the perimysium if you do that you've now created what's called a fascicle so fascicles again are just bundles of skeletal muscle cells now if you look at a muscle you're going to see that it has fiber orientation what you're looking at are actually groups of fasciculi that are so you're seeing this the pathway you know the uh the angle that those muscle fibers are going those muscle cells that those are just groups of fascicles all traveling in a similar Direction that's What dictates the fiber orientation now if you take all of those fascicles and the entirety of the muscle and then you wrap them all together with another dense piece of connective tissue that we call the epimysium you now have what we call a muscle you can now officially name it so you could say this is the pectoralis major if you'd like so just think of muscles as just you know it's protein wrapped in connective tissue and more connective tissue which by the way the connective tissues are made of protein so it's protein wrapped in protein wrapped in protein but it's just a bunch it's a series of wraps now the next thing that's important to understand are what tendons are and how they relate to muscles so if we go back to here so what you're looking at again now we're looking at like the that lower leg so by the way if you're wondering about the sock it just helps keep the foot hydrated so it doesn't dry out because we haven't dissected it but if we look say at this muscle here so this is going to be like the knee so you're actually looking at the patella here we're going down and that makes this the tibia or the shin bone so you're looking at the front or anterior aspect of the lower leg if you look at this muscle here this muscle is called the tibialis anterior and if we look at it you're going to see that all of a sudden it transitions into a tendon a tendon is actually a continuation of the the connective tissues that were inside and on the outside of the muscle itself so if you recall me just saying a moment ago we had the perimysium that creates the fascicles and then the epimysium that wraps the entirety of the muscle but what happens is they continue once the skeletal muscle cells are done and they continue on as the tendon and will then blend into bone so really really interesting because what this means then is when the proteins of the skeletal muscle cell contract that'll pull on the endomysium which pulls on the perimysium and the epimysium and since those will continue on as the tendon and then blend into the bone that means the muscle as it generates tension it pulls on the tendon which pulls on the bone which assuming that you have one bone here and another bone here and then there's a joint in the middle you produce a movement so this is how skeletal muscles produce movement but another important thing we have to understand is that tendons have there's different sides to the tendon so I'm actually going to move this leg over here and what I want to do is I want to look at this this is a right Upper Limb so you can see the hand down here then we can see the elbow you can even see the scapula which is going to be right here and then the clavicle but I want to focus our attention grab my probe here to this muscle which is known as the biceps brachii so if you're looking at biceps brachii biceps just means two heads and you can see that as I split it apart with my probe you can see that we have two heads here which also means you can see there are two tendons see if I don't make sure this is super clear on the camera so we have two tendons that are going up like this then you'll notice down here towards the elbow there's only going to be one tendon that is then going to insert on the radius now typically if we were to like say if I was teaching an intro to Anatomy course I would say that these two tendons up here are the tendons of origin these are the origins of the muscle and then I would say this is the tendon of insertion or the insertion of the muscle now the reason why I say that is only for an intro to Anatomy course is because well maybe I should say this first the origin all that means is this is the less mobile end of the muscle while the insertion is going to be the more mobile end of the muscle so I know I'm kind of getting worried here but when that means when the muscle contracts this end moves a greater distance than this end so let me show you right so the action of biceps brachii is actually it's going to supinate so it kind of rotates the Palm so the Palm is facing up and then what it's going to do is it's going to flex the elbow and flex the shoulder a bit so as it does that action in the entire in its entirety more distance is covered at the elbow than up at the shoulder therefore this elbow attachment is considered the insertion so again the reason why that's only an intro to Anatomy type of understanding is because that's based off of the anatomical position anatomical position is a reference point it's just a way that we can you know effectively teach Anatomy right the reason why I can say that the head is above the knee is because we're talking about that from anatomical position right if you were laying down then obviously that's no longer true but the thing is eventually you get to the point where you have to start talking about human anatomy in more Dynamic terms right humans are not just standing in an anatomical position we are moving all over the place so let's take a push-up for example if I started to do a push-up right when I'm doing the push-up what's now going to happen is my shoulder is moving more or covering a greater distance than my elbow would be and and so biceps is still Contracting during this process and what that then means is we've flipped the origin insertion if the if the tendons up in the shoulder moving more this is now the insertion and this is moving less down here at the elbow this is now the origin so really when if you want to be accurate when you're talking about tendons we really shouldn't be saying origin and insertion that's just an effective teaching tool instead what we really should be saying is just proximal or distal attachment or Superior or inferior attachment or just saying the shoulder attachment or the radial attachment but again origin insertion do have important functions so with all that said now let's see how we can put all this together and start understanding the unique architecture of the various muscles the reason why you're looking at an anatomical model instead of a face on one of the cadavers here in the lab is because we want to protect the identities of the cadavers but also if you're looking at this anatomical model you can very clearly see the fiber orientations this is a very effective teaching tool so what we're going to be looking at are two muscles and these are going to be examples of circular muscles or circular fiber orientations so the first is going to be this one which is surrounding the eye this is called the orbicularis oculi it's super cool if you just kind of look at those fibers as it's surrounding the eye and going on to the eyelid and then the next is going to be the orbicularis Oris which is going around the lips now both of these muscles are essentially sphincters and their job is to protect you know the eyes the mouth from you know anything going inside of them right you're essentially stopping something from going from an external surface into an internal surface now the eye isn't directly an internal surface I mean I guess it kind of is but not as internal as say the oral cavity of the mouth but you still want to protect those delicate tissues so in the event that say like sunlight or rain or some you name it trying to get into the eye this can very quickly cinch shut right again you can look at those fibers and just very clearly see how this would just quickly tighten and slam the eyes shut and the same goes for that mouth right so you can see orbicularis Oris here you can just picture that would just tighten up cinch it down and then nothing's getting inside of that oral cavity next up we have parallel fiber orientations and as the name suggests all this means is that the fascicles those fibers are running in parallel to one another and within the longitudinal axis of that muscle itself now I've always taught there being two primary examples of these parallel oriented muscles but depending on the text you may see others being included in this but the first is what we call a strap muscle and again to no one's surprise that's because it looks like a strap You Can Think Like A Towing strap the classic example is the Sartorius muscle it's the long longest skeletal muscle in the body it runs from the anterior side of the hip all the way down to the medial or inside of your knee and it's going to produce a lot of range of motion it's going to swing your hip it's going to swing your knee it is a very mobile muscle it's a very long muscle that's because I mean for that entire length of the muscle that's how long those proteins are the fascicles the contractile components the muscle it's a really really long muscle then you have what's called a fusiform muscle shape now the classic example here is going to be biceps brachii so a fusiform you can think of it like a spindle shape so you on either end of the muscle where those tendons are you're going to have more narrow tendons right that the muscle is actually going to take more narrow appearance but in the center where that muscle belly is it's going to be more bulbous and so what this allows you to do is have a significant amount of muscle mass that is then able to insert in a really small tight area and that's exactly what biceps brachi does by especially going into its radial attachment it's just pushing through this really tight area and hitting that radial tuberosity it's just a really cool shape next you have the oblique fiber orientation muscles and so again to no one's surprise that's because the fascicles or fibers are going at an angle at least in relation to the longitudinal axis of that muscle now the first type is what's known as a convergent muscle type so easy example here is going to be the pectoralis major and this is such a cool muscle to look at because when you see it you can see this really wide attachment on the sternum going to the clavicle then all those fibers are just Fanning and converging together and then attaching at the humerus at the intertubercular groove it's just a really cool muscle to look at it's probably my favorite muscle to look at then we have the penated muscles so pennate means feather or feather light and so the first one is called a unipenate so in this type of muscle you have a central tendon and then you have a bunch of fascicles that are on one side of that tendon all coming at an angle what will happen is when they end those fascicles that is their connective tissues turn into an aponeurosis which is a nap Neurosis is a sheet-like tendon which will then attach to that more chord-like central tendon so then what you have is all these tiny little contractions occurring so the easy example here is extensor digitorum when you see extensor digitorum which is in the forearm it's in the extensor side of your forearm or antibrachium it's just a I mean you have all these fibers just coming at one angle attaching That central tendon so what will happen is they pull it pulls on that central tendon and you generate movement the next example is called a bipening this is the exact same thing as a unipening except with a unit Penny all the fibers were on one side by penate it's mirrored so now you have fibers on either side of that central tendon easy example here is the rectus femoris it's a quadriceps muscle so it's going to be in the anterior side of your hip and as you can see there's just this central tendon running down the center and then you have two side on either side of it you have the oblique angle so again now what you've done is you've just doubled the amount of protein that you can fit in that space then the third type is what's called a multi-penate this one is really really cool because what you have is just fibers just going and fascicles just going in every direction you can pretty much imagine all pulling on their own little tendons which are all going to start converging into one larger tendon so easy example here is the deltoid muscle deltoid has to do a lot it has to do flexion of the shoulder Abduction the shoulder extension the shoulder it's rotating deltoid is it has to do a lot of functions but the thing to understand is it also has to overcome gravity to do it it's kind of hard to just lift your shoulder in the way that's needed so deltoid is obscenely strong because you can fit in a ton of protein by shoving it and going in all these different directions all holding on these little tendons which are converging onto one tendon which will eventually produce one massive movement such a cool muscle so you may be wondering now that we've gone over all these different architectures is why even have them in the first place what function do they possibly serve well it really comes down to four different things so first how much force needs to be applied by that muscle essentially we're asking how strong does that muscle need to be second how much range of motion is needed at the Joint where that muscle is located right some muscles need to produce far more range of motion than others say like if you're walking versus talking third we have how well what's the space look like or the surrounding space the occupiable space for that area right if there's a lot of other muscles and structures that muscle has to fit into I mean that's going to dictate basically how it's going to form and then fourth we have attachment sites how does it have a broad attachment side or does it have a very narrow attachment site when you put all those together that's when you're going to start seeing these nuanced muscle shapes but you really also have to think about it in terms of two things right because there's a pro and a con for each basically if you look at the parallel fiber orientations those are going to be able to produce more range of motion but if you look at the oblique fiber types those are going to be able to produce more force and it really just comes down to how many proteins can you stack or shove into that same amount of space if you were able to say like make a Sartorius or a rectus femoris the exact same length right everything is all equal and then you measured you took a cross section of them and were able to measure how many fascicles essentially are in each you're going to see a much larger amount of protein inside of that bipinate that rectus femoris muscle meaning it's stronger even if they were the same size they're you're going to have a stronger muscle because you're able to apply more Force because there's more protein in those oblique fiber orientations so that's what it really comes down to do we need more range of motion or do we need more strength and force because you can't have both equally I mean well I guess you could have equal but sometimes you want to have a muscle that's stronger and less range of motion or other times you might want to have one that has more range of motion but isn't as strong and when you put that together and you just like change that in subtle ways all over the body that's how you're able to get you know human Locomotion and how we're able to move around and navigate our environment these muscles have different shapes because we have different requirements for the muscles at different joints for different times thanks for watching everybody I hope you enjoyed today's video it's always a blast to just nerd out on pure Anatomy as always be sure to like comment subscribe if you feel so inclined and I'll see in the next video thank you [Music] [Music]

Channel: Institute of Human Anatomy

Views: 704,446

Keywords: muscles, building muscle, muscle shape, biceps, pecs, bigger pecs, bigger biceps, biceps shape, pec shape, muscle anatomy, what are tendons, what are muscles, what are muscles made of, how do muscles work, sartorius, extensor digitorum, strap muscle, fusiform muscle, pennate muscles, unipennate, bipennate, multipennate, deltoid, convergent muscle, muscle strength vs muscle mobility, strength vs mobility, muscle strength, origin vs insertion, muscle origin, muscle insertion, muscle

Id: WkAG-K0bIx4

Length: 19min 27sec (1167 seconds)

Published: Sat Dec 10 2022