Science of Muscle Hypertrophy

[00:00] hi everybody dr. Mike here in this video

[00:02] we're gonna take a look at skeletal

[00:03] muscle hypertrophy now we all know that

[00:15] going into the gym lifting weights

[00:17] undergoing resistance training increases

[00:19] our muscle mass muscle volume muscle

[00:21] size and muscle cross-sectional area all

[00:24] of which we term skeletal muscle

[00:26] hypertrophy but the question is how does

[00:29] this occur so in this video I'm going to

[00:30] go through the mechanisms that promote

[00:32] skeletal muscle hypertrophy but the

[00:34] first thing we need to go through is the

[00:36] skeletal muscle itself so let's just say

[00:39] we have a whole muscle like a bicep for

[00:41] example now we know that this whole

[00:42] muscle is surrounded by connective

[00:44] tissue that we term fashio and if you

[00:46] have a look inside of that whole muscle

[00:48] you'll find that there's these discrete

[00:50] areas called fascicles they themselves

[00:53] are surrounded by connective tissue

[00:55] which we call perimysium now you can see

[00:57] within each fascicle are gonna we're

[01:01] gonna have skeletal muscle cells known

[01:03] as muscle fibers and you can see these

[01:05] fibers now if I would have take one of

[01:07] these fascicles and pull out one of

[01:09] these muscle fibers which we call a

[01:11] muscle cell you're gonna see a couple of

[01:13] things firstly it's surrounded by

[01:15] connective tissue as well so the whole

[01:16] muscle connective tissue right the

[01:20] fascicle connective tissue and then the

[01:22] muscle fiber connective tissue now this

[01:25] is called the endomysium that connective

[01:26] tissue around the muscle fiber and

[01:28] underneath that you've got the cell

[01:30] membrane cuz all cells have a cell

[01:32] membrane and we called this four muscle

[01:34] cells the Sarco lemma alright now you

[01:37] can see that I've drawn up a couple

[01:38] things first of which these little blue

[01:40] things here are called satellite cells

[01:42] they're going to be very important when

[01:43] it comes to hypertrophy sunlight cells

[01:46] are sitting between the sarcolemma so

[01:48] the cell membrane and a connective

[01:50] tissue the basal lamina okay and they're

[01:52] sitting there in the quiescent which

[01:54] means they're asleep and they're waiting

[01:55] to be stimulated and do something very

[01:57] specific in order first skeletal muscle

[01:59] hypertrophy to occur the other thing you

[02:01] can see is the nuclei of skeletal muscle

[02:04] they have more than one and again this

[02:07] is important when it comes to sunlight

[02:08] cells remember the nucleus is where DNA

[02:11] is transcribed we make more DNA

[02:13] now remember proteins come from amino

[02:15] acids which come from DNA that's

[02:17] important you can also see that if we

[02:20] were to take out one muscle fiber that

[02:22] inside they're filled they're really

[02:24] filled up with these things could

[02:26] myofibrillar

[02:27] tubes now these myofibrils are made up

[02:31] of proteins two major types of proteins

[02:34] there's more but two major types you

[02:36] need to know called actin and myosin now

[02:39] what you're going to find is that these

[02:40] proteins inside the myofibrils their

[02:42] contractile proteins because not all

[02:44] proteins are contractile right but these

[02:46] are contractile proteins now you'll see

[02:49] that dispersed between the myofibrillar

[02:51] have some organelles some sub cellular

[02:54] components things like mitochondria

[02:56] right mitochondria is important for

[02:58] producing ATP energy which we need for

[03:00] skeletal muscle contraction we also have

[03:02] things like sarcoplasmic reticulum

[03:05] now the sarcoplasmic reticulum is the

[03:07] endoplasmic reticulum but for skeletal

[03:09] muscle and their important role is that

[03:11] they are the storage unit for calcium we

[03:14] also need calcium for muscle contraction

[03:15] actual fact calcium and ATP are two of

[03:18] the major things that we need for muscle

[03:20] contraction there's other organelles as

[03:22] well but let's just focus on those two

[03:24] all right now let's take a myofibrillar

[03:26] out have a look at this right we've got

[03:28] the Maya febrile sitting within the

[03:30] muscle fiber sitting within the fascicle

[03:31] sitting within the whole muscle each

[03:33] component is surrounded by connective

[03:35] tissue we take a my fibrillate and we

[03:37] looked at look at the actin and myosin

[03:39] contractile proteins within and you'll

[03:41] see they have a particular arrangement

[03:43] what I've drawn up here is something

[03:45] called a sarcomere now you keep hearing

[03:47] this word Sarco as a prefix when we talk

[03:49] about scalar muscle because it means

[03:51] flesh all right so you can see the two

[03:53] major types actin which we call the thin

[03:55] filament and myosin that we call the

[03:58] thick filament now in order for muscle

[04:00] to contract muscle its job is to

[04:03] contract so that force can be generated

[04:05] usually things can move and you've got

[04:07] cardiac muscle to pump blood smooth

[04:09] muscle to push things through the hollow

[04:11] insides of those of that lumen and we've

[04:13] got skeletal muscle attached to the

[04:15] skeleton so things can move right so

[04:17] what we need to do is that this thick

[04:20] myosin filament needs to bind to the

[04:22] thin actin filament and these little

[04:24] myosin heads need to walk their way

[04:26] along the actin filament and it pulls it

[04:28] in what this does is it shortens the

[04:30] skeletal muscle in actual fact it

[04:32] shortens this thing called the sarcomere

[04:34] now you're gonna have sarcomeres lined

[04:36] up in series like this or or I should

[04:39] say and lined up in parallel okay and

[04:42] this is going to be important when it

[04:43] comes to skeletal muscle hypertrophy as

[04:45] well now remember the myosin can't bind

[04:48] to the actin unless calcium is present

[04:50] calcium frees the actin so it can bind

[04:52] and calcium sits within the sarcoplasmic

[04:55] reticulum and we need ATP the thing with

[04:58] ATP is we don't actually have a lot of

[05:00] it just freely floating around you think

[05:02] we would but we don't we need to

[05:03] generate ATP and so skeletal muscle

[05:06] needs to generate ATP fast and we'll

[05:08] talk about that with skeletal muscle

[05:09] hypertrophy soon all right

[05:11] couple things now when we talk about

[05:13] hypertrophy I told you increasing the

[05:16] size increasing the volume increase in

[05:17] the mass increasing the cross-sectional

[05:19] area what do you think is increasing

[05:22] here is it the whole muscle is that the

[05:24] fascicle is it the muscle fiber or is it

[05:26] the sarcomere or is it the protein

[05:28] subunits of the sarcomere well it's not

[05:31] just these individual things so for

[05:34] example a lot of people rely on scooter

[05:36] muscle hypertrophy has just been an

[05:38] abundance of the proteins that

[05:39] contractile proteins and their

[05:41] arrangement within the sarcomere people

[05:43] think that scooter muscle hypertrophy is

[05:45] only more sarcomeres lined up in series

[05:49] or lineup in parallel but that's only

[05:51] one type of skeletal muscle hypertrophy

[05:53] right called myofibrillar hypertrophy I

[05:56] think we should write this down right so

[05:59] you can have myofibrillar hypertrophy

[06:04] and like I said what that is is an

[06:09] increase in the protein subunits for

[06:12] contraction and an increase in the

[06:14] amount of sarcomeres we have either in

[06:17] series or in parallel but we know that

[06:21] up to 20% of the whole muscle is

[06:23] connective tissue like I stated before

[06:25] right so you've got that fashion you've

[06:28] got the Paramecium you got the

[06:30] endomysium you have the epimysium on the

[06:32] outside here so up to 20% is connective

[06:36] tissue so in connective tissue is

[06:38] dynamic it doesn't

[06:39] sit there connective tissue can grow and

[06:41] it can contribute to strength so you can

[06:44] have connective tissue hypertrophy now

[06:53] the last or third type of hypertrophy

[06:56] that we need to talk about is

[06:57] hypertrophy of non contractile subunits

[07:00] and non connective tissue which has to

[07:02] do with the stuff sitting between the

[07:05] cells and in the cells for example which

[07:08] includes things like the organelles and

[07:10] the fluid and also the metabolic energy

[07:15] sources that are stored inside of these

[07:17] muscle cells so for example now we call

[07:20] this let's just write this down

[07:22] we call this sarcoplasmic hypertrophy so

[07:32] what we're referring to for sarcoplasmic

[07:34] hypertrophy is an increase in the size

[07:36] or abundance or volume of the organelle

[07:39] so it could be the mitochondria it could

[07:41] be the sarcoplasmic reticulum could be

[07:43] the T tubules that skeletal muscle needs

[07:45] to propagate that action potential to

[07:47] tell it to contract right it could be an

[07:50] accumulation of fluid inside and it

[07:52] could be an accumulation of the

[07:54] metabolic products needed to produce

[07:56] energy so up to three percent of

[08:00] skeletal muscle is made up of glycogen

[08:03] up to five percent is made up of

[08:05] triglycerides so you can increase the

[08:07] abundance of these and they're going to

[08:08] come back later when we talk about

[08:09] hypertrophy so these are the three major

[08:12] types and the thing is what causes these

[08:15] types of hypertrophy so doctor shown

[08:18] field dr. Brad shown field is the king

[08:21] of skeletal muscle hypertrophy and all

[08:23] the research that I've performed most of

[08:25] it has come from dr. Shawn field and so

[08:28] what dr. Schoenfield states is the three

[08:30] major causes or stimuli for hypertrophy

[08:33] include the following mechanical tension

[08:43] metabolic stress and muscle damage so

[08:53] these three stimuli are what can result

[08:59] in these three types of hypertrophy now

[09:02] your question may be well which of these

[09:03] hypertrophy is occurring usually all of

[09:05] them are going to be occurring to some

[09:07] degree you're probably going to think

[09:09] with resistance training probably the

[09:10] most common type of hypertrophy is Maya

[09:13] febrile hypertrophy but in saying that

[09:15] when you look at bodybuilders and

[09:16] compare them to power lifters their

[09:18] training regime is different but both of

[09:20] them exhibit quite significant

[09:22] musculature quite significant muscle

[09:24] growth and they train differently right

[09:26] so for example bodybuilders have a

[09:28] moderate load with shorter rest periods

[09:31] and you're going to find that power

[09:32] lifters have a higher load with longer

[09:35] rest periods and what you might find is

[09:38] that some bodybuilders may more so have

[09:40] a connective tissue based and

[09:42] sarcoplasmic based hypertrophy because

[09:44] they tend to have more stores of

[09:45] glycogen within their cells and they

[09:47] tend to have more connective tissue

[09:49] products as well compared to the power

[09:51] lifters so training type can be specific

[09:55] to the type of hypertrophy that you get

[09:58] all right so mechanical tension

[10:00] metabolic stress and muscle damage of

[10:03] these mechanical mechanical tension is

[10:06] king right and you'll find that

[10:08] metabolic stress and muscle damage are

[10:10] additive to this process because you

[10:12] really get skeletal muscle hypertrophy

[10:14] on metabolic stress alone and muscle

[10:17] damage alone now let's talk about some

[10:19] things let's talk about how this can

[10:22] result in this all right so when you've

[10:25] got mechanical tension on a muscle so

[10:27] you lifting a particular load over time

[10:30] and so we know that we have eccentric

[10:32] portions of a movement and concentric

[10:33] portions in the eccentric portions where

[10:36] you've got lengthening of the muscle but

[10:38] these sarcomeres are contracting you can

[10:41] have damage occurring to the

[10:43] myofibrillar units now damage promote

[10:46] some form of inflammatory response it

[10:48] can recruit cytokines and inflammatory

[10:50] cells and this promotes your repair

[10:52] that's great what also happens is this

[10:55] type of damage

[10:56] wakes up the sleeping satellite cells

[10:58] the quiescent satellite cells and they

[11:00] are myogenic cells that means they're

[11:03] basically muscle stem cells and what

[11:05] they can do is they fuse since they're

[11:06] sitting underneath the basal lamina

[11:08] right but above the sarcolemma they fuse

[11:10] with the muscle cell they're all muscle

[11:12] cells remember they fuse with them and

[11:14] they donate a nuclei that's why I've got

[11:17] more nuclear here donates a nuclei and

[11:20] what that means is there's now more

[11:21] nuclei more DNA more transcriptional

[11:25] activity more amino acids and proteins

[11:27] being produced in actual fact when you

[11:29] look at skeletal muscle the larger the

[11:31] muscle is correlated with more nuclei

[11:34] and this has to do with that satellite

[11:36] cell so the satellite cell is really

[11:38] important for donating the nuclear but

[11:39] in addition the satellite cell can call

[11:42] upon particular transcriptional

[11:43] activities right since it's got this

[11:45] additional nuclei transcribe more

[11:49] pathways associated with anabolic or

[11:51] growth pathways so for example mTOR map

[11:55] kinase calcium signaling pathways all of

[11:59] these can be recruited pathways for

[12:01] growth and ab ilysm alright so we'll

[12:05] focus on that now when you look at the e

[12:07] centric and you start to go into that

[12:09] pattern of moment eccentric stretching

[12:11] at the same time that it's contracting

[12:13] you can find that in some studies animal

[12:15] studies predominantly that the types of

[12:18] growth that you get at the sarcomere is

[12:21] an addition of sarcomeres in series and

[12:24] when you get more column centric

[12:27] movements the addition of sarcomeres is

[12:30] in parallel alright so again the type of

[12:33] that movement can change what type of

[12:35] hypertrophy you have at the sarcomere so

[12:37] talking about the my fibrillar

[12:39] hypertrophy if we actually take all them

[12:41] all the proteins within a skeletal

[12:43] muscle what you're gonna find is up to

[12:45] 70% of them are my fibrillar proteins

[12:48] right seventy percent twenty percent of

[12:50] them are sarcoplasmic proteins and

[12:53] around about 10% our mitochondrial

[12:56] proteins alright now a couple of other

[12:59] things is when so if we have a look at

[13:02] different types of loads so when we look

[13:04] at load lifting load it's usually going

[13:07] to be represented as a percentage of our

[13:08] one-hour

[13:09] and we usually equate that to how many

[13:11] reps we can perform other particular

[13:13] weight all right so you can have a low

[13:17] rep scheme a moderate rep skein and a

[13:19] high rep scheme

[13:20] all right low rep scheme zero to six

[13:21] reps mutter at six to twelve reps

[13:24] anything above 12 13 14 15 reps and

[13:26] above is going to be a high rep scheme

[13:28] so what they've found is that the low to

[13:30] moderate rep scheme seems to be more

[13:32] beneficial to hypertrophy compared to

[13:34] high rep skeins and the reason is a

[13:37] little bit complex but has to do with a

[13:39] couple of things has to do with

[13:40] mechanical tension and has to do with

[13:42] metabolic stress and muscle damage but

[13:44] let's look at metabolic stress now so

[13:46] when you lift a particular load we need

[13:50] ATP and I told you that ATP is needed

[13:52] for muscle contraction and I told you we

[13:54] don't have many reserves of ATP so we

[13:57] need to produce it now when we need to

[13:59] produce it immediately we use something

[14:01] called the Fausto creatine pathway

[14:03] creatine likes to hold onto phosphate

[14:05] called phosphor creatine and it donates

[14:07] that phosphate to an adp to basically

[14:10] turn it into ATP we have energy but that

[14:13] only lasts for like one two three

[14:14] seconds not very long at all so the low

[14:16] rep scheme tends to favor the

[14:18] phosphocreatine pathway when we go into

[14:20] the moderate rep scheme right six to

[14:22] twelve reps we go past that and we start

[14:25] to go into glycolysis we start to use

[14:27] glucose for energy now if we're doing

[14:28] this quick and fast and remember when

[14:31] you have glycolysis and it jumps into

[14:32] the mitochondria a user's oxygen to

[14:35] produce heaps of ATP if we need more ATP

[14:37] than we have available oxygen has to go

[14:40] through another pathway which is

[14:41] producing lactate right and ATP as well

[14:45] another thing is lactate production is

[14:47] associated with hypertrophy in this

[14:49] sense lactate can pull water has a

[14:52] strong osmotic gradient right it pulls

[14:54] water into the cell and causes the

[14:56] muscle cell to swell this swelling of

[14:59] the muscle cell puts pressure on the

[15:00] sarcolemma sort of cell membrane and

[15:02] this actually stimulates a couple of

[15:04] things it stimulates amino acid

[15:06] transport and it stimulates anabolism or

[15:09] protein synthesis brilliant so this is

[15:12] something that lactate can do lactate

[15:15] production is also associated with

[15:18] testosterone levels and growth hormone

[15:20] levels as well alright so it seems to be

[15:22] this is

[15:23] why the moderate reps game seems to be

[15:25] represented as potentially the most

[15:27] beneficial when it comes to hypertrophy

[15:29] but let's not forget volume all right so

[15:32] that's load volume is adding up all your

[15:35] reps and sets in the single session and

[15:37] it seems to be the higher the volume the

[15:39] better it is for hypertrophy as well now

[15:42] let's talk about something that involves

[15:44] both metabolic stress and muscle damage

[15:46] which is hypoxia

[15:47] so hypoxia is a reduction in oxygen

[15:49] going to that tissue and feeding that

[15:51] tissue so often we call this vascular

[15:54] occlusion and the some sort there's some

[15:56] types of training where you occlude the

[15:58] vasculature with a cuff for example and

[16:01] it seems to be that this type of hypoxic

[16:03] or or banded vascular occlusion training

[16:05] can increase muscle hypertrophy if done

[16:09] in accordance with exercise and it

[16:10] doesn't even need to be under high load

[16:12] so what the found is that hypoxia

[16:15] training or vascular occlusion training

[16:17] without any exercise just the vascular

[16:19] occlusion can maintain muscle size and

[16:21] strength for individuals who are

[16:23] bedridden if you mix it in with exercise

[16:26] it seems to be an additive effects with

[16:28] hypoxia and exercise to promote

[16:32] hypertrophy as well so that's really

[16:34] interesting why why does this hypoxic

[16:37] event promote hypertrophy couple of

[16:39] theories one of which is that of lactate

[16:41] so when you've got no oxygen we're

[16:43] forced to use glucose to produce ATP and

[16:47] lactate and like I said lactate pulls

[16:49] water into the cell it swells promotes

[16:51] amino acids and protein synthesis and

[16:53] also promotes

[16:54] growth hormone and testosterone coming

[16:58] in the other thing is when you have a

[17:00] hypoxic environment low oxygen you get

[17:02] the production of reactive oxygen

[17:03] species one of which is nitric oxide

[17:06] nitric oxide tells blood vessels to

[17:08] dilate so after that training when you

[17:11] release the cuff or the band you get

[17:13] increased in nitric oxide tells blood

[17:15] vessels to dilate you get hyperemia

[17:17] which is more blood to that area

[17:18] carrying all the metabolites that you

[17:20] require for growth so maybe that is also

[17:23] another factor coming into play so what

[17:26] I've gone through here is the anatomy of

[17:28] the skeletal muscle and gone through the

[17:31] different types of hypertrophy and also

[17:33] the different causes of these particular

[17:36] high

[17:37] a hypertrophic events hopefully that

[17:40] helps them make sense