0:19

Welcome back to the Stronger By Science podcast.

0:21

I'm Greg Knuckles. I

0:24

am Pac, and I'm Milo.

0:27

And we have another great episode

0:30

for you guys today. Today

0:33

we're talking about stretch mediated

0:35

hypertrophy. And for

0:38

people listening, before you start getting nervous

0:40

that this is going to be our

0:43

second recent-ish episode on whether

0:46

or not muscles grow more

0:48

when training at longer muscle

0:50

lengths. Our second episode

0:53

in recent times and

0:55

the millionth episode and piece of content

0:57

around the internet about that topic in

1:00

recent times, fear not. That

1:02

is not what we're discussing. This

1:06

is an episode about

1:08

the concept of stretch

1:10

mediated hypertrophy. And

1:12

whether or not it's something we really

1:14

even observe at all

1:17

in normal resistance training

1:19

interventions. So I will

1:22

fully admit on the front end,

1:24

this episode is

1:26

mostly about a pedantic

1:29

point. It's not about

1:31

whether or not muscles grow

1:34

more when training at long muscle lengths.

1:36

It's about whether it's correct

1:39

to call that stretch mediated

1:41

hypertrophy. The stretch mediated hypertrophy

1:44

is a very specific thing, but

1:46

I think when people use that term, they often

1:48

use it as more of a

1:51

broad descriptor of a lot of

1:53

things that maybe shouldn't rightly be

1:55

called stretch mediated hypertrophy. And

1:58

it's not just about whether pedantic

2:00

point, which even if it was,

2:02

I still think that would be fun as an episode. I'm

2:04

a fan of using

2:06

language precisely in a scientific context.

2:10

But it's not just that, it is also

2:14

an important distinction to make

2:16

to discuss whether

2:18

the effect is actually

2:21

mediated by stretch because

2:23

that carries with it different implications

2:25

about what sorts of

2:27

hypotheses one might make about why training

2:29

at longer muscle links might lead to

2:32

more muscle growth and it

2:34

leads to different hypotheses about the type of

2:36

training one might do in order to try

2:38

to grow more. So yes,

2:42

it's pet entry with a point, which is

2:44

one of my favorite things in the world. So

2:48

yeah, we're gonna get into all of that in

2:50

a second, but yeah, just here

2:52

at the top of the episode, how are

2:54

you guys doing today? We

2:57

are good. I am doing

2:59

just fine. We are working on

3:02

a bunch of cool things behind

3:04

the scenes, both research and

3:07

content related, so lots

3:09

of cool stuff to look forward to. Echoing

3:13

pack, we've been working on a lot of strong

3:15

by science related content, a lot of videos that

3:17

are coming up soon and we're

3:19

also in fact not to turn this

3:21

into another LinkedIn partial episode. But

3:24

preparing to run a study in the summer

3:26

on LinkedIn partials. So a lot of

3:28

cool things behind the scenes going on and hopefully more

3:31

on the general topic of stretch

3:35

media hypertrophy or maybe not in this case and

3:38

specifically LinkedIn partials. Very

3:40

nice. What's going on in the study?

3:42

Like what are you hoping it will

3:44

add to the literature? Sure.

3:47

So to jump ahead a little bit on

3:49

one of the claims made about stretch media

3:51

hypertrophy, it's that it's only really relevant in

3:55

trained lifters. And so if you

3:57

think that stretch media hypertrophy is what's going on

3:59

with length and partials or length and training by and

4:01

large. Then one of the common assumptions

4:04

is, well, length and training may or may not

4:06

be beneficial in beginners, but in more

4:08

advanced trainees it certainly won't be. And

4:10

so that's essentially a claim we're looking

4:12

to assess a little bit. There's not

4:15

too much research currently on length and

4:17

training in trained lifters. And so we'll

4:19

be conducting a study in trained lifters with at

4:21

least six months of training experience in

4:23

the summer comparing a full range of motion approach

4:26

to a length and partial approach, but specifically

4:28

using a within participant design so

4:30

as to wash out a lot of potential

4:33

confounding variables like differences in

4:35

sleep, stress, nutrition, etc. that

4:37

could be otherwise causing the results. That's

4:41

very cool. That's very cool. Well,

4:43

I'm excited to see and hear

4:45

how that goes. It

4:48

will also be the first one on another

4:51

first one. It will be the first one

4:53

in trained individuals and upper body musculature. Oh

4:56

yeah, yeah. Technically. Technically,

4:59

technically. Yeah,

5:02

we're not going to litigate that again.

5:07

All right, yeah. So we'll get into

5:10

the content here in a brief moment,

5:12

but first our standard plugs here at

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all relatively active in those three places,

7:04

or in those two places. And

7:06

also if you're just a fan of the

7:08

pod, that is where we make

7:11

posts soliciting questions for the episode.

7:13

So at the end of this episode, you'll

7:17

hear some questions about stretch mediated

7:19

hypertrophy and if you think to yourself, man,

7:22

I didn't know that they were taking questions

7:26

on that topic, I would have liked to ask something. Well,

7:28

you would have known if you were in the Facebook

7:30

group or subreddit, so yeah, head on over there. And

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where every couple of

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weeks we send you high quality,

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informative content. We're not just spamming

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you with a bunch of ads. I

7:53

think all of us are subscribed to too

7:55

many things via Email. The

8:00

email and too many. Ah, you know

8:02

you put your email and somewhere once

8:04

and then. It feels like

8:07

your inbox is just inundated with

8:09

marketing emails until the end of

8:11

time on. You know very very

8:13

sensitive to that. That is not what you

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get from the Stronger by Science newsletter. So

8:17

if you want to get ah you know

8:20

in emails every couple of weeks or to

8:22

actually look forward to and don't as. Auto.

8:25

Delete or auto archive eyes.

8:27

To. Good thing to check out. On.

8:30

The. Up with unlicensed to demonstrate to

8:32

listener how much value or think providing

8:34

her or to school bus on some

8:37

generals promote have club well. I'm.

8:39

Subscribed to newsletters or think was a

8:41

four or five different email addresses. And

8:44

I haven't linked inbox every time release

8:46

a newsletter. Guess. What I get it

8:48

in times four, or five. That's how valuable

8:51

I think it is. you know? And to

8:53

be honest though, that's been the case for.

8:56

Years and years and years now just because

8:58

Trouble Signs truly don't spam you. and whenever

9:00

they send you emails and mostly now we

9:02

send you an email I do think we

9:04

trying provide. The. Most

9:06

up to the scientific research or

9:08

least nothing of egregiously spamming. That's

9:11

that's crazy that you said that I had

9:13

the same I had a sign up with

9:15

I think three or four emails all linked

9:17

to the main inbox say was times for

9:19

baby. But. yes I is

9:21

totally echo of my lawyer said. It's

9:24

crazy both of you say that because the

9:26

same is also true of me on any

9:28

time I sent an email as the people,

9:31

I want to get it back Four times

9:33

I've. You know if you put something

9:35

out into the universe and if it comes back

9:37

to that means. You. Have good karma.

9:40

That's the secret, but you can.

9:42

You can have the secret by

9:44

putting things out into the universe

9:46

via your own email newsletter and

9:48

then subscribe to the newsletter. It

9:50

automatically comes back. it's it's free

9:52

card of like it's an. Easy

9:54

if is the infinite karma hacked. I think

9:57

more people need to be aware of that.

9:59

actually know it's. Damn. You.

10:01

Know we We try to

10:03

do things with our email

10:05

software and are. We. Just

10:07

use my email addresses for testing

10:10

purposes. So I'm subscribed all her

10:12

stuff like forty textbooks. I

10:15

said unsubscribe, but I don't.

10:17

Whatever, it's fine on. The

10:21

wind. Up sorry. The

10:23

one thing that is worth noting

10:25

here is that there is multiple

10:27

witnesses to us being big fans of

10:30

the newsletter and as be as in

10:32

general way way before the was even

10:34

any remote affiliations including multiple university students

10:37

when I taught that a couple universe

10:39

here in the in the Uk where

10:41

I spam them with hey guys, stronger

10:44

by science as that's what you should

10:46

befall. It's just to avoid anybody saying

10:48

okay guys, I can see Greg sliding

10:51

his card under the table while you're

10:53

talking. So that you can add more

10:55

sauce here and taught even more when

10:57

I was about sixteen years old. That's

10:59

how time tested stronger signs as a

11:01

bronze is and providing something from A

11:03

from when I was fifteen years old.

11:06

For. Christmas. I. Asked for

11:08

former science he books and that's what got

11:10

me on a newsletter. So it's straw by

11:12

science has been around it's been doing but

11:14

I'm thing so if your interests cause a

11:17

newsletter what are you doing. Be.

11:20

You guys are both He passing such

11:22

systems makes me feel very of four

11:24

foot. Of

11:27

snow. A bad ah

11:29

okay yeah, let's let's let's

11:31

get into the episode now.

11:37

See. I just turned, just set

11:39

the table a little bit and.

11:43

We are are like a

11:45

set up top and as

11:47

I'm sure the title of

11:49

this episode of reveals this

11:51

is an episode on stretch

11:53

meet mediated hypertrophied on. The.

11:55

Reason this is relevant is

11:57

that. the idea of

12:02

observing more muscle growth when people

12:07

are currently discussing very of

12:37

a stretch and that's

12:40

why you see more growth.

12:42

It's a stretch mediated effect.

12:44

Similar with with length

12:47

and partials which are all

12:49

deranged, there's also research just

12:51

comparing isometric training at longer

12:53

versus shorter muscle links. I think a

12:56

2018 meta-analysis by

12:58

Oren Chuck if memory serves.

13:00

So yeah, there's multiple lines

13:02

of evidence suggesting that

13:04

muscles grow more when they're

13:06

trained at longer lengths and

13:09

to explain that finding people

13:11

use the phrase stretch mediated

13:13

hypertrophy. So what we want

13:15

to do in this episode is just discuss

13:19

is that right? You

13:21

know we see more muscle growth when

13:23

training at longer muscle links but

13:26

is that due to stretch, is

13:28

that mediated by stretch, is

13:31

stretch mediated hypertrophy the correct term

13:34

to describe that? And

13:37

just up top this is I

13:39

think one of the first things Milo is going to talk about

13:42

here. Stretch mediated hypertrophy

13:45

is a thing. It's something we've known about

13:47

for a long time. It is something we've

13:49

observed in humans but there is

13:52

still the question

13:54

of Is that what is

13:57

actually going on to explain why? Resistance

13:59

training at Longer. The muscle wings. Tends

14:01

to lead to more growth. And and

14:03

like I said at the very top of

14:06

the episode the reason as relevant is. Is

14:09

be effect is mediated by stress.

14:11

You know if. Ah, If

14:14

we see more muscle growth when

14:17

printing at longer muscle wings due

14:19

to stress mediated hypertrophy that carries

14:21

with a clear implications that would

14:23

mean that in order for longer

14:25

muscling training to be to more

14:27

close. He would need

14:29

to induce a stress, right? so

14:32

that would therefore imploded some muscles.

14:34

Maybe wouldn't be amenable to growing

14:36

Mormons who knew longer muscle links

14:38

because there are difficult to stress

14:40

in a resistance training context. It

14:43

would also generally lead to the

14:45

hypothesis that training at longer muscle

14:47

links soon into lead to more

14:49

growth. Unless. It

14:52

also causes stress. Because.

14:56

How could you have he scratched mediated

14:58

effect without. A significant

15:01

strikes been present on.

15:03

Which. Would therefore lead to implications

15:05

about maybe the the ranges emotion

15:08

you would need to train through

15:10

in order to expect. To.

15:12

Achieve greater hypertrophied on.

15:15

And. So yeah, if if someone

15:17

is interested in the practical

15:19

aspects of applying the findings,

15:22

Related. To more growth in

15:24

training a longer muscling six feet

15:26

are very practical questions. So again,

15:29

This is a little bit pedantic, which

15:31

is right in my second. We'll have

15:34

a one it, but it it it

15:36

is. Also stole very practical and relevant

15:38

because. It influences how you might

15:40

want to apply the findings. Of

15:43

the research looking at actual

15:45

hypertrophy with longer muscle links

15:47

trading interventions on fear that

15:49

settle Urdu in this episode

15:52

and as. As my intro

15:54

I think I think taken away from here milo.

15:57

i think that was really solid one

15:59

thing I'd like to preface the discussion

16:01

with is why we're even

16:04

having this chat in the first place. So

16:07

when people have been discussing length and training,

16:09

why it may or may not lead to

16:11

more hypertrophy, if you're

16:13

not aware that stretch-me is hypertrophy, has

16:16

some degree of history behind it as a term,

16:18

like it's been around for a while, it

16:21

actually first originated in the 1970s

16:23

or so. If

16:25

you're not aware of that, it can be very intuitive to just

16:27

say, oh, training at longer

16:29

muscle lengths in the more stretched position causes

16:31

more growth. Therefore, it

16:34

is stretch-me and hypertrophy. But

16:36

it's worth just being a little bit pedantic about nomenclature

16:39

and realizing that that term has

16:41

a scientific connotation and an origin

16:43

that I think many people aren't

16:46

aware of. So the first

16:48

thing we need to do really is to

16:50

delve into where did the term originate and

16:53

as an extension, whether or not

16:55

that term is appropriate when describing

16:58

what happens with length and training. Now,

17:00

the research for this podcast episode

17:02

was actually done in the context of writing a

17:04

full article on the topic and that will be

17:06

up on Strong by Science in

17:08

the next couple of weeks. So if you want more

17:11

reading and more detail on

17:13

all the studies we'll mention throughout the

17:16

podcast episode, keep an eye out.

17:18

It'll either be out by the time this podcast

17:20

is released or it'll be out in

17:22

the next few days or a week or two at the most.

17:24

So it should be around quite soon. But

17:27

within this podcast episode, the aim is really just

17:29

to provide an overview of

17:32

first where stretch-me and hypertrophy originated

17:34

from, then whether or not

17:37

stretch-me and hypertrophy even occurs in humans to

17:40

a meaningful extent, and then

17:42

finally just seeing whether or not the

17:44

adaptations we see with stretching interventions in

17:46

humans and animals even are

17:48

generalizable to what we see from lifting weights

17:50

because that is also somewhat of an open

17:52

question. So first, where

17:55

did we first come

17:57

across the concept of stretch-me and hypertrophy?

18:00

In around the 1970s and the earliest study

18:02

I was able to find was a study

18:04

by Sowlung colleagues from 1973. There might be

18:07

earlier ones but that was certainly the earliest

18:09

I was able to find. There

18:11

were quite a few studies utilizing animal

18:13

models to investigate the

18:15

effect of chronic stretch-metered interventions

18:17

on muscle mass. And

18:20

so for these experiments you often

18:23

had a variety of animals stretch

18:25

out one of their muscles. Frequently

18:27

they would use the anterior lat

18:30

muscle essentially and stretch

18:32

that out with some amount of

18:34

weight. A stretching device and the amount of

18:36

weight typically would be relatively large between

18:38

around 10 to 35 percent of

18:40

the animal's body weight. So we're talking

18:43

about relatively high amounts of weight being used to

18:45

stretch out the muscle and

18:48

the duration of stretching in these studies

18:50

was frequently on the order of you

18:53

know at least an hour a day to frequently up

18:55

to the whole day so 24 hours per day four

18:57

weeks on end. And within these

19:00

studies they generally looked at muscle

19:02

mass but also things like muscle

19:05

hyperplasia were essentially the creation of

19:07

new muscle fibers which is something that's notoriously

19:09

difficult to look at in the context of

19:11

humans. But just to give you an idea

19:13

of the overall research and what

19:16

like common research designs are within

19:19

this data, as I mentioned

19:21

earlier one of the first studies was by Sowlung

19:23

colleagues in 1973 and

19:25

in his study they essentially had

19:27

a within participant or

19:30

within animal design wherein they

19:32

essentially took birds and

19:36

specifically their anterior lat muscle or the

19:38

hertz minor and they stretched

19:40

out their muscles with one to 200 gram

19:42

weights to one look at the impact of

19:45

the weight being used during stretching intervention on

19:47

hypertrophy but two another

19:50

variable they manipulated was essentially controlling

19:52

whether the wing was innervated so

19:54

it had functioning nerve

19:56

endings that were

19:59

essentially capable of making the muscle contract versus

20:02

having the muscle be denervated.

20:04

So devoid of functional nerve

20:08

endings that therefore allow for the

20:10

muscle to actively contract. And so

20:12

the idea essentially is to compare innervated

20:14

muscle to denervated muscle and to see

20:16

whether in denervated muscle that had its

20:19

nerve endings removed and therefore is unable

20:21

to actively contract, we still

20:23

observe truly stretch mediated hypertrophy or

20:25

whether there's an effect of simply

20:27

the stretching intervention on hypertrophy.

20:30

And the second question was is there a

20:32

difference between different weights being used for hypertrophy.

20:37

And so in this study they stretched out these bird

20:39

wings with 1 to 200 gram weights and

20:42

they observed quite substantial hypertrophy of

20:44

both the denervated wing and the

20:46

innervated wing. Specifically on average

20:49

we observed around 140% of an increase in muscle mass

20:51

in the wing

20:53

that still had functional nerve endings. And

20:56

so what we can kind of get at through this

20:58

study and through the results is how much of the increase

21:01

in muscle mass is truly stretch mediated. So

21:04

when you lift weights for example, there's a few things

21:06

going on. One,

21:08

in order for you to actually be able to lift

21:10

the weight, your muscle is contracting, producing active tension, overcoming gravity and

21:12

tada, you're able to lift the weight. But

21:16

what if your muscle was able to lift the weight and you

21:18

were able to lift the weight What

21:22

if your muscle was no longer able to produce

21:24

active tension? That would then

21:26

essentially isolate the question of okay, how much

21:29

of the hypertrophy observed is just stretch mediated?

21:31

And so in this case it appears that

21:34

around 140% of the increase in muscle mass

21:36

was attributable to simply the

21:38

stretch intervention. Whereas potentially

21:40

the difference in hypertrophy observed

21:43

between the innervated and denervated

21:45

muscle was attributable to active

21:47

contraction, that is to

21:49

say more so contraction mediated hypertrophy

21:52

versus stretch mediated hypertrophy. But

21:54

the bulk of the hypertrophy observed did seem

21:56

to be related to the stretch

21:59

intervention. Another

22:02

thing that was noted was an increase in the total

22:04

number of muscle fibers and that's

22:06

something that we don't frequently,

22:09

well, we don't have much

22:11

if any direct research in humans so it's difficult

22:13

to speak about how that is in humans but

22:15

I know Greg is a big fan

22:17

of this topic and has written about it a fair

22:20

bit so I'll let him give us two

22:22

cents there. Yeah, I'm

22:24

not gonna do my full hyperplasia

22:27

rant here. That would be

22:29

far too far off topic and I'm sure

22:31

I've talked about this on the podcast before

22:34

at some point but yeah,

22:36

there is a common

22:40

statement you will see that who

22:42

knows it may be right but

22:44

it's also far

22:47

beyond what we have evidence to

22:50

directly support. A common

22:52

statement you'll see that drives me a

22:54

little bit insane for those reasons is

22:57

that hyperplasia doesn't occur in

22:59

humans. So hypertrophy increase in

23:01

muscle fiber size, hyperplasia increase

23:04

in total number of muscle

23:06

fibers and

23:08

yeah, in these animal models you

23:11

observe hypertrophy and hyperplasia but a

23:15

thing you will commonly hear is that like,

23:18

oh hey, in humans we only

23:20

observe hypertrophy, humans

23:22

don't experience hyperplasia, it doesn't occur.

23:26

And what

23:28

would be more correct to

23:31

say is hyperplasia has never

23:33

been directly experimentally observed in

23:35

humans and

23:37

that is true but there's

23:39

a big difference between that and

23:42

saying that hyperplasia doesn't occur

23:44

in humans. It's kind of like the

23:46

absence of evidence doesn't necessarily imply evidence

23:48

of absence type of deal and

23:50

there is a really good reason why hyperplasia

23:52

hasn't been observed in humans because the thing

23:57

about live animals is like you can kill them

23:59

and people are chill. with it. You

24:02

can't do that with human research

24:04

subjects and there are

24:11

ways you need... there are things

24:13

you need to do if you want to

24:15

count the number of muscle fibers in order

24:18

to determine if hyperplasia has occurred and

24:20

it just means taking

24:22

the muscle. Like you either

24:25

need to kill the animal that you're getting

24:27

the muscle from or maybe

24:30

just find someone like extremely chill who would

24:32

be like yeah sure like you can remove

24:34

one of my hamstring muscles for science. Like

24:36

no one's gonna do that you know. But

24:39

yeah like there's no there's

24:42

no validated technique

24:44

to like precisely

24:47

estimate muscle fiber

24:49

number in vivo. Like you can't take

24:51

a living animal and maybe like give

24:54

them an MRI or something and count

24:56

muscle fibers from there. You

24:59

can't do to fiber

25:02

growth being in homogenous

25:04

throughout a muscle. You can't take

25:06

a biopsy and compare changes

25:09

in fiber size to changes in

25:11

whole muscle size and like make

25:13

inferences about fiber number from there.

25:17

Like all of these

25:19

studies that observe hyperplasia animals

25:22

undergo a training intervention. They kill

25:24

the animal and take

25:28

like a cross-section of the muscle and

25:30

one by one count every

25:33

individual muscle fiber. And

25:35

that is another thing with humans. We're

25:38

a lot bigger than birds and mice.

25:40

Like that's one of the things

25:43

that is true of humans. And

25:45

you gotta count all of those fibers one by

25:47

one. And at this point you could maybe use

25:49

like a machine vision program

25:51

to like automate it. But back

25:54

in the day you're looking

25:57

at a microscope and you're counting one by one

25:59

by one. And I think, I

26:01

think in these avian stretch studies, if memory

26:04

serves, the birds had like

26:06

somewhere around 70,000 fibers

26:08

per muscle that you would have to

26:10

count one at a time, which is

26:12

a lot. But like human biceps, for

26:15

instance, have closer to like 500,000 fibers.

26:19

And if you're doing like quads,

26:21

like it's just bigger muscles, like number

26:24

of fiber scales proportionally with that. If

26:27

you want decent statistical power, say you

26:29

have like 20 subjects or something, you're

26:31

going to be spending months literally just

26:33

like driving yourself crazy counting fibers. And

26:35

you know, that's assuming the, what

26:39

is it? The

26:43

declaration of Helsinki goes away and we

26:45

can start doing like unethical experiments again.

26:49

You know, like, so there's reasons

26:51

that hyperplasia hasn't been

26:53

observed in humans. And it's just that

26:55

it would require like unethical and unfeasible

26:57

experimental models to be able to like

27:00

directly observe it. But

27:02

there are like indirect lines

27:05

of evidence that suggest that,

27:07

yeah, hyperplasia probably occurs in

27:09

humans. The first is just

27:11

that like, if

27:13

we're setting a baseline hypothesis

27:15

here, you would

27:18

probably expect it to occur. You

27:22

know, I said I wasn't going to do my whole

27:24

hyperplasia thing. I'm doing my whole hyperplasia thing, whatever. Like

27:26

I'm, I've already started. It's fine.

27:31

But yeah, so, you know, a

27:35

lot of muscle physiology is pretty

27:37

highly conserved between species. Like biology

27:39

figured out how muscles do their

27:41

thing and muscles kind

27:43

of kind of do their thing in similar ways

27:45

across different species. Not identical. Like

27:47

the way our muscles work isn't identical

27:49

to the way that like

27:51

mice muscles or bird muscles work. But

27:55

yeah, like, like muscle

27:57

physiology generalizes between species

27:59

relatively. relatively well most of the time. And

28:02

in every

28:07

animal experimental model where

28:10

people have attempted to observe hyperplasia,

28:12

they've done it. So

28:14

there are studies in birds, there are

28:16

studies in rodents, there are studies in

28:18

cats, there are studies in

28:21

rabbits. And

28:24

not just extreme stretching

28:26

interventions that cause just

28:28

huge amounts of overall growth. Like

28:30

the avian stretch studies were seeing

28:33

absurd amounts of total growth. So

28:35

yeah, maybe it makes sense that

28:37

hyperplasia occurs. But like in

28:39

some of the research in like rodents and

28:41

cats, like

28:43

in instances where overall total

28:46

increases in muscle size were

28:48

like 15, 20%, they

28:50

still observed hyperplasia occurring.

28:53

So it doesn't require extreme

28:55

growth. It's not

28:58

only observed after like stretching

29:00

based stimuli. So in

29:03

like some of the rodent studies and like the cat

29:06

study, it was kind of like a pretty

29:09

normal resistance training intervention.

29:12

They weren't putting them on

29:14

like starting strength. But you

29:17

know, just standard eccentric concentric

29:19

muscle actions in ways that

29:21

like resemble how people would

29:23

train, not stretching

29:26

muscles for like weeks and months on end. So

29:29

it's observed in multiple species. It's observed

29:31

with like pretty normal

29:34

resistance training type interventions. And

29:37

so just as a baseline assumption, you know,

29:40

I kind of

29:42

think that you should assume that

29:47

it occurs in humans unless there's like

29:49

pretty strong evidence against it because like

29:51

why wouldn't that generalize? But

29:53

yeah, that's like super indirect. Then

29:56

in terms of like more directly relevant

29:58

stuff. there's

30:02

been research on cadavers

30:04

looking at number of muscle

30:07

fibers like like

30:09

side to side in the body. So

30:13

specifically your non-dominant

30:15

leg in general,

30:19

like the tibialis anterior of it

30:22

over the course of your life probably gets

30:24

a little more work than the tibialis anterior

30:26

of your dominant leg because

30:28

anytime you're doing something with your

30:30

dominant leg, you're planting on your

30:32

non-dominant leg and your tibialis anterior

30:35

is like a important kind

30:37

of like postural control muscle to like stabilize

30:39

the ankle when you're planting on one leg.

30:43

And so you know we're not even talking

30:45

about intense like intensive

30:48

resistance training because

30:50

some people do tibialis anterior training. There's

30:52

some people that argue that folks should do more.

30:55

I don't have an opinion there. I don't care.

30:57

But most people aren't going to the gym being

30:59

like dude I need to get a

31:01

jacked tibialis interior. So yeah

31:04

it's a muscle that the

31:07

stress it's exposed to throughout life is like

31:10

just kind of normal stuff.

31:13

You know not even like

31:15

dedicated training interventions for it. But

31:17

yeah in cadaver studies they find

31:19

that there are more muscle

31:22

fibers on the non-dominant like

31:25

in people's non-dominant tibialis

31:27

interior than their dominant side which

31:30

would be maybe consistent with just

31:32

the slight increase in demands

31:35

over a lifespan causing some

31:37

hyperplasia. It is possible that it's

31:39

not a causal thing and just something

31:42

about how our biology is arranged just

31:44

knows that this leg is gonna be

31:46

the non-dominant one and so it just

31:48

needs more muscle fibers and let's take

31:51

care of that in utero or like

31:53

very early childhood such that no hyperplasia

31:55

actually has to occur. That is that

31:57

is possible given that we're

32:00

not actually observing changes over time. It's just,

32:02

hey, how many fibers do we see in

32:04

one leg versus the other after someone actually

32:07

dies? You can't

32:09

draw a direct causal inference there,

32:11

but it gives a pretty strong

32:13

suggestion. Another

32:19

bit of indirect evidence comes from a 1982, 82

32:24

or 84. I don't have the paper in front of me, whatever. But

32:27

a study from the 80s by

32:29

McLaughlin and colleagues where

32:31

they compared

32:34

the muscle fiber size

32:39

of untrained versus pretty

32:42

high level strength

32:45

athletes, I believe, either strength athletes

32:47

or strength and physique athletes. They

32:52

looked at total bicep

32:54

size, bicep fiber size, and

32:58

bicep strength in untrained

33:00

versus pretty elite strength

33:02

and or strength and

33:05

physique athletes. They found that, obviously,

33:08

and pretty intuitively, the untrained folks

33:10

had fibers that were way, way

33:13

smaller than the elite athletes

33:17

that do a lot of lifting. But

33:20

then after a six month

33:23

training intervention, the average

33:26

fiber size wasn't all that different

33:28

between the people who have now

33:30

been training for six months and the

33:32

people who've been training for way, way longer

33:34

and are overall

33:36

way more muscular

33:39

and way, way

33:41

stronger still. There

33:44

are multiple inferences one could draw from that.

33:46

It could just be that people who are

33:48

predisposed to being high level strength and or

33:50

physique athletes are just born with more muscle

33:52

fibers than other people, which is

33:55

likely true. I find that pretty plausible. Or it

34:00

potentially suggest that folks who dream

34:02

hard for a long time might

34:04

experience some hyperplasia, which helps them

34:06

continue to grow. I

34:08

personally find that quite plausible. The

34:11

other inference one would draw is that

34:13

the people who had been doing bicep

34:15

curls, I think like twice a week

34:17

for six months, since

34:20

their fibers were now as large as

34:22

people who are already like elite level

34:24

strength and physique athletes, that

34:26

would suggest that at the nurture limit now

34:28

your biceps aren't going to grow anymore. Like

34:30

your fibers are already as big as these

34:32

people who are probably very

34:35

close to their muscular limits. So

34:37

guess what? Doing bicep curls twice a week for

34:39

six months, that's it. Like that's about

34:41

as much as you're going to grow. I find

34:43

that very implausible. So

34:46

yeah, yeah, I don't know. I

34:50

really think hyperplasia occurs in

34:52

humans. Like I can't

34:55

say that there's like a direct RCT

34:57

that proves it, but

34:59

if I'm a betting

35:01

man, I'd say there's like a 90%

35:04

chance. Like I would

35:06

take pretty long odds on the proposition

35:08

that hyperplasia

35:11

occurs in humans. So

35:14

yeah, it has never been directly observed,

35:17

but don't conflate absence of evidence with

35:19

evidence of absence. Yeah,

35:23

there's a difference between saying it hasn't been

35:25

observed and it doesn't happen. And I'm like

35:28

pretty confident it happens, but you

35:31

know, that's something for

35:35

hopefully people to observe in the future.

35:37

Like I really don't know

35:39

what an experimental model to like validate

35:41

that would look like. You

35:45

know, potentially, potentially,

35:51

you could do something where like,

35:54

and this is also never going to happen, but

35:56

I'm just trying to think of like something that

35:58

wouldn't necessarily be violation

36:01

of like the declaration of research

36:04

ethics that would actually allow you to do this.

36:07

I think that maybe you could

36:10

do some stuff with like amputees

36:12

where if

36:15

someone is getting an amputation and they

36:18

have never engaged in resistance

36:20

training before and the muscles

36:23

on the arm or leg that are

36:25

going to be amputated are

36:27

in good enough shape that you can actually remove

36:29

them, take a cross section, count

36:31

fiber number and

36:34

then they're willing to agree to

36:37

do intensive resistance

36:39

training basically

36:43

until their death but

36:45

like you know maybe just due to

36:48

like the atrophy and like maybe decrease

36:50

in fiber numbers due to progressive denervation

36:52

with advanced age, you

36:55

wouldn't actually end up studying

36:57

the folks unless maybe they died within the

36:59

next like 5 or 10 years or something

37:02

but then if they do die in relatively

37:04

close proximity to when

37:06

their amputation occurred but with enough

37:08

time intervening that they had actually

37:11

been able to get in several

37:13

like pretty hard years of resistance

37:15

training with their remaining limb

37:18

then they agree to give

37:23

their body to science and then

37:26

on their contralateral limb

37:29

you can remove the muscles that they

37:31

have trained, count fiber number there. Theoretically

37:34

that might be an experimental model that

37:36

one could use to make inferences about

37:38

hyperplasia in humans but that's never going

37:40

to happen so until then it's

37:44

not going to be conclusively proven but that

37:46

doesn't mean that it doesn't exist and I

37:48

really think it does and that's it with hyperplasia,

37:50

I'm going to shut up about it now. First

37:54

of all, my written knowledge, second

37:57

of all it is interesting to see just

37:59

how different your takers because back when I

38:01

was a young first

38:04

year sports science undergraduate and that was years

38:06

after I first came across Strong by Science

38:08

just to give you an idea of you

38:10

know Strong by Science really lies

38:12

at the center of everything and it's been around longer than I

38:14

have been around but

38:17

when I asked my lab

38:19

tutor at the time, hey does

38:22

hyperplasia occur in humans? Because

38:24

I'd briefly come across some of the stretch studies

38:26

in animals and was like wow imagine

38:28

if humans could like grow new fibers and

38:30

that was really the key to getting more

38:32

ducked you know? I

38:35

asked him by email and initially

38:37

I got like a two line

38:39

response saying no it doesn't happen

38:41

goodbye and then like a week

38:44

later unsolicited he replied again and being like

38:46

yeah no actually I realized I was a

38:48

bit brief it probably doesn't happen and

38:50

so now from that to Mr. Knuckles

38:52

himself telling me hey it probably does happen in

38:54

humans as well but we just don't have

38:57

the studies right now to be able to ascertain with

39:00

any high degree of confidence that it

39:02

does. So

39:05

yeah at the very least what we can say from

39:08

the solo study I mentioned earlier is that true

39:11

stretch-mediated hypertrophy in

39:13

its sort of purest form in the most internally

39:16

valid and controlled setting and

39:18

experimental design does

39:20

seem to occur independently of

39:22

active contraction. So even

39:24

if a muscle is inactive

39:27

or even unable to contract in the case of

39:29

a denervated muscle it can

39:31

still experience stretch-mediated hypertrophy. So

39:34

that's a noteworthy implication of

39:36

these findings because it

39:38

doesn't form what might or might

39:40

not be happening with humans

39:43

performing resistance training and just with stretching

39:45

interventions overall. Now importantly

39:47

this wasn't the only study the reason

39:50

I like to mention this study in

39:52

the context of stretch-made hypertrophy is

39:54

because I do think it serves as a

39:56

good starting place and it kind of

39:59

illustrates what the general study design looks like in

40:01

these kind of studies and also to

40:03

point out that hey, it doesn't really need to

40:06

be active contraction based. You can

40:09

still experience stretch-me-hypertry even in the

40:11

absence of any active contraction by

40:13

that mouthful. But then

40:16

there are more studies out there essentially

40:18

finding similar findings. Specifically, we have a

40:20

recent meta-analysis by Warneking colleagues who I

40:23

think is a recently

40:26

crowned doctor in

40:28

sports science after finishing his PhD on the

40:30

effects of stretching. I could be

40:32

wrong but I think he has been a

40:34

student in Germany somewhere for the past few

40:36

years looking at stretching. Do you guys get

40:38

crowned now? We, crowned doctors, you know, it's

40:41

Europe, different place. Romes?

40:43

Are you judging swords? Yeah, I

40:47

was going to say in Finland, don't they get

40:49

swords? We

40:51

get swords, like... That is pretty sick. You

40:53

get swords too? No, no, no, no, we don't

40:55

get it. They just made it up. Unfortunately, we

40:57

get fine looking heads about it. What

40:59

the hell? Which we don't keep, we have to

41:01

return. We rent some hats. Ah,

41:04

that's annoying. Anyway... What

41:06

swords? Just rented hats. Very disappointing. No

41:10

crowns either. That's a bummer. Anyways,

41:12

this meta-analysis by Warneking colleagues,

41:14

as far as I'm aware,

41:17

Constanfin Warneke has been looking at a lot

41:19

of stretch-related stuff in humans and animals. One

41:22

of his studies was a meta-analysis on

41:24

the effect of stretching interventions in animals

41:26

on hypertrophy, hyperplasia, and a variety of

41:28

other stuff. In

41:30

this meta-analysis, across around a dozen

41:32

studies, they found that stretching interventions

41:34

in animals led to very notable

41:36

hypertrophy. To give you some

41:38

context of how large the

41:40

effect size is, we're talking about a

41:42

Cohen's D of about 8.5. Now,

41:46

in the context of, I think Cohen

41:48

gave these recommendations for how to interpret

41:51

effect sizes initially, not even

41:53

as a blanket recommendation. In fact,

41:55

he recommended that people individualize the

41:57

thresholds they used by

41:59

which... to classify effect sizes as small,

42:01

medium, large, etc. But when he first

42:04

came up with effect sizes and

42:06

published on them, he recommended that small effect

42:08

sizes were considered between 0.2 and 0.5, moderate

42:10

between 0.5 and 0.8, and above 0.8 would

42:12

be considered large. In

42:17

this case, we're talking about an effect size per hypertrophy of

42:20

8.5. So comfortably an

42:22

order of magnitude larger than what

42:25

would be considered large in most

42:27

studies looking at different phenomena. So

42:29

we're talking about a very, very

42:31

substantial hypertrophy. Similarly,

42:33

another thing that was examined

42:36

in this mass analysis was

42:38

the impact of stretching interventions on fiber length.

42:41

And once again, they observed a very notable

42:43

increase in fiber length of an effect size

42:45

of about 7.8. And

42:48

finally, as we just mentioned, hyperplasia to

42:50

a fair extent, they also looked at

42:53

the impact of stretching interventions in fewer

42:55

studies and about five studies, I think,

42:57

on the number of muscle fibers. And

43:00

once again, they did observe a notable

43:03

amount of hyperplasia with an effect size of

43:05

about 4.6. And

43:07

so when you're talking about stretch-mediated

43:09

hypertrophy and how it was first

43:11

conceptualized, there's a few things that

43:14

kind of stand out. First,

43:16

it can occur even when a muscle

43:18

isn't actively contracting or motor units aren't

43:20

necessarily being recruited, right, because it can

43:23

occur even in denobated muscle. And

43:25

secondly, we observe dramatic, consistent

43:28

hypertrophy with effect sizes being

43:31

quite a lot larger than what we

43:33

observe in humans. So this just gives you an idea of what

43:36

effect size we typically see in humans

43:38

performing resistance training interventions, a.k.a. for example

43:41

training in the gym, on

43:43

average across a pretty

43:45

large dataset that was actually put together

43:47

by James Steele in a method analysis

43:49

on variants in sports science, we

43:52

observe an effect size on average of about 0.34. And

43:55

that's from humans lifting weights. And as we'll

43:57

come to later, lifting weights is

43:59

likely, well... We can say

44:01

it's pretty high confidence that lifting weights does

44:03

induce more hypertrophy than stretching in humans, most

44:05

like, at least for most interventions we've

44:08

tested. And so we're talking about

44:10

a pretty big disparity between how much hypertrophy

44:12

we see in these stretching interventions in animals

44:15

versus how much hypertrophy we typically observe with

44:18

lifting or even stretching as we'll come to in a

44:20

moment in humans. And

44:23

the final thing we observe with stretching interventions

44:25

in animals is very large

44:27

increases in fiber length and also in

44:29

number. Now, as we've

44:31

mentioned, as we transition into more of the human

44:34

side of things, we don't really have

44:36

any data on the effects of stretching

44:38

interventions on fiber number because

44:40

you have to take out a muscle or

44:43

sacrifice the human, which generally

44:45

frowned upon in today's society. So

44:49

essentially that is the origin of

44:51

the term stretch-mediated hypertrophy and the

44:53

adaptations that we observe when stretching

44:56

interventions are being opposed upon animal

44:58

models. So

45:03

whenever someone claims

45:05

that length and partials are

45:07

causing stretch-mediated hypertrophy, I think

45:09

that's kind of two things they could be saying. One

45:11

is just a very naive, well-meaning

45:15

thing to say, which is that, oh, I

45:17

heard that lower muscle length training causes more

45:19

hypertrophy. So it's stretch-mediated. They

45:22

are wrong in the scientific sense, but their

45:24

mind is in the right place essentially. But

45:27

then if they're claiming that stretch-mediated hypertrophy in

45:29

the scientific sense, in the way that it

45:31

was first conceptualized and originated in the animal

45:33

data, is what is occurring with length and partials,

45:36

you have to go through a

45:39

lot of these considerations that I don't think

45:41

many people are going through. Specifically, how do

45:43

these results actually generalize to humans performing

45:46

resistance training? So the

45:48

first thing I want to do is to kind of talk about how

45:51

muscle even grows. Now

45:53

Greg just went through quite a bit of

45:56

detail on whether or not hyperplasia occurs in

45:58

humans and the TL... LDR there

46:00

I think is it probably does

46:03

but we currently just don't have a good way

46:05

of assessing to what extent it does and to

46:08

really have an experimental model

46:10

in place to establish causality there even

46:13

as regards what forms of training might

46:15

cause more hyperplasia in humans. And

46:18

so we're essentially left with how does

46:20

muscle grow specifically as far

46:22

as how individual muscle fibers grow. So

46:25

muscle can certainly grow in size visually and

46:27

what have you by the addition of new

46:29

muscle fibers through hyperplasia as we just mentioned

46:32

but we don't have any data there. But

46:34

muscle can also grow by each myofibril

46:36

or muscle fiber increasing in size

46:38

individually. Although

46:41

this is going to be a bit difficult to explain verbally

46:44

but I will do my best. If you're

46:46

interested in more visual explanations on

46:48

the topic I would highly recommend you go check out

46:50

the full article on strong methines that will

46:52

likely be out at the time of this recording. But

46:55

I think one relatively straightforward way

46:57

of visualizing how individual muscle

46:59

fibers can grow is

47:02

to visualize them as cylinders and

47:04

to think of them essentially just as

47:06

a geometric shape. So

47:09

a muscle fiber can grow essentially

47:11

either in series or in

47:14

parallel. A muscle fiber

47:16

growing in series you can conceptualize

47:18

it as the cylinder increasing in

47:20

length essentially whereas a

47:22

muscle fiber growing in parallel you

47:24

can conceptualize as the radius of

47:27

the cylinder increasing. So essentially it becoming

47:29

thicker or it becoming longer. Now

47:32

specifically how that growth is likely to occur

47:34

based on a lot of our understanding of

47:36

muscle physiology at this point is

47:38

through addition of sarcomeres either

47:40

in parallel or in series.

47:43

So each muscle fiber can be broken down even

47:45

further as far as the scale of things go

47:47

into sarcomeres. And

47:49

a muscle fiber is essentially just a

47:52

string of sarcomeres strung together

47:54

making up the whole muscle fiber. And

47:56

ultimately the sarcomere is made up of a

47:58

variety of filaments. specifically Titan,

48:01

Axton and Myosin, that

48:03

enable your muscle to contract in the first place and

48:05

enable you to be able to move around, contract your

48:07

muscles and do all that stuff. So the

48:09

sorcomere is kind of the smallest functional unit making up

48:11

the muscle fiber. And the muscle fiber

48:13

is just kind of a string of sorcomere being

48:16

strung together. And so when you're

48:18

growing an individual muscle fiber being made up of

48:20

sorcomere, you can either grow it by adding sorcomere

48:22

next to each other or in

48:24

that string of sorcomere in line or

48:27

in series essentially. And

48:29

going back to the cylinder thing, that would essentially

48:31

just correspond to increasing the radius of the cylinder

48:33

or the muscle in the case

48:35

of parallel hypertrophy or

48:37

increasing its length in the case of in

48:40

series hypertrophy. To give you some even more

48:42

confusing terminology that we'll probably be using for the rest of

48:44

the podcast just because that's how things are

48:46

typically referred to in the research, growing

48:49

a muscle fiber in series is

48:51

typically referred to as longitudinal hypertrophy

48:54

as it's growing it on its

48:56

longitudinal axis. So increasing its length,

48:58

longitudinal length kind of makes sense.

49:00

And growing a muscle fiber in parallel

49:03

is typically referred to as radial hypertrophy,

49:05

which makes sense going back to the

49:08

cylinder example of increasing the radius

49:10

of the cylinder causing radial hypertrophy.

49:12

So just kind of a quick aside on how

49:15

muscle fibers are typically thought to grow.

49:18

And these broad concepts were illustrated

49:20

in a recent review by Jorgensen

49:22

colleagues which essentially defined

49:24

longitudinal hypertrophy and radial hypertrophy

49:26

as the following. Longitudinal

49:29

hypertrophy refers to the increase

49:31

in muscle fiber length. So again going

49:33

back to the metanosis by Wernicke and

49:35

colleagues, they directly assessed this increase in

49:37

muscle fiber from stretching interventions and felt

49:39

quite substantial increase in muscle fiber. This

49:42

type of hypertrophy occurs through the addition of

49:44

sorghum years in series and it

49:46

involves the muscle fibers becoming longer, which

49:49

can happen generally as a response to

49:51

specific types of training or mechanical loading

49:53

that emphasize stretching and lengthening the muscle

49:56

and specifically as we'll come to later

49:58

potentially might be preferent. caused

50:00

in humans by eccentric contractions as

50:03

opposed to constant contractions. So different

50:05

styles of training can influence what

50:08

kind of hypertrophy is occurring, right?

50:10

Because both radial hypertrophy and longitudinal

50:12

hypertrophy are fundamentally hypertrophy

50:15

and the way that we measure hypertrophy

50:17

in practice whether that's via B-mode ultrasound,

50:20

MRI or most other methods

50:22

in assessing muscle thickness,

50:24

cross-sectional area or muscle volume will

50:27

be impacted by increases in both

50:29

longitudinal hypertrophy and radial hypertrophy. And

50:31

to come back to radial hypertrophy that

50:34

involves the increase in the diameter of the

50:36

muscle fibers. So again just going back to

50:38

the whole cylinder analogy we would be talking

50:40

about an increase in the radius or diameter

50:42

of the muscle fiber where essentially that cylinder

50:44

becoming thicker as opposed to longer. So

50:48

that's essentially just a quick primer on

50:51

how hypertrophy is thought to occur in

50:53

humans. Hyperplasia probably plays a role and

50:55

as far as the increase of individual

50:57

muscle fibers goes it probably

50:59

comes down mostly to longitudinal and

51:01

radial hypertrophy. Importantly as

51:03

I mentioned an increase in the length of a

51:06

muscle fiber or a fascicle of

51:08

fibers and to give some context to

51:10

a listener a fascicle of muscle fibers

51:12

is essentially just a bundle of muscle

51:14

fibers put together. It's

51:16

kind of like when you accidentally can't

51:19

open a cable you have and

51:21

you realize that the cable is made up

51:23

of individual smaller wires you can kind of

51:25

think that whole cable as a muscle fascicle

51:27

because it's putting together or stringing together several

51:30

muscle fibers into one bundle of

51:32

muscle fibers that we call a

51:34

fascicle. It also

51:36

has the same root and same etymology

51:39

as fascism. Is

51:42

that true? Yeah

51:45

yeah. Where fascism comes from is

51:50

There was like this

51:52

term I think in Latin from

51:55

like Rome for like a bound bundle

51:57

of sticks. It was like a fisces

52:00

or something and

52:03

the the iconography of fascism where it would

52:06

be kind of like a bound bundle of

52:08

sticks with like a spear in the middle

52:10

was About like

52:12

the binding together of the nation and

52:14

the vogue and whatnot and

52:18

yeah, a fascicle

52:21

is the same

52:23

kind of like Structure of like bound together

52:25

muscle fibers like it looks similar

52:27

to that bundle of sticks when you look at

52:29

it through a microscope Anyhow,

52:32

so they have like the same the same

52:34

root and etymology and I'm pretty sure I'll

52:38

Verify that while you continue talking but

52:40

I mean I heard that somewhere and

52:42

I'm pretty sure that's true So it's

52:44

very very citation. It's verified just because

52:47

of how in depth it was like

52:49

either Hey either were in the

52:51

middle of either either dreaming or

52:53

a psychotic break or You're

52:56

just correct and I suspect it's the

52:58

second option. See you later. I checked

53:00

Well, just to add something to this

53:02

episode. I have checked this

53:04

has been Pack verified as

53:06

a Greek. I'm also gonna use my Latin

53:08

card because I Greek Latin same thing, but

53:10

uh, you know verified

53:13

and you got the even the Origin

53:16

word, correct. I'm not sure if you pronounce

53:19

it right, but it's fasces

53:21

f-a-s-c-e-s Great

53:24

yeah, I think dangerously close to feces is all

53:26

I could think about when you're pronouncing that to

53:28

be honest but hey back

53:30

to fast calls right fascicles bundles

53:32

of muscle fibers strung together and

53:36

specifically just for the listeners

53:39

Education I guess when we're assessing

53:41

fiber length in humans in living

53:44

humans Using ultrasound

53:46

typically we're well typically

53:48

I'm actually not aware of any other method

53:50

of assessing fascic length so when we're all

53:52

for sounding humans, we specifically measure

53:55

fascic length because visualizing

53:58

individual muscle fibers using B-mode

54:00

ultrasound is actually quite difficult whereas fascicles

54:02

are a bit more visible and thus

54:04

we can measure fascicle length and

54:06

that is often thought to represent the

54:08

length of individual fibers pretty

54:10

well because ultimately fascicles

54:12

should have a similar orientation of muscle fibers

54:15

and should generally correspond pretty closely to the

54:17

length of the muscle fibers as well. Although

54:21

individual muscle fibers can have intra-fascicular

54:25

terminations which is

54:27

a big word to say that they don't necessarily

54:29

span the whole fascicle length to my knowledge. I

54:31

could be wrong, hey Greg, if

54:34

you have something to add there. No,

54:37

I mean that's true but also the

54:41

resting length of the sarcomeres can

54:43

change such that fiber

54:45

length can change with fascicle length but

54:48

it might not even necessarily denote the

54:50

change in increase in sarcomeres

54:53

in series. Yeah,

54:56

a lot of people assume that a

54:58

change in fiber length implies a change

55:00

in sarcomeres in series. Sometimes it does,

55:02

not always. On that

55:04

note, do you want to briefly touch on the one

55:07

study we have on sarcomere length in humans by Pincher

55:09

and colleagues? Is

55:11

it necessary

55:13

for this episode? I

55:16

mean I guess it's just worth mentioning that we

55:18

have one study on whether or

55:20

not an increase in fascicle length stems from

55:22

an increase in the number of sarcomeres in

55:24

series in humans or whether

55:26

it's simply an increase in the individual length

55:28

of each sarcomere. Because

55:30

we only have one study, there's not much clarity

55:33

there but the ones today we do have

55:35

suggest that it may not even be when we observe

55:37

an increase in fascicle length that we're adding

55:39

more sarcomeres in series, it could just be

55:41

each individual sarcomere becoming longer. That's what the

55:43

only study we have in humans by Pincher

55:45

and colleagues seem to suggest. So

55:48

I'm trying to keep things simple here just

55:50

because we're explaining physiology. Well, and

55:52

if people want to hear more about that, I'm

55:56

like 95% sure

55:58

we talked about that study in more detail. in

56:01

the episode you were a guest on a few

56:22

months ago. So if people want to hear more

56:25

about that study, you can check out that episode. We

56:30

have a lot of research on how

56:32

to do stretch-mediated hypertrophy in short-end training.

56:34

We need to figure out do we

56:36

even see this concept of stretch-mediated hypertrophy

56:38

in humans. At the very

56:40

least, in the closest thing we have

56:43

to animals being stretched out, which is

56:45

human stretching interventions. Up

56:47

front, there's a few things I want to say

56:49

about how the literature from animals

56:53

compares to the literature in humans.

56:56

For one, the rate of adaptations in animals and

56:58

humans tends to be different. So

57:01

you typically will observe a

57:03

larger magnitude of change in animals than

57:05

humans, all else being equal. So that

57:07

will explain why in humans

57:09

we observe much smaller effect sizes in

57:11

terms of how much hypertrophy

57:13

stretching interventions cause and so forth.

57:16

Another thing, though, is that typically in humans,

57:19

you're not really able to have them do

57:21

24-hour per day stretching

57:23

interventions. Again, going back to

57:25

that whole pesky ethics thing where when

57:29

you do a study, you need to pass it by

57:31

an ethics board. They often have scruples

57:35

that we might not necessarily

57:37

have about essentially having participants

57:39

undergo intense pain through stretching for 24

57:41

hours a day for a week on

57:43

end. So oftentimes in stretching

57:45

studies, we're talking about protocols

57:47

that are much ford-ruined

57:50

duration on a per-day basis than

57:52

they are in animal studies. So for example,

57:55

one of the more extreme studies in humans

57:57

was a study by Wernicke and Colley's where they had produced

58:00

been stretched out their calves for one hour per day. So in

58:02

terms of duration we are talking about

58:04

much smaller durations of exposure to stretching

58:07

than we typically do in human, in

58:09

animals sorry. So that's one difference. The

58:11

other difference is as I mentioned the

58:13

load being used for stretching interventions in

58:15

animals is typically

58:17

quite large and it's usually a

58:21

factor of body weight so it's often

58:23

like 10 or 20% of body weight or

58:25

100 grams or 200 grams for example in the

58:28

case of the study by soloin colleagues that

58:31

is a substantial amount of weight

58:34

being applied to stretch out the muscle as

58:36

compared to most human interventions.

58:38

By contrast in most human studies

58:40

on stretching intensity is set as

58:42

a pain reading on a

58:44

visual analog scale and so

58:47

essentially in all likelihood we're

58:49

talking about much lower intensity stretching in

58:51

humans than in animals. So

58:54

with those kind of caveats out of the way I want to

58:56

briefly discuss how humans tend

58:58

to respond to stretching interventions. Fortunately

59:00

for us we don't have to delve into each study

59:03

we can look at a couple of review papers on

59:05

the topic that were published in the last few years. First

59:08

was a narrative review by Warnock and colleagues where

59:10

just to give you a quickly of the land

59:12

and not dwell for too long in this study

59:15

there were 10 studies on stretching

59:17

in humans looking at hypertrophy. Of

59:21

those 10 studies four found no

59:23

significant improvements in muscle size. Now

59:25

we've gone at length before as

59:27

to why significance is not

59:29

everything but it's just to give you

59:31

a lay of the land of okay compared to lifting

59:33

weights how much hypertrophy might we expect. To

59:35

give you some more accurate estimates of

59:37

the effect sizes we see in terms

59:39

of hypertrophy and so forth from

59:42

stretching in humans there is another metanalysis

59:44

by, well in this case Warnock

59:46

he conducted a narrative review but as

59:48

far as getting us a quantitative estimate

59:50

of how large the effect is we

59:53

do have a metanalysis by Panadian colleagues from a few years

59:55

ago as well and they

59:57

looked at all of the stretching interventions

59:59

in humans and

1:00:02

essentially I'll summarize fascicle

1:00:06

length as I just mentioned as

1:00:08

a proxy for fiber length and

1:00:10

potentially for longitudinal hypertrophy and

1:00:13

also fascicle angle which

1:00:16

is thought to be a proxy for

1:00:18

radial hypertrophy. Now as

1:00:21

we mentioned earlier there's already a

1:00:24

fair bit of opacity or a

1:00:26

lack of clarity when it comes

1:00:28

to okay if we observe an

1:00:30

increase in fascicle length that is then thought

1:00:32

to represent an increase in fiber length which

1:00:34

is in turn thought to represent an increase

1:00:37

in the number of sonorm years in series.

1:00:41

Generally whenever you're talking about this research there

1:00:43

are quite a few assumptions baked into the

1:00:46

proxy measurements for different things that

1:00:48

make any conclusions relatively

1:00:51

tentative. So when for

1:00:53

example I'm mentioning that fascicle length is

1:00:56

representative potentially of longitudinal

1:00:58

hypertrophy predominantly and that

1:01:01

increases in pinatian angle or

1:01:03

essentially the angle at which the

1:01:06

fascicles are orientated within the muscle relative

1:01:08

to like an axis that

1:01:11

is representative of radial hypertrophy when I'm saying

1:01:13

those things take them with

1:01:15

a slight green of salt because

1:01:17

there are a lot of assumptions baked into the

1:01:20

stuff to the point that while we can look

1:01:22

for overall trends and make tentative

1:01:24

conclusions about what's going on and

1:01:26

whether we're observing longitudinal hypertrophy or

1:01:28

radial hypertrophy there's a good chance

1:01:30

things aren't as clear-cut as we would like them to

1:01:32

be as often tends to be

1:01:34

the case with muscle physiology. Anything you want to

1:01:36

add there Greg? No.

1:01:41

Wow that was succinct. I thought

1:01:44

for sure you would have something to disagree with because

1:01:46

I was like okay I'm talking about something relatively

1:01:48

complex it is certainly something I

1:01:51

must have messed up. Cool

1:01:53

okay so to summarize the findings

1:01:55

by Canadian colleagues into

1:01:58

three sections the first one talk about

1:02:00

muscle size. First, they

1:02:03

observed relatively small

1:02:05

to non-existent changes in hypertrophy

1:02:08

depending on the exact studies

1:02:10

they looked at. So

1:02:12

they performed a few subgroup analyses to look at

1:02:14

how did hypertrophy or fascicle length

1:02:17

adaptations or fascicle angle

1:02:19

adaptations change as we looked

1:02:21

at, for example, stretching interventions with higher

1:02:23

intensities. So presumably with higher

1:02:25

tension being imposed upon the muscle

1:02:28

or a greater muscle length

1:02:30

or how do you. And likewise with the

1:02:32

duration of the stretching interventions. So for example,

1:02:34

talking about interventions lasting more than

1:02:36

one and a half hours of stretching per week versus

1:02:38

under an hour and a half of stretching a week.

1:02:41

And so when you simply looked

1:02:44

at the durations

1:02:46

of stretching below one and a half

1:02:49

hours or above one and a half

1:02:51

hours, we actually observed

1:02:53

relatively similar hypertrophy.

1:02:57

But when you specifically looked at higher

1:03:00

versus lower intensity stretching interventions, you

1:03:02

did go from about essentially a

1:03:05

negative effect size for hypertrophy or

1:03:07

negligible effect size on hypertrophy or

1:03:09

essentially no increase in muscle size

1:03:11

when you looked at studies that

1:03:13

had lower intensity stretching

1:03:15

interventions to a small

1:03:17

but potentially meaningful improvement in muscle

1:03:19

size when stretching interventions were conducted

1:03:22

with a higher intensity. So

1:03:24

to give you some

1:03:26

context, when stretching was performed at lower

1:03:28

intensity, the effect size was minus 0.11,

1:03:31

suggesting that we didn't observe

1:03:34

much additional hypertrophy. Whereas

1:03:36

when stretching was performed with higher intensities, the

1:03:38

effect size was 0.27, which

1:03:41

would be classified as a small effect size. Again,

1:03:44

to give you some context with

1:03:46

resistance training, aka lifting weights, the

1:03:50

average effect size across quite a few studies

1:03:52

that we put together in the metanosis by

1:03:54

stealing colleagues or that stealing colleagues put together,

1:03:57

I wasn't involved in this paper. The

1:04:00

effect size for lifting, for hypertrophy, is about

1:04:02

0.34. So we're

1:04:04

talking about potentially meaningful changes in

1:04:06

muscle size, and hypertrophy does seem to

1:04:09

occur from stretching, but they do

1:04:11

seem to be smaller than those you see

1:04:13

from lifting weights. So if you're

1:04:16

thinking, oh, stretch me to hypertrophy, it's this

1:04:18

new big thing, I must now go and

1:04:20

stretch all day to get jacked and get

1:04:23

on stage next year and demolish everyone as a

1:04:25

bodybuilder. Probably not the

1:04:27

wisest decision, lifting weights does

1:04:30

still seem to be more efficacious at

1:04:33

increasing muscle size compared to stretching

1:04:35

interventions. Then

1:04:39

when it comes to fast going, hit it.

1:04:42

I will say, I will say, this is

1:04:44

another experiment that's

1:04:46

never going to happen, but I

1:04:49

would love to see the avian

1:04:51

stretch studies repeated on humans. The

1:04:56

way that our posture is different, we

1:04:59

walk upright instead of being slightly leaned forward,

1:05:01

and there's a reason that

1:05:03

all of the studies used the anterior

1:05:06

latissimus muscle, like that's the muscle

1:05:08

that is just under stretch when

1:05:11

you hang weights from a bird's wings. So

1:05:13

I guess really the only muscle you could

1:05:15

do it in for humans would be the

1:05:17

traps, but yeah,

1:05:20

dude, I would love to see a study

1:05:22

where they just hang 50 pound weights off

1:05:24

of people's wrists for six months and see

1:05:27

do their traps get fucking

1:05:30

enormous? Because who knows?

1:05:32

I am open to the possibility that

1:05:35

if you ran back like

1:05:38

the Sola or the Antonio or just

1:05:40

like any of the protocols used in

1:05:43

the avian stretch research

1:05:46

in humans, I'm open to

1:05:48

the possibility that we might see some

1:05:50

absolutely wild growth, but

1:05:52

in terms of like normal stretching

1:05:55

interventions and even abnormal stretching

1:05:57

interventions like the... the

1:06:00

the warnicke calf stretch

1:06:02

studies where you have

1:06:04

your your calf in a foot stretching orthosis

1:06:07

on a eight out of ten on the

1:06:09

pain scale for an hour a day that's

1:06:12

that's a lot of stretching you're not going to do that

1:06:14

by accident um so

1:06:17

yeah i mean even with pretty intense

1:06:19

stretching interventions you're right we don't see

1:06:21

crazy amounts of growth but i i would

1:06:24

like to see if crazy amounts of growth are

1:06:27

possible if someone wants to volunteer to be

1:06:29

to be our little baby bird and hang

1:06:32

really heavy weights from their wrists for like

1:06:34

six months to see if your traps get

1:06:36

huge um who knows

1:06:38

who knows it might it might be cool but

1:06:40

yeah you're right for the most part you

1:06:43

don't see quite

1:06:45

as much growth with stretch only interventions

1:06:47

as resistance training interventions and i think

1:06:49

all of the you know

1:06:52

all or most of the studies

1:06:54

observing hypertrophy after stretch only interventions

1:06:56

to this point have used untrained

1:06:58

individuals so you know especially

1:07:00

if you have some years of training under your

1:07:02

belt i i

1:07:04

think it's possible that doing some

1:07:06

like long duration intense stretching

1:07:09

might yield a little growth but yeah it's probably

1:07:11

not going to be the thing that really takes

1:07:13

you to the next level and makes a huge

1:07:15

huge difference yeah

1:07:18

it's interesting that you mentioned that because i

1:07:20

think there has been one study by warning

1:07:22

king colleagues that compared calf stretching for an

1:07:25

hour a day if i'm not mistaken um

1:07:28

to resistance training and specifically calf raises

1:07:30

so kind of assessing whether at least

1:07:32

like a reasonable

1:07:34

uh reasonable

1:07:36

stretching protocol is comparable to a

1:07:38

reasonable stretching uh training protocol and

1:07:41

if i'm not mistaken um they

1:07:44

didn't observe substantial differences in hypertrophy

1:07:46

between stretching for an hour a

1:07:48

day for six weeks versus

1:07:51

doing just uh five sets

1:07:53

three days a week so five six half

1:07:56

training so you

1:07:58

know in context five six of cap training might take

1:08:00

you 10 minutes total, three times a week, so

1:08:02

we're talking about half an hour total time spent training. Whereas

1:08:05

with stretching for an hour a day, we're talking about

1:08:07

seven hours spent stretching per week. So

1:08:10

just as far as time commitment goes for

1:08:12

the two groups to observe similar hypertrophy, I

1:08:15

don't know. I think we would need to

1:08:18

go quite deep into the

1:08:20

stretching game, all pun intended, to observe

1:08:24

a lot of hypertrophy, at least anything that

1:08:26

we would not get from just lifting weights.

1:08:29

Oh, I agree. I agree. That's

1:08:31

why I said I want to see someone hang 50

1:08:33

pound weights from their wrists for six months. Why

1:08:36

don't you do it? That's... How

1:08:38

many... How many... How many... The

1:08:40

cow thing? For a while at least, I think.

1:08:43

Yeah, yeah. I know he did a little

1:08:45

case study on himself. Yeah,

1:08:48

no. I'm not

1:08:50

going to do the hang things

1:08:52

from my wrist because it would get in

1:08:54

the way... I wouldn't be able to type.

1:08:57

I have a little desk job.

1:09:00

50 pounds of weights hanging from your wrist, that would be a... They'd

1:09:04

be propped away up. I'd be... Yeah.

1:09:07

If you want to buy it enough, you'll be able to do it. Every

1:09:09

day as you get stronger and stronger, you'll be able to

1:09:11

type more and more and that paycheck isn't going to keep

1:09:13

coming unless you get stronger. So really it's the most intense

1:09:15

form for us to overload there is. Yeah,

1:09:18

and to be as direct as

1:09:20

possible. I'm not... I

1:09:23

don't want it bad enough. I never said that

1:09:25

I did want it bad enough. I

1:09:27

have never in my life been accused of

1:09:29

wanting it bad enough. I

1:09:32

want the knowledge that can be gleaned from

1:09:34

someone else wanting it bad enough. That's

1:09:37

the thing. Knowledge. But what's

1:09:39

the point of the knowledge if we're not getting jacked in the

1:09:41

process, is what I'm saying? We've

1:09:43

got to be our own test subjects and

1:09:45

of one, bro, and one in fact. Yeah,

1:09:49

I mean I do... I

1:09:52

do that with little experiments that

1:09:54

I do want bad enough. But

1:09:57

yeah. Yeah,

1:10:01

I don't want to be the test subject for that, but

1:10:03

I want someone else to be. That

1:10:05

is entirely fair. Don't

1:10:08

you want to get stronger by science?

1:10:11

It's true. Yeah,

1:10:13

I guess. Strength theory was a much cooler

1:10:15

name, at least the much less amenable

1:10:18

to being called out. Yeah,

1:10:20

I... Getting

1:10:23

stronger by science would be nice, but also

1:10:27

maintaining my strength and just

1:10:30

generally getting in better shape as

1:10:32

I near my mid-30s and

1:10:34

I'm looking

1:10:36

ahead towards the

1:10:39

horizon to the great beyond and

1:10:41

trying to push it out as

1:10:43

far as possible. Do

1:10:46

I necessarily need to maximize

1:10:48

strength for that? Probably not. Probably

1:10:50

not. I've been pretty strong and

1:10:52

I'm happy to look at what

1:10:55

I was lifting in my 20s and be like, yeah,

1:10:57

it's pretty good. And I could be a little

1:10:59

less strong by science and still be pretty strong

1:11:01

and it's fine. Since you

1:11:03

mentioned looking to the great beyond and more on topic

1:11:05

of stretching, one completely tangential

1:11:08

question I have is, are

1:11:11

you aware of much, if any, research

1:11:13

looking at flexibility and longevity or overall

1:11:16

health? So because I'm thinking stretching, I'm

1:11:18

thinking flexibility, and you mentioned the great beyond, are

1:11:21

you aware of any research? Because I've kind of looked

1:11:23

around and haven't really

1:11:25

found all that much. Yeah,

1:11:28

yeah, it's... I

1:11:30

don't know. It's one of those

1:11:33

things where most

1:11:37

of what people would try

1:11:39

to use to draw inferences

1:11:42

would be sort of like

1:11:44

associations where you do

1:11:46

see decreases in flexibility as people get

1:11:49

older, which

1:11:51

is in part probably due to decreases

1:11:53

in activity levels. You

1:11:56

know, being active helps... maintain

1:12:00

how well your body moves. You

1:12:06

also get some joint

1:12:09

structure changes potentially downstream

1:12:11

of inflammation. You could get

1:12:13

some thickening of joint capsules which could

1:12:15

reduce range of

1:12:17

motion independent of muscle extensibility.

1:12:24

You get some glycation

1:12:26

type cross linkages between

1:12:29

muscle fibers and fascia which

1:12:32

reduces extensibility to some extent.

1:12:36

Those are things that we tend to

1:12:38

see with aging. I do think that

1:12:40

people who do quite a bit of

1:12:42

flexibility training do tend to maintain flexibility

1:12:45

better into older age. There

1:12:49

are plenty of scary associations

1:12:51

you can find where as

1:12:54

flexibility decreases a lot of scary

1:12:56

bad things increase. Is

1:13:00

that because flexibility is decreasing or is that

1:13:02

because both of these things are just jointly

1:13:05

associated with the aging process. I

1:13:09

tend to think the latter. This

1:13:13

isn't something I've looked into for

1:13:15

a long time. If memory

1:13:18

serves one

1:13:20

of the ways that flexibility

1:13:23

training and interventions haven't panned

1:13:25

out is people

1:13:28

were thinking slash hoping

1:13:31

that flexibility

1:13:34

stretching interventions might help

1:13:37

reduce fall risk by

1:13:40

giving people longer ranges of motion that

1:13:42

they could operate

1:13:44

through and therefore not

1:13:46

fall because they get

1:13:50

off balance because they put

1:13:52

their lower body in a position where they don't

1:13:54

have the flexibility for it. If

1:13:57

memory serves that by and large hasn't panned out.

1:14:00

because people

1:14:02

tend to fall because if

1:14:07

you have a longer range of motion independence

1:14:36

and older age and

1:14:39

you do functional

1:14:43

improvements due to the flexibility or due to

1:14:45

more kind of like the movement practice, and

1:14:47

like maybe increasing

1:14:49

the proprioception, even some

1:14:55

strength benefits, just it's

1:14:57

bodyweight, but people tend

1:14:59

to get quite weak. So,

1:15:02

who knows? I do think...

1:15:04

like you tend to see a decrease in flexibility with

1:15:06

age. So if you want to maintain your flexibility, probably

1:15:09

not a bad idea to do some stretching

1:15:11

as you start getting older, but in

1:15:14

terms of will that necessarily improve

1:15:16

like health and longevity outcomes? I'm

1:15:19

skeptical, but I also don't

1:15:22

think it's a bad thing, you know? Just

1:15:25

continuing to be bendier as you get older?

1:15:27

Nothing wrong with that. Yeah,

1:15:30

I think that's a solid take.

1:15:32

And to agree with

1:15:34

your point, I don't think I've

1:15:36

ever seen an RCT on stretching...

1:15:39

not many at least, stretching interventions as

1:15:42

a stand-alone modality and looking at whether or not

1:15:44

that improves a lot of markers of

1:15:46

health. So

1:15:49

yeah, it seems like it's something that we have notably

1:15:52

less research on compared to something

1:15:54

like aerobic training

1:15:56

or strength training or what have you. There's

1:15:58

some stuff on... on blood

1:16:00

pressure. You have

1:16:02

a acute

1:16:05

hemostatic response to stretching,

1:16:07

which I

1:16:10

also don't think that a ton of people are

1:16:12

pursuing that because it's like pretty short-lived.

1:16:14

But yeah, I don't

1:16:17

know. I don't know. Anyways,

1:16:21

stretching used to be like very hot back

1:16:23

in the day. I feel like it's

1:16:26

one of those things where I'm

1:16:28

just barely enough older than you guys

1:16:30

that I kind of came

1:16:32

up in the

1:16:34

generation where people were

1:16:37

very high on stretching.

1:16:40

I want to say

1:16:42

the study that everyone cites that

1:16:46

kind of started turning the

1:16:48

tides against stretching. The first

1:16:50

one that showed

1:16:54

that intense static stretching

1:16:57

before it

1:16:59

attempted either max force or max power

1:17:02

output, reduced force and or power output.

1:17:04

I want to say that study was

1:17:06

published in 2004. The thing that people

1:17:08

fight about on the internet

1:17:20

comes and goes. It changes all the

1:17:22

time. I remember I started

1:17:28

reading more about research

1:17:31

and strength and conditioning and all of that

1:17:33

stuff in

1:17:38

probably somewhere around 2003-2004-ish. I

1:17:48

started getting more into

1:17:50

the research side of

1:17:52

things and maybe like

1:17:54

07 or so, like

1:17:56

06-07. That was kind of

1:17:58

like the period immediately post it

1:18:01

seems like attitudes starting to

1:18:03

shift about stretching were like

1:18:05

free that time people were

1:18:07

so fucking stoked about stretching

1:18:09

like they were they were

1:18:11

all about that life which

1:18:13

seems so weird like thinking

1:18:15

back on it but uh

1:18:18

like 90s and like early early

1:18:20

2000s it's like dude you got

1:18:22

to stretch it's gonna prevent injury

1:18:24

it's gonna improve performance it's gonna

1:18:26

do like all of this stuff

1:18:28

stretching is the tits it is the

1:18:30

best and then

1:18:33

one study is published showing hmm you

1:18:35

might acutely decrease force output a little

1:18:37

bit and then things just turned

1:18:39

on a dime in the span of just

1:18:41

like a couple years and now you have

1:18:43

people saying like no stretching will

1:18:46

actually it's the worst it's going to

1:18:48

make you so much weaker and like

1:18:50

less athletic and it's horrible and like

1:18:52

yeah i remember in that era when

1:18:56

people were like fighting and relationships

1:18:58

were being ruined on the internet

1:19:00

uh about something related

1:19:02

to science and

1:19:04

training and whatnot it was it was

1:19:06

people like losing their shit about stretching

1:19:08

is it good is it bad um

1:19:11

and yeah that's that's way in the past now

1:19:13

but yeah yeah

1:19:16

i when i was coming up there were

1:19:18

still a lot of people who were like

1:19:20

very very stoked about stretching

1:19:22

and thought that like everyone should do it and it

1:19:24

was like super great um but i

1:19:26

i think by the time you guys

1:19:28

would have been coming into it that was

1:19:31

a little bit in the rear view and people

1:19:33

had kind of more of a neutral

1:19:36

to anti-view of stretching

1:19:38

so yeah

1:19:40

just yeah how things change i

1:19:43

mean it's interesting because

1:19:45

obviously i guess in the past at

1:19:47

the time was stretch made hypertrophy as hot over top

1:19:49

because it is now as well um

1:19:53

let's see you

1:19:55

know back then the big thing was just like

1:19:57

training through a full range of motion um

1:20:00

And that was I

1:20:02

think pretty uncontroversial

1:20:09

You had I I think

1:20:11

by that point the What

1:20:15

is it Bloomquist when was Bloomquist

1:20:17

published 2014 aspect I Was

1:20:21

about to say 2014 as well. Well Hmm,

1:20:26

that's bad crime. I'm trying I'm

1:20:29

trying to think I Feel

1:20:32

like there was at least one full range

1:20:34

of motion study that had been published back

1:20:36

then Tinto I

1:20:38

think 2012

1:20:44

is sound. I'm pretty sure that's the first hypertrophy one Damn

1:20:49

yeah, I don't know I think I think I

1:20:54

Guess back then people were just saying train through

1:20:56

a full range of motion and they had no

1:20:58

research to cite for it. But Yeah,

1:21:02

no one no one was talking stench

1:21:05

me mediated hypertrophy But

1:21:08

folks in generally say like oh,

1:21:10

yeah, you should train through a full range of motion.

1:21:12

It'll it'll cause more growth And

1:21:14

yeah, I guess I guess maybe they didn't

1:21:16

have much to lean on until Bloomquist. I didn't realize

1:21:18

it was that late I thought it was like Now

1:21:23

Bloomquist is relatively reasons as well. Dang

1:21:28

Hey Claims like could

1:21:31

not even sometimes I see the claim that for range

1:21:33

of motions inherently less injurious Well, how do you were

1:21:35

the claims like that around time as well? So

1:21:41

like squat in particular people

1:21:43

were very leery of There

1:21:47

there was In

1:21:49

in like the early to mid aughts there

1:21:52

was a lot of like deep squats kill

1:21:54

your knees type of deal That

1:21:57

was that was a very common thing you would come

1:21:59

across across there

1:22:02

was a man

1:22:12

I'm blanking on all of the all

1:22:14

of the names and papers from that

1:22:16

era there was there was a review

1:22:19

paper looking

1:22:21

at like we got you and do

1:22:24

what we got you we got you we

1:22:27

recently did a mini deep

1:22:29

dive into the whole squatter

1:22:31

back for your knees era and the original

1:22:33

papers and then what followed after that give

1:22:36

us it was Hartman 2013 that that was a one that really

1:22:42

that was squirting yeah yeah

1:22:44

yeah that was the one so pre

1:22:47

pre Hartman 2013 there there was

1:22:49

a lot of debate

1:22:52

of like oh well well

1:22:54

deep squats like destroy your knees and whatnot

1:22:57

and I do think

1:22:59

that things started really really shifting

1:23:02

around that topic when that review

1:23:04

was was published showing like oh

1:23:06

yeah forces on the knees do

1:23:08

increase as as

1:23:11

knee joint angle increases but we also

1:23:14

know the stress

1:23:16

tolerances of all of the

1:23:18

ligaments and tendons around the

1:23:20

knees and yeah forces increase

1:23:23

but they're still way way low like

1:23:25

way way below the loading capacities of

1:23:27

those tissues so it's

1:23:29

fine but yeah yeah

1:23:31

like in general people tended to promote

1:23:34

training through a full range of motion

1:23:37

for most things

1:23:40

and it was just squats they're like a

1:23:42

deep deep squats are scary but like you

1:23:44

know you should you

1:23:46

should touch the bar to your chest on just

1:23:50

you know what let the weight go all

1:23:52

the way down when you're doing bicep curls

1:23:54

stuff like that there was a contingent of

1:23:56

bodybuilders that were that

1:24:00

were like anti touching the bar to

1:24:02

your chest, like flare your elbows

1:24:04

all the way and only go down to like 90 degree

1:24:07

elbow angle. Anything

1:24:09

beyond that will destroy your shoulders. Like there

1:24:11

was some of that. So

1:24:14

it was kind of like my memory

1:24:17

of like the zeitgeist at the time

1:24:20

was that in general, full

1:24:22

range of motion was preferable, but there were like

1:24:24

a handful of movements with

1:24:26

squat and bench being like the two

1:24:29

most notable where people

1:24:31

were pretty, where

1:24:34

people were scared about going through a full

1:24:36

range of motion due to like shoulder and

1:24:38

knee concerns. Dan,

1:24:41

yeah, no, I remember the strange

1:24:43

double think around squats definitely being

1:24:45

dangerous with full range of motion,

1:24:48

but the same rationales around squats being

1:24:50

dangerous weren't also being applied to other

1:24:52

exercises quite as much. But

1:24:56

yeah, squatting deep has always been, now

1:24:58

it's glamorized and it used to be absolutely

1:25:02

vilified for sort of

1:25:04

overall joint integrity or health or other buzz

1:25:06

ones. Yeah,

1:25:08

yeah, I mean, I don't know.

1:25:11

It is weird like

1:25:14

to think back about how,

1:25:19

I don't know, like things that we just

1:25:21

take for granted now in terms of like

1:25:24

research interpretation that were

1:25:26

relatively foreign to people at

1:25:28

the time. Like a

1:25:31

good example of this is like these days, if

1:25:35

all you have to support some sort of statement

1:25:37

or supposition is just like, ah, there's an EMG

1:25:39

study, people will be like, ah,

1:25:42

that's weak sauce. Like we don't

1:25:44

know if that's like predictive of

1:25:47

hypertrophy over time, but like, dude,

1:25:49

not even like, well, I was gonna say not

1:25:51

even that long ago. I guess this is pretty

1:25:53

long ago now, but

1:25:56

I would say like pre 2016, people

1:26:00

were making like pretty strong predictive

1:26:06

of hypertrophy. Like you know

1:26:11

we know more. Shoutouts to Andrew Vygotsky.

1:26:40

He was the person that I think put

1:26:42

this on a lot of kind of

1:26:44

industry people's radar. Even though I'm sure

1:26:46

folks like Anoka and DeLuca and whatnot

1:26:49

had been tearing their hair out if

1:26:51

they were even aware of like sports

1:26:53

science research. But yeah,

1:26:56

yeah, yeah. So it's

1:26:59

similar with kind of the

1:27:02

like deep squatting thing because

1:27:06

people would point to research back then. They'd be

1:27:08

like yeah like as

1:27:10

you squat deeper like peak

1:27:12

ACL forces keep

1:27:15

going up. Peak

1:27:18

forces on the patellar tendon they

1:27:20

keep going up. Like we

1:27:22

see these these forces on soft tissues go

1:27:24

up as people get below like get

1:27:28

beyond like a 90 degree knee angle in the squat.

1:27:30

And you know I do

1:27:32

think like like post Hartman

1:27:35

that kind of like set the paradigm that

1:27:37

when people are reading that research they're like okay

1:27:40

well these forces are going up

1:27:42

but what are the tolerances of these tissues? And

1:27:44

if you're not seeing forces particularly

1:27:46

close to the tolerances of the

1:27:48

tissues who cares? Like it's fine.

1:27:51

But before then it's just like numbers go

1:27:53

up and it's when numbers

1:27:55

get bigger that's scary you

1:27:57

know. Yeah I

1:27:59

don't know. in

1:28:02

many ways,

1:28:04

yeah, a lot

1:28:07

of knowledge has accumulated, I think.

1:28:10

Even amongst people, man,

1:28:13

you go back and you read research from 2010, there

1:28:18

are a lot of wild claims that

1:28:20

people would make in discussion sections. Even

1:28:22

a lot of the researchers did not

1:28:24

have a strong

1:28:27

theoretical understanding of

1:28:30

the sorts of evidence required to

1:28:32

make inferences. There was

1:28:35

a lot of correlation necessarily

1:28:38

implies causation type language that

1:28:40

you'd come across all the

1:28:42

time. And

1:28:45

yeah, I don't know. I do think that in

1:28:48

terms of just kind of like basic

1:28:50

statistical and like research interpretation stuff, people

1:28:52

are quite a bit smarter

1:28:54

about that than they were a decade

1:28:56

ago. Yeah,

1:28:58

it's crazy how

1:29:00

many absurd claims can

1:29:05

be made in the literature and some would

1:29:07

get unnoticed or not G-checked

1:29:10

because in many discussion sections

1:29:12

you see that

1:29:14

there's speculation with like expressed not

1:29:17

very cautiously but still there's the

1:29:19

odd may, this may be true

1:29:21

because of this than a citation

1:29:24

but then if you look at the citation you're like, is

1:29:27

this even supporting

1:29:30

the speculative claim? And

1:29:32

yeah, welcome to research,

1:29:34

baby. Yeah, this is

1:29:36

probably not a rabbit hole to go

1:29:38

down fully but it is,

1:29:44

yeah, I don't know. One of the things that

1:29:46

I'm like pretty

1:29:48

sympathetic to is

1:29:53

like, whatever,

1:29:57

okay, yeah, I'm just gonna do this.

1:30:00

That's fine. One

1:30:03

of the things that like I think about a

1:30:05

lot and one of the things that frustrates me.

1:30:10

Is. If

1:30:13

if someone if someone asks

1:30:16

me, like, hey, I

1:30:18

want to know how to find good

1:30:21

sources of information about a

1:30:23

particular topic, what

1:30:26

should I look for? Like. I

1:30:30

really struggle to come up

1:30:32

with the rules in

1:30:35

like heuristics that wouldn't.

1:30:40

I don't know that would like be fucking

1:30:42

useful, I guess. Because

1:30:45

like. I don't

1:30:48

know. There are a lot of people

1:30:50

in places that one would think would

1:30:52

have like sufficient expertise and be good,

1:30:55

reliable sources of information that end

1:30:58

up very much not

1:31:00

being good sources of information. And

1:31:04

one of the things that I'm like really

1:31:06

sympathetic to is when folks

1:31:08

try to read some research

1:31:11

and like dive into the

1:31:13

literature and they come

1:31:15

across. Claims

1:31:18

in papers by the researchers

1:31:20

doing the study who should

1:31:24

one would think be experts on

1:31:26

the topic that they're researching that

1:31:29

are just just wrong

1:31:32

or making claims that go like way, way

1:31:34

out over their skis and.

1:31:38

You know, it's one of those things where

1:31:40

like unless the person reading that also has

1:31:42

like the requisite level of

1:31:44

expertise to see through that. I

1:31:47

don't understand like I can't see why someone wouldn't just kind of

1:31:49

take their word for it. You know what I mean? And

1:31:53

like a good a good object lesson in

1:31:56

this, I think, is. Do

1:31:58

you remember the last one? old

1:32:00

the old Cori paper that

1:32:03

people will cite to show that like

1:32:06

a drug-free person can't achieve a fat-free

1:32:08

mass index of above 25. You

1:32:11

know that that old that old gym

1:32:15

like there are so just

1:32:17

just for people listening essentially they had

1:32:19

a sample of like 74 subjects that

1:32:21

they recruited from some gyms

1:32:24

in Boston if memory serves and

1:32:26

they got

1:32:28

their body composition and they

1:32:33

calculated their fat-free mass index

1:32:35

and not

1:32:38

even raw fat-free mass index which is

1:32:40

just fat-free mass divided by

1:32:43

height in meter squared it's like BMI

1:32:45

but just fat-free mass instead of weight

1:32:47

like on the numerator position

1:32:50

there but

1:32:53

yeah like they also

1:32:55

they applied a like quote-unquote

1:32:57

correction for height like

1:33:00

the raw FFMI values even in

1:33:02

their sample had some people above

1:33:04

25 but yeah after

1:33:06

they did like this correction they didn't

1:33:09

find any people like the highest they

1:33:11

observed with the corrected FFMI metric was

1:33:13

like 24.8

1:33:16

and they

1:33:18

like pretty I can't

1:33:20

remember if they directly stated or

1:33:22

just like very strongly implied that

1:33:24

like yeah without without drugs

1:33:26

like you're not you're not gonna see people

1:33:29

getting a fat-free mass index over 25 and

1:33:31

like don't

1:33:35

like like proposing that is like not

1:33:38

a complete like unimpeachable limit

1:33:40

but like a functional limit

1:33:42

like you know you're not a

1:33:44

hundred percent sure someone's on gear if their FFMI

1:33:46

is over 25 but like you can be about

1:33:48

95 percent sure like that's that's

1:33:50

what you would take away from the paper and

1:33:54

like I don't know if you know

1:33:57

about this stuff reasonably well like if you

1:33:59

if you understand things

1:34:01

about like sampling and

1:34:04

inferences then if I

1:34:06

told you hey we're going to take a

1:34:08

sample of 74 people

1:34:10

and whatever the like

1:34:12

peak characteristic of whatever we're observing

1:34:14

we find in that sample of

1:34:16

74 people even if they're

1:34:18

like pre-selected to be pretty

1:34:20

high like exemplars of a particular

1:34:23

ability if I said yeah

1:34:26

and the highest value we observe that that's as that's

1:34:28

as good as it gets in

1:34:30

most areas people would be

1:34:32

like nah like that's that's wild you know

1:34:35

like if you went to like

1:34:38

a random track and field meet and you're

1:34:40

like hey let's uh let's

1:34:42

let's just observe 74 people run a hundred

1:34:44

meters and the fastest someone runs like

1:34:46

that that is the limit humans can't

1:34:48

run faster than that unless

1:34:51

your sample happened to include Usain Bolt

1:34:53

you didn't find a limit you know like you

1:34:57

can only make inferences but so strong

1:34:59

from like that type of sample and

1:35:03

it's not even like they went to like a bodybuilding

1:35:05

show and sampled like 74 bodybuilders

1:35:07

they note in the paper that

1:35:09

like there were a handful of

1:35:11

subjects that were successful like strength

1:35:14

or physique athletes but the only

1:35:16

criteria was they

1:35:19

had to be over 18 and have at

1:35:21

least six months of training experience and

1:35:24

I gotta tell you you're not gonna

1:35:26

find like a hard limit in that

1:35:28

type of sample but like yeah if

1:35:30

you you know more about research and you

1:35:32

read the paper you're like yeah no like

1:35:35

these these authors are getting pretty far out

1:35:37

over their skis but if you're someone who

1:35:39

doesn't know quite as much

1:35:41

about like research interpretation and you read that

1:35:43

study I can understand why you come away

1:35:45

with it thinking that like a 25 ffmi

1:35:49

is like the so-called natty

1:35:51

limit and that

1:35:54

that was like a thing that just a lot

1:35:57

of people just believed for like

1:35:59

a decade if not longer.

1:36:01

And if you'd say like, oh

1:36:04

no, like people were getting like

1:36:06

the researchers here were being a

1:36:08

little over eager with the inferences

1:36:10

they're trying to draw. You know,

1:36:13

just in terms of like external

1:36:15

markers of expertise, they

1:36:17

have PhDs and they're the ones that actually

1:36:19

did the research. And so if someone

1:36:22

is making like a very valid critique of

1:36:24

it but they don't have like the same

1:36:26

credentials or even if they have an advanced

1:36:28

degree but it's like not they're not doing

1:36:31

work in that field, any

1:36:33

sort of like external marker of expertise

1:36:35

would suggest that like, oh

1:36:37

no, like these like the

1:36:39

people doing the research would have like a stronger claim

1:36:41

to expertise and if you yourself are not an expert,

1:36:44

you just go with the interpretation the

1:36:46

researchers have of their own findings.

1:36:49

And so I don't know

1:36:51

like that that in sort of like related

1:36:54

instances really, really kind of like

1:36:56

black pill me a little bit

1:36:59

on the idea of just like anyone

1:37:03

being able to

1:37:05

like reliably find

1:37:08

credible sources and understand

1:37:12

things relatively well in

1:37:14

any field where they're

1:37:16

not like able, capable

1:37:18

and willing to invest a

1:37:21

ton of time to develop

1:37:24

like intense expertise of their own. Like

1:37:28

I don't know, like I don't want to put

1:37:30

anyone on blast like name any names but like

1:37:33

there are a lot of people who

1:37:36

like in the fitness industry who

1:37:40

like purport to be like quote unquote

1:37:42

science based or evidence based that like

1:37:46

the stuff they put out just sucks and

1:37:48

at least like a lot of it does

1:37:51

and like I can't think of

1:37:53

any like reliable external markers

1:37:56

that I would use to

1:37:58

like discriminate those folks. from

1:38:01

people who I think are doing good

1:38:03

work and putting out good content. Like

1:38:06

I don't... yeah I think

1:38:08

it's uh... I

1:38:10

don't know. I think it's basically

1:38:13

an impossible problem and I don't

1:38:15

remember... oh yeah, yeah, talking about squats

1:38:18

kill your knees. Um yeah,

1:38:20

like a lot of people

1:38:22

came away with that idea because a lot of researchers

1:38:24

were saying things along those lines. It's just like, well

1:38:27

they were wrong but like I'm not sure how

1:38:30

like non-experts would have not been wrong there.

1:38:32

You know what I mean? Unless they

1:38:35

pulled a Hartman and they just had

1:38:37

enough expertise to like critically appraise it

1:38:40

for themselves. And yeah, I don't know.

1:38:42

I think by and large a

1:38:44

lot of people are just um kind

1:38:48

of held hostage by the

1:38:50

limitations of researchers themselves where

1:38:53

if the stuff at the top, if

1:38:55

they get things wrong and draw incorrect

1:38:57

inferences, um most

1:39:00

people just aren't going to be able to see

1:39:02

through that and they just get shit wrong and

1:39:04

I am very sympathetic to it because I understand

1:39:06

why. Like how are you going to

1:39:08

see through that? You know? Yeah,

1:39:13

it's hard as well because obviously on

1:39:15

any topic you always want to have

1:39:17

some sort of consensus and

1:39:19

I think if you're overconfident about what a

1:39:21

certain research design can tell you about a

1:39:23

topic you can very hastily form a

1:39:26

consensus like in the case of the Hartman stuff.

1:39:28

Oh, we observe high forces at the knee when

1:39:30

you go deeper. That is

1:39:33

probably maybe a bad thing and

1:39:35

so just because directionally it is

1:39:38

thought to be potentially a bad

1:39:40

thing, the consensus is temporarily in

1:39:42

favor of it being a bad

1:39:44

thing but then that's without

1:39:46

observing the fact that hey

1:39:48

this research design is

1:39:50

not necessarily going to tell you about whether or not the

1:39:53

squats are bad for your knees. Like it is not well

1:39:55

equipped to do so and I think it's

1:39:57

just like the haste with which some people like

1:39:59

to come to. conclusions

1:40:01

about a topic based on an insufficient

1:40:06

number of studies or more specifically in

1:40:08

this case an insufficiently direct

1:40:10

way of answering the

1:40:13

question. Cool. Yeah. Yeah. A lot

1:40:15

of acute

1:40:18

proxies that have never been validated

1:40:22

to be predictive of longitudinal outcomes. People

1:40:24

just assuming that they're predictive

1:40:26

of longitudinal outcomes. Often the proxy

1:40:28

for a proxy which is then thought to

1:40:30

roughly mirror a physiological variable that

1:40:32

is then roughly thought to it for

1:40:35

hypertrophy. Yeah. It

1:40:37

rocks dude. It's so cool. Okay.

1:40:40

We should get back to stretch

1:40:42

mediated hypertrophy. Alright. So

1:40:44

just to get back to

1:40:46

the panedia analysis I mentioned earlier, essentially

1:40:50

relatively modest hypertrophy was observed

1:40:52

that was improved upon not so much

1:40:54

by the duration of stretching but specifically

1:40:56

with higher intensities of stretching. And

1:41:01

generally the magnitude of hypertrophy being observed

1:41:03

was lower than what you would see

1:41:05

with resistance training studies. Now

1:41:07

when it comes to fascicle length and fascicle

1:41:09

angle which are thought to roughly represent longitudinal

1:41:14

hypertrophy and radial hypertrophy respectively so

1:41:16

an increase in the length of

1:41:18

that cylindrical muscle shape or

1:41:21

an increase in the radius or thickness of that

1:41:23

cylindrical muscle shape. When it comes to fascicle

1:41:25

length the increases only became meaningful

1:41:27

once the

1:41:30

stretching intervention lasted at least an hour

1:41:32

and a half a week. So when

1:41:34

stretching interventions lasted under an hour and a half

1:41:36

a week the change in fascicle length was

1:41:39

actually slightly negative but altogether negligible at minus

1:41:42

0.06 so a negative trivial effect size.

1:41:46

Whereas with interventions lasting for

1:41:51

at least an hour and a half stretching a week the increase in fascicle

1:41:53

length or longitudinal hypertrophy was then increased

1:41:56

to 0.29. or

1:42:00

what we call a small effect size. Likewise,

1:42:04

increasing the intensity of stretching, so

1:42:07

comparing lower intensity stretching to higher

1:42:09

intensity stretching, also seem

1:42:11

to increase fast-cal length changes with

1:42:13

lower intensity stretching, causing a change in fast-cal

1:42:16

length of minus 0.04, and

1:42:18

higher intensity stretching causing a change of 0.28, so

1:42:22

again, a small increase. Specifically

1:42:25

for fast-cal length and what

1:42:27

we think is longitudinal hypertrophy, it

1:42:29

seems like both the duration of the stretching being

1:42:32

quite high and the intensity of

1:42:34

the stretching being quite high are important factors

1:42:36

in making sure that we actually observe any

1:42:39

meaningful change in fast-cal length. And

1:42:43

finally, for fast-cal angle, which is

1:42:45

thought to represent increases in radial

1:42:48

hypertrophy, these changes

1:42:50

were actually more meaningful with

1:42:52

lower durations of stretching. So

1:42:55

when duration of stretching was under an hour and

1:42:57

a half stretching a week, we observed

1:42:59

a small effect size in favor of

1:43:02

stretching of 0.31 versus

1:43:04

essentially no change when stretching interventions lasted over

1:43:06

an hour and a half a week. And

1:43:10

likewise, fast-cal angle

1:43:13

changes or panacea angle changes didn't really

1:43:15

differ whether intensity of stretching was high

1:43:17

or low. So

1:43:20

it seems like, essentially, with

1:43:22

muscle size changes, intensity of stretching is

1:43:24

important. With fast-cal

1:43:26

length changes or longitudinal hypertrophy, both

1:43:29

intensity and durations seem to be

1:43:31

important, such as higher intensity stretching

1:43:33

and longer duration stretching both

1:43:36

increase change in fast-cal length. And

1:43:39

finally, for panacea angle, lower

1:43:41

durations of stretching, if anything, seem more

1:43:43

favorable. But with a relatively

1:43:46

limited number of studies, I think with some

1:43:48

of these findings, it's difficult to tell. Is

1:43:50

there really a dose-response relationship here where you

1:43:53

need to be spending less time stretching if

1:43:55

you want to induce radial hypertrophy or more time

1:43:57

stretching if you want to induce? more...

1:44:02

classical increases. But broadly

1:44:04

speaking, it is just worth noting that many

1:44:06

of these stretching interventions were talking about minutes

1:44:08

to like, in some cases,

1:44:10

up to an hour of stretching per day. That

1:44:14

duration of exposure is relatively important and something we'll

1:44:16

come back to. So

1:44:19

yeah, those are the rough takeaways from the

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1:45:16

One thing that Greg actually brought up, so he

1:45:18

might be best positioned to touch on it unless

1:45:20

you want me to cover this, is just how

1:45:22

these results relate to potentially

1:45:25

the influence of length and

1:45:27

resistance training on hypertrophy or

1:45:30

stretch-made hypertrophy. So,

1:45:33

is that something you want to cover, Greg? Do you want me to

1:45:35

cover it? No, I

1:45:37

got it. I got it. Okay,

1:45:40

so I'm going to attempt

1:45:42

to share my screen. Okay,

1:45:45

cool. So this

1:45:49

is like a very pedantic point, but I think

1:45:51

that it's fairly relevant. It's

1:45:56

very mean things, and when you're

1:45:58

talking about stretch-mediated hypertrophy, you

1:46:03

are hoping that you're observing

1:46:05

an example

1:46:09

of the outcome of interest.

1:46:11

Mediation has a technical, statistical

1:46:13

definition where

1:46:16

if something is mediating in

1:46:18

effect, that

1:46:24

means that it is something

1:46:26

that influences the

1:46:28

outcome of interest, that is being influenced by

1:46:31

whatever stimulus you're dealing with

1:46:34

or characteristic you're interested in, such

1:46:38

that the thing, in terms of

1:46:40

if you're dealing with

1:46:42

direct mediation, that means that

1:46:44

thing A causes thing B,

1:46:46

thing B causes thing C, and

1:46:49

thing A only causes thing C

1:46:51

because of thing B. If

1:46:54

you're dealing with partial mediation, which is what

1:46:56

we'd be dealing with here, the

1:47:01

stimulus directly affects the

1:47:03

outcome and the stimulus directly

1:47:06

affects the mediator, and the mediator

1:47:08

directly affects the outcome, such

1:47:10

that the outcome is

1:47:12

the result of both

1:47:14

the stimulus and the thing

1:47:16

that is mediating the stimulus. So

1:47:19

that might sound like a

1:47:22

bunch of gobbledygook, but

1:47:25

oh man, I'm trying

1:47:27

to think of an example on

1:47:29

the spot, but

1:47:33

oh yeah, so here's

1:47:37

like a classic example

1:47:40

of mediation that comes up

1:47:42