Welcome to Huberman Lab Essentials,

>> [music]

>> where we revisit past episodes for the

most potent and actionable science-based

tools for mental health, physical

health, and performance.

I'm Andrew Huberman and I'm a professor

of neurobiology and ophthalmology at

Stanford School of Medicine. Today we

are going to discuss the science and

practice of flexibility and stretching.

The important thing that I'd like you to

know is that flexibility and the process

of stretching and getting more flexible

involves three major components. Neural,

meaning of the nervous system, muscular,

muscles, and connective tissue.

Connective tissue is the stuff that

surrounds the neural stuff and the

muscular stuff, although it's all kind

of weave together and braided together

in complicated ways. So, here's a key

thing that everyone should know, whether

or not you're talking about flexibility

or not.

Your nervous system controls your

muscles. It's what gets your muscles to

contract. So, within your spinal cord

you have a category of neurons, nerve

cells, that are called motor neurons.

Those neurons release a chemical. That

chemical is called acetylcholine. The

release of acetylcholine from these

nerve cells, these neurons, onto the

muscles causes the muscles to contract.

And when muscles contract, they are able

to move

limbs by way of changing the length of

the muscle, adjusting the function of

connective tissue like tendons and

ligaments. Now, within the muscles

themselves, there are nerve connections.

And these are nerve connections that

arise from a different set of neurons in

the spinal cord that we call sensory

neurons. These

spindle

connections within the muscle that wrap

around the muscle fibers sense the

stretch of those muscle fibers.

So, now we have two parts to the system

that I've described. You've got motor

neurons that can cause muscles to

contract and shorten, and we have these

spindles within the muscles themselves

that wrap around the muscle fibers, and

that information is sent from the muscle

back to the spinal cord. It's a form of

sensing what's going on in the muscle.

Now, why would that be useful? Well,

what this does is it creates a situation

where if a muscle is or is stretching

too much because the range of motion of

a limb is increased too much, then the

muscle will contract to bring that limb

range of motion into a a safe range

again. Okay, so just to clarify, this

whole thing looks like a loop, and the

essential components of the loop are

motor neurons contract muscles, sensory

neurons that we call spindles are

sensing stretch within the muscles, and

if a given muscle is elongating because

of the

increased range of motion of a limb,

those sensory neurons send an electrical

signal into the spinal cord such that

there is an activation of the motor

neuron, which by now should make perfect

sense as to why that's useful. It then

shortens up the muscle. It actually

doesn't really shorten the muscle, but

contracts the muscle. It brings the limb

back into a safe range of motion. So,

that's one basic mechanism that we want

to hold in mind. This idea of a spindle

that senses stretch and can activate

contraction of the muscles and shorten

the muscles. The next mechanism I want

to describe, and once again, there are

only two that you need to hold in mind

for this episode, has to do with sensing

loads.

So, at the end of each muscles, you have

tendons typically, and there are neurons

that are closely associated with those

tendons

that are called Golgi tendon organs,

right? These are neurons that are

sensory neurons that sense how much load

is on a given muscle, right? So, if

you're lifting up something very, very

heavy, these neurons are going to fire,

meaning they're going to send electrical

activity into the spinal cord,

and then those neurons have the ability

to shut down, not activate, but shut

down motor neurons and to prevent the

contraction of a given muscle. So, for

instance, if you were to walk over and

try and pick up

a weight that is

much too heavy for you, meaning you

could not do it without injuring

yourself. There are a number of reasons

why you might not be able to lift it,

but let's say you start to get it a

little bit off the ground or you start

to get some

force generated that would allow it to

move.

But, the force that you're generating

could potentially rip your muscles or

your tendons off of the bone, right?

That it could disrupt the joints, that

could tear ligaments. Well, you have a

safety mechanism in place. It's these

Golgi tendon organs, these GTOs as

they're called, that get activated and

shut down the motor neurons and make it

impossible for those muscles to

contract. There are also mechanisms that

arrive to the neuromuscular system from

higher up in the nervous system, from

the brain.

And those mechanisms involve a couple of

different facets that are really

interesting

and I think that we should all know

about. In fact, today I'm going to teach

you about a set of neurons that I'm

guessing 99.9%

of you have never heard of, including

all you neuroscientists out there, if

you're out there.

And I know you're out there.

That seem uniquely enriched in humans

and probably perform essential roles in

our ability to regulate our physiology

and our emotional state. So, within the

brain we have the ability to sense

things in the external world, something

we called exteroception, and we have the

ability to sense things in our internal

world, within our body, called

interoception. Interoception can be the

volume of food in your gut, whether or

not you're experiencing any organ pain

or discomfort, whether or not you feel

good in your gut and in your organs. The

main brain area that's associated with

interpreting what's going on in our body

is called the insula, i n s u l a. It's

a very interesting brain region. It's

got two major parts. The front of it is

mainly

concerned with things like smell and to

some extent vision. Like if you smell

something good to approach it or if you

smell something bad to avoid it. The

posterior insula, the back of the insula

that is,

has a very interesting and distinct set

of functions.

The posterior insula is mainly concerned

with what's going on with your somatic

experience. How do you feel internally?

It mainly batches information into yum,

I want to keep doing this or approach

this thing,

or continue down some path of movement

or eating or staying in a temperature

environment, etc. Or yuck, I need to get

out of here. I don't want any more of

this. I don't want to keep doing this.

This is painful or aversive or

stressful. In your posterior insula,

you have a very interesting population

of very large neurons. These are

exceptionally large neurons called von

Economo neurons. Neurons that are again,

unbeknownst to most neuroscientists, and

they seem uniquely enriched in humans.

Why is that interesting? Well, these von

Economo neurons have the unique property

of integrating our

knowledge about our body movements,

our sense of pain and discomfort, and

can drive motivational processes that

allow us to lean into discomfort and

indeed to overcome any discomfort if we

decide that the discomfort that we are

experiencing is good for us or directed

toward a specific specific goal. And

then, there's the other really

interesting aspect of these von Economo

neurons, which is that these von Economo

neurons are connected to a number of

different brain areas

that can shift our internal state from

one of so-called sympathetic activation.

So, this is a pattern of alertness and

even stress, sometimes even panic, but

typically alertness stress, to one of

so-called parasympathetic activation.

To one of relaxation. Oftentimes you'll

hear that stretching should be done by

relaxing into the stretch. Well, what

does it actually mean to relax into the

stretch? Well, these von Economo neurons

sit at this junction where they're able

to evaluate what's going on inside our

body and allow us to access neural

circuitries by which we can shift our

relative level of alertness down a bit

or our relative level of stress down a

bit and thereby to increase so-called

parasympathetic activation and to

literally override some of those spindle

mechanisms, even the GTO mechanisms, but

especially the spindle mechanisms at the

neuromuscular and muscular spinal

junction. I'll give you a brief example

of this that you've already done in your

life and that we all have the capacity

for. What I'm referring to is the

monosynaptic stretch reflex.

This is something that every first-year

neuroscience graduate student learns,

which is that if you were to step on a

sharp object with a bare foot, you would

not need to make the decision to retract

your foot. You would automatically do

that, provided you have a healthy

nervous system. There are mechanisms in

place that cause the retraction of that

limb by way of ensuring that the proper

muscles contract and other muscles do

not contract, in fact, that they fully

relax. Okay? So, in the case of stepping

on a sharp object like a piece of glass

or a nail or a tack, you would

essentially activate the hip flexor to

lift up your foot as quickly as

possible.

In doing so, that same neural circuit

would activate a contralateral, meaning

opposite side of the body, circuit to

ensure that the leg, the foot that's not

stepping on the sharp object, would do

exactly the opposite and would extend to

make sure that you don't fall over. All

of that happens reflexively. It does not

require any thought or decision-making.

However,

if your life depended on walking across

some sharp objects, let's say let's make

it a little less dramatic so it's not

like the Die Hard movie or something

where you have to run barefoot across

the glass, although that's a pretty good

example of what I'm describing here. But

let's say you had to walk across some

very hot stones to get away from

something that you wanted to avoid, you

could override that stretch reflex by

way of a decision made with your upper

motor neurons, your insula, and your

cognition, and almost certainly those

van Economo neurons, which would be

screaming, "Don't do this. Don't do

this. Don't do this." could shuttle that

information to brain areas that would

allow you to override the reflex and

essentially push through the pain. And

maybe even, in fact, even

not experience the pain to the same

degree or even at all.

So, these van Economo neurons sit at a

very important junction within the

brain. They pay attention to what's

going on in your body, pain, pleasure,

etc. And that includes what's going on

with your limbs and your limb range of

motion. They also are paying attention

and can control the amount of

activation, kind of alertness or

calmness that you are able to create

within your body

in response to a given sensory

experience.

And as I mentioned before, they seem to

be uniquely enriched in humans. They

seem to be related to the aspects of our

evolution that allow us to make

decisions about what to do with our body

in ways that other animals just simply

can't. Now, there are a number of

different types of stretching or methods

of stretching.

Broadly defined,

we can describe these as dynamic,

ballistic, static, and what's called PNF

stretching. PNF stands for

proprioceptive neuromuscular

facilitation. The first two that I

mentioned, dynamic and ballistic

stretching, both involve some degree of

momentum and can be distinguished from

static and PNF type stretching.

Now, to distinguish dynamic stretching

from ballistic stretching,

I'd like to focus on this element of

momentum.

Both involve moving a limb through a

given range of motion.

In dynamic stretching, however,

it tends to be more controlled, less use

of momentum, especially towards the end

range of motion. Whereas in ballistic

stretch there tends to be a bit more

swinging of the limb

or use of momentum. But again, dynamic

and ballistic stretching both involve

movement, so we have to generate some

force in order to create that movement.

Ballistic stretching involving a bit

more momentum or sometimes a lot more

momentum, especially at the end range of

of motion. Now, both of those are highly

distinct from static stretching, which

involves holding the end range of

motion, so minimizing the amount of

momentum that's used. Static stretching

can be further subdivided into active or

passive, right? There are different

names for these kinds of approaches. You

can hear about the Anderson approach or

the Janda approach. You can look these

sorts of things up online. There's also

passive static stretching, in which it's

more of a relaxation into a further

range of motion, and that can be a

subtle distinction. Nevertheless, static

stretching involves

both those types of elements, active and

passive, but is really about eliminating

momentum.

And then there's the PNF, the

proprioceptive neuromuscular

facilitation. And proprioception has

several different meanings in the

context of neuroscience and physiology.

To just keep it really simple for today,

proprioception involves both a knowledge

and understanding of where our limbs are

in space and relative to our body,

typically relative to the midline. So,

the brain is often trying to figure out

where are our limbs relative to our

midline down the center of our body. And

if your goal is to increase your

hamstring flexibility and the

flexibility and range of motion of other

related muscle systems, you might put a

strap around your ankle and pull that

muscle, or I should say, excuse me, that

limb toward you. You're not going to

pull the muscle toward you. You're going

to pull that limb, your ankle, toward

you to try and get it sort of back over

your head, and then progressively

relaxing into that, or maybe even

putting some additional force to push

the end range of motion, and then

relaxing it, and then actually trying to

stretch that same limb or increase the

limb range of motion without the strap.

There's a huge range of PNF protocols.

Those protocols can be done both by

oneself, with or without straps, with

machines, with actual weights, or with

training partners. So, specific

exercises to target specific muscle

groups aside, we've now established that

there are four major categories of

stretching, or at least those are the

four major categories I'm defining

today. But in terms of increasing limb

range of motion in the long term, of

truly becoming more flexible, as opposed

to transiently more flexible, static

stretching, which includes PNF, appears

to be the best route to go. So, whether

or not you want to maintain,

reestablish, or gain limb range of

motion, static stretching of holds of 30

seconds appear to be best. Now, the

question is, how long should you do

that, and how many sets should you do

that, and how many times a week should

you do that? To answer those questions,

I'm going to turn to what I think is a

really spectacular review. The title of

the paper is "The Relation Between

Stretching Typology and Stretching

Duration: The Effects on Range of

Motion." First of all, and I quote, "All

stretching typologies showed range of

motion improvements over a long-term

period. However, the static protocols

showed significant gains with a P value

less than 0.05, which means a

probability that cannot be explained by

chance alone,

when compared to ballistic or PNF

protocols." So, again, what we're

hearing is that static stretching is the

preferred mode for increasing limb range

of motion. Although, here they make the

additional point

that static stretching might even be

superior not just to ballistic

stretching, but also to PNF protocols.

The authors go on to say

time spent stretching per week seems

fundamental to elicit range of movement

improvements when stretches are applied

for at least or more than 5 minutes per

week. Okay, this is critical. This is

not 5 minutes per stretch. Remember, 30

seconds per static stretch, but at least

5 minutes per week. So, what this means

is that we should probably be doing

anywhere from two to four sets of

30-second static hold stretches 5 days

per week. So, what would effective

stretching protocol look like?

We're all trying to improve limb range

of motion for different limbs and

different muscle groups. Let's talk

about hamstrings

for the time being. This could, of

course, be applied to other muscle

groups. Let's say you want to improve

hamstring flexibility and limb range of

motion about and around the hamstring.

And involving the hamstring, you would

want to do three sets

of static stretching for the hamstring.

You would do that by

holding the stretch for 30 seconds,

resting some period of time, then doing

it again, holding for 30 seconds,

resting some period of time, and then

holding it for 30 seconds. That would be

one training session for the hamstrings.

I have to imagine that you'd probably

want to stretch other muscle groups as

well in that same session. So, three

sets of 30 seconds each,

get 90 seconds, and you would do that

ideally five times a week, or maybe even

more. One thing that did show up in my

exploration of the peer-reviewed

research is this notion of warming up

for all this. We haven't talked about

that yet. In general, to avoid injury,

it's a good idea to raise your core body

temperature a bit before doing these

kinds of stretches,

even these static stretches, which can

sort of ease into and don't involve

ballistic movement by definition.

And

the basic takeaway that I was able to

find was that if we are already warm

from running or from weight training or

from some other activity, that doing the

static stretching

practice at the end of that weight

training or cardiovascular or other

physical session would allow us to go

immediately into the stretching session.

Because we're already warm, so to speak.

Otherwise,

raising one's core body temperature by a

bit by doing

5 to 7, maybe even 10 minutes of

easy cardiovascular exercise or

calisthenic movements, provided you can

do those without getting injured,

seems to be an ideal way to warm up the

body for stretching. We should be warm

or warm up to stretch, although those

warm-ups don't have to be extremely

extensive. And then just by way of

logic, doing the static stretching after

resistance training or cardiovascular

training seems to be most beneficial. In

fact, and unfortunately, we don't have

time to go into this in too much detail

today. I was able to find a number of

papers that make the argument that

static stretching prior to

cardiovascular training, and maybe even

prior to

resistance training,

can limit our performance in running and

resistance training. I realize that's a

controversial area. You have those who

say, "No, it's immensely beneficial."

You have those who say, "No, it inhibits

performance." And the those that say,

"No, it's a matter of how exactly you

perform that static stretching and which

muscle groups and how you're doing this

and how much time in between static

stretching and performance." But to

leave all that aside, doing static

stretching after some other form of

exercise,

and

if you not after some form of exercise,

after a brief warm-up to raise your core

body temperature, definitely seems like

the right way to go. I'm guessing that

most people are not doing 5 days a week

of dedicated static stretch range of

motion

directed training. But it does appear

that that frequency about the week,

getting those repeated sessions even if

they are short for an individual muscle

group, turns out to be important.

They're going to offset the age-related

losses in flexibility for sure if one is

dedicated about these practices. Some of

you may be familiar with the so-called

Anderson method. It's been around for a

long time. Anderson has an interesting

idea and principle which is thread

through a lot of his teachings that I

think are very much in keeping with the

study that I'm about to describe next

where

he emphasizes to yes to stretch to the

end of the range of motion, but not to

focus so much on where that range of

motion happens to be that day. So for

instance, not thinking, "Oh, I can

always touch my toes for instance, and

therefore that's the starting place for

my flexibility training today." But

rather take the entirety of your system

into account each day and understand

that okay, provided you're warmed up

appropriately,

that you're now going to stretch your

hamstrings for instance, and you're

going to reach down for your toes, but

that your range of motion might be

adjusted that day by way of tension and

stress or by way of ambient temperature

in the room. And to basically define the

end range of motion as the place where

you can feel the stretch in the relevant

muscle groups. So what does this mean?

This means feel the muscles as you

stretch them. Don't just go through the

motions. And this means don't get so

attached to being able to always achieve

for instance a stretch of a given

distance on a within a given session.

You might actually find that by just

finding the place where you can't get

much further and holding the static

stretch there, that on the second and

third set that you happen to be doing

that day that your range of motion will

be increased considerably. Now,

along these lines, there's this even

more nebulous variable, this even more

kind of subjective thing of

how much effort to put into it. Should

you push into the stretch? Would you

even want to bounce a tiny bit? Would

you want to reach into that end point

and try and extend it within a given set

and session?

And for that reason I was excited to

find this paper entitled a comparison of

two stretching modalities on lower limb

range of motion measurements in

recreational dancers. It's a six-week

intervention program that compared

low-intensity stretching, which they

call micro stretching, but to be very

clear, micro stretching in the case of

this manuscript is low-intensity

stretching and they compared that with

moderate-intensity static stretching on

an active and passive ranges of motion.

Basically, what they found was that a

six-week training program using very

low-intensity stretching had a greater

positive effect on lower limb range of

motion than did moderate-intensity

static stretching. Here I'm quoting

them.

The most interesting aspect of the study

was the greater increase in active range

of motion compared to passive range of

motion by the micro stretching group.

So, this relates to what we were just

talking about a few moments ago as it

relates to the Anderson method, which is

that

very low-intensity stretching

meaning effort that

feels not painful

and in fact might even

feel easy or at least not straining to

exceed a given range of motion turns out

to not just be as effective but more

effective than moderate intensity

stretching. So, what is low-intensity

static stretching? Well, they define

this as the stretches were completed at

an intensity of 30 to 40%

where 100% equals the point of pain,

right? So,

30 to 40% in these individuals, and

again I'm paraphrasing, induced a

relaxed state within the individual and

the specific muscle. And here they were

holding these static stretches, I should

mention, for 1 minute, not 30 seconds.

Now, the control group was doing the

exact same overall protocol, so daily

stretching for 6 weeks,

the same exercises, holding each set for

60 seconds, but we're using an intensity

of stretch of 80% where again 100

represents the point of pain, the point

where the person would want to stop

stretching. I find these data incredibly

interesting for I think what ought to be

obvious reasons. If you're going to

embark on a flexibility and stretching

training program, you don't need to push

to the point of pain. In fact, it seems

that even just approaching the point of

pain is going to be less effective than

operating at this 30 to 40% of

intensity prior to reaching that pain

threshold, the pain threshold being

100%. Now, of course, this is pretty

subjective, but I think all of us should

be able to register within ourselves as

to whether a given range of motion or

extending a given range of motion brings

us to that threshold of pain or near

pain. And according to this study at

least, operating or performing

stretching at an intensity that's quite

low, that's very relaxing, turns out to

be more beneficial in increasing range

of motion than is doing

exercises aimed at increasing range of

motion at a higher intensity. Okay, so

lower intensity stretching, I should say

lower intensity static stretching,

appears to be the most beneficial way to

approach stretching, and I think that's

a relief um probably to many of us

because it also suggests that the injury

risk is going to be lower than if one

were pushing into the pain zone, so to

speak. I want to just briefly return to

this idea of whether or not to do

ballistic or static stretching before

some sort of skill training or weight

training, any kind of sport or even

cardiovascular exercise like running.

There are instances

for example, where an individual might

want to do some static stretching to

increase limb range of motion prior to

doing weight training, even if it's

going to to

that person's ability to lift as much

weight. Why would you want to do that?

Well, for instance, if somebody has a

tightness or a limitation in their

neuromuscular connective tissue system

someplace in their body and system that

prevents them from using proper form

that they can overcome by doing some

static stretching,

well, that would be a great idea. There

are instances where people are trying to

overcome injuries, where they're trying

to

come back from a reparative surgery or

something of that sort, coming back from

a layoff where some additional static

stretching prior to cardiovascular

weight training or skill training or

sport of some kind is going to be useful

because it's going to put us in a

position of greater safety and

confidence and performance overall, even

if it's adjusting down our speed or the

total amount of loads that we use. And

similarly,

there are a lot of data points in the

fact that doing some dynamic or even

ballistic stretching prior to skill

training or cardiovascular weight

training can be beneficial in part to

warm up the relevant neural circuits,

joints, and connective tissue, and

muscles, and as well to perhaps improve

range of motion or ability to perform

those movements more accurately,

with more stability, and therefore with

more confidence. Thus far, we've been

talking about stretching for sake of

increasing limb flexibility and range of

motion, but there are other reasons,

perhaps, to embark on a stretching

protocol that include both our ability

to relax and access deep relaxation

quickly. I'd like to return this to this

idea and this place, this real estate

within our brain that we call the

insular cortex, the insula.

As you recall, way back at the

beginning of this episode, we were

talking about the von Economo neurons

that Constantin von Economo, the

Austrian

uh scientist discovered. And the fact

that we are able to make

and perform interpretations of our

internal landscape, pain, our

dedication to a practice. For instance,

whether or not we are in pain because

it's a practice that we are doing

intentionally and want to improve

ourselves, or whether or not it's pain

that's arriving through some externally

imposed demands or situations. The

insula is handling all that. And

fortunately, there's a wonderful paper

that was published is a few years ago

now in the journal Cerebral Cortex

entitled Insular Cortex Mediates

Increased Pain Tolerance in Yoga

Practitioners. This study explored

the effects on brain structure volume in

yoga practitioners. And for those of you

out there that are aficionados in yoga,

they they pulled subjects from having

backgrounds in the Here I'm probably

going to mispronounce these different

things and for forgive me, the Vinyasa

yogas, the Ashtanga yogas, the younger

yogas, the Sivananda yogas. Okay, so

some people were new to these practices,

some were experienced. The The important

takeaways

were that they took these yoga

practitioners and they didn't explore

their brain structure in the context of

yoga itself. They looked at things like

pain tolerance. So they used thermal

stimulation. Basically, they put people

into conditions where they gave them

very hot or very cold stimuli and

compared those yoga practitioners of

varying levels of yoga experience to

those that had no experience with yoga,

so-called controls. And they found some

really interesting things.

There are a lot of data in this paper,

but

here's something I'd like to highlight.

The pain tolerance of yoga practitioners

was double or more to that of non-yoga

practitioners. They also found

significant increases in insular, again,

the insula, this brain region, gray

matter volume. Typically, when we talk

about gray matter, we're talking about

the so-called cell bodies, the

the location in neurons where the genome

is housed and where the kind of all the

housekeeping stuff is there, and then

white matter volume tends to be the

axons, the wires, because they're in

sheets with this stuff that appears

white in MRIs, and indeed is white under

the microscope, and indeed is white.

It's actually lipid, which is myelin.

So, increased gray matter volume of the

insula is a significant finding

because what it suggests is that people

that are doing yoga have an increased

volume of these areas of the brain that

are associated with interoceptive

awareness and for being able to make

judgments about pain and why one is

experiencing pain. Not just to lean away

from pain, but to utilize or leverage or

even overcome pain. And I find this

interesting because there are a lot of

activities out there that don't create

these kind of changes in brain volume,

especially within the insula. So, it

appears that it's not just the

performance of the yogic movements, but

the overcoming or the kind of pushing

into the end ranges of motion and to

push through discomfort to some extent.

Of course, we want people doing that in

a in a healthy, safe way, but that

allows yoga practitioners to build up

the structure and function of these

brain areas that allow them to cope with

pain better than other individuals and

to cope with other kinds of

interoceptive challenges, if you will.

Not just pain, but cold.

Not just pain, but discomfort of being

in a particular position to do that. And

again, we wouldn't want people placing

themselves into a compromised position,

literally, that would harm them,

especially given that earlier we heard

that micro-stretching of the kind of

non-painful sort, low-intensity sort, is

actually going to be more effective for

increasing end range of motion. But this

study really emphasized the extent to

which practitioners of yoga don't just

learn movements, they learn how to

control their nervous system in ways

that really reshapes their relationship

to pain, to flexibility, and to the

kinds of things that the neuromuscular

system was designed to do. So, if ever

there was a practice that one could

embark on that would not only increase

flexibility and limb range of motion,

but would also allow one to cultivate

some improved mental functioning as it

relates to pain tolerance and other

features of stress management that no

doubt wick out into other areas of life,

appears that yoga is a quite useful

practice. But, of course, yoga isn't the

only way to increase limb range of

motion and flexibility. Up until now,

we've described a number of different

ways to do that and we've arrived at

some general themes and protocols.

Again, we can revisit a couple of them

now just in summary and synthesis.

Static stretching appears to be at least

among the more useful forms of

stretching. It really does appear that

getting

at least 5 minutes per week total of

stretching for a given muscle group is

important for creating meaningful

lasting changes in limb range of motion

and that is best achieved by 5-day week

or 6-day week or even 7-day week

protocols, but those can be very short

protocols limited to, say, three sets of

30, maybe even 45 or 60 seconds of

static hold, although 30 seconds seems

to be

a key threshold there

um that can get you maximum benefit.

And, of course, to always warm up or to

arrive at the stretching session warm.

Thank you once again for joining me

today for a discussion about the neural

and neuromuscular and connective tissue

and skeletal aspects of flexibility and

stretching. And as always, thank [music]

you for your interest in science.