- Stretching improves flexibility and range of motion
- The brain and nervous system play a role in stretching and flexibility
- Muscle spindles detect muscle length and send information to the brain
- The brain uses this information to coordinate muscle contractions and create proprioception
- Proprioception is the awareness of body position in space
- Proprioceptive input is important for body coordination and awareness
- The brain can adjust the sensitivity of muscle spindles and muscle tone based on the information received

- The brain and nervous system can adjust the sensitivity and tone of muscles throughout the body
- The nervous system modulates and prioritizes different sensory input
- The stretch reflex is a protective mechanism that contracts muscles when they are stretched too far or too fast
- Consistent stretching can lead to neurological changes that increase flexibility and range of motion
- More research is needed to understand the interaction between the brain, nervous system, and soft tissues in improving flexibility
- Static stretching is the best supported method for long-term flexibility improvements
- Stretching muscle groups for 30-60 seconds, 5-6 days a week, in 2 sets is recommended
- It is important to also train muscles to be strong in lengthened positions
- The video creator is heading to Florida for a collaboration and will discuss the importance of flexibility and muscle strength in lengthened positions.

Thanks to YOGABODY Teachers College http://www.yogabody.com/iha for sponsoring this video. Check out their science-based, online yoga certification courses.

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How Stretching REALLY Works

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In this video, Jonathan from the Institute of Human Anatomy discusses the surprising influences that the nervous system has on flexibility and the adaptations that can occur with consistent stretching. He also goes over various reflexes as well as stretching protocols that tend to improve flexibility the most. 

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Video Timeline

00:00 - 00:59 Intro
01:00 - 01:12 Measuring Our Own Flexibility 
01:13 - 03:15 Muscle Flexibility Translating to Improve Joint ROM. 
03:16 - 04:33 Yoga in the Lab and YogaBody!
04:34 - 05:18 Specialized Stretch Receptors - Muscle Spindles
05:19 - 06:04 The Importance of Detecting Muscle Length
06:05 - 07:42 Cerebellum & Sensory Cortex Processing Muscle Length Information
07:43 - 09:28 Proprioception: Knowing Where Your Body Parts Are 
09:29 - 10:21 Brain Adjusting Muscle Spindles & Tone From Proprioceptive Input
10:22 - 11:52 Underwear Example: Modulating & Prioritizing Sensations
11:53 - 13:47 Stretch Reflex - Brain Protecting Muscles Being Overstretched
13:48 - 15:49 How the Brain Allows For Improved Flexibility 
15:50 - 16:18 The Need For Even More Information
16:19 - 17:20 Best Type of Stretching For Improved Flexibility 
17:21 - 18:38 Teaser: The Link Between Flexibility & Strength - Thank You!!!

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Audio Credit: https://www.bensound.com
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#flexibility #stretching #anatomy

Many of us have probably thought about including stretching into our daily routines, as there are many potential benefits to stretching, 1 of the more obvious and common benefits being improved flexibility and range of motion.

But what is actually happening to our bodies When we stretch and develop adaptations like improved flexibility?

Well, part of this answer might actually surprise you, as a big part of this resides in your brain and nervous system.

Who would have thought that your brain and nervous system had an influence or any say over your stretching and flexibility?

So in today's video, we're going to take a look at the brain, certain nerves, as well as typical muscles that we stretch so that we can figure out what's going on here.

We'll also talk about some of the most effective types of stretching for these adaptations or the best ways to improve flexibility over time.

It's going to be a stretchy 1, if you will, filled with some obvious cheesy jokes.

But let's jump right into this anatomical awesomeness.

ANATOMICAL AWESOMENESS So when we think about our own flexibility or how flexible we are, we often judge or gauge that by how far we can move a joint through its range of motion.

Or that point in the joint range of motion where we're like, that's far enough.

So let's kind of set the stage with an example here, specifically a stretching example, with the typical hamstring stretch of bending over and touching your toes.

And we'll also use some of these plastic bones to help us with this example.

This is called the os coxa, it forms part of your pelvis and then you can see the femur plugging in there.

Now when I stretch or bend forward to stretch my hamstrings, I'm going to actually hinge forward at the hip joint.

This is technically called flexion of the hip.

If I bring this a little bit closer, you can definitely see what that hinging motion looks like.

Now this area that I'm tapping with my thumb is significant because this is where the hamstrings actually attach.

For you anatomy nerds, it's called the ischial tuberosity.

A lot of people just call it the sit bone.

But again, let's say we're stretching the hamstring, we hinge forward and we get to that point where the hamstrings are like, ah, that's far enough.

And we're all likely not to be terribly happy with that limited amount of flexibility in range of motion because a lot of us might think we need the hamstring flexibility to be able to, say, successfully kick somebody in the head if necessary.

You just never know when you might need to engage ninja mode in self-defense.

But for whatever reason, we decide or choose to engage in a stretching routine for a couple of weeks or maybe a couple months and we improve that hamstring flexibility.

Now instead of maybe this being the end point in that range of motion, now because of that increased hamstring flexibility maybe I can go this far.

And you can see how that could translate to touching your toes easier, but also just the overall increased range of motion of a joint.

Now this principle of improving the flexibility of the muscle and that translating to more range of motion of the joint can be applied to the various muscle groups in their associated joints throughout the body.

For example, if we improve the flexibility of the calf muscles, that could translate to improved range of motion at the associated ankle joint.

But what is again accounting for these stopping points, that feeling of, ah, I don't want to go any further, as well as the potential changes and improvements in flexibility.

Yes, things like the muscles, tendons, and other connective tissues play a role, but as we've strongly implied, this amazing structure also plays a big role.

But real quick before I get into the brain and nervous system I want to take a second to say thank you to the sponsor of today's video Yoga Body Teachers College Since we've opened the lab We've had a ton of different yoga teachers come through and learn about the human body And you can probably imagine that we talked a great deal about the science of stretching, as well as other relevant anatomical and physiological processes.

And this is why I'm so impressed with Yoga Body, because they specialize in science-based online certification programs for yoga teachers, yoga breathing coaches, yoga trapeze teachers, and stretching coaches.

So if you're interested in starting a new fulfilling career or side job, helping people improve their health, overcome injuries, manage stress, and live their best lives longer, Yoga Body's courses might be right for you.

Since 2007, Yoga Body has certified over 23,000 teachers in 41 countries.

They are also backed by Yoga Alliance, American Council on Exercise, and even American Council on Education, making them 1 of the only schools in the world eligible for college credits.

Yoga Body has also put together a free report for you called How to Choose a Yoga Teacher Training Program, and you can access this immediately by going to yogabody.com.

We'll also include that link in the description below.

So in order for us to understand how the brain and spinal cord get involved with stretching and flexibility, we first need to see how they communicate with the actual muscles.

And if we were to zoom into the muscle tissue, specifically the meat of the muscle which is known as the muscle belly.

Embedded within the muscle belly, we would see these specialized sensory receptors called muscle spindles.

These little muscle spindles are encapsulated structures that contain these specialized muscle fibers called intrafusal fibers.

Intrafusal just refers to inside the spindle, so it's a pretty good name.

Now, these intrafusal fibers inside the capsule are also going to be wrapped with these sensory nerve endings, which will then provide information to the brain about the muscle.

But what type of information is this providing?

Muscle spindles detect and provide information about muscle length.

So let's use the biceps in this example, but again, keep in mind, this could be applied to nearly any muscle in the human body.

And again, those muscle spindles will be embedded in the belly of the muscle, and they're going to detect the length of the muscle and even changes in the length of that muscle.

And it might actually be easier to use my biceps first here.

So for example, my biceps is at a certain length right now, the muscle spindle sending information into my brain about this length.

This is a different length, new information.

It not only tells my brain the difference between, say, like, this length of the muscle versus that length of the muscle, it also tells me this versus this, How fast those length changes occur.

So what does the brain do with this information?

And of course, how does this relate to stretching and flexibility?

Well, first let's get the signal up to the brain.

And with any muscle, it's going to have to travel up a nerve.

So in this particular example, we have the biceps and there's a nerve here called the musculocutaneous nerve, but it would be a different nerve for different muscle groups.

And those signals from the muscle spindle cells would travel up this nerve and eventually get to the spinal cord, then move up the spinal cord, and get to the brain.

Once this information is in the brain, it's going to relay to 2 areas that are important for our discussion.

1 is my personal favorite structure of the brain, and that is this, which you can see here, the cerebellum.

Now, besides looking quite amazing, it also participates in some amazing functions like smoothing out and coordinating skeletal muscle contractions.

And it makes sense that it's receiving that information from the muscle spindles about length changes so that it can make the appropriate adjustments to muscle contractions and therefore coordination.

The other area of the brain that this information is relayed to is an area called the somatosensory cortex.

The somatosensory cortex is located in the parietal lobe, specifically in this fold, or gyrus, that I'm probing here, all the way up to the midline of the brain.

Now, the somatosensory cortex receives all sorts of different somatic senses from the body.

Things like temperature, touch, pressure, pain, and of course, information from the muscle spindles about those muscle length changes.

And what this does for you is creates a conscious awareness about body position and even sensation about when you're tugging or pulling on a muscle when you're stretching.

Now this conscious awareness about body position, this understanding of where your limbs are in three-dimensional space, and even awareness about trunk or torso position, is referred to as proprioception, understanding where your body parts are in three-dimensional space.

And that's why sometimes the muscle spindles are even referred to as proprioceptors.

They're not the only proprioceptors in the body.

We can talk about some of the others in a later video.

But I like to give 2 examples to help illustrate why proprioception is so important.

And 1 of those examples definitely relates to stretching.

The first example that I kind of want you to think of is imagine if your eyes, the input from your eyes, was the only thing that brought you information about where your body parts were in three-dimensional space.

Like, yes, you can look at your arms, see where it is, look at your torso and other body parts and your eyes bring that information in.

But Imagine the problems that would arise if that was the only information that you got about your body position.

Because if we all held out our hand in front of us like this, when was the last time you closed your eyes and this happened?

Now I apologize if I scared anybody with that.

I do that all the time in class to make sure people are awake and paying attention.

But that crazy example doesn't really happen, right?

Because we would be a hot mess in a dark room or whenever we closed our eyes if we didn't have proprioceptive input coming from the muscle spindles and other sources.

So next time you turn out the lights or close your eyes to maybe make out with a significant other, be grateful that you have proprioceptive input to be aware of where your body parts are going, and also be grateful that the somatosensory cortex can also make sense and process sensations like tactile stimulation so you can also be aware of someone else's body parts.

And the second example as to why proprioceptive input is so important, and I promise this is finally gonna get us to how this all relates to stretching and flexibility.

But the second example has to do with all of this information that's coming into the brain from the muscle spindles and even other proprioceptive sources.

The brain's gonna get this information and be able to process it, and actually will be able to send signals back to the muscle spindles and the skeletal muscles throughout the body.

What it can do is adjust the sensitivity of the muscle spindles, as well as adjust the tone of the muscles throughout the body.

So your skeletal muscles are never fully relaxed.

There's always some level of tone or some level of contraction that's being stimulated by the nervous system.

And because the brain can take this information and modulate it, it can make some really cool and important adjustments that I just mentioned that'll have to do with stretching and flexibility in just a second.

Our brain and nervous system modulates all sorts of different sensory information.

And so if I said to you, you're probably wearing underwear and or pants.

If you're not wearing any of those, how you consume your online content is your business, but I'm assuming most of you are probably wearing underwear and or pants.

Now if I said to you, can you feel your underwear and pants?

Up to this point you probably weren't aware of that sensation, but now you can probably feel them around your legs and your nether regions.

And this is just another example of how your nervous system modulates and prioritizes different sensory input.

When you're first putting on the underwear and the pants, your nervous system's like, okay, I can feel the sensation.

And when your brain's like, okay, we're good, underwear and pants are safe, it'll modulate or kind of deprioritize or lower the priority of that sensation to the point where you're kind of not really worrying about it in your conscious thought.

This also can be applied to the proprioceptive input coming from the muscle spindles.

When you first change a position, your muscle spindles will fire up a little bit and you're aware of the change in position, but Once you kind of settle into that position, as long as it's safe and not compromising you, your nervous system again is going to kind of modulate that or put that at a lower priority.

But, if I were to come up to you and grab your arm and quickly jerk it in 1 direction, your muscle spindles would really be fired up by that.

And they would likely start to protect them by initiating this thing called the stretch reflex.

And what I mean by protecting them is that this information or this stretch reflex that's coming from the muscle spindles is going to protect the skeletal muscles from being stretched too far.

Now I often give my students this textbook definition of the stretch reflex and it's this, when a muscle is stretched too far or too fast, it's going to contract and the antagonistic muscle will relax.

And the classic example of the stretch reflex that many of us have probably experienced occurred likely in the doctor's office.

When your leg was dangling off the table and the doctor comes up with that little hammer and quickly taps your patellar tendon.

Some people call it the patellar ligament.

I prefer patellar tendon because it's just a continuation of the quadriceps tendon, but we don't need to go down that road.

So the doctor quickly taps that patellar tendon.

That will cause a quick stretch of the quad muscles.

And the muscle spindles are like, nope, that's too quickly.

So the signal goes right into the spinal cord.

Now up to this point, we've talked a lot about the muscle spindles sending information up to the brain.

But in the case of the stretch reflex, that signal's gonna go right into the spinal cord and right back out through a motor neuron to engage the muscle to contract.

Because the opposite of a stretch is a muscle contraction and that will protect the muscle from being stretched too quickly.

At the same time, another motor signal's gonna go out of the spinal cord to the opposing or antagonistic muscle, and in this case, this is the hamstring, because you wouldn't want the hamstring to contract because that would create this tug-of-war situation and the stretch reflex wouldn't work properly.

Now, some sort of a signal will make it to the brain.

It's kind of a little bit delayed or you could think of it as a little bit delayed Because we do become aware that the doctor tapped us on that patellar tendon But the stretch reflex the main signal again goes right into the spinal cord and right out Because it does not want to wait for the brain's permission in order to protect the muscle.

So let's apply this information to the example that we used at the beginning of the video of stretching the hamstrings.

And remember, we use these plastic bones to help us with this.

And as we hinge forward and stretch the hamstring, we eventually get to that point where the hamstrings are like, that's far enough, we don't want to stretch anymore.

And we need to acknowledge like we did at the beginning that the nature or the elasticity of the muscles, tendons and surrounding connective tissues do matter and apply to this.

But as we've seen from this video, the nervous system also matters.

And so when we hinge forward, the idea is that as that hamstring is lengthening and lengthening, the muscle spindles are sending that information to the brain about those length changes.

And eventually we get to that point where the brain might say, you know, that's far enough.

I don't really trust you to go any further.

And it sends a signal back to the hamstring to change or increase the tone, almost like it's a slight increase in contraction to stop that stretched hamstring from going any further.

Now, if we were to quickly go into that stretch, almost bounce into it, we might actually stimulate that stronger stretch reflex, and you might feel a quicker resistance, or almost like this pullback that's a little more forceful than you would if you were to go more passively and slowly into that stretch.

But let's go to this idea again of doing stretching consistently for weeks or months.

The idea is that the nervous system will adjust.

And instead of having this stop point here, that stopping point will be later in the range of motion.

Almost as if the brain, through that consistent stretching routine is like, okay, you've been stretching consistently for a few weeks, for a few months.

I'm going to adjust the sensitivity of those muscle spindles and even where in that range of motion, I'm going to increase the tone to stop you from stretching any further.

So instead of stop having that stop point here, it's almost as if the nervous system allows you to have that stop point a little bit later, which is really fascinating to think about and how you can potentially increase your flexibility and therefore range of motion neurologically.

And so let's wrap this up with a few housekeeping items.

1, and like many things with the human body, we still need more information about how exactly the brain and nervous system can account for improvements in flexibility.

And even comparing that, like we alluded to earlier, the changes or potential changes in the soft tissues like the muscles, tendons, and ligaments.

How are these interacting together and how much does 1 versus the other account for improvements in flexibility?

It's definitely gonna be interesting as we gain more knowledge in this area.

And the second housekeeping item we need to wrap up with is the type of stretching.

In the examples we were using in this video, we were referring to this static passive stretching where you get to a certain point in the stretch and then hold for an extended period of time.

There are definitely different types of stretching like dynamic, ballistic, PNF to name a few, and they definitely have their place.

But if our goal is to have long-term improvements and flexibility, static stretching tends to be the best supported for achieving that goal.

And a routine that tends to work the best would be stretching the muscle groups that you're looking to improve the flexibility in about 5 to 6 days a week for 30 to 60 seconds for like 2 sets.

You can think of like 2 sets of 30 seconds.

So if you're gonna stretch your hamstrings, you could stretch into that, get to the point where you feel the stretch, hold for at least 30 seconds, and then come back up and rest for a second.

You could even stretch an antagonistic or an opposing muscle in between, and then go back in for a second time for 30 seconds.

So again, kind of like 2 sets of 30 seconds for each muscle group, 5 to 6 days a week.

And lastly, if you've made it this far, I appreciate it because we definitely had to go through a bit of information before we actually got to the stretching part.

But hopefully along the way, you'll learn some really cool things about the brain, the nervous system, and how it interacts with the muscles.

Another thing that I'm really excited about is I'm about to head to Florida to do a YouTube collaboration with another creator, and 1 of the things we're gonna talk about is yes, it's definitely important to have flexibility, good range of motion, but on the other hand, it's also important to train your muscles to be strong in those lengthened positions.

So it's gonna be a lot of fun to come together with this video, and I'm excited to show you it when I get back.

But, thanks again for watching this video.

If you're interested in checking out Yoga Body, we have that link in the description below.

If you feel the need, like and subscribe.

We love reading through the comments, even though we can't respond to all of them, we definitely read through as many as we can and like your guys's video ideas and your feedback.

And of course, we'll see in the next video.

See all Institute of Human Anatomy transcripts on Youtube

How Stretching REALLY Works