Improve Flexibility with Research-Supported Stretching Protocols

1. 0:00 – 2:57

   Flexibility & Stretching

   1. AHAndrew Huberman0:00

      (Instrumental music) Welcome to the Huberman Lab Podcast, where we discuss science and science-based tools for everyday life. 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. Flexibility and stretching are topics that I believe do not receive nearly as much attention as they deserve. For most people, the topics of flexibility and stretching bring to mind things like yoga, injury prevention, or maybe even contortionism. But it turns out that flexibility and stretching are features that are built into our basic body plan. Young children, young animals, and adults, and indeed older children and animals, all stretch and all have some degree of flexibility. It turns out that having flexibility and our ability to stretch and the interaction between stretching and f- flexibility are fundamental to how we move, our ability to learn new movements, indeed also to prevent injury or repair injuries, and to offsetting and reducing inflammation throughout the body. In fact, today I'm going to share with you a remarkable set of studies that show that stretching can actually adjust things like tumor growth. This is work that was done by one of the major directors of the National Institutes of Health. So, today's discussion will start with a description of the mechanisms, literally the cells and the connections from your nervous system that mediate flexibility and stretching. And I promise that I'll make that information accessible to you, whether or not you have a biology background or not. Then, with that information in hand, I'm going to present to you what the scientific literature says about the best times and ways to stretch, everything right down to the detail of how long to hold a stretch, whether or not to hold a stretch at all, because it turns out there are multiple kinds of stretching. So, you can imagine, you have stretches where you hold the stretch for a very long time and use as little momentum as possible, and then there's also what's called dynamic and ballistic stretching, where you're literally swinging your limbs, trying to increase the range of motion. I will explain the science and application of flexibility and stretching in the context of sports performance, whether or not you're engaging in cardiovascular exercise or resistance exercise or both, whether or not you're a competitive athlete or simply a recreational exerciser, as I am, whether or not you are trying to increase your range of motion and flexibility for longevity purposes, or whether or not you're trying to do it in order to access different parts of your nervous system. 'Cause we'll soon learn today that your ability to improve flexibility and indeed to engage in specific stretching exercises can actually be used to powerfully modulate your ability to tolerate pain, both emotional and physical pain. So, this thing that we call flexibility and stretching is actually a vast landscape. We're going to simplify and organize all that for you today. And by the end of today's episode, you're going to have a number of simple, easy-to-apply tools that are grounded in the best scientific research that you can apply for your

2. 2:57 – 7:22

   Thesis, InsideTracker, Eight Sleep

   1. AHAndrew Huberman2:57

      specific goals. Before we begin, I'd like to emphasize that this podcast is separate from my teaching and research roles at Stanford. It is, however, part of my desire and effort to bring zero-cost-to-consumer information about science and science-related tools to the general public. In keeping with that theme, I'd like to thank the sponsors of today's podcast. Our first sponsor is Thesis. Thesis makes custom nootropics that are designed to get your brain and body into the optimal state for the cognitive and physical things that you need to perform at the highest level. I have to confess, in fact I've said it many times before, I am not a fan of the word nootropics because it means smart drugs. And frankly, as a neuroscientist, I'd be remiss if I didn't acknowledge that there's really no circuit in your brain for being smart. You have neural circuits in your brain that are designed to get you to focus very well or to task-switch very well or to be creative. Thesis understands this, and as a consequence they've designed nootropics that are tailored to your specific needs in the cognitive and physical realm. What I mean by that is if you go to the Thesis site, you fill out a short quiz, and they'll give you the opportunity to try a small kit of different nootropics with different ingredients. You have the opportunity to try several different blends over the course of the month and discover which nootropics work best for your unique brain chemistry and genetics. I've been using Thesis for about eight and a half months now, and I can confidently say that their nootropics have been a game changer. To get your own personalized nootropic starter kit, you can go online to takethesis.com/huberman. There you'll find that three-minute quiz, and Thesis will send you four different formulas to try in your first month. That's takethesis.com/huberman and use the code Huberman at checkout to get 10% off your first box. Today's episode is also brought to us by InsideTracker. InsideTracker is a personalized nutrition platform that analyzes data from your blood and DNA to help you better understand your body and help you reach your health goals. I've long been a believer in getting regular blood work done, for the simple reason that many of the factors that impact your immediate and long-term health can only be analyzed from a quality blood test. One issue with a lot of blood tests and DNA tests out there is that you get information back about hormone levels, metabolic factors, et cetera, but you don't know what to do with that information. InsideTracker has a very easy-to-use personalized platform that lets you look at those numbers and then you can literally move your cursor over those numbers and there are little pop-up windows that will tell you the things that you can do in terms of lifestyle, so exercise and nutrition, supplementation, and so on to bring those numbers into the ranges that are optimal for you. So, it really takes all the guesswork out of what to do with that blood work and DNA information. If you'd like to try InsideTracker, you can visit insidetracker.com/huberman to get 20% off any of InsideTracker's plans. Just use the code Huberman at checkout. That's insidetracker.com/huberman to get 20% off any of InsideTracker's plans. Again, just use the code Huberman at checkout. Today's episode is also brought to us by Eight Sleep. Eight Sleep makes smart mattress covers that have cooling, heating, and sleep tracking capacity. And indeed you can dial in, you can literally program the temperature of your sleeping environment from the time you go to sleep until the time you wake up in the morning. This turns out to be immensely powerful because, as I've talked about on the podcast before, in order to fall asleep and stay deeply asleep throughout the night, your body has to drop by about one to three degrees, and waking up in the morning actually involves a warming up of your body temperature.For many people, they just can't precisely control their sleep environment well enough in order for all that to go well. I was one such person. So, for a long time, I'd fall asleep pretty easily, but then I'd wake up in the middle of the night. I tended to run warm, but then sometimes I'd feel really tired in the morning as if I couldn't wake up. I started sleeping on an Eight Sleep mattress cover. I programmed it so that the temperature would be rather cool in the early part of the evening when I would get into bed, and then would drop into the deeper phases of the night when I was entering deep sleep, and then rapid eye movement sleep, and then would warm towards morning. It would help me wake up quickly. And as a consequence, I'm sleeping throughout the night now and I'm waking up feeling completely refreshed. If you'd like to try an Eight Sleep mattress cover, you can go to eightsleep.com/huberman to check out the Pro Pod cover and save $150 at checkout. Eight Sleep currently ships within the USA, Canada, and the United Kingdom. Again, that's eightsleep.com/huberman to save $150 at

3. 7:22 – 9:23

   Innate Flexibility

   1. AHAndrew Huberman7:22

      checkout. Let's talk about flexibility and stretching. Before we talk about the practices of flexibility and stretching, I'd like to just highlight some of the features that are already built into your nervous system and into your body that allow you to be flexible. Some of us feel tighter than others, sometimes in specific limbs or areas of our body. Some people feel really loose and limber. Some people even have what's called a hyperflexibility. I, for instance, have a relative that can take her fingers and bend them back to the point where they touch her wrist (laughs) and it always, uh, you know, makes me cringe a little bit, but she can do that without any pain. She seems to have some hyperflexibility in her joints. I do not have that feature. Some of you may find that you are more flexible than others naturally, and some of you might be thinking you don't need to build in additional flexibility. Well, I think by the end of today's episode, you'll realize that almost all of us can benefit from having some sort of understanding about flexibility and having some stretching protocol that we incorporate into our life, if not just for physical performance reasons and for postural reasons, then also for cognitive and mental reasons. And I'll be sure to clarify what all of that means. Right now, I'd like to take a moment and just highlight the flexibility that you already have. For instance, if you were to move your arm behind your torso a little bit and then sort of let go or stop exerting any effort in doing that, you would find that the limb would return more or less to a position next to your torso, at least I would hope so. Now, why is that? Well, it turns out that there are aspects of your nervous system, aspects of your skeletal system, aspects of your muscles, and aspects of the connective tissue that binds all of that together that try and restore a particular order or position to your limbs and your limbs relative to one another. So, that reflects a very specific set of processes that it turns out are the same set of processes that you use when you are trying to enhance flexibility and stretching.

4. 9:23 – 17:51

   Movement: Nervous System, Connective Tissue & Muscle; Range of Motion

   1. AHAndrew Huberman9:24

      So, I'd like to just take a moment and review the basic elements of nervous system, muscle, connective tissue, and skeletal tissue, bone, that allow for flexibility and stretching. And here we can point to two major mechanisms by which your nervous system, neurons, meaning nerve cells, communicate with muscles and those muscles communicate back to your nervous system to make sure that your limbs don't stretch too far, they don't move too far such that you get injured. And in addition to that, mechanisms that ensure that you don't overload your muscles too much with weight, or with tension, or with effort and damage them that way, because it turns out that the second security mechanism of making sure that you don't overload muscles can be leveraged toward increasing your flexibility almost immediately. That's right. There are protocols and tools that I'll share with you that are going to allow you to vastly improve your flexibility over time, but there are also mechanisms that allow you to quite significantly increase your degree of flexibility in a very short period of time, i- within just a few seconds. So, let's establish some of the basic biological mechanisms. Anytime we talk about biology or physiology, we're going to talk about structure, meaning the cells and their connections, and functions, what they do. They're just a few names to understand. You do not have to memorize these names. 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 weaved together and braided together in complicated ways. Some of you may have heard of fascia. We're going to talk a little bit about fascia today, although it's such an interesting tissue that it's really deserving of its own episode. Fascial tissue, we're going to talk about some of the stuff that surrounds muscles that really gives you your shape and holds everything together and allows for flexibility to occur. 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. To be precise, they are lower motor neurons 'cause they're in your spinal cord. We call them lower to distinguish them from the motor neurons that are in your brain up in your skull. Those lower motor neurons, hereafter I'll just refer to them as motor neurons. If I want to talk about the other kind of motor neurons, I'll say upper motor neurons. So, if I say motor neurons, I just mean the ones in your spinal cord. Those motor neurons send a little wire or set of wires out to your muscles, and that creates what's called a neuromuscular junction, which just means that the neurons meet the muscles at a particular place. Those neurons release a chemical. That chemical is called acetylcholine.Some of you may have heard about acetylcholine before. Acetylcholine also exists in your brain and does other things in your brain, mainly it's involved in focus and attention. But at the neuromuscular junction, 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, and for instance, if you're bringing your wrist closer to your shoulder, that biceps muscle is contracting, it's getting shorter. I mean, in reality, it hasn't gotten shorter overall, it's just temporarily shorter, of course. All of that is controlled by neurons, and it's those motor neurons from the spinal cord that are really responsible for the major movement of your limbs by way of causing contraction of specific muscles at specific times. So, the key thing to take away is that nerve controls the contraction of muscles. 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. The sensory neurons exist in a different part of the spinal cord, and they send a little wire or set of wires into the muscles, and there's a particular kind of sensory neuron that comes out of your spinal cord and into your muscles, which are called spindle neurons. They create, or they actually wrap around muscle fibers, kind of corkscrew around them and give kind of a spring-like appearance. For you aficionados out there, these are intrafusal connections or neurons. Intrafusal means within the muscle, but you really don't need to know that unless you're really curious about it, or you're going to become a neuroscientist, or you're in medical school or something. 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, much in the same way that you have neurons in your eye that sense light in your external environment, you have neurons in your ear that sense sound waves in your external environment, you have neurons in your spinal cord that are sensory neurons that are sensing the amount of stretch in the muscles. What happens is if a given muscle is stretching really far, those sensory neurons, those spindles within the muscle, will activate and will send a electrical potential, literally a bit of electricity along that wire's length into the spinal cord, and then within the spinal cord, that sensory neuron communicates through a series of intermediate steps, but to the motor neuron and make sure that that motor neuron contracts. Now, why would that be useful? Well, what this does is it creates a situation where if a muscle is s- 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. Now, what determines whether or not a range of motion is, quote unquote, safe or not is dictated by a number of things. It's dictated by things that are happening in this kind of loop of neural connections in the spinal cord and muscle. It's also determined by what's going on in your head, literally in your mind cognitively about whether or not the movement of that limb, its increasing range of motion is good for you, whether or not you're doing it deliberately, whether or not it's bad for you. And then there are also some basic safety mechanisms that are put in there that really try and restrict our limb range of motion. 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, of which there are a bunch of different varieties, in this case what we're calling the 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 that brings the limb back into a safe range of motion. Okay? So, this process is very fast. It was designed to keep your body together and safe. It's designed to make sure that you don't, you know, take your arm and swing it behind your torso and it just goes all the way back to the middle of your back. I mean, unless you're a contortionist or you've trained that kind of level of flexibility, that would be terrible because it could provide a lot of damage to the muscles and to the connective tissue and so forth. 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

5. 17:51 – 20:20

   Golgi Tendon Organs (GTOs) & Load Sensing Mechanisms

   1. AHAndrew Huberman17:51

      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, this other mechanism has a lot of the same features as the one I just described, but it has less to do with stretch, in fact, it doesn't have to do with stretch, as much as it 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, and you start to try and heave that weight off the ground. 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, and it could tear ligaments. Well, you have a safety mechanism in place. It's these Golgi tendon organs, these GTOs as they're called. They get activated and shut down the motor neurons and make it impossible for those muscles to contract. Okay? So, on the one hand, we have a mechanism that senses stretch and can figure out when stretch is excessive, and when the system detects that stretch is excessive, it activates the contraction of muscles. And then we have a second mechanism that senses loads, and when tension or loads is deemed excessive by these circuits... And remember, these circuits don't have a mind. They don't go, "Oh, this is excessive." They just sense loads, and when those loads exceed a certain threshold, well, then those GTOs, those Golgi tendon organs, send signals into the spinal cord that shut down your motor neurons' ability to contract muscle so that you no longer can lift that heavy load. So, both of these are protective mechanisms, but both of these can be leveraged in a very logical way and in a very safe way in order to increase your limb range of motion.

6. 20:20 – 22:38

   Decreased Flexibility & Aging

   1. AHAndrew Huberman20:20

      So, there are a couple of things I want to point out before going a little bit further into how your nervous system controls flexibility and stretching, and those key points are the following. There are now dozens, if not hundreds, of studies that show that a dedicated stretching practice can improve limb range of motion. Now, for many of you listening, you're probably saying, "Duh," but I think it's important to point that out, that a dedicated stretching practice can increase limb range of motion, and as you'll soon learn, there are specific mechanisms that can explain that effect. The second point is one of longevity, and when I say longevity, I don't necessarily mean late-stage aging. We all undergo a decrease in limb range of motion unless we do something to offset that decrease, and the current numbers vary from study to study, but if you look en masse, you look at all of those studies, and what you basically find is that we start to experience a decrease in flexibility from about age 20 until about age 49. That's pretty dramatic, and then, of course, it will continue after age 49. But basically, it's a 10% decrease every 10 years. So, we could say it's a 1% decrease per year, although it's not necessarily linear. What do I mean by that? Well, it's not necessarily that on your 21st birthday, you are 1% less flexible than you were on your 20th birthday, and it decreases by 1% per year. Some of these changes can be non-linear. So, you can imagine the person who's doing just fine in terms of flexibility between 20 and 30, and then, you know, they get to 32, and suddenly they've lost 5% of their flexibility. Now, of course, there will be a ton of lifestyle factors. If you're a regular practitioner of yoga, if you have a dedicated stretching practice, if you're doing other things to improve your muscle contractibility, so you're doing resistance training, it turns out can actually indirectly improve flexibility. There are a number of different factors, but the key point is that maintaining some degree of flexibility and maybe even enhancing range of motion and flexibility is of immense benefit for offsetting injury provided it's not pushed too far. There are a number of people who have pushed their limb range of motion so far that they experience all sorts of injuries, both acute and chronic injuries. Today, we'll also talk about how to avoid those scenarios.

7. 22:38 – 30:02

   Insula, Body Discomfort & Choice

   1. AHAndrew Huberman22:38

      Okay, so we've established that there are mechanisms within the spinal cord, muscles, and connective tissue. Those, remember, it's the motor neurons, the spindles, the GTOs, and of course, the muscles themselves and connective tissue, tendons, but also other forms of connective tissue, that establish whether or not a limb is going to stay within a particular range of motion or not and whether or not a limb is going to be allowed by the nervous system to pursue or handle a given load, a given tension. 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 call 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. That's actually a, you know, kind of feeling, "Mm, I feel great, I feel sated, I feel relaxed." Thi- those are all different forms of interoception. 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, and to some extent, other things that are arriving from the external world and combining with what's going on internally and making sense of that o- of all that, or at least routing that information elsewhere in your nervous system to make decision. Like, if you smell something good, to approach it, or if you smell something bad, to avoid it. The front of the insula is really doing all of that kind of stuff, along with other brain areas. 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 and how is the movement that you happen to be doing combining with your internal state to allow you to feel, as I always like to say, the nervous system mainly batches things into yum, like, "Oh, this is really good for me." Yuck, "This is really bad for me, and I need to stop." Or meh, "This is kind of neutral." Okay, so this isn't about food, but we could say for most stimuli, most senses, whether or not they're senses of things internally or externally, our nervous system is trying to make decisions about what to do with that information. And so 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, et cetera. 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." And then meh, sort of, "It doesn't really matter. I can just kind of stay right here or whatnot." Yum, yuck, and meh. Well, in your posterior insula, you have a very interesting population of very large neurons. These are exceptionally nar- large neurons called von Economo neurons. These are v- neurons that are again unbeknownst to most neuroscientists, and they seem uniquely enriched in humans. Chimpanzees have them and some other large animals have them. So they're found in whales, chimpanzees, elephants, and in humans. But even though we are much smaller than most whales, and even though we are much smaller than most elephants, I mean, remember there are baby elephants. As far as I know, they haven't bred up, um, like, like mini elephants yet. They seem to have a- a teacup version of pretty much every dog breed. Um, you can look that up. I don't, I certainly have mixed feelings about this notion of, of trying to downsize everything to the point where you could kind of like the pocket size bulldog I think will, someday will arrive. I'm not a fan of that kind of downsizing of, of different breeds. But because there aren't teacup elephants and teacup gorillas and teacup chimpanzees and so forth, most all of those other species are larger than us. They have these von Economo neurons, and we have these von Economo neurons. But we have in upwards of 80,000 of these things in our posterior insula. These other species tend to have somewhere in the range of 1,000 to maybe 10,000 or so. 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 pacif- specific goal. This knowledge turns out to be very important to keep in mind, because as we migrate this conversation toward the things that we can do to enhance flexibility and stretching, you'll soon learn that there are moments within a stretching protocol where you have the opportunity to either override pain and discomfort, to kind of relax through it or push through it, right? There's a decision fork in the road there, and I'll tell you which fork in the road to take. Or to say, "Uh-uh, I'm not going to do that, I'm going to allow these natural reflexes of the spindle to kick in and just essentially stop me from stretching if a given limb isn't designed or shouldn't be stretched that far." So, I'd like you to keep these von Economo neurons in mind. I should mention they're named von Economo because the guy, Constantine von Economo that discovered them at the end of the 1800s, early 1900s decided to name them after himself, as many scientists do, or certainly the neurologists and, and physicians are famous for naming things after themselves. These von Economo neurons turn out to be very important to keep in mind as we embark on our exploration of what sorts of stretching practices can be best applied to increase flexibility, because whether or not you undertake a mild, moderate, or intense flexibility training, you will no doubt encounter a scenario at some point where you will have to ask yourself, "Do I, quote unquote, relax into this stretch? Or do I try and push through just a little bit of discomfort?" And I'll explain how to gauge that decision in a very specific and ideally safe way, and I'll give you some tools that will allow you to make that decision in the way that best preserves the integrity of those neural circuits that I described earlier and can keep you safe. These von Economo neurons sit in the exact position that one would want to be able to evaluate what's going on in the body, in particular what's going on in terms of limb movements, how that relates to our feelings of discomfort. And then

8. 30:02 – 42:00

   von Economo Neurons, Parasympathetic Activation & Relaxation

   1. AHAndrew Huberman30:02

      there's the other 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 and 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 are 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 musculospinal junction. And in that way, gently, subtly override the reflex that would otherwise cause us to contract those muscles back. The reason that's possible is because your brain has those other kinds of motor neurons, the upper motor neurons that can both direct, meaning control, and can override lower motor neurons. 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. (smacks lips) 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. In fact, humans without any neocortex, literally, that who are decerebrate, or an animal that doesn't have, when I say decerebrate, I mean lack of cerebral cortex, they can perform that because it's all controlled by circuits that are basically below the brain and in the spinal cord. There's a little bit of activation of circuits in the kind of deeper parts of the brain, but basically, you don't need to think or decide in order to do that. However, if your life depended on walking across some sharp objects, let's say, um, let's make it a little less dramatic so it's not like the Die Hard movie or something where he has 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 von 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 von Economo neurons sit at a very important junction within the brain. They pay attention to what's going on in your body, pain, pleasure, et cetera. 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. Before we go any further, I want to give you a practical tool that you can, of course, use, but that will also give you insight and experience into your muscle spindle spinal cord circuit mechanisms. So, what I'd like you to do is if you're in a proper place to do this, you're going to stand with legs straight, meaning knees not bent, and you're going to try and touch your toes, or for some of you, that's going to be very easy, and you might even be able to put your hands f- flat on the floor. I don't have that kind of flexibility. It's pretty easy for me to touch my toes. I don't care if you round your back or not, although ideally, I would say don't round your back, not because it's bad to do so necessarily, but just to try and keep this, uh, the same from trial to trial, as it were. So, try and get a sense of what your range of motion is in terms of bending over, um, at the waist while maintaining a flat back and trying to touch your toes or even touch the floor. Maybe you, again, you can even go hands flat to the floor, maybe even far out in front of you. Okay. Now, what I'd like you to do is stand back up and I'd like you to contract your quadriceps as hard as you possibly can for about 5 to 15 seconds. Let's say 10 seconds just to keep things more or less normalized. This obviously is not (laughs) a super controlled experiment. So, to contract your quadriceps, for those of you who don't know, you're going to extend your lower limb out. So, this would be like kicking, although don't do it too quickly. You're going to kick out your, uh, your foot. Um, you should feel your quadriceps contract on the top of your thighs, and you're going to try and consciously contract them as hard as you can. Okay? Typically, uh, if you want to point your toe back towards your near shin, that's also going to help somewhat to contract even harder and harder. Okay? So, do that for about 10 seconds. A lot of you will do this just while standing. Contract, contract, contract. Okay, then release it. And then now, go ahead and repeat that stretch where you're trying to touch your toes or touch the floor. So, this is, again, relying more or less on hamstring flexibility among other things. Okay? What most of you will find is that you have an immediate increase in hamstring flexibility or your range of motion has increased.If you didn't experience that, then I would encourage you to try and contract your quadriceps harder and longer, so maybe 20 or 30 seconds, and then try this so-called experiment again. (inhales) Why would contracting your quadriceps allow your hamstring flexibility to suddenly increase? Well, the way that our muscles are organized is such that we have muscles that are antagonistic to one another. So, our quadriceps and our hamstrings work in sort of a push-pull fashion, if you will. They can antagonize one another. So when you move your heel towards your glutes, you are using your hamstring. The hamstring obviously also does other things related to hip movement. And when you lift your knee or when e- you extend your foot and contract your quadriceps, you are essentially relaxing the hamstrings. Now, of course, most movements involve both quadricep and hamstring in synchrony, and that synchrony is really an elegant one, but here we're more or less isolating the quadriceps from the hamstrings, at least to the extent that it can leverage these spindle stretch mechanisms. So, what happens is when you contract your quadriceps hard, you are relaxing or releasing some of the stretch that's occurring in those intrafusal spindle sensory fibers going into your spinal cord. And as a consequence, you're able then to stretch your hamstrings further, or we can be more accurate and say that your range of motion about the hamstring and its related joints is greater when you aren't engaging that spindle reflex which would cause the hamstrings to contract. Okay? So if you are somebody who has tight hamstrings, there could be a variety of reasons for that, but part of the reason is likely to be neural, and you can release that neural spindle reflex by contracting the opposite antagonistic muscle, which in this case is the quadriceps. The same thing i- is true and can be leveraged for stretching other muscles. So for instance, if you're going to do a triceps stretch, the typical kind of overhead where you grab your elbow and, you know, uh, move it toward the midline of your body with the other ha- uh, using your opposite hand, well, you can do that and then I would suggest trying to flex your bicep, contract your bicep that is, while doing that. And for most people you'll notice a increase in the triceps range of motion or ability to kind of lean into, or to relax into, or to push that stress, stretch, excuse me, a little bit further. Now, for you physios out there, and for those of you that have backgrounds in kinesiology, I want to acknowledge, of course, there are other mechanisms that are coming into play. There are actually neural connections within the joints themselves that are providing proprioceptive feedback, et cetera, et cetera, but this is simply to illustrate that part of our range of motion is determined by these spindle mechanisms that I spent some time, uh, focusing on earlier. And indeed, this approach can be leveraged toward creating increased limb range of motion, not just for the hamstrings, but for your quadriceps. So for instance, if you have tight quadriceps, you can do the opposite. You can contract your hamstring very intensely for, let's say, 10 seconds or 20 seconds or 30 seconds, so that would take some conscious effort of bringing your heel up towards your glutes. Um, you could do that in a way that you're really trying to contract those muscles hard. You'd have to use some deliberate hamstring activation there, meaning you have to use those upper motor neurons and the other aspects of your, your upper brain power as it were, to try and really contract your hamstrings as intensely as possible. Then you would relax that, and then you would do your quadriceps stretch again. And if you did a pre-hamstring contraction measurement of your quadriceps flexibility and then you did a post-hamstring contraction measure of your quadriceps flexibility, almost certainly you would find that that flexibility had increased. Now, of course, the muscle really didn't change much. The tendons didn't change much. What changed was the patterns of neural activation that were restricting you from, in the first case, s- stretching your hamstring or having a, to be more accurate we should say, to having a certain range of motion about the hamstring and its related joints, and those brake mechanisms were removed. And of course then when you contract your hamstring, you're removing some of the neural brakes, the spindle acting as a brake and inhibiting that quadriceps range of motion. Okay? So, you can imagine this, and in fact you can apply this for any number of different muscles. The larger muscles and the sort of biceps, triceps, and, uh, hamstrings, quadriceps th- are sort of the simplest place to think about this and to apply it, but in theory, and indeed in practice, it really works for all the various muscle groups. It's just sometimes harder to access these so-called antagonistic muscle groups.

9. 42:00 – 47:16

   Muscle Anatomy & Cellular ‘Lengthening,’ Range of Motion

   1. AHAndrew Huberman42:00

      Now, we should take a moment and just discuss what actually happens as we get more flexible in the short-term and long-term. I just mentioned what happens in the short-term. Clearly, those don't involve lengthening of the muscles. It's not like the muscles slide along the bones or that the tendons really stretch out that much more than they had prior to that kind of, uh, you know, exercise. But it is the case that if people stretch consistently over a given period of several weeks or more, that there are changes in the muscles. This gets a little bit tricky in terms of nomenclature, and I just want to highlight that because I think that a number of people, um, get frustrated, uh, and confused, in fact, when we talk about muscles getting longer. You know, the- the whole concept of a muscle getting longer isn't really in keeping with reality, but there are elements within the muscles that can change their conformation. So, to get a little bit detailed here, and we won't spend too much time on this, but I just want to acknowledge this for those of you that are interested in neuromuscular physiology and how it relates to flexibility. You know, you have your muscle fibers and then you have your so-called myofibrils. So, you can imagine kind of a- a- a single fiber. Um, that fiber of course will get input from those motor neurons. And then within those fibers you have what are called sarcomeres. And you can kind of think about sarcomeres as little segments, kind of like the segments of bamboo. If you ever look at bamboo, it's not just one big stalk. It's got those little out-pouchings along the way.... that, um, kind of break up the- what would be just one big stalk of bamboo into different segments, but they're all connected. The sarcomeres are somewhat like that. And within the sarcomeres, you have a couple of different components. One thing is called myosin, which is like a thick layer, and then the other is actin. And those are interdigitated, as we say. They're kind of connected to one another, kind of like if you were to put your, your fingers together from your two hands. Um, if you were going to ge- put your fingers in between one another, that's interdigitated. Literally interdigitated in this case, so pun intended. (smacks lips) And the myosin and actin kind of move relative to one another, and they have a lot to do with your ability to contract muscles. When we stretch muscles, when we go through a stretching practice, there are a number of things that change, some neural, some related directly to connective tissue. But also, it appears, from really nice work mainly done from McGill University, I'll provide a link to a couple of these studies if you want to dig in- there deep- more deeply, that change the conformation, the relative size and spacing of some of these things like sarcomeres and the way that myosin and actin kind of work together. But we don't want to think of muscles as lengthening. We can, however, think about the resting state of a muscle being slightly different or indeed very different than the resting state of a muscle of somebody or of a limb that has not undergone regular flexibility training. So, that's as much time as I want to spend on that, because we could spend an entire hour getting right down into the details. But I do want to emphasize, however, that muscles have different parts. They have fibers. They have sarcomeres. They have myosin. They have actin. But the idea of making our muscles longer, that reflects a number of processes that occur basically within an existing muscle length. Our- the length of our muscle bellies and where our insertions are, uh, relative to our connective tissue in our limbs is genetically determined, right? Some people have, for instance, a bicep that goes all the way from the crook of their elbow up to their shoulder, right? Um, and some people can, you know, if they were to put their arm at a 90-degree angle, could put two or three fingers between their bicep and their elbow. They have a, we can say, a shorter bicep, relatively shorter. Now, the reason I mention these highly detailed cellular mechanisms is because as we start to embark on different protocols for using stretching to increase flexibility and range of motion, we need to ask ourselves, what is preventing our ability to extend range of motion? Is it the spindle, right? Is it because the muscle is stretching too much? Oftentimes, it can be because of that and/or because of a sense of pain or simply a sense that the muscle is not in a position that it's been in before that's unrelated to pain or to spindle activation. And oftentimes, it can be related directly to these changes in the conformation of myosin and actin and within the context of the sarcomeres. Now, of course, you can't peer into or sense your individual sarcomeres. However, you do have neurons that innervate these areas and that send that sensory information back into the spinal cord and up to your brain to interpret. So, you'll find that as we move along, there are specific adjustments that you can make at the- both the macro level, meaning how much movement to insert into your stretching, right? Is it going to be a static or a dynamic or even a ballistic stretch? Or, for instance, at the micro level, that even just a slight sub-millimeter or millimeter increase in the stretching of a given muscle and i- related tissues can translate into an increased range of motion performance.

10. 47:16 – 51:57

    Tool: Protocol - Antagonistic Muscles, Pushing vs. Pulling Exercises

    1. AHAndrew Huberman47:16

       As a quick but relevant aside, I thought I'd share with you something useful that's also grounded in this notion of antagonistic muscles. So, for those of you that do resistance training, whether or not it's with body weight or with physical weights or machines, what have you, you may have found that if you, let's say, were to do three sets of a pushing exercise, so this could be push-ups, uh, this could be bench presses, this could be shoulder presses, something of that sort, and then later in the workout you were to do, let's say, machine pull-downs or pull-ups or chin-ups of some sort, so a pulling exercise, typically what you would find is if you were to do what's often called straight sets, so you would do three sets of push-ups, let's say, with two minutes of rest in between, that you might be able to get a certain number of repetitions on the first set. S- just for sake of example, let's say you can get ten repetitions on the first set, and then you get eight repetitions on the second set, and then you get six repetitions on the third set with two minutes in between. And then you would move on at some point to your pulling exercises, and similarly, let's say you were doing chin-ups or pull-downs and you would get ten repetitions, rest two minutes, eight repetitions, rest two minutes, and six repetitions. Okay, fine. Well, typically what people discover is that if they interleave their pushing and pulling exercises, provided they do that for muscles that are antagonistic to one another, so in this case pushing with the chest, shoulders, and triceps for the pushing exercises and pulling with the back and biceps, and of course there are other muscles involved as well. But because those muscle groups are at least in part antagonistic to one another, what people often find is that if they were to, say, do their pushing set, get ten repetitions, then move to a pulling set after just, say, 60 seconds and perform that pulling set, then go back to the pushing set, then go back to a pulling set, push, pull, push, pull, in other words interleaving their sets, even if they were to maintain the same amount of rest between sets of pushing and sets of pulling, what they discover often is that the drop in the number of repetitions that they get is somewhat offset. So, rather than get ten, eight, six-... as it were with the straight sets. It will be 10, nine, eight. So, what this means is not that you're increasing the total rest time to four minutes between sets, because then, of course, it wouldn't be, uh, equivalent. But rather, that while maintaining the same amount of rest between sets for this same muscle group, by going from push-pull-push-pull of antagonistic muscles, you're able to have improved performance. And the reason for that has everything to do with what we were describing before, which is that typically if you were to do push, set, rest, push, set, rest, push, set, rest, well, in between those sets, and in fact, actually during those sets of pushing, the pulling muscles that would be involved in the chin-ups or pull-downs, et cetera, are actually relaxing or at least are being released of some tension, including the activation of the spindles among other things. So, that's a long-winded way of saying that interleaving push and pull of anti- antagonistic sets can leverage some of the same neural circuits that we're talking about leveraging for sake of increasing flexibility. Now, I offer this to you as a tool that you can try. Uh, one of the challenges with using this tool, however, is that you often have to occupy multiple sites within the gym. Um, you know, if you're doing this at home and you have your own gym, that's one thing. If you're doing this in a gym where you have multiple pieces of equipment, well, then you become that person who has essentially taken over some small corner or multiple corners or machines within the gym. And oftentimes, you'll find that you'll walk back to a machine or you'll walk back to a, a given resistance exercise and someone has now taken it over and the whole thing could be thrown off. So, it takes a little bit of orchestrating, uh, in order to do properly. But in general, what people find is that this can allow you to enhance performance overall of these individual movements, again, while maintaining the same amount of rest. And even if you choose not to do this, I encourage you to pay attention to this as a concept, because again, it's leveraging this idea of antagonistic muscles, flexors and extensors, antagonistic neural relationships between the spinal cord mechanisms that control one set of muscles, and activating those muscles, allowing the opposite antagonistic muscle to relax and therefore to perform better on its next

11. 51:57 – 59:36

    Types of Stretching: Dynamic, Ballistic, Static & PNF (Proprioceptive Neuromuscular Facilitation)

    1. AHAndrew Huberman51:57

       set. So, now I'd like to shift to the question of, what types of stretching can and should we do to increase limb range of motion? If our goal is to do that in the most efficient way possible, 'cause I realize that most people don't have endless amounts of time to dedicate to a stretching practice. And even for those of us that do, I'm sure that you want to get the most outcome for a given effort. And what are the modes of stretching that are going to allow us to increase our flexibility and limb range of motion most safely? 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, and it involves and leverages many of the mechanisms that I described to you earlier. 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 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 stretching, there tends to be a bit more swinging of the limb or use of momentum. So, I invite you to visualize what dynamic and ballistic stretching might look like in your mind. You can even try it if it's safe for you to try it. You know, you could imagine, you know, swinging your arm up overhead as much as possible and bringing it down. I'm doing this because I'm seated, and it's kind of ridiculous movement to do while seated or perhaps at all. But for instance, you can see dynamic and ballistic stretching anytime someone, for instance, is holding onto something with one arm or maybe not holding on and swinging out their, their foot, so essentially getting movement about the hip joint. And you'll notice that some people raise it up and pause it and bring it down. That's one form of dynamic stretching. Whereas others will swing it up and k- sort of let it carry itself a bit further due to the momentum at the top of the movement and then just let it drop back down or maybe even control the descent. There is an enormous range of parameter space here, or variables that one could imagine. And there's just simply no way that we could subdivide all those. 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. So, to stay with a simple example that we are all now familiar with from our earlier discussion, slowly bending over at the waist and trying to touch your toes or putting your hands to the floor and then holding that end position before coming up in a slow and controlled way such that you reduce the amount of momentum to near zero would be one example of static stretching. 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. And again, people tend to name things after themselves, so some of these are proprietary related to specific programs, I'm not focusing on those. Others come to be named after the physiologists or the practitioners that initially popularized them. As is always the case, there's always a naming and renaming and claiming of territory with these things.For the time being, I'd like to just emphasize that static stretching can be both active, where there's a dedicated effort on the part of the stretcher, you, to put force behind the hold to kind of extend, or literally to extend the range of motion. And then, m- 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. And there are other ways in which we can further distinguish active and passive static stretching. But nonetheless, 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 we know where our limbs are based on so-called proprioceptive feedback, so that's feedback that comes from sensory neurons, right? Now, you know what sensory neurons... That are essentially monitoring or responding to events within the joints, the connective tissue, and the muscles, and within the deep components of the muscles, like the spindle reflex, and within the tendons, like the GTO, the Golgi tendon organ. So, PNF-type stretching leverages these sorts of mechanisms, these l- these neural circuits by way of, for instance, you would lie on your back 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 (laughs) towards you. You're not going to pull the muscle towards you. You're gonna pull that limb, your ankle towards 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 l- limb range of motion without the strap, right? Sometimes these are assisted by other people, so people will even use loads, sometimes they'll even use machines. Uh, there are a number of different, um, apparati that have been designed for this. Sometimes it'll involve a training partner. There's a huge range of PNF protocols, and those protocols can be done both by oneself, with or without straps, with machines, with actual weights, or with training partners. If you're interested in the variation of exercises to, say, target your hamstrings versus your quadriceps versus your shoulders versus your chest muscles, et cetera, your neck muscles, and so on, there is an enormous range of information on dynamic, ballistic, static, and PNF stretches for all the various muscle groups. And I should say, there are some excellent books on those topics. There are also some excellent videos on YouTube and elsewhere. Nowadays, it's pretty easy to find exercises that allow you to target specific muscle groups. Again, I encourage you to be safe in how you approach this and I would encourage you also to pay attention to the information that soon follows as to what sorts of protocols one would use to apply those exercises. But the number of exercises and the availability of those exercises for targeting different muscle groups with these four different kinds of stretching is both immense and fortunately, thankfully, immediately accessible to all of us, often at zero cost. So, specific exercises to target specific muscle groups

12. 59:36 – 1:05:56

    Tool: Increasing Range of Motion, Static Stretching Protocol, Duration

    1. AHAndrew Huberman59:36

       aside, we've now established that there are four major categories of stretching, or at least those are the f- four major categories I'm defining today. And we can further divide those categories into which are the ones that are going to be most effective for increasing range of motion in the long term, not just in one individual session. And there have been a number of studies exploring this. I can list out at least four, and we'll put those four as a kind of a cluster under one heading in the show note captions, that arrive at essentially the same answer, which is that for increasing limb range of motion, it does appear that static type, including PNF, but static type stretching is going to be more effective than dynamic and ballistic stretching. So, at least to my mind, this is good news. (laughs) Why is it good news to me? Well, while dynamic and ballistic stretching can be immensely useful for improving performance of specific movements, in particular in the context of particular sports like tennis, or in sprinting, or frankly for any sport, they do carry with them a certain amount of risk because of the use of momentum. So, you don't need to be highly trained in order to perform them. In fact, there is a place, and we will describe when one would want to apply dynamic or ballistic stretching. I'll just give a- a way for now. I think that most physios out there, and certainly the ones that I spoke to, Dr. Andy Galpin, Dr. Kelly Starrett, and a few others, point to the fact that doing some safe dynamic and ballistic stretching prior to, say, a resistance training session, or maybe even prior to a cardiovascular training session, can be useful both in terms of range of motion effects and in terms of neural activation effects. I don't want to use the words warm-up because warming up is typically associated with increasing core body temperature, as it should be. But for engaging the neural circuits and becoming familiarized with the neural circuits that you're about to use in other movements while also increasing the range of motion of the joints involved in those movements so that you can perform them more safely and more confidently. So, I'm certainly not saying...I want to repeat, I'm certainly not saying that dynamic and ballistic stretching are not useful, they absolutely are, but in terms of increasing limb range of motion in the long-term of be- truly becoming more flexible as opposed to transiently more flexible, static stretching, which includes PNF, appears to be the best route to go. So, if your goal is to increase your limb range of motion for a given muscle group, or perhaps for all muscle groups, although I can imagine that would be pretty tough. I mean, you're not going to spend time, I could imagine, working on your tongue muscle control or neck muscle control and every muscle control. But most of us want to reduce so-called "tightness" in air quotes and increase limb range of motion for certain muscle groups, and it appears that the best way to do that is going to be static stretching of some kind. Which raises the question of how often to do that static stretching and how long to hold those static stretches. And we can also ask the question, we should ask the question, where to hold those static stretches. Is it always a good idea to hold those static stretches at the end or the point of maximal range of motion? We're going to address that now. There's some terrific science around this. A slightly older study, but nonetheless a powerful one because it provided a foundation for a lot of subsequent work which basically served to just confirm the answer they got here, is a study from Bandy et al., and the title of this study is The Effect of Time and Frequency of Static Stretching on the Flexibility of the Hamstring Muscles. It was a study involving 93 subjects, so 61 men, 32 women, ranging in age from 21 to 39 years, so a pretty broad, uh, demographic, who had limited hamstring muscle flexibility, here I'm paraphrasing, and randomly assigned to one of five groups. So, the four stretching groups stretched five days per week, uh, for six weeks. The fifth group, which served as a control, did not stretch. The results clearly show that, quote, "The change in flexibility appeared to be dependent on the duration and frequency of stretching." This is great. This tells us that stretching (laughs) uh, for a given amount of time scales with the amount of r- limb range of motion improvement that one will see. There were many interesting findings within this study, but the one that I'd like to highlight most is, quote, "The results of this study suggest that a 30-second duration is an effective amount of time to sustain a hamstring muscle stretch in order to increase range of motion. No increase in flexibility occurred when the duration of stretching was increased from 30 seconds to 60 seconds or when the frequency of stretching was increased from one to three times per day." Okay, so w- now we're starting to lay down some parameters. What this study reveals and what subsequent studies tell us, and we will get into those subsequent studies, is that ideally one would do static stretches that are held for 30 seconds, perhaps more in certain instances, and I'll explain when that can be useful, but here holding those stretches for more than 30 seconds did not turn out to be additionally useful. So, if you're going to stretch your quadriceps for instance and you're going to hold that stretch in static fashion, remember not using momentum, and you can use the mental tricks of either trying to push through the pain, which I don't recommend necessarily, I think that makes us prone to injury, or to relax into the stretch but nonetheless providing some force typically with the o- with the hand in order to pull your ankle back if you're doing a quadriceps stretch, some people might do this on the edge of a sofa. Remember there are a lot of different exercises and ways to do this that you can explore elsewhere. Well, holding that static stretch for 30 seconds appears to be sufficient to stimulate an increase in limb range of motion over time. Again, these are protocols that were used repeatedly over time and we'll talk about how often to repeat them in order to get maximal effect. But 30-second holds for static stretches is the number that I think we want to focus on and that most of us are going to want

13. 1:05:56 – 1:13:55

    Tool: Static Stretching Protocol & Frequency

    1. AHAndrew Huberman1:05:56

       to utilize. So, now let's explore how many sets of static stretching one ought to do in order to get a maximum range of motion improvement while not placing us into a system that's going to create injury nor a situation where we have to be constantly stretching throughout the day, because again, most of us don't have time to do that. This issue of sets is an important one. In the context of cardiovascular exercise we've talked about the data that support the fact that doing at least 150 and ideally as much as 200 minutes per week of zone two cardiovascular exercise is very useful for cardiovascular health and for other aspects of health, and of course there are other aspects of cardiovascular exercise that could be layered onto and into that that can be useful like 90-second maximal sprints, et cetera. Discuss this a lot in the episode with Dr. Andy Galpin and on our episode about endurance. And we also talked about sets in the context of strength and hypertrophy building, building muscle size and/or strength in the episode about that, and in particular in the episode with Dr. Andy Galpin, and there we could also arrive at some specific parameters. And it's going to vary, of course, between individuals depending on how hard you train, whether or not you take sets to failure, your repetition range, et cetera, but in the context of strength and hypertrophy building, we arrived at a approximately six, maybe as many as 10 sets per week per muscle group. Some of that work is done as direct work to a given muscle group, some of that work is indirect, so doing certain pulling exercises of course will target the latissimus dorsi muscles but also the biceps, so if you... That doesn't necessarily mean you have to do 10 sets for the biceps and for the lats, sometimes you're getting some indirect work, et cetera. All of that was delineated in the episode with Dr. Andy Galpin and we arrived at those numbers of sets according to the same criteria that we will apply here. What is the minimum number of sets both to maintain and to improve a given mode of performance?... strength and hypertrophy, or cardiovascular health, again, to either maintain or improve. And we can do the same thing for improving or maintaining range of motion. Because, as I mentioned earlier, the data points to the fact that if we don't do some dedicated work to improve range of motion over time, we will lose our flexibility and limb range of motion over time, just by virtue of the fact that we're not doing anything to offset that. So, whether or not you want to maintain, re-establish, 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? And to answer those questions, I'm going to turn to what I think is a really spectacular review. This was a review that was published in the year 2018, so it's fairly recent. First author, Thomas, Eoghan Thomas. Last author, Palma. We will put a link to this in the show note caption. The title of the paper is, "The Relation between Stretching Typology and Stretching Duration: The Effects on Range of Motion." It's a very straightforward title. This is a review article that explored a number of different studies, had criteria for whether or not those studies could be evaluated in the context of the questions here, had some quality standards and some other standards that they applied, and basically winnowed down a large collection of studies to a remaining 23 articles that were able to be considered, quote, "eligible and included in the quantitative synthesis done here." So, key points from that quantification and synthesis done in this paper. 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. Because before, as you may recall, there was a distinction between ballistic and dynamic, and static and PNF. And so, here it appears again that static stretching is com- sort of rising to the top of the list as the optimal approach relative to all other stretching approaches, at least in the context of increasing limb range of motion. 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 five minutes per week." Okay, this is critical. This is not five minutes per stretch, remember? 30 seconds per static stretch, but at least five minutes per week. "Whereas the time spent stretching within a single session does not seem to have a significant effects for range of motion gains." If this is getting confusing, I'll make sure that you soon understand exactly what we can export from these conclusions. "The data indicate that performing stretching at least five days a week..." Now, some of you may already be groaning. "...for at least five minutes per week..." Okay, so five days per week, that's a lot, but f- at least five minutes per week? Five minutes per week is not that much. "...using static stretching may be beneficial to promote range of motion improvements." Okay, I've read this study in detail now. Uh, they highlight again the reduction in flexibility that occurs from 20 to 49 years of age and so on, how acute bouts of short-term stretching up to three weeks can improve stretch tolerance. I think that's a key point, that in the short term, the first three weeks of embarking on a stretching and flexibility program, much of the improvements come from the short-term neural improvements that we talked about before of inhibiting the spindle reflex and so on, and also a stretch tolerance, a comfort with doing the movements, and maybe even a comfort in overriding some of the pain mechanisms. I'll talk a little bit more about that in, in just a bit, and the particular utility of yoga, something that I don't often practice, but that after reading this article that I'll mention in a little bit, I'm considering perhaps taking up some form of yoga protocol. Now, I've already highlighted some of the key takeaways from the study, namely that we need to get at least five minutes per week of static stretching per muscle group, and based on the previous paper that we talked about, we need to divide that five minutes into sets of 30 seconds each. And as I mentioned earlier, it doesn't seem to be the case that you can do all of that in one day, unfortunately. It does seem important that the frequency of stretching practice distributed throughout the week is important. So, let's talk protocols. We are now talking about doing static stretching, so holding, so limiting momentum, and holding a stretch for 30 seconds per set. We're talking about trying to achieve five minutes per week of those static holds, but that we can't do it all in one session, because the frequency of sessions distributed throughout the week correlates with the improvements in limb range of motion. So, what this means is that we should probably be doing anywhere from two to four sets of 30-second static hold stretches five days per week, or some variant thereof. And I do say some variant thereof, because it turns out that even though there was that earlier study that we talked about, that holding a stretch for more than 30 seconds, in that case 60 seconds, didn't turn out to be additionally beneficial. It appears that if you do hold those stretches for 60 seconds per static stretching set, for instance, you can get away with stretching fewer days per week overall. So, in order to make

14. 1:13:55 – 1:17:12

    Tool: Effective Stretching Protocol

    1. AHAndrew Huberman1:13:55

       this as clear as possible, 'cause I do realize there are a lot of parameters, and you might be asking, "Why didn't you just make me a list of the exact things I should do?" Well, it doesn't work that way (laughs) because once you understand the mechanisms and once you understand your particular goals, this information is designed for you to be able to construct a stretching program that is tailored to your specific goals.If I just gave you the stretching program that I'm doing, or I should say that I'm soon to be doing, 'cause I'm soon to be doing one based on the research for this particular episode, well, that wouldn't be beneficial for you. S- because, for instance, if you have very flexible hamstrings but not very flexible quadriceps or you are somebody who is engaged in sport or not engaged in sport, what you need to do is going to vary somewhat. So, what would an effective stretching protocol look like? We're all trying to improve limb range of motion for different limbs and different muscle groups, but just by way of example, and it's because it's the one we've been using, 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. Again, easy to find such exercises on the internet. 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. Although, at least as far as I could tell, there were s- no data pointing to the fact that you couldn't do your hamstring stretching one part of the day and your quadriceps stretching another part of the day. But presumably, you're going to want to combine your flexibility training in- into one single 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, because it does seem like frequency distributed throughout the week is an important parameter. Now, one thing that we have not highlighted, or at least described, is how long to rest between stretching sets. And despite my efforts, I could not find research-back information that pointed to whether or not 30 seconds of rest for every 30-second stretching or 60 seconds rest for every 30-second stretching was ideal. I think it's reasonable to assume that doubling the amount of time for the interleaving rest would be appropriate, or at least doable. If anyone out there has knowledge about rest between stretching sets and has some physiology or some biology or some experiential information as to why a given ratio of duration of static stretch to rest in between static stretch sets, uh, ought to be used, please put it in, uh, the comments on YouTube, that'd be a terrific way for us to get that information. I'd love to do any follow-up to links that you provide, and so on. But now we're starting to build into a protocol that is backed by the scientific data. Three sets of 30 seconds of holds done five times or maybe even six times per week. One thing

15. 1:17:12 – 1:19:17

    Tool: Warming Up & Stretching

    1. AHAndrew Huberman1:17:12

       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 we 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 five to seven, 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 y- not after some form of exercise, after a brief warm-up to raise your core body temperature definitely seems like the right way

16. 1:19:17 – 1:25:30

    Limb Range of Motion & General Health Benefits

    1. AHAndrew Huberman1:19:17

       to go. Now, for some of you out there, and I confess for me as well, doing something five days a week seems like a big commitment, even if that commitment is one to only do three sets of 30-second static stretches. I say this because you've got the warm-up. I generally like to bring a- a kind of a focus and dedication to a practice, and of course, because when doing these kinds of protocols, it's likely that you're not just stretching your hamstrings, so it's not just 90 seconds of work with a minute of rest in between, but very likely that you're also doing quadriceps stretching and also doing stretching for the shoulders and stretching for the back and the neck and so on. And so, that entire session is going to take some time, and five days a week is a pretty serious commitment for most, especially for those of us that don't exercise or do athletics for a living, which I don't. So, there is some evidence from the literature that one can get away with, or I don't even know that we should think about it as getting away with, but that one can do longer hold static stretches of up to, say, 60 seconds, but.... do fewer total sessions per week. So, rather than three 30-second static holds, doing three 60-second static holds, and doing those every other day. And there really hasn't been a systematic exploration of this. The article that I was referring to just a few moments ago, um, this analysis of the, uh, 23 articles was combined into this enormous, uh, set of tables and some, um, really quite nice graphs that you're welcome to look at, um, since we're going to provide a link to the study. Um, there are a couple of key takeaways that I want to mention that are separate from this issue of how long to stretch and how often. Um, first of all, they describe in their discussion that there were improvements in range of motion independent of whether or not people did static stretching, active stretching, passive stretching, ballistic stretching, e- or PNF stretching. So, all of those forms of stretching will improve limb range of motion. This is essential to point out, and I want to emphasize this. Static stretching, however, gave the greatest degree of gains in limb range of motion, and on average they saw a 20.9% increase, but some of the other increases they observed were also quite substantial. So, ballistic stretching can also provide some pretty impressive limb range of motion improvements. However, they tended to be in the range of, here they point out, 11.65% increase, or in the case of PNF, a 15% increase. So, it appears that the greatest improvements in limb range of motion for your time spent and effort spent is going to be this minimum of five minutes per week to elicit a significant response, with five days being the minimum weekly recommended frequency to achieve signi- significant range of motion improvements. I confess, this was pretty surprising to me, uh, when I compare flexibility training to, say, resistance training for strength and hypertrophy. I've had the experience and I know that other people have had the experience, and I think, uh, Dr. Andy Galpin, uh, would probably agree that provided one trains hard enough and appropriately, that you don't need to train resistance training five days a week in order to get significant improvements in strength and hypertrophy. Some people might need to, but you can get a lot of positive results in those variables with less frequent training, certainly with three or four days a week of training. And for cardiovascular training, I'm not aware of anyone having tested whether or not one very long run each week can actually increase cardiovascular fitness and you're not doing anything else, although I have to imagine you'd probably see some improvement compared to not doing anything. But most people are doing repeated training sessions of cardiovascular or strength training. Not a lot of people are doing five days a week of strength training and r- at least that I'm aware of. Some people are, but most people, I think, are not. And some people are doing five or more days a week of cardiovascular training. I'm guessing that most people are not doing five 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. And so, that points to the, perhaps the reason why so few people are doing dedicated range of motion work, but it also reminds me that all of the studies that

Episode duration: 2:06:08