Essentials: Increase Strength & Endurance with Cooling Protocols | Dr. Craig Heller

Dr. Craig Heller:
Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health, and performance. I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. Today, I have the pleasure of introducing Dr. Craig Heller as my guest on the Huberman Lab podcast. And now for my discussion with Dr. Craig Heller. Great to have you here.

Andrew Huberman:
It's good to be here.

Dr. Craig Heller:
Yeah. I know that I and many people have a lot of questions about the use of cold. So one of the things that's happened in recent years is that for many reasons, people have become interested in things like taking cold showers and taking ice baths for many different purposes.

Andrew Huberman:
Mm-hmm.

Dr. Craig Heller:
Could you just tell me a little bit about what happens when I get into a cold shower or an ice bath?

Andrew Huberman:
Well, first of all, you get a tremendous shock, and what that's going to translate into is a bit of a shot of adrenaline. And I think this is really the so-called benefit, but it doesn't necessarily translate into any benefit in terms of your physiology or performance, and so forth. Now, if you take a cold bath or a cold shower, a couple things are happening. One is you're going to stimulate vasoconstriction. So if anything, it's going to make it a little bit more difficult for your body to get rid of heat because you're shutting off your avenues of heat loss. If you're in a true cold bath, the overall surface area of your body is so great that it doesn't matter if you vasoconstricted, you're still going to lose heat. The primary sites of heat loss, which we're going to get into, are the palms of your hands, the soles of your feet, and the upper part of your face. And the reason these are avenues for heat loss is they're underlain by special blood vessels, and these blood vessels are able to shunt the blood from the arteries, which coming from the heart, directly to the veins, which are returning to the heart, and bypassing the capillaries, which are the nutritive vessels, but high resistance. So you can tell when you shake someone's hand what his or her thermal status is. The hand's hot or it's cold.

Dr. Craig Heller:
A couple of questions before we get into these specialized-

Andrew Huberman:
Yeah

Dr. Craig Heller:
... vascular compartments on the soles, the palms, and the upper face. Is there anything that's really important to understand about the difference in the physiological response evoked by cold shower versus immersion in cold?

Andrew Huberman:
Well, there are differences that are more physical than anything else. So if you are in a cold bath and you're still, you develop a boundary layer. It's best to explain it in terms of a hot bath because everybody's experienced that. You get into a hot bath and, oh my god, it's really hot, almost painful. And then you sit down, and eventually, it doesn't feel so hot anymore because the still water, which is close to your skin, is coming into equilibrium with your skin. So it's like having a blanket on you or an insulator on you. And then if you move around, you disturb that still water layer, you feel the hot temperature again.

Dr. Craig Heller:
Got it.

Andrew Huberman:
Yeah. But I think getting back to your original question about benefits, you have to keep in mind whether you're talking about aerobic activity or anaerobic activity, if you're referring to performance in exercise and so forth. So if you're doing aerobic activity that you can sustain for a long time, your production of heat is rising gradually and is being distributed throughout your body. So eventually, your body temperature is going to come up to a level that's going to impair your performance. So the benefit of a cold bath or a cold shower before aerobic activity is that you increase the capacity of your body mass to absorb that excess heat.

Dr. Craig Heller:
I see. So could you say that in a rough sense, that a protocol that one might use if they're going to head out for a long run-

Andrew Huberman:
Yeah

Dr. Craig Heller:
... even on a reasonably warm day, not super hot-

Andrew Huberman:
Right

Dr. Craig Heller:
... or maybe it is super hot, would be to take a cool shower before they go run? Would that be beneficial?

Andrew Huberman:
Sure. It'll take them longer to get to the sweat point and to heat up.

Dr. Craig Heller:
And what will that translate to in terms of a performance benefit?

Andrew Huberman:
Well, could increase your speed, or it depends on how you use that benefit. Some people are pacers. They will go at the same pace, and then they will go farther. Or some people are forcers, and they will take that advantage and use it up as fast as they can. So they will go faster, but not necessarily farther.

Dr. Craig Heller:
And what about for the anaerobic athlete, the strength athlete?

Andrew Huberman:
Right. For the anaerobic athlete, and let's say they're doing several sets, their core temperature's not going to rise that fast because it's only certain muscles which are being used, but the temperature of those muscles will go up.

Dr. Craig Heller:
So it's a local effect.

Andrew Huberman:
It's a local effect. Right.

Dr. Craig Heller:
Okay. So if somebody, let's say, is doing a large body compound movement like barbell squats, where there are a lot of large body movements, hip hinging, et cetera. But for instance, the biceps are not-- They're involved, but more or less indirectly.

Andrew Huberman:
Right.

Dr. Craig Heller:
So the effect is going to be to heat up the quadriceps, heat up the hamstrings, heat up the glutes, this kind of thing.

Andrew Huberman:
Right. And then during rest, that heat will leave the muscle. But it's not fast, and certainly, the heat can't leave the muscle very fast while you're working out because when the muscle contracts, it squeezes the blood vessels. And the only way heat gets out of a muscle is in the blood And your muscle metabolism can go up 50 or 60-fold during anaerobic activity. That means the heat production in the muscle goes up 50 or 60-fold. The blood flow to that muscle cannot go up 50 or 60-fold. So you literally have the capacity to cook your muscles. So to keep you from damaging your muscle by hyperthermia, we have fail-safe mechanisms. And one of those fail-safe mechanisms is an enzyme which is critical for getting fuel, in other words, the results of metabolism of glucose, getting that fuel into the mitochondria, which is making our major coinage of energy exchange, ATP. So that particular enzyme is temperature sensitive. So when the muscle temperature gets above 39 or 39.5, it shuts off. And that essentially shuts off the fuel supply to the mitochondria. That's when you cannot do one more rep.

Dr. Craig Heller:
So failure, could we say that-

Andrew Huberman:
Muscle failure

Dr. Craig Heller:
... one component of muscular failure is overheating of the muscle-

Andrew Huberman:
Right

Dr. Craig Heller:
... locally?

Andrew Huberman:
Right.

Dr. Craig Heller:
There are probably other things too.

Andrew Huberman:
The most immediate impairment of muscle activity, muscle fatigue, in other words, is the rise in the temperature of the muscle.

Dr. Craig Heller:
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Andrew Huberman:
Mm-hmm.

Dr. Craig Heller:
I hit muscular failure at a given weight.

Andrew Huberman:
Mm-hmm.

Dr. Craig Heller:
And according to what I now know, it's my quadriceps and the muscles associated mainly with the squat that have failed because of this mechanism triggered by heat that shuts off the muscle. But my biceps are nice and cool-

Andrew Huberman:
Yeah

Dr. Craig Heller:
... you're telling me. They're not doing too much work. It's only indirect work.

Andrew Huberman:
Mm-hmm.

Dr. Craig Heller:
So why is it that I can't set the bar down in the squat rack, walk over and do barbell curls with the same intensity that I could if I were to do those barbell curls fresh, not having done anything prior?

Andrew Huberman:
Well, you will still have a fatigue curve with your upper body.

Dr. Craig Heller:
Okay.

Andrew Huberman:
And that will be influenced by any rise in temperature that has been generated by your lower body exercise.

Dr. Craig Heller:
So temperature in both cases is the limiting factor.

Andrew Huberman:
It's one limiting factor.

Dr. Craig Heller:
I find that amazing.

Andrew Huberman:
Right.

Dr. Craig Heller:
So I realize there might be other mechanisms involved. Sounds like heat is, if not the dominant mechanism that prevents more work, it's one of them.

Andrew Huberman:
It's one of them, and it's a quick one. It's a fast one.

Dr. Craig Heller:
Why is it that if I finish a set of squats, I can't simply cool off my quadriceps by throwing a nice cool towel on my quadriceps? Why is that not the best way to go about it?

Andrew Huberman:
Because your body surface is a very good insulator. The skin, the fascia, the muscles underneath, they're all very good insulators. And that's why I said earlier that the way the heat gets out of the muscle is in the blood.

Dr. Craig Heller:
So if throwing a cold towel or even ice cold towel on my quadriceps isn't going to work, or standing in front of the fan because I'm insulated from that cool, I can't cool off my blood fast enough. What about drinking 16 ounces of ice water?

Andrew Huberman:
Sure, you can do that, but you can calculate how much heat that can absorb.

Dr. Craig Heller:
Okay.

Andrew Huberman:
And you can't continue drinking liters of ice water. You're going to dilute your blood and have other problems. But yes, it'll help. Sure, it will help, but it doesn't have the full capacity you will need.

Dr. Craig Heller:
What about an ice pack to the back of my neck or to my head or-

Andrew Huberman:
Okay

Dr. Craig Heller:
... squeezing the cold sponge over the head? How good is that, or how poor is that as a strategy, since now we know that being overheated locally and systemically throughout the body is a serious limiting factor on performance?

Andrew Huberman:
Well, you have to understand something about our thermoregulatory system. We have a thermostat, just like you have a thermostat in your house, and that thermostat is in the brain. It's called the preoptic anterior hypothalamus. It does many things in terms of physiological regulation, but it serves as a thermostat. Now that thermostat has to have information. It has to have input. Where does that input come from? It comes from our overall body surface, where we sense temperature. So one of the things that can happen when you're overheated is that you can send in a cold stimulus to your thermostat, and that's sort of like wanting to cool your house by putting a wet washcloth over your thermostat. It's doing the wrong thing. So we've actually had experiences where we've had people exercising, getting overheated, and then cooling the body surface, and they say, "It feels great. This is fantastic." And their core temperature is going up. So what can happen if you, let's say, cool the torso with an ice vest, you can actually cause vasoconstriction of your portals, your heat loss portals. So that's what impairs the rate at which you're losing heat. Feels good. Now, back to the head. That's really interesting. The major blood flow to the brain comes up four arteries through the neck. There is the carotid arteries, and there's the vertebral arteries. So when you put a cold towel around the neck, you're going to be putting a cold stimulus into the brain. Well, that's great for protecting the brain. You want to protect the brain, but it's also going to make you feel cooler than you are. So you will think you're ready to go again quickly when you've just essentially cooled the thermostat.

Dr. Craig Heller:
So you're saying that if somebody's hyperthermic, they could trick themselves into subjectively thinking that they are cooling off by putting a cold towel-

Andrew Huberman:
They can go farther

Dr. Craig Heller:
... and that they can go further, but their brain could cook.

Andrew Huberman:
Well, if they stop the cooling, then that hot blood from the body core is going to go to the brain.

Dr. Craig Heller:
Interesting.

Andrew Huberman:
Yeah. You can feel great and have a dangerously hyperthermic temperature. But I should say that when you get into the danger zone, things get bad fast.

Dr. Craig Heller:
What are some of the symptoms that people could be on the lookout for, for hyperthermia?

Andrew Huberman:
Essentially, it's almost ironic that if individuals are transitioning into heat stroke, they actually vasoconstrict, and they stop sweating. And that's a pathological situation. I couldn't begin to explain it. But essentially, you are just feeling exhausted. You're feeling miserable. The heart rate is very high. Your heart rate goes up as your core temperature goes up, called cardiac drift. So you just feel rotten. It's not a danger signal that you can translate immediately into, "Nope, I'm going into heat stroke." That's why people can overcome their bad feeling with motivation to continue going, to work harder. So there have been a number of high-profile athletic deaths due to heat stroke that were during practice. Not in competition when people are really trying to do it, but in practice.

Dr. Craig Heller:
Yeah.

Andrew Huberman:
Which shows they were just motivated to push.

Dr. Craig Heller:
So let's talk about these magnificent portals that not just humans but other animals, mammals, are equipped with.

Andrew Huberman:
Mm-hmm.

Dr. Craig Heller:
If putting cold on the neck or on the head or on the torso is not optimal, what is optimal? And maybe walk us through a theory as to why we would have these portals located where they are, and then we can talk about how one might leverage them for performance.

Andrew Huberman:
Okay. Where the portals are are in the glabrous skin. Big word, okay? Glabrous just means no hair. So it's the hairless skin. You say, "Well, most of my body is without hair." No. Most of your body has hair follicles. We are mammals. Mammals have fur. We've lost the fur, but we still have that hairy skin phenotype all over our body except for those skin surfaces where our mammal relatives didn't have fur. So the pads of the feet, and for the primates, upper part of the face. For rabbits, no portions of the ears, the inner surface of the ears.

Dr. Craig Heller:
Oh, I never thought about that.

Andrew Huberman:
Our mammalian relatives can't lose heat over their overall body surface. So probably very early on in mammalian evolution, they evolved these special blood vessels in the limited surface areas that don't have fur. And as I said, what these blood vessels are, are shunts between the arteries and the veins. Arteries and veins are both low resistance vessels, so you can have high flow rate. Capillaries, which normally are between arteries and veins, are high resistance because they're very tiny.

Dr. Craig Heller:
So you're saying that in this glabrous or beneath the glabrous skin-

Andrew Huberman:
There are these shunts

Dr. Craig Heller:
... and those go directly from arteries to veins.

Andrew Huberman:
Right.

Dr. Craig Heller:
So you skip the capillaries.

Andrew Huberman:
The capillaries. Yeah.

Dr. Craig Heller:
I see.

Andrew Huberman:
If you are warm and you look at just palms of your hands, they are fairly red.

Dr. Craig Heller:
Mm-hmm.

Andrew Huberman:
The backs of your hands aren't.

Dr. Craig Heller:
Mm-hmm.

Andrew Huberman:
You don't have these vessels in the backs of your hands. Now, if you take a glass, like a water tumbler, right, and you grab it, you can see if you squeeze a little bit, the hand goes white.

Dr. Craig Heller:
Mm-hmm.

Andrew Huberman:
That's because you've shut off that blood flow.

Dr. Craig Heller:
Oh, interesting. I'm going to do that little home experiment.

Andrew Huberman:
So if you're bicycling on a hot day, you don't want to be grabbing your handlebars all the time. You want to periodically

Dr. Craig Heller:
Well, this is important. I know you're privy to some really amazing results that we're going to talk about, but I actually heard you say this during this lecture recently, and you mentioned this, that if you're cycling-

Andrew Huberman:
Yeah

Dr. Craig Heller:
... and you're working hard and you want to be able to do more work, we now know why you want to remain cool In order to continue to do work, and if you get too warm, that's bad, that gripping the handlebars too tightly will actually limit your performance.

Andrew Huberman:
Right.

Dr. Craig Heller:
And that's probably also true on the Peloton or any other-

Andrew Huberman:
Yeah, right

Dr. Craig Heller:
... kind of device, or the skier or anything like that.

Andrew Huberman:
Right.

Dr. Craig Heller:
So loosen the grip, or if you safely can, you want to actually expose your hands-

Andrew Huberman:
Right

Dr. Craig Heller:
... to the world. Now, what about for people wearing gloves? To me, that just seems crazy based on everything you're telling me.

Andrew Huberman:
Well, gloves definitely impede heat loss from the hands, just as socks impede heat loss from the feet. Okay? So if you want to maximize your heat loss, you want to have as thin a protectors as possible on your hands. And, of course, the feet are more problematical because you have to be using them in certain ways.

Dr. Craig Heller:
Interesting. Yeah. So heating up at the level of the hands obviously is going to hinder performance. How about with running? I ran cross country briefly in high school, and not particularly well at that. But we were told to run as if we were holding crackers in our fingers or something, very lightly, and to keep hands kind of loose. So running like this would actually be-

Andrew Huberman:
Yeah

Dr. Craig Heller:
... more beneficial performance than-

Andrew Huberman:
Oh, than-

Dr. Craig Heller:
Or gripping a phone.

Andrew Huberman:
Yeah. Yeah. Right.

Dr. Craig Heller:
Which is probably what most people are doing nowadays.

Andrew Huberman:
Right. Right.

Dr. Craig Heller:
Interesting.

Andrew Huberman:
Let me introduce one more thing.

Dr. Craig Heller:
Sure.

Andrew Huberman:
Because you asked earlier about the pouring of water on the head. Okay? One of the things which is not appreciated fully is that the blood which is perfusing these special blood vessels in the face above the beard line, that's the non-hairy skin, that blood then returns in the venous supply to the heart, but it actually does it in a very strange way. They go through the skull.

Dr. Craig Heller:
Hmm.

Andrew Huberman:
Okay? And that's why the scalp bleeds a lot if you cut-

Dr. Craig Heller:
Mm-hmm

Andrew Huberman:
... the scalp. And these blood vessels were primarily thought to be ways that blood is leaving the brain. But when you're overheated, the direction of flow in those blood vessels reverses. So the cool blood that's coming from your facial region goes into that circulation and actually is a cooling source for the brain. So you can cool the brain, you can have a cooling effect on the brain by pouring water on your head.

Dr. Craig Heller:
Interesting. So that practice, which at least for me, I most commonly associate with combat sports, that you're saying is somewhat effective in cooling the brain.

Andrew Huberman:
Yeah. It's one of the natural mechanisms for cooling the brain.

Dr. Craig Heller:
I'd like to take a quick break and acknowledge our sponsor, AG1. AG1 is a vitamin mineral probiotic drink that also includes prebiotics and adaptogens. As many of you know, I've been taking AG1 for more than 13 years now. I discovered it way back in 2012, long before I ever had a podcast, and I've been drinking it every day since. For the past 13 years, AG1 has been the same original flavor. They've updated the formulation, but the flavor has always remained the same. And now, for the first time, AG1 is available in three new flavors, berry, citrus, and tropical. All the flavors include the highest quality ingredients in exactly the right doses to together provide support for your gut microbiome, support for your immune health, and support for better energy and more. So now you can find the flavor of AG1 that you like the most. While I've always loved the AG1 original flavor, especially when I mix it with water and a little bit of lemon or lime juice, that's how I've been doing it for basically 13 years, now I really enjoy the new berry flavor in particular. It tastes great, and I don't have to add any lemon or lime juice. I just mix it up with water. If you'd like to try AG1 and these new flavors, you can go to drinkag1.com/huberman to claim a special offer. Right now, AG1 is giving away an AG1 welcome kit that includes five free travel packs and a free bottle of vitamin D3+K2. Again, go to drinkag1.com/huberman to claim the special welcome kit of five free travel packs and a free bottle of vitamin D3+K2. Is there any known benefit to cooling the brain in terms of offsetting physical damage, offsetting the negative effects of concussion? Because one of the reasons why fighters will often get a cold item on the back of the neck or on the head is not just to cool them down, but the theory is that it might offset some of the damage of neurons.

Andrew Huberman:
I'm aware of those ideas, but they're controversial. One of the things that you want to do for injury to the brain is to decrease swelling, and one of the ways that you decrease swelling in many parts of the body is to cool. It decreases inflammation. It decreases the blood flow. So I think it's a really interesting topic, and it's something that should be investigated. It's kind of hard to investigate.

Dr. Craig Heller:
Interesting. Okay, so I hear these stories, and I've seen the data, so I believe the stories. Maybe tell us a story about an observation that your group has made with respect to anaerobic exercise and proper cooling of these glabrous surfaces.

Andrew Huberman:
Yeah.

Dr. Craig Heller:
And we can talk about the technology. What happens when a skilled athlete comes in and does dips for multiple sets, and then what happens when they cool properly using the glabrous skin surfaces?

Andrew Huberman:
Right. This was a story that occurred early on in our investigations when we first made the discoveries that cooling has a benefit to increase your work volume, your capacity to do more reps. Okay? So the word got over, I think, to the 49ers camp, and one of their players, Greg Clark, who was a tight end at the time, he had been tight end at Stanford, he decided to come over and check it out. So Greg came over, and we said, "Greg, what are you good at? What activity do you like to do?" He said, "Dips. I can do a lot of dips. I can do 40 dips in a first set, and I can probably do five sets. That's a usual workout for me." And we said, "Okay." So he came over to the gym one day, and that's exactly what he did. He did 40 dips the first set, and then maybe 25 and 15, and down from there.

Dr. Craig Heller:
Do you recall roughly what kind of rest periods he was taking between sets?

Andrew Huberman:
Yeah. We standardized the rest period to three minutes.

Dr. Craig Heller:
Mm-hmm.

Andrew Huberman:
So several days later, he came back, and his first set he did, I think, maybe 42. Then his second set was, I don't remember the numbers, but very much above the second set on the control day. This was after we cooled his-

Dr. Craig Heller:
Okay, so he does-

Andrew Huberman:
... palmar surface.

Dr. Craig Heller:
When is he doing the cooling?

Andrew Huberman:
He's sitting down and putting his hands in the devices that we had built, which were cooling the palms of his hands.

Dr. Craig Heller:
For how long does that cooling take? Can he do it inside of a three-minute rest period?

Andrew Huberman:
Yeah.

Dr. Craig Heller:
Yeah.

Andrew Huberman:
That's what we were doing.

Dr. Craig Heller:
Yeah.

Andrew Huberman:
We standardized the-

Dr. Craig Heller:
Okay

Andrew Huberman:
... the interval for resting or cooling. The point is, he got to his fifth set, and all of the sets were above what he had done on the previous day, and he said, "You know, I'm not tired. I can do another set." And then, "I can do another set. I can do another set. I can do another set." So from one day to two or three days later, with cooling, he doubled the total number of dips.

Dr. Craig Heller:
By adding more sets and more repetitions to each set.

Andrew Huberman:
Right. So then he kept coming back for four more weeks, twice a week, and by the end of that month, he was doing 300 dips.

Dr. Craig Heller:
Wow. So what percentage-

Andrew Huberman:
So he tripled.

Dr. Craig Heller:
He tripled-

Andrew Huberman:
He essentially tripled. And so here is a professional athlete-

Dr. Craig Heller:
Wow

Andrew Huberman:
... at peak physical conditioning, and he triples-

Dr. Craig Heller:
Amazing

Andrew Huberman:
... what he can do.

Dr. Craig Heller:
Amazing. And I know there are also published results, and we will provide links to some of these papers for people, seeing similar effects of, I should say, similar performance-enhancing effects using bench presses-

Andrew Huberman:
Right

Dr. Craig Heller:
... in a bench press or pushups or other-

Andrew Huberman:
Yeah

Dr. Craig Heller:
... sorts of things. So, what's your favorite example of endurance?

Andrew Huberman:
We haven't done a lot in the field, I mean, outdoors. Most of our endurance has been in a hot room with treadmill work and so forth. So the very first experiment we had, I think, maybe 18 subjects just off the street. For this group, with one trial with and without cooling, we could double their endurance walking on the treadmill, walking uphill on the treadmill in the heat, like maybe 40 degrees ambient temperature, 40 degrees centigrade.

Dr. Craig Heller:
So what does that experiment look like? You're having people walk on an incline. It's really warm. Some people are just going to hit the quit button and say, "I've had enough," and get off the treadmill.

Andrew Huberman:
Right.

Dr. Craig Heller:
With proper cooling, when are they doing the cooling?

Andrew Huberman:
They're doing it continuously.

Dr. Craig Heller:
I see.

Andrew Huberman:
Because in the laboratory, we can suspend devices from the ceiling, for example.

Dr. Craig Heller:
Some people might wonder, if there are all these studies and there are these incredible results over the years, why haven't we heard more about it? And I will ask your opinion on that as well, but I'll just editorialize a little bit. Is that the best laboratory work and its practical applications oftentimes requires many studies, and oftentimes there isn't a portal, so to speak, to get that information out into the technology sector. So there is a company that's developing this technology for people to use and-

Andrew Huberman:
Right

Dr. Craig Heller:
... to purchase and use.

Andrew Huberman:
Right.

Dr. Craig Heller:
You might as well just tell us now, what is the name of that company, and do they have a website?

Andrew Huberman:
Right.

Dr. Craig Heller:
People are going to want to know where can they get this magical technology.

Andrew Huberman:
Right.

Dr. Craig Heller:
And is there a poor man's version of it as well?

Andrew Huberman:
Well, the company is Arteria, A-R-T-E-R-I-A, and the website is www.coolmitt.com.

Dr. Craig Heller:
Mm-hmm.

Andrew Huberman:
So CoolMitt is just C-O-O-L-M-I-T-T.

Dr. Craig Heller:
Mm-hmm. Yep.

Andrew Huberman:
Coolmitt.com. The new version of the technology is sort of in beta test versions. We got it into the hands of people who had used the technology before. So there's NFL teams that are using, there's college teams, there's Olympics, there's the Navy SEALs, Major League Baseball, the NBA, the National Tennis Association. They have locations where now they are trying this out and reporting back, how's it working? How could you change it? How could you improve it?

Dr. Craig Heller:
Great. Let's talk about the technology in a little more detail for a moment. The CoolMitt, as I understand, is it's a mitt, it's a glove.

Andrew Huberman:
Yeah.

Dr. Craig Heller:
You put your hand into, you hold onto a surface, and that surface cools your hand and-

Andrew Huberman:
Right

Dr. Craig Heller:
... thereby, through this specialized portal, cools your core body temperature and all the muscles of the body. Subjectively, if I were to do this right now, would I think that it was ice cold, or would I think it was just cool?

Andrew Huberman:
Just cool.

Dr. Craig Heller:
I see.

Andrew Huberman:
Ice cold is too cold.

Dr. Craig Heller:
Mm-hmm.

Andrew Huberman:
So people always ask, "Well, why can't you just stick your hand in a bucket of ice water?" It's too cold. What that does is that causes reflex vasoconstriction of the very portals that you're trying to maximize the heat loss from. So you stick your hand in cold water, when it comes out, it's cold. You know?

Dr. Craig Heller:
You just sealed up all the heat in your body.

Andrew Huberman:
Yeah. Right.

Dr. Craig Heller:
How long, in the CoolMitt, at the proper temperature-

Andrew Huberman:
Yeah

Dr. Craig Heller:
... how long are people putting their hands into the mitt?

Andrew Huberman:
We, once again, had just standardized on three minutes.

Dr. Craig Heller:
Mm-hmm.

Andrew Huberman:
And part of the reason for that is that the rate of heat loss is an exponentially declining curve. Okay? And three minutes sort of gets the best part of the curve. So you can go longer and get more benefit, but the biggest bang for the buck is in the first two, three minutes.

Dr. Craig Heller:
I'd like to take a quick break and acknowledge one of our sponsors, Function. Last year, I became a Function member after searching for the most comprehensive approach to lab testing. Function provides over 100 advanced lab tests that give you a key snapshot of your entire bodily health. This snapshot offers you with insights on your heart health, hormone health, immune functioning, nutrient levels, and much more. Function not only provides testing of over 100 biomarkers key to your physical and mental health, but it also analyzes these results and provides insights from top doctors who are expert in the relevant areas. For example, in one of my first tests with Function, I learned that I had elevated levels of mercury in my blood. Function not only helped me detect that, but offered insights into how best to reduce my mercury levels, which included limiting my tuna consumption, I'd been eating a lot of tuna, while also making an effort to eat more leafy greens and supplementing with NAC, N-acetylcysteine, both of which can support glutathione production and detoxification. And I should say, by taking a second Function test, that approach worked. Comprehensive blood testing is vitally important. There are so many things related to your mental and physical health that can only be detected in a blood test. The problem is, blood testing has always been very expensive and complicated. In contrast, I've been super impressed by Function's simplicity and at the level of cost. It is very affordable. If you'd like to try Function, you can go to functionhealth.com/huberman. Function currently has a wait list of over 250,000 people, but they're offering early access to Huberman Podcast listeners. Again, that's functionhealth.com/huberman to get early access to Function. A number of people said to me after learning a little bit about this science and technology that they've experienced some big effects, positive effects of cooling by, and I confess, I've done this, taking a package of frozen blueberries and just kind of passing it back and forth-

Andrew Huberman:
Yeah

Dr. Craig Heller:
... between my hands. If you were going to give a crude protocol for, let's just say for the gym, because with running it's a little bit tricky, but what would that look like if people wanted to just play with this in some sort of fashion?

Andrew Huberman:
It would be experimental.

Dr. Craig Heller:
Sure.

Andrew Huberman:
Your idea of frozen peas is a good idea. After you hold the cold peas in one hand and you switch it to the other hand, if someone then comes and feels your hand, is it warm or cold? If it's cold, it means you've vasoconstricted.

Dr. Craig Heller:
Oh.

Andrew Huberman:
If it's warm, it means the hot blood is still going there.

Dr. Craig Heller:
And the key is for it to not vasoconstrict.

Andrew Huberman:
Right.

Dr. Craig Heller:
Okay. So there's a test out there, folks. If you're going to try this in kind of a crude fashion, at least until the CoolMit is available more broadly to the general public, you want to assess whether or not your palms actually feel cool to the touch by somebody else.

Andrew Huberman:
Right.

Dr. Craig Heller:
And if it does, that means you've essentially shut down the portal. You're sealing in more heat-

Andrew Huberman:
Right

Dr. Craig Heller:
... which is bad. What about putting this cold pack of some sort on the face or could I put my feet on them?

Andrew Huberman:
The problem is back to boundary layers again. If you don't have a convective stream of the cooling medium, the heat sink is not as effective because there'll be a boundary layer developed between the heat sink material and your skin.

Dr. Craig Heller:
Mm-hmm.

Andrew Huberman:
So that decreases its efficacy.

Dr. Craig Heller:
Right. So this is why just planting my bare feet on two packages of frozen peas, there's really no opportunity for circulation-

Andrew Huberman:
Right

Dr. Craig Heller:
... of, and therefore heat transfer. So it's not really optimal.

Andrew Huberman:
But once again, it depends on the surface area to get any benefit at all. We have a study that we published, which was investigating the standard treatment for hyperthermia in the field, and the standard treatment that's recommended by medical organizations is you take cold packs and you put them in the axilla, the groin-

Dr. Craig Heller:
The axilla are the armpits?

Andrew Huberman:
The armpits, yeah, and the neck.

Dr. Craig Heller:
Mm-hmm.

Andrew Huberman:
So what we did is we did studies in which we made people hyperthermic, and then we measured the rate at which we could cool them by putting those heat exchange bags in the recommended location versus palms, soles, and face.

Dr. Craig Heller:
Uh-huh.

Andrew Huberman:
The cooling rate was double.

Dr. Craig Heller:
Wow. So face, hands, and bottoms of feet will cool you twice as fast as-

Andrew Huberman:
Right

Dr. Craig Heller:
... putting cold packs into your armpits, your groin-

Andrew Huberman:
Right

Dr. Craig Heller:
... or back of neck.

Andrew Huberman:
Right.

Dr. Craig Heller:
I realize there was a question that I failed to ask earlier. If you do this cooling in between sets in the gym-

Andrew Huberman:
Mm-hmm

Dr. Craig Heller:
... you get this performance-enhancing effect.

Andrew Huberman:
Mm-hmm.

Dr. Craig Heller:
So presumably, the body is adapting.

Andrew Huberman:
Mm-hmm.

Dr. Craig Heller:
You're getting better as a consequence-

Andrew Huberman:
Yep

Dr. Craig Heller:
... of being able to do more work-

Andrew Huberman:
Yep

Dr. Craig Heller:
... per unit time or to go harder in some way-

Andrew Huberman:
Right

Dr. Craig Heller:
... of course. You get that adaptation. Does that mean that you see a performance-enhancing effect even when you don't cool if you've previously done the cooling workouts?

Andrew Huberman:
You keep your gains. It's a true conditioning effect. You respond to the increased work volume by all of those mechanisms you mentioned.

Dr. Craig Heller:
Amazing.

Andrew Huberman:
You increase the number of contractile elements in your muscles.

Dr. Craig Heller:
Amazing.

Andrew Huberman:
Your muscles get bigger.

Dr. Craig Heller:
Well, Craig, thank you so much. You gave so much information that's actionable and interesting. I know a lot of people are going to be really interested in the palmar cooling technology from CoolMit. I do encourage people to play around with, so to speak, the palmar cooling-

Andrew Huberman:
Mm-hmm

Dr. Craig Heller:
... technology that we all have, which are-

Andrew Huberman:
Yeah

Dr. Craig Heller:
... these glabrous surfaces. And also just want to thank you for taking time out of your busy schedule to share-

Andrew Huberman:
Oh, you're welcome

Dr. Craig Heller:
... this information.

Andrew Huberman:
It was fun.

Speaker 3:
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