Using Temperature for Performance, Brain & Body Health | Dr. Craig Heller

Andrew Huberman 0:00 (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, I have the pleasure of introducing Dr. Craig Heller as my guest on the Huberman Lab Podcast. Dr. Heller is a professor of biology and neurosciences at Stanford. His laboratory works on a range of topics, including thermal regulation, Down syndrome, and circadian rhythms. Today, we talk about thermal regulation, how the body heats and cools itself and maintains what we call homeostasis, which is an equilibrium of processes that keeps our neurons healthy, our organs functioning well. And as Dr. Heller teaches us, thermal regulation can be leveraged in order to greatly increase our performance in athletics and mental performance as well. Learning to control your core body temperature is one of the most, if not the most powerful thing that you can do to optimize mental and physical performance regardless of the environment that you're in. He also dispels many common myths about heating and cooling the body, including the idea that putting a cold pack on your head or neck is the optimal way to cool down quickly. And in fact, as Dr. Heller tells us, it actually can be counterproductive and lead to hyperthermia. It's a fascinating conversation from which I learned a tremendous amount of new information, and we didn't even get into the other incredibly interesting work that Dr. Heller does on Down syndrome and circadian rhythms and sleep, so we hope to have him back in the future to discuss those topics. As you'll soon see, Dr. Heller is a wealth of knowledge on all things human physiology, biology, and human performance. It's no surprise then that he's been chair of the Biology Department at Stanford for many years, as well as director of the Human Biology Program. So, if you're interested in human biology and how to improve your performance in any context or setting, athletic

Andrew Huberman 2:00 or otherwise, I think you'll very much enjoy today's conversation. 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 ROKA. ROKA makes sunglasses and eyeglasses that are of the absolute highest quality. I've spent a lifetime working on the visual system, and I can tell you that the visual system has to go through a lot of work in order to maintain clarity of what you see when there are shadows, when you go into different types of indoor lighting, and so on. 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Andrew Huberman 6:45 And now for my discussion with Dr. Craig Heller. Great to have you here.

Craig Heller 6:49 It's good to be here.

Andrew Huberman 6:50 Yeah. It's, it's been a long time coming. Uh, 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.

Craig Heller 7:13 Mm-hmm.

Andrew Huberman 7:13 You know, sometimes this is introduced as just a general health tonic, you know, but other times people get specific about how it can improve resilience or it can improve one's metabolism. C- could you just tell me a little bit about what happens when I get into a cold shower or an ice bath? What, what are some of the basic responses at the level of metabolism? Obviously, psychologically, we don't know exactly. It'll vary from person to person. But what happens when I submerge myself into an ice bath if I've never done it before?

Craig Heller 7:49 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, uh, so-called benefit, but I wouldn't call it a benefit of the cryo chambers. You go into a cryo chamber and it's a shock, so you get a shot of adrenaline. So sure, you're gonna feel different when you come out. (laughs) You've had a shot of adrenaline. 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, uh, 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. Uh, 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.

Andrew Huberman 8:51 Okay, so, um, so vasoconstriction, the constriction of... Is it capillaries, vessels, and arteries all constrict? Or just one or two?

Craig Heller 9:01 Well, this is an area of controversy. Uh, in general, when people talk of vasoconstriction, they talk of the overall skin surface, and that is not true. Uh, 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. Sometimes it's-

Andrew Huberman 9:51 Do you think that's part of the reason why humans evolved this practice of, uh, shaking hands?

Craig Heller 9:55 (laughs)

Andrew Huberman 9:56 Assessing each other's level of anxiety? We all know that a limp handshake is pretty, uh-

Craig Heller 10:01 (laughs)

Andrew Huberman 10:01 ... indicative of something and a firm handshake is indicative of something, as is the crushing handshake, for that matter. Right.

Craig Heller 10:07 Yeah, I really don't know what the evolutionary origin of handshaking is other than to get your hand away from your weapon (laughs) -

Andrew Huberman 10:14 Right.

Craig Heller 10:14 ... perhaps. (laughs)

Andrew Huberman 10:15 Uh, a couple of questions before we get into the specialized, um-

Craig Heller 10:18 Yeah.

Andrew Huberman 10:19 ... uh, vascular sh- compartments on the soles, the palms, and, and the upper face. Um, you mentioned whole body immersion like into an ice bath or very cold water up to the neck versus a cold shower. Is, is there something fundamentally different about those two besides the fact that they both provide this release of adrenaline? Is there anything that's, that's really important to understand about the difference in the physiological response evoked by th- by sh-

Andrew Huberman 10:45 cold shower versus immersion in cold?

Craig Heller 10:48 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. If you're in a shower, you can't develop a boundary layer.

Andrew Huberman 11:00 Could you explain what a boundary layer is?

Craig Heller 11:01 Yes, uh, i- i- g- if you... Uh, 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.

Andrew Huberman 11:35 I see. So if I were to get into a cold ice bath or very cold-

Craig Heller 11:39 Right.

Andrew Huberman 11:40 ... uh, body of water of some kind and stay still, I'd likely feel warmer, at least until I start-

Craig Heller 11:45 Y- you're, you're not going to be losing as much heat.

Andrew Huberman 11:47 I see.

Craig Heller 11:48 Right.

Andrew Huberman 11:48 And then when I move and start-

Craig Heller 11:49 If you flail around-

Andrew Huberman 11:49 Uh-huh.

Craig Heller 11:50 ... flail around, then you're going to lose more heat.

Andrew Huberman 11:52 Got it.

Craig Heller 11:53 Yeah. But I think getting back to your original

Craig Heller 11:55 question about benefits, uh, you have to keep in mind whether you're talking about aerobic activity or anaerobic activity if you're referring to performance and 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.

Andrew Huberman 12:36 I see. So could you say that, um, in a c- in a rough sense that a protocol that one might use if they're going to head out for a, a long run-

Craig Heller 12:44 Yeah.

Andrew Huberman 12:44 ... even on a reasonably warm day, not, not super hot-

Craig Heller 12:48 Right.

Andrew Huberman 12:48 ... or maybe it is super hot, would be to take a cool shower before they go run. Would that be beneficial?

Craig Heller 12:53 Sure. It'll take them longer to get to the sweat point and to heat up.

Andrew Huberman 12:57 And what will that translate to in terms of a performance benefit?

Craig Heller 13:00 I- increase your, well, could increase your speed, uh, or 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, um, uh, what I say, pacers and regulators and, uh, no, no, pacers or forcers (laughs) . They will take that advantage and use it up as fast as they can. So they will go faster but not necessarily farther.

Andrew Huberman 13:27 I see. As far as I know, not many athletes, at least not the ones that I know, are getting into cool bodies of water, taking cold showers before they head out to train. But it sounds like there could be a real performance benefit there.

Craig Heller 13:39 It could be a benefit. Uh, I know our, we're going to talk about our technology for cooling. But, uh, at one point, our, I don't know if they're using it now, but our cross country team, when they would go to compete in a very hot place, they would do their warm-up exercises, their stretching, then they would extract heat before the beginning of the race. So they, I like to think of it is you have greater scope for heat absorption.

Andrew Huberman 14:04 Interesting. About how long, uh, would one need to take one of these showers or cold immersions before heading out for run? R- roughly speaking. We don't have to get into details because everyone's performance level and regimen is going to be different, where they live is going to be different, et cetera.

Craig Heller 14:18 Right. It's not as long as you think. It's minutes.

Andrew Huberman 14:21 Couple minutes?

Craig Heller 14:22 Yeah, for, for, because what's going to happen is, uh, as your core temperature goes down, you will eventually shut off your heat loss and that keeps it from going below normal. So, eh, it, you can, if you're, if you've warmed up and your temperature has risen by half a degree, let's say, uh, it doesn't take more than a few minutes to extract that heat

Craig Heller 14:45 if you're vasodilated.

Andrew Huberman 14:46 Interesting. And what about for the anaerobic athlete? The strength athlete?

Craig Heller 14:50 Right. For the anaerobic athlete, and let's say they're doing several s- several, uh, they're doing several sets, uh, and how many reps, whatever they're doing, um, th- their core temperature's not going to rise that fast because it's only, uh, certain muscles which are being used. But the temperature of those muscles will go up.

Andrew Huberman 15:11 So it's a local effect.

Craig Heller 15:13 It's a local effect, right.

Andrew Huberman 15:14 Okay.

Craig Heller 15:14 Because if you're-

Andrew Huberman 15:14 So let's say, let's for sake of today, maybe for this discussion, let's, if we assume that the, uh, basic workout, even though people do variation on this, is, you know, five sets of 5 or 10 sets of 10.

Craig Heller 15:25 Yeah.

Andrew Huberman 15:26 Uh, so for those listening, it would be, um, (laughs) five sets of 10, of five rep- repetitions or 10 sets of 10 repetitions, 10 by 10, five by five.

Craig Heller 15:35 Uh-huh.

Andrew Huberman 15:35 Yeah. So if somebody, let's say, is doing, um, a large body compound movement like barbell squats where there's, there are a lot of large body movements, hip hinging-

Craig Heller 15:45 Yeah.

Andrew Huberman 15:45 ... and et cetera. Um, but for instance, the, the biceps are not par- they're involved, but more or less indirectly.

Craig Heller 15:54 Right.

Andrew Huberman 15:55 So the effect is going to be to heat up the quadriceps, heat up the hamstrings, heat up the glutes, this kind of thing.

Craig Heller 16:01 Right.

Andrew Huberman 16:01 I see.

Craig Heller 16:02 And then during rest, that heat will leave the muscle. Eh, 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 th- 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. (laughs)

Andrew Huberman 16:38 Mm-hmm. So, um, this is, uh, probably an appropriate time to just, um, mention briefly what the underlying mechanism of

Andrew Huberman 16:45 this is. Could you just... We, we will return to the specifics of what one can do to mitigate this heating up, but, um, could you just explain the relationship between energy production, ATP and pyruvate kinase, and the role of heat there?

Craig Heller 17:00 Sure. Um, we don't get something for nothing. So like a steam engine, most of the energy in our food is lost as heat. So we are roughly about 20% efficient. So of the energy that we take in in our food, about 20% of that can go into doing work and the rest of it is lost as heat. Now, we're mammals, we use that heat to keep our body temperature considerably above the environment. But if you raise body temperature a few degrees higher, you're in trouble. That's hyperthermia. So individual muscles can reach hyperthermic limits before you might experience it in the whole body. 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. Okay? 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. You-

Andrew Huberman 18:29 So failure, could we say that-

Craig Heller 18:30 Muscle failure.

Andrew Huberman 18:31 ... one, one component of muscular failure is overheating of the muscle-

Craig Heller 18:34 Right.

Andrew Huberman 18:35 ... locally?

Craig Heller 18:36 Right.

Andrew Huberman 18:36 There are probably other things, too. I-

Craig Heller 18:38 Well, if you, yeah, if you lack oxygen.

Andrew Huberman 18:39 Mm-hmm.

Craig Heller 18:40 Yeah. But our oxygen delivery is pretty good to the, to, to the muscle. Uh, if you run out of glucose, yeah, that's going to impair you. But the most immediate, the most immediate impairment of muscle activity, muscle fatigue, in other words, is the rise in temperature of the muscle.

Andrew Huberman 18:57 Interesting. Um, I want

Andrew Huberman 19:00 to talk about how that muscle fails locally, but I have this burning question in my mind that I cannot seem to answer for myself. I'm hoping you can answer it for me. So let's say I'm doing, um, five sets of five with squats.

Craig Heller 19:13 Mm-hmm.

Andrew Huberman 19:14 I hit f- muscular failure at a given weight.

Craig Heller 19:16 Mm-hmm.

Andrew Huberman 19:17 And according to what I now know, it's my quadriceps and the muscles associated, I mean, with the squat that have failed because of this heat triggering, this mechanism triggered by heat that shuts off the muscle. But my biceps are nice and cool-

Craig Heller 19:33 Yeah.

Andrew Huberman 19:33 ... you're telling me. They're not, they're, they're not doing too much work. It's only indirect work.

Craig Heller 19:37 Mm-hmm.

Andrew Huberman 19:37 So why is it that I can't set the s- 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, w- uh, not having done anything prior?

Craig Heller 19:53 Well, you will still have a fatigue curve with your upper body. Okay? And that will be influenced by any rise in temperature that has been generated by your lower body exercise. So-

Andrew Huberman 20:06 So, so temperature, in both cases, is the limiting factor. Th- or-

Craig Heller 20:09 It's one limiting factor. It's one limiting factor.

Andrew Huberman 20:13 I find that amazing. I find that amazing, because, uh, I always thought, naively, that the reason muscles fail is because we, quote, "don't have the strength" to do another repetition, or it's that you lack glycogen or some ability to access that glycogen. But of course we still have glycogen. I, it's naive for me to think that, because if I wait three minutes and go back, I can do those repetitions again.

Craig Heller 20:35 Right.

Andrew Huberman 20:36 So the glycogen wasn't restored in that three minutes.

Craig Heller 20:38 Right.

Andrew Huberman 20:38 Obviously, it was there.

Craig Heller 20:40 Right.

Andrew Huberman 20:40 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.

Craig Heller 20:50 It's one of them, and it's a f- quick one. It's a fast one. Um, so it can happen with, let's say you are a really experienced weightlifter. Okay? You may be doing very, very high weights with sets of five or six.

Andrew Huberman 21:07 Yeah, to be clear for the audience, I'm not doing very high weights for sets of five. (laughs)

Craig Heller 21:11 (laughs)

Andrew Huberman 21:11 I'm not particularly strong. I, I'm not, uh, super weak, but I'm not particularly strong. But Craig's referring in the general sense to, with, to you. So it, why, 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 would, why is that not the best way to go about it?

Craig Heller 21:34 Because your body surface is a very good insulator. Okay? We, we think we don't have fur and therefore we're not insulated. But the skin, the fascia, the, uh, the muscles underlief- underneath, that, 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.

Andrew Huberman 21:56 So I, I want to step through a couple other portals by which one might think that heating and cooling would be ideal and then get back to these-

Craig Heller 22:05 Sure.

Andrew Huberman 22:06 ... specialized surfaces on the, the hands, the feet, and the face.

Craig Heller 22:09 Yeah.

Andrew Huberman 22:09 So if

Andrew Huberman 22:10 throwing a cold towel or ice, 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?

Craig Heller 22:22 Uh, sure, you can do that. But you can calculate how much heat that can absorb. Okay? And you can't continue drinking liters of ice water. You're going to dilute your, your blood and have other problems.

Andrew Huberman 22:34 Right.

Craig Heller 22:34 But yes, it'll help. Sure it will help. But it is not, doesn't have the, the full capacity you will need.

Andrew Huberman 22:42 What about an ice pack to the back of my neck or to my head or-

Craig Heller 22:45 Okay.

Andrew Huberman 22:45 ... squeezing the cold sponge over the head? I'm, I'm deliberately moving through these options, because these are the ones that we see most often. We were actually just watching the Olympic track and field trials-

Craig Heller 22:54 Yeah.

Andrew Huberman 22:54 ... last night-

Craig Heller 22:55 Yep.

Andrew Huberman 22:55 ... up in Oregon. I'm a huge track and field fan. And, um, there were a lot of, uh, there were a lot of sponges on the backs of necks, um, before, in between, and after events. And, um, how good is that or how poor is that as a strategy? Since now we know that h- being overheated locally and systemically throughout the body is, is a serious limiting factor on performance.

Craig Heller 23:18 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. Okay?

Andrew Huberman 23:30 Do we know the specific site?

Craig Heller 23:31 Yes.

Andrew Huberman 23:32 Yes.

Craig Heller 23:32 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, uh, have input. Where does that input come from? It comes from our overall body surface where we sense temperature. Okay? 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. You know, it's-

Andrew Huberman 24:07 (laughs)

Craig Heller 24:07 ... 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's going up.

Andrew Huberman 24:21 Well, I think this is such an important point. First of all, I wa- I, uh, was weaned in a laboratory where there were always battles over the temperature in the lab.

Craig Heller 24:29 (laughs)

Andrew Huberman 24:29 So people were always putting ice packs on thermostats-

Craig Heller 24:32 To make them hot.

Andrew Huberman 24:33 ... or putting fans towards thermostats and trying to play this game. Good to know we were all being foolish, um, even though we're neurobiologists. Um, putting a cold towel over my torso-

Craig Heller 24:45 Yeah.

Andrew Huberman 24:45 ... or putting ice on the back of my upper back-

Craig Heller 24:48 Right.

Andrew Huberman 24:48 ... you're saying could actually heat up my core?

Craig Heller 24:52 It'll at least decrease your heat loss, your rate of heat loss. As we're, you're going to raise the issue a little later, I, I know, and that is our natural portals for heat loss. So you can think of the natural porters, portals for heat loss as our air conditioners, okay? The thermostat's in the brain and the information from the thermos- to the thermostat is coming from the overall body surface. 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. Um, there's 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, uh, cooled the thermostat.

Andrew Huberman 26:08 Um, this is an important point and there's a lot of, um, interest nowadays in people doing marathons and-

Craig Heller 26:14 Yeah, yeah.

Andrew Huberman 26:14 ... or even some people do these ultras, ultra running-

Craig Heller 26:17 Yeah.

Andrew Huberman 26:17 ... which I guess is everything longer than a marathon and go and go last man standing, last man, last woman standing kind of things. 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-

Craig Heller 26:33 They can go farther.

Andrew Huberman 26:34 ... and then they can go further, but their brain could cook.

Craig Heller 26:36 Uh, well, if they stop the cooling, then that hot blood from the body core is going to go to the brain.

Andrew Huberman 26:41 Interesting. Well many, um,

Andrew Huberman 26:43 it's a bit of a, of a tangent, but many people report after long bouts of exercise-

Craig Heller 26:48 Mm-hmm.

Andrew Huberman 26:48 ... or even just very intense bouts of exercise, feeling a kind of brain fog or mental fatigue. I, I assumed that that was due to lowered brain oxygenation post-exercise, but is it possible that there are some post-exercise effects on heating and cooling of the brain that might impact cognition, or I should say negatively impact cognition?

Craig Heller 27:11 It's certainly possible because we know that, um, a rise in temperature decreases cognitive capacity.

Andrew Huberman 27:19 Mm-hmm.

Craig Heller 27:20 I mean, you can experience that yourself. You can get on a treadmill, you know, and follow your temperature and then just do a simple activity like adding and subtracting. You get to about 39 degrees, you can't do that anymore. You can't just calculate how m- how long you've been on the treadmill.

Andrew Huberman 27:36 So the, the phrase cool, calm and collected is a, is-

Craig Heller 27:39 Cool, calm and collected. (laughs)

Andrew Huberman 27:40 That's the goal in, in all pursuits.

Craig Heller 27:42 That's right. (laughs)

Andrew Huberman 27:43 So, um,

Andrew Huberman 27:45 I want to talk about these portals-

Craig Heller 27:46 Yeah.

Andrew Huberman 27:47 ... 'cause you've mentioned them a few times. Before I ask about what the portals are exactly and how they work and how they can be leveraged for performance, I just, there's a question that my neurobiologist self can't resist but ask. We have this thermostat-

Craig Heller 28:03 Yeah.

Andrew Huberman 28:04 ... in the preoptic area of the hypothalamus, which is interesting to me that preop- the medial preoptic area is also one that's known to be, um, sexually dimorphic dependent on testosterone exposure early in life, or, uh, et cetera. Although, um, people should just note that it's not actually testosterone that c- creates these sexual dimorphisms, these difference, it's actually testosterone converted into estrogen. Um, it's actually estrogen is the effector, uh, which is fascinating. Nonetheless, we've got this area that acts as a thermostat and you said it's collecting information from the whole body. Does that mean that there are pathways as the neuroscientists like you, you and I refer to them as these, these afferent or input pathways from the body to the preoptic area? Is there a map of our body in the preoptic area? 'Cause that, yeah, I have to imagine that you can't have the information just coming from the left shoulder, just from the right toe. It sounds like you need a pretty, uh, cr- probably a pretty crude map, but that you need a complete map of the body surface there.

Craig Heller 29:05 Well, you don't need a complete map in the hypothalamus. I mean, that thermal afferent information that you mentioned, it also goes to the somatosensory cortex. So you know if an ice cube has touched you on the back, but that doesn't necessarily translate into a change in, let's say you're shivering or, or sweating. Uh, so the information that's going to the hypothalamus is more integrated, uh, representation of, of body temperature.

Andrew Huberman 29:36 So it's sort of an average of what's happening across the body.

Craig Heller 29:39 It's an average. Right.

Andrew Huberman 29:39 So if I were to, let's say I get hot on a hot day and, uh, Popsicles when we were in summer camp-

Craig Heller 29:44 Yeah.

Andrew Huberman 29:44 ... I went to a sports camp near here actually, and we'd run around like crazy and then we get into the shade if we could, but we were, you know, Popsicles, it was all about Popsicles.

Craig Heller 29:50 Brain freeze.

Narrator 29:51 (laughs)

Andrew Huberman 29:52 Or the kids were putting ice cubes down each other's-

Craig Heller 29:54 Yeah, yeah, yeah.

Andrew Huberman 29:54 ... you know, shirts or something. Um, but that's an average because other parts of the body aren't exposed. The mouth is exposed to the ice in the Popsicle case or the, the cold cubes are in the hands.As you said, it feels really good.

Craig Heller 30:07 It feels good, yeah.

Andrew Huberman 30:08 But it sounds like it- it's feels deceptively good, because in reality could still be quite warm internally.

Craig Heller 30:16 Absolutely. Yeah. Yeah.

Andrew Huberman 30:18 Interesting.

Craig Heller 30:18 Yeah. You can feel great and have a- a dangerously hyperthermic temperature. But I should say that when (laughs) you get into the danger zone, things get bad fast.

Andrew Huberman 30:29 What are some of the symptoms that people could be on the lookout for, for hyperthermia?

Craig Heller 30:34 Essentially, it's- it's almost ironic that if individuals are trans- trans- transitioning into heatstroke, they actually vasoconstrict and they stop sweating. And th- that's a pathological situation. I- I couldn't begin to explain it. But, uh, essentially, uh, you are just feeling exhausted. You're feeling, uh, miserable. Um, uh, the heart rate is very high. Um, your heart rate goes up as your core temperature goes up, uh, called cardiac drift. Um, so you just feel rotten. Uh, but that's why... since- since it's not an- an- an- it's not a danger signal that you can translate immediately into, "Nope, I'm going into heatstroke." Uh, 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 heatstroke that were during practice, not in competition when people, you know, are really trying to do it, but in practice-

Andrew Huberman 31:46 Yeah.

Craig Heller 31:46 ... which shows they were just motivated to push.

Andrew Huberman 31:50 So let's talk about these magnificent portals-

Craig Heller 31:53 Yeah.

Andrew Huberman 31:53 ... that not just humans, but other animals, mammals are equipped with.

Craig Heller 31:58 Right.

Andrew Huberman 31:58 So, um, if putting cold on the neck or on the head or on the torso is not optimal, um, what is optimal? And, um, 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.

Craig Heller 32:18 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, I'm- you know, most of my body is without hair." No. Your- most of your body has hair follicles. We are mammals. Mammals have fur. We've lost the fur, but we still have those that hairy skin phenotype all over our body, except, 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.

Andrew Huberman 33:03 Oh, I never thought about that. Yeah.

Craig Heller 33:04 For bears, you know, the tongue. Bears have big tongues, huge tongues. (laughs) So-

Andrew Huberman 33:10 I didn't know that either. I haven't, I haven't been that close to a bear yet.

Craig Heller 33:13 (laughs) Yeah. Haven't had a licking match with a bear.

Andrew Huberman 33:15 (laughs) Not yet. No.

Craig Heller 33:16 Okay. So anyway, um, our mama- 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, okay?

Andrew Huberman 33:54 Is it- is it fair to say that, um, what I was taught is that blood flows flo- from arteries then to capillaries and then to veins and then-

Craig Heller 34:02 Yes.

Andrew Huberman 34:02 ... back to the heart?

Craig Heller 34:03 Yes.

Andrew Huberman 34:03 So it's sort of like from the heart, through arteries, then through these little capillaries, which are like little estuaries and streams, and then to the veins, back to the heart.

Craig Heller 34:11 Right.

Andrew Huberman 34:11 Is that- is that generally true?

Craig Heller 34:12 Yeah. Abs- absolutely.

Andrew Huberman 34:13 Okay. So what I learned in basic physiology is still-

Craig Heller 34:16 Is- is still true.

Andrew Huberman 34:16 I wouldn't- I wouldn't get an F in your class anyway.

Craig Heller 34:18 No. (laughs)

Andrew Huberman 34:19 Maybe a D or a C, but not an F. Um-

Craig Heller 34:22 (laughs) So that's excellent.

Andrew Huberman 34:23 Okay. And so you're saying that in this glabrous or beneath the glabrous skin...

Craig Heller 34:29 There are these shunts.

Andrew Huberman 34:30 And those go directly from arteries to veins.

Craig Heller 34:33 Right.

Andrew Huberman 34:33 So you skip the- the capillaries.

Craig Heller 34:36 Capillaries. Yeah.

Andrew Huberman 34:36 I see.

Craig Heller 34:37 Now the-

Andrew Huberman 34:37 And is it actually- it- as long as I- as I'm, um, say that in the skin, you know, when I feel the pads of my hands, um, w- how deep to the surface do these- do these vessels reside?

Craig Heller 34:48 Well, they're- they're below the, obviously-

Andrew Huberman 34:51 Mm-hmm. Sure.

Craig Heller 34:52 ... the- the- the- the- the epidermis. Uh, so- so if you are warm and you look at just palms of your hands, they are fairly red.

Andrew Huberman 35:01 Mm-hmm.

Craig Heller 35:02 The backs of your hands aren't.

Andrew Huberman 35:04 Mm-hmm.

Craig Heller 35:04 You don't have these vessels in the backs of your hands. Now if you take a, a glass, like a water tumbler, right? And you grab it, uh, you can see if you squeeze a little bit, the hand goes white.

Andrew Huberman 35:18 Mm-hmm.

Craig Heller 35:19 That's because you've shut off that blood flow.

Andrew Huberman 35:21 Oh, interesting. I'm going to do that little home experiment.

Craig Heller 35:23 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... (laughs)

Andrew Huberman 35:30 Well, this is important. I know you- you, um, you're pr- uh, privy to some really amazing results that we're going to talk about, but I actually heard you say this during this lecture recently, uh, that Stanford held about, uh, human performance that we- w- were both part of. And you mentioned this, that if you're cycling-

Craig Heller 35:45 Yeah.

Andrew Huberman 35:46 ... and you're working hard and you want to be able to do more work at, 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.

Craig Heller 36:01 Right.

Andrew Huberman 36:01 And that's probably also true on the Peloton or any other-

Craig Heller 36:04 Yeah, right.

Andrew Huberman 36:04 ... kind of device or the skier or anything like that.

Craig Heller 36:06 Right. Right.

Andrew Huberman 36:06 So loosen the grip, or if you safely can-

Craig Heller 36:09 Right.

Andrew Huberman 36:09 ... you want to actually expose your hands-

Craig Heller 36:11 Yeah. It's... right.

Andrew Huberman 36:11 ... to the world. Now what about for people wearing gloves? What about the- the- the... To me, that just seems crazy based on everything you're telling me.

Craig Heller 36:18 Well, gloves definitely impede heat loss, uh, 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 of protectors as possible on your hands. And, of course, the feet are more problematical, because you have to be using them in certain ways.

Andrew Huberman 36:38 Some people run barefoot.

Craig Heller 36:40 (laughs) Yeah. Well, yeah.

Andrew Huberman 36:41 But yeah. That's, that's become somewhat popular. It seems like it kind of came and went. They had those toe shoes things, but they looked so ridiculous that I think most people just were willing to take the performance hindrance of regular shoes.

Craig Heller 36:52 Actually, we had a track coach here at Stanford, who for a while was famous for introducing, uh, training without shoes, running n-

Andrew Huberman 37:00 Interesting.

Craig Heller 37:01 And he thought it was because it changed the posture of-

Andrew Huberman 37:04 Hmm.

Craig Heller 37:04 ... the runner. And I think it was just due to the fact that (laughs) it was increasing the capacity of his runners to lose heat.

Andrew Huberman 37:10 Interesting. Yeah, so heating up at the level of the hands obviously is going to hinder performance. So if I can, uh, how about with running? I noticed, um, I ran across the country briefly in high school and, and not particularly well at that. But that we were told to run as if we were holding, you know, crackers in our, in our fingers or something, like very lightly, and to keep hands kind of loose. So running like this-

Craig Heller 37:32 Yeah.

Andrew Huberman 37:32 ... would actually be more beneficial-

Craig Heller 37:33 Yeah.

Andrew Huberman 37:33 ... performance than-

Craig Heller 37:34 Oh, than, than-

Andrew Huberman 37:35 ... or gripping a phone-

Craig Heller 37:36 Yeah, yeah.

Andrew Huberman 37:36 ... which is probably what most people are doing nowadays.

Craig Heller 37:39 Right, right, right, right.

Andrew Huberman 37:39 Right? Interesting. And, um-

Craig Heller 37:41 I, once, I'll tell you an experience I had once. I was in Alaska in the winter and I went out running, and I absentmindedly forgot gloves. And I realized this after a short period running, because the backs of my hands were aching from the cold. The palms of my hands

Craig Heller 38:00 were sweating and were hot.

Andrew Huberman 38:01 Oh, amazing, amazing. So these compartments are a real thing. And you mentioned the upper half of the face.

Craig Heller 38:06 Upper parts, that's where our primate ancestors don't have fur.

Andrew Huberman 38:09 Mm-hmm. And the bottoms of our feet. So, um, let's just take a moment and talk about some of the more amazing results that have been associated-

Craig Heller 38:18 Yeah.

Andrew Huberman 38:19 ... with proper cooling of these glabrous skin surfaces. Um-

Craig Heller 38:23 Let me introduce one more thing-

Andrew Huberman 38:25 Sure.

Craig Heller 38:25 ... 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. It actually goes through what are called, um, I'm blocking on the name now.

Andrew Huberman 38:59 Take your time.

Craig Heller 39:00 Uh, these are blood vessels that go through the skull, okay?

Andrew Huberman 39:03 Hmm.

Craig Heller 39:03 And that's why the scalp bleeds a lot if you cut-

Andrew Huberman 39:06 Mm-hmm.

Craig Heller 39:06 ... cut the scalp. And these blood vessels, which are called, I want to say emergent, but it's not emergent. It's a word that means leaving. And these blood vessels were primarily thought to be ways that blood is leaving, uh, the brain. But when you're overheated, the fl, direction of flow in those blood vessels reverses. So the cooled 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 c, pouring water on, on your head.

Andrew Huberman 39:45 Interesting. So that practice, which we, at least for me, I most commonly associate with, um, combat sports-

Craig Heller 39:52 Yeah.

Andrew Huberman 39:52 ... where someone, the fighter goes to their corner. They usually sit down on a, uh, on a stool, unless they're trying to, um, uh, do some mental, uh, warfare from the corner, in which case they, they don't even take a seat. And they'll, their, um, corner crew will, will squeeze a, a glove, or excuse me, a sponge full of cold water over them, or-

Craig Heller 40:13 Over their head.

Andrew Huberman 40:13 Um, that you're saying is somewhat effective in cooling the brain.

Craig Heller 40:17 Yeah. It's one of the natural mechanisms for, uh, cooling the brain.

Andrew Huberman 40:21 I want to return to this at some point as well, but is there any known benefit to cooling the brain in terms of offsetting physical damage, you know, offsetting the negative effects of concussion? Because one of the reasons why, um, fighters will often get a, a, a col- on the back, you know, 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.

Craig Heller 40:49 Um, I just can't comment on that. I'm aware of those ideas, but they're controversial. Uh, one of the things that you want to do for injury to the brain is to decrease swelling. And, uh, one of the ways that you decrease swelling in many parts of the body is to cool. Uh, uh, uh, it, it decreases inflammation. It decreases the blood flow. Uh, so, you know, I, I think it's a really interesting topic, and it's something that should be investigated. Uh, it's kind of hard to investigate.

Andrew Huberman 41:23 Yeah. Um,

Andrew Huberman 41:25 interesting. Okay, so I hear these s- stories and I've seen the data, so I believe the stories. Um, maybe tell us a story about an observation that y- your group has made with respect to anaerobic exercise and the, and this prop- and proper, uh, cooling of the, these glabrous surfaces.

Craig Heller 41:46 Yeah.

Andrew Huberman 41:47 And we can talk about the technology.

Craig Heller 41:48 Yeah, yeah.

Andrew Huberman 41:49 Um, maybe give us the dips example first.

Craig Heller 41:52 Okay.

Andrew Huberman 41:52 Dips, of course, you know, I think most people are familiar with dips. You're supposed to, I guess, get down.

Craig Heller 41:56 Raise and lower your body mass.

Andrew Huberman 41:57 Yeah, raise and lower your body, raise and lower your body mass, usually with your legs dangling down. Sometimes people are strong enough to attach a weight there and, um, they'll do, it's essentially a compound upper body exercise.

Craig Heller 42:08 Right.

Andrew Huberman 42:09 Um, uh, one dip would not be particularly impressive for most people. A hundred would be very impressive. Um, 20 would be im- impressive for some, et cetera. What happens when s- a, a skilled athlete comes in and does dips for multiple sets? And then what happens when they cool properly using the glabrous-

Craig Heller 42:28 Right.

Andrew Huberman 42:28 ... skin surfaces?

Craig Heller 42:30 Um, 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, uh, the word got over, I think, to the 49ers camp and, uh, one of their players, Greg Clark, who was a tight end at the time, he had been tight end at Stanford, um, he decided, or I don't know if he was asked or what, um, to come over and check it out. So, uh, Greg came over and we said, "Greg, what are you good at? What- what ex- activity do you like to do?" He said, "Dips. I can do a lot of dips. I- 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, you know, down- down from there.

Andrew Huberman 43:31 Do you recall wh- roughly what kind of rest periods he was taking between sets?

Craig Heller 43:35 Yeah. We- we- and s- we- we standardized the rest period to three minutes.

Andrew Huberman 43:39 Mm-hmm.

Craig Heller 43:40 Because that's what we had set on for cooling as the interval.

Andrew Huberman 43:44 That's a good long rest period for-

Craig Heller 43:46 Yeah. It- it is. It- it-

Andrew Huberman 43:46 Yeah. Still a lot of dips. I got to-

Craig Heller 43:48 Yeah. It's actually-

Andrew Huberman 43:49 Yeah.

Craig Heller 43:49 ... a longer rest period than many, uh, p- people would prefer during workouts. They want to make the most of their time. (laughs)

Andrew Huberman 43:54 Not me. I prefer to take as much rest as I possibly can. (laughs) Yeah.

Craig Heller 43:58 (laughs) So several days later, he came back and, uh, his first set he did, I think, maybe 42. Uh, a little bit better, but now people were standing around watching. So there was a little impetus there-

Andrew Huberman 44:09 Mm-hmm.

Craig Heller 44:10 ... to show off.

Andrew Huberman 44:10 Mm-hmm.

Craig Heller 44:11 Uh, so then his second d- 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-

Andrew Huberman 44:21 Okay. So he does-

Craig Heller 44:22 ... palm surface.

Andrew Huberman 44:22 When- when is he doing co- the cooling?

Craig Heller 44:24 He's- he's sitting down and putting his hands in the devices that we had built which were cooling the palms of his hands.

Andrew Huberman 44:31 For how long does that cooling take? Can he do it inside of a three-minute rest period?

Craig Heller 44:35 Yeah.

Andrew Huberman 44:35 Yeah?

Craig Heller 44:35 That's what we were doing.

Andrew Huberman 44:36 Yeah.

Craig Heller 44:36 We standardized the-

Andrew Huberman 44:37 Okay.

Craig Heller 44:38 ... the interval for resting or cooling, uh, to three minutes. Okay. But the- the point is he got to his fifth set and he s- and h- 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 work volume. He doubled the total number of dips.

Andrew Huberman 45:08 By adding more sets and more repetitions to each set.

Craig Heller 45:12 Right. Right. So then he kept coming back, uh, for four more weeks, uh, twice a week. And by the end of that month, uh, he was doing 300 dips.

Andrew Huberman 45:24 Wow. So what percentage-

Craig Heller 45:25 So he tripled.

Andrew Huberman 45:26 He tripled them.

Craig Heller 45:27 He essentially tripled. And so here's a, here is a professional athlete at peak physical conditioning and he triples-

Andrew Huberman 45:33 Amazing.

Craig Heller 45:34 ... what he can do.

Andrew Huberman 45:34 Amazing.

Andrew Huberman 45:35 And in terms of his ability to recover, um, did, was that explored or discussed at all? Um, because my understanding is that if we cause enough stress to a muscle during anaerobic training, we provide the stimulus for compensatory regrowth, et cetera.

Craig Heller 45:53 Right. Right.

Andrew Huberman 45:54 But if we do more work, we essentially scale up the amount of recovery that's needed or the recovery time. I'm- I'm very curious about whether or not he needed longer to recover between these super performing workouts.

Craig Heller 46:06 That's very interesting. That was a major discovery which we didn't realize we were making at the time. There is this phenomenon you're referring to as delayed onset muscle soreness, DOMS.

Andrew Huberman 46:18 Mm-hmm.

Craig Heller 46:19 And this is due to those little micro tears and so forth that are happening as we extend our workout capacity, volume, okay? So we've had this experience so many times that an athlete or anyone will come in to the lab and they will exceed what their previous goals were, their previous expectations. And I can always see the words coming out of their mouth, "I'm going to be so sore tomorrow." They never are.

Andrew Huberman 46:49 Interesting.

Craig Heller 46:49 And we've actually demonstrated that, uh, with a naive group. We had a class, a physical conditioning class, and, uh, we had half of them a- uh, well, the first days of the class, we had to establish their true capacity, what they could do. So these were pretty heavy workouts for these new recruits. And, uh, we gave half of them the benefit of cooling and the other half not. And then we had them record their subjective levels of delayed onset muscle soreness. And they, those that were cooled, didn't have significant muscle soreness.

Andrew Huberman 47:25 Amazing. And I know there are also published results and we, we will provide links to some of these papers for people, um, seeing similar effects, uh, I should say similar performance enhancing effects using, um, bench presses-

Craig Heller 47:39 Right.

Andrew Huberman 47:39 ... in a bench press or push-ups or other-

Craig Heller 47:41 Yeah.

Andrew Huberman 47:41 ... other sorts of things. Maybe you could give us an example from the realm of endurance work or- or-

Craig Heller 47:47 Sure.

Andrew Huberman 47:47 ... aero- aerobic work. Uh, running, cycling, things of that sort.

Craig Heller 47:51 Well, one of the problems with, uh, for us is that our equipment now is not really portable. I mean, it's portable in the sense you can carry it to the gym or to the football field-

Andrew Huberman 48:04 But you're not going to run with it.

Craig Heller 48:04 ... but you're not going to run with it.

Andrew Huberman 48:06 Right.

Craig Heller 48:06 (laughs) Right.

Andrew Huberman 48:06 Or equip a bicycle with it. Although when are the cooling handles on bicycles coming?

Craig Heller 48:10 (laughs) Yeah. That would be- that would be good. But one- one, uh, itinerant activity is golfing and people have put it on their golf carts and, uh, they're out.

Andrew Huberman 48:18 Do people really heat up that much in golf?

Craig Heller 48:20 They do.

Andrew Huberman 48:21 Not to- to be disparaging of the golfers, but I, the way I c- conceptualize golf, it's like a swing and then a walk and then a- and then a cart ride and then a meal. I probably just offended all the golfers out there.

Craig Heller 48:31 Well, we, one- one time we had, uh, we were doing work for the, uh, for the, um, Department of Defense. And they wanted to check it out whether or not what we were doing was really worthwhile. So they sent out a team of special...... s- uh, special ops soldiers to be our subjects and test it out. They were here for a week. So, (laughs) they, w- that was a fun week. (laughs)

Andrew Huberman 48:56 Yeah. They're, uh, th- I do some work with those guys. They're, they're hard-driving guys.

Craig Heller 48:59 (laughs)

Andrew Huberman 49:00 They, they also know how to have fun.

Craig Heller 49:01 Right. (laughs)

Andrew Huberman 49:01 But they're, they, but yeah, they, they definitely have, um... If they have an off or a s- quit switch, it's buried s- deep within their nervous system.

Craig Heller 49:11 Right.

Andrew Huberman 49:11 Uh, they don't like to hit that, that quit switch.

Craig Heller 49:13 So the guy who wrote the final report, he gave an addendum to the report and he said, "Well, I'll tell you this, after I'd gotten home, uh, it's added..." That technolo- they took the technology with them. (laughs) They wanted to keep it.

Andrew Huberman 49:26 Oh, yeah.

Craig Heller 49:26 Right?

Andrew Huberman 49:26 That's, uh, that sounds about right.

Craig Heller 49:28 As I said.

Andrew Huberman 49:28 Yeah.

Craig Heller 49:28 "And, and using it has added 20 yards to every club in my bag. And that's no effing small-" (laughs)

Andrew Huberman 49:35 Wow.

Craig Heller 49:35 "... deal." (laughs)

Andrew Huberman 49:36 So it's allowing people to hit further-

Craig Heller 49:38 (laughs)

Andrew Huberman 49:38 ... hit the golf ball further.

Craig Heller 49:39 (laughs) Right.

Andrew Huberman 49:40 Interesting.

Craig Heller 49:41 (laughs)

Andrew Huberman 49:42 Um, if, you'll go, all right, so for the, for the, uh, golf, um, players out there and the, um... It, then, uh, that's the, um, uh, that's a reward you get back from Craig for all my, my little knocks on golf. I actually, I, I don't have any knock on golf. I just don't think about it as a sport where heating up is a

Andrew Huberman 50:00 limiting factor. So-

Craig Heller 50:01 Well, you-

Andrew Huberman 50:01 ... since they're getting more, more out of their drive, what's, what do you think's going on there?

Craig Heller 50:06 Well, they can be heating up. Uh-

Andrew Huberman 50:08 And they're wearing gloves, right?

Craig Heller 50:08 ... especially, uh, they're wearing gloves-

Andrew Huberman 50:10 Yeah.

Craig Heller 50:10 ... on a hot day-

Andrew Huberman 50:11 Yeah.

Craig Heller 50:11 ... and so forth. But let me just tell you one more serious, uh, story about golfers and that is, individuals with multiple sclerosis are exceedingly temperature sensitive.

Andrew Huberman 50:21 I didn't know that.

Craig Heller 50:22 So they may still be mobile, uh, but they have to stay in cool locations and not increase their exercise to any great extent. But we've had, uh, subjects that have, with multiple sclerosis, who have just essentially put the device on their golf cart and they're back out playing golf in the middle of the summer.

Andrew Huberman 50:40 Oh, that's great.

Craig Heller 50:41 Yeah.

Andrew Huberman 50:41 That's great.

Craig Heller 50:42 It doe- does help.

Andrew Huberman 50:42 Yeah, anything that allows people to have normal levels-

Craig Heller 50:45 Right.

Andrew Huberman 50:45 ... of, um, you know, livelihood and, um, and recreation is great. We always think about performance as the, at these kind of like peak and elite levels, and, um, pushing harder. But yeah, anything that allows people to be, to be mobile-

Craig Heller 50:58 Right.

Andrew Huberman 50:58 ... and functional is great.

Andrew Huberman 51:00 So, um, w- what's your favorite i- example of endurance? And feel free to give us the extreme one, and then we'll talk about averages at, um, to be, you know, make sure we're thorough about averages versus exceptions.

Craig Heller 51:12 Right. We haven't done a lot in the field. I mean, out- outdoors. Uh, most of our endurance has been in, uh, 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. I mean, we just recruited people in the hallways, "Come on in and do this." And what we found is we could, 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.

Andrew Huberman 51:49 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.

Craig Heller 51:58 Right.

Andrew Huberman 51:59 With proper cooling, when are they doing the cooling?

Craig Heller 52:02 They're, they're doing it continuously.

Andrew Huberman 52:04 I see.

Craig Heller 52:04 Because in the laboratory, we can suspend devices from the ceiling, for example. Now-

Andrew Huberman 52:10 Sure.

Craig Heller 52:10 ... now we do have prototype wearable devices. We did them, uh, y- in response to emails from, uh, Ebola workers a number of years ago in, uh, Sierra Leone. They said, "We've read about your work with athletes. Can't you do something for us? I mean, we're in the personal protective gear, and we can't be in the hot zone for more than 15 or 20 minutes." So that was, started us on the, uh, challenge of developing wearable systems that could go under the PPE. Um, we've published that work now. But-

Andrew Huberman 52:40 That's great.

Craig Heller 52:41 ... there's nothing-

Andrew Huberman 52:41 And I'm guessing the military special operators that are out in the desert and other locations-

Craig Heller 52:45 Right.

Andrew Huberman 52:45 ... are probably excited about this technology.

Craig Heller 52:48 Well, once they get it. (laughs)

Andrew Huberman 52:49 Once they get it. It's coming.

Craig Heller 52:50 It's c-

Andrew Huberman 52:51 It's coming. Uh, yeah, you know, I think some people, um, might wonder, you know, if there are all these studies and there are these incredible results over the years, uh, why haven't we heard

Andrew Huberman 53:00 more about it? And I, I will ask your opinion on that as well, but I'll just editorialize a little bit, is that, y- the, the best laboratory work and its practical applications oftentimes requires many studies. Uh, and oftentimes, there isn't a portal, uh, so to speak, uh, to get that information out into the technology sector, so there is a, a company that's developing this technology for people to use and-

Craig Heller 53:28 Right.

Andrew Huberman 53:28 ... to purchase and use.

Craig Heller 53:30 Right.

Andrew Huberman 53:30 Um, you might as well just tell us now, what is the name of that company and, and do they have a website? People are going to want to know, um, where can they get this magical technology?

Craig Heller 53:38 Right.

Andrew Huberman 53:38 And, and is there a poor man's version of it as well?

Craig Heller 53:42 Well, the company is Arteria, A-R-T-E-R-I-A, and the website is www.coolmitt.com. So Coolmitt is just C-O-O-L-M-I-T-T.

Andrew Huberman 53:55 Mm-hmm. Yeah.

Craig Heller 53:56 Coolmitt.com.

Andrew Huberman 53:57 Yeah. It's a great website. When I went there, it says that right now, the technology is only available to professional sports teams and military. Is that true?

Craig Heller 54:04 Well, where we stand now is, uh, 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, uh, NFL, uh, teams that are using the... There's, uh, uh, college teams. There's, uh, Olympics. There's the, uh, Navy SEALs, uh, uh, Major League Baseball, the NBA, uh, 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-"

Andrew Huberman 54:37 Great.

Craig Heller 54:38 "... and so forth." So that's, that's where we are. But, uh, on the website, you can actually sign up for b-... being one who will be able to get one (laughs) when they are finally manufactured. They're now being made in fairly small lots, because you want to change things-

Andrew Huberman 54:54 Sure.

Craig Heller 54:54 ... as you realize how it can be improved.

Andrew Huberman 54:57 Yeah, this is Stanford after all. You want to get the technology right. I, I like to joke that, uh, one of the reasons I like being at Stanford so much is that not only are my colleagues amazing and they're so forward-thinking, but they're all perfectionists. And so, the, the perfectionist mindset is that it has to be perfect before it can go, go live, so to speak. Well, I think there will be a lot of interest. Um, let's talk about the technology in a little more detail for a moment, and then let's talk about whether or not cruder forms of that technology exist, either for sake of safety and/or performance. Um, so what is, um... The, the CoolMitt, as I understand, is it's a, it's a mitt, it's a glove-

Craig Heller 55:35 Yeah.

Andrew Huberman 55:35 ... you put your hand into. You, you hold onto, uh, a, a surface and that surface, um, cools you, cools your hand and-

Craig Heller 55:42 Right.

Andrew Huberman 55:42 ... thereby through this, uh, specialized, um, portal, cools your, your core body temperature and all the, 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?

Craig Heller 55:58 Just cool.

Andrew Huberman 55:59 I see.

Craig Heller 55:59 Ice cold is too cold. 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. Uh, so you stick your hand in cold water, uh, when it comes out, it's cold.

Andrew Huberman 56:20 You just sealed up all the heat in your body.

Craig Heller 56:22 You, you... Yeah, right. Uh, so, well, what I sort of recommended to someone at one point, they said, "Well, when I'm running, can't I just carry a frozen juice can and it will gradually melt?" And I said, "Well, no, because that's going to decrease the heat loss from that hand. But if every couple minutes you switched hands-" (laughs)

Andrew Huberman 56:40 Exac-

Craig Heller 56:40 "... it might work." (laughs)

Andrew Huberman 56:41 Well, I have a feeling that there are people now doing that as well as trying, trying this. So, um, how long in, in the CoolMitt at the proper temperature-

Craig Heller 56:51 Yeah.

Andrew Huberman 56:51 ... um, how long are, are people putting their hands into the mitt?

Craig Heller 56:55 Well, we, we once again had just standardized on three minutes. Uh, and part of the reason for that is that the heat lo- 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.

Andrew Huberman 57:18 Okay. You mentioned, uh, a number of impressive, uh, organizations, sports teams, and military that are using this. This is not something that I typically see on the sidelines of games, although to be honest, I haven't looked very carefully. Um, I'm guessing that they are probably keeping the technology somewhat under wraps. Uh, where and how are they doing this? Are they running back to the locker room? I mean, the, the military special operators are doing their thing, but in terms of the athletes, um, is it possible, hypothetically, that athletes are doing this, um, somewhat incognito?

Craig Heller 57:51 It, it's possible, but I really don't know. Uh, people have mentioned here at Stanford, um, they don't see the football team using it. Well, the football team here at Stanford is mostly playing in cold weather, cool weather. The night games are cool. Even day games are not very hot frequently here. But when they go to a hot place like Arizona or Utah, uh, at least, uh, our coach, uh, Shaw says that they take it with them and that's when they, uh, find the benefit.

Craig Heller 58:20 That's when they use it.

Andrew Huberman 58:21 Interesting. So is there a poor person's, uh, poor man or woman's version of this? Uh, you mentioned the juice can passing back and forth. You mentioned cooling the hands. Uh, a number of people said to me after learning a little bit about this science and technology that they've experienced some big effects, uh, positive effects of, of cooling by, uh... And I confess I've done this, taking a, a, a package of frozen blueberries and just kind of passing it back and forth-

Craig Heller 58:51 Yeah.

Andrew Huberman 58:51 ... between my hands.

Craig Heller 58:52 Yeah.

Andrew Huberman 58:52 Now talking to you, I realize I probably didn't do it long enough. I probably was... I was only doing maybe 30 seconds passing it back and forth between my hands and then going back into sets. I did see a performance-enhancing effect-

Craig Heller 59:04 Uh-huh.

Andrew Huberman 59:05 ... ab- absolutely. But, um, I realize I probably wasn't optimizing the protocol. If you were going to give a, um, a crude protocol for, let's just say for the gym, because with running it's a little bit tricky, but, um, what would that look like if people wanted to just play with this in, in some sort of fashion?

Craig Heller 59:23 Well, that, it, you know, it's would be experimental. (laughs)

Andrew Huberman 59:28 Sure.

Craig Heller 59:29 And I-

Andrew Huberman 59:29 Yeah, none of that is con- very controlled.

Craig Heller 59:31 Your idea of frozen peas is a good idea, uh, and I think s- since there's been no actual study of that, it would have to be you working out what is the best for you. But one way to figure it out is that if after you ho- 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 vasoconstricted.

Andrew Huberman 59:59 Ah.

Craig Heller 1:00:00 If it's warm, it means the hot blood is still going there. Okay, so we do that in the lab.

Andrew Huberman 1:00:06 And the key is for it to not vasoconstrict?

Craig Heller 1:00:08 Right.

Andrew Huberman 1:00:09 Okay. So, so there's a test out there, folks. If you're gonna try this in kind of crude fashion, at least until the, uh, the CoolMitt is available more broadly, um, to the general public, you could assess, you want to assess whether or not the ha- your palms actually feel cool to the touch by somebody else-

Craig Heller 1:00:27 Right.

Andrew Huberman 1:00:27 ... to es- and if it does, that means you sh- you've essentially shut down the portal. You're sealing in more heat-

Craig Heller 1:00:31 Right.

Andrew Huberman 1:00:31 ... which is bad. What about, um, putting this cold pack of some sort on the face or, um-

Craig Heller 1:00:39 Or on the feet.

Andrew Huberman 1:00:39 ... or on the feet? I work out at home. I, I don't often work out barefooted, but I suppose I could, like they did in the '70s, you know, when those guys were walking around, uh, without shoes and squatting without shoe- uh, without any shoes or socks on. Could I put my feet on them?

Craig Heller 1:00:53 You, you could.Um, if you had- simply had a water-profused pad and you were circulating cool water through it, uh, you could just put your feet on it, okay? Um, part of the problem is, um, that you don't want... I- if, let's say you have just a cold pack

Craig Heller 1:01:15 of something. 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. Uh, so that decreases its, its efficacy.

Andrew Huberman 1:01:35 I see, but maybe we should just for a moment talk about convection, uh, radiation and convection, and just make that clear. Like if I put my hands, um... Let's say it's a cold night and I'm at a campfire and I take my hands and I put them out to the fire.

Craig Heller 1:01:48 You're getting radiation.

Andrew Huberman 1:01:49 You're getting radiation.

Craig Heller 1:01:50 Right.

Andrew Huberman 1:01:50 Okay.

Craig Heller 1:01:51 Right.

Andrew Huberman 1:01:51 (laughs) And, and then if it's a windy, warm night... No, I don't know if that's the best example. Give us a good example of convection, um.

Craig Heller 1:01:59 Convection, sure, is, is in a cool breeze.

Andrew Huberman 1:02:01 Yeah.

Craig Heller 1:02:01 You know, the wind chill factor.

Andrew Huberman 1:02:03 Sure.

Craig Heller 1:02:03 That's due to convection.

Andrew Huberman 1:02:04 Mm-hmm.

Craig Heller 1:02:04 Okay? But in terms of heat transfer between two objects, uh, if you have convection of the medium, whether it's blood on the inside and water on the outside, you increase the heat exchange if you have convection on both sides.

Andrew Huberman 1:02:23 Right, so this is why just planting my feet on two, um, packages of fro- my bare feet on two packages of frozen peas, there's really no opportunity for circulation-

Craig Heller 1:02:33 Right.

Andrew Huberman 1:02:33 ... of, and, and therefore heat transfer, so it's not really optimal, which is ag- I, and I-

Craig Heller 1:02:38 But once again, it depends on the surface area to get any benefit at all. We have a study that we published, um, which was investigating the standard treatment for hyperthermia in the field, and the standard, uh, treatment, the, the, uh, that's recommended by, uh, medical organizations is you take cold packs and you put them in the axilla, the groin.

Andrew Huberman 1:03:03 The axilla or the... Are the, are the armpits?

Craig Heller 1:03:05 The armpits, yeah, the groin, which is, uh, uh-

Andrew Huberman 1:03:09 Thin skin, lots of vasculature.

Craig Heller 1:03:11 Right, (laughs) and the f- and the neck. 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 positions in the r- those heat exchange bags in the recommended location versus on the glabrous skin, versus palms, soles, and face. The, the cooling rate was double.

Andrew Huberman 1:03:36 Wow, so-

Craig Heller 1:03:37 If we put the same ice packs, the same cold packs, uh, on the, uh, heat portals, rather than, uh, the axilla, the groin, and the face.

Andrew Huberman 1:03:47 Wow.

Craig Heller 1:03:48 Or the neck.

Andrew Huberman 1:03:49 Wow, so face, hands, and bottoms of feet will cool you twice as fast-

Craig Heller 1:03:56 Th- right.

Andrew Huberman 1:03:56 ... as putting cold packs into your armpits, your groin, or back of neck? Amazing.

Craig Heller 1:04:02 So, so I like to give the analogy of if your car is overheating, okay, and you have a hose, a garden hose. Where should you spray your cooling system? Should you spray the radiator or should you spray the tubes going in and out of the radiator? Well, the rationale with putting these cold packs in the axilla, the groin, and the neck is that you're getting close to the major arteries, okay? Sure, that's going to be effective, but (laughs) it's much more effective if you actually increase the heat loss capacity of the radiating surface, the radiators.

Andrew Huberman 1:04:34 So you cool the hot stuff heading toward the core.

Craig Heller 1:04:38 That, that's essentially

Craig Heller 1:04:40 what the standard operating procedure is.

Andrew Huberman 1:04:43 Mm-hmm.

Craig Heller 1:04:43 The... That you hit the arteries.

Andrew Huberman 1:04:45 Mm-hmm, amazing.

Craig Heller 1:04:47 And the veins. The arteries and veins.

Andrew Huberman 1:04:48 I'm going to just tell a brief story that, um, illustrates how almost everybody gets this stuff wrong, and then I'm going to use that as an opportunity to ask you about heating. Deliberate heating as opposed to deliberate cooling. So about four months ago, a friend of mine, a- and incidentally a, a guy who did nine years in the SEAL Team, is a really skilled cold water swimmer. We went out for a swim in the morning. Um, I'm not nearly even close to the... Being in the same universe of his, um, output potential. We do these swims. I'm familiar with them. I got enough blubber on me that I'm f- stay warm enough in the cold Pacific, no wetsuits. We do the morning col- cold swim for about a mile or so, and we brought with us a, a young kid that I know real well that hangs out with us sometimes and trains with us who's got very little body fat. He's just exceptionally lean despite eating everything in sight, right?

Craig Heller 1:05:42 (laughs)

Andrew Huberman 1:05:42 Teenager. Great athlete, great kid. Great swimmer. So we're out there swimming, and at some point, we're talking to him and it's clear that he's gone hyperthermic. He's slurring his words. He's not doing well. So we get him onto the beach. His teeth are turning yellow. He's quaking. He's not... He's got, um, you know, his saliva has taken on that consistency that's clear, like, he's hyperthermic. We go to the lifeguard station. Lifeguard says, "Okay, let's get his vitals. Let's do all this." Meanwhile, trying stand next to him, you know, y- and heat him up by heating up his torso. So there we are, like, pressing against this guy, our friend, trying to heat him up. They get a blanket on him. He's... I'm realizing he was barefoot. His face was exposed, although we did cover his head with the blanket, and he eventually came back. We got some warm liquids into him and he, he was okay. He was fine. I don't know that his mother is ever going to let him swim with us again. Um, if, if I ever-

Craig Heller 1:06:42 Yes.

Andrew Huberman 1:06:42 ... disappear and go missing, it's because of that incident. Anyway, um, he did great. He recovered. He's back in the water and doing well. But I realized that pretty much everything from the point where we got back on the beach-... Until he was back to normal was, we did incorrectly. We heated his torso, we left his extremities exposed, and we assumed we were doing the right thing. And the lifeguard is a skilled lifeguard at a major public beach. So I guess the simple question is, did we get everything wrong? Did we get anything right? And what would have been the better option to heat up a hypothermic person in that or a similar situation?

Craig Heller 1:07:26 Well, it's interesting you ask that, because that is the way we got into this area of investigation. Um, I worked on how the hypothalamus regulates body temperature, neurophysiology. And one day, uh, we were having a discussion with a colleague in the Department of Anesthesia. And, uh, he, he jokingly said to my colleague, he said, "Yeah, you guys think you know so much about temperature. I bet you couldn't solve a problem we have in the recovery room." "What's that?" "Well, the patients come out of surgery, they're hypothermic, and it takes us hours to get them to stop shivering." What do they do in the recovery room? Exactly what you suggested. They put in warm blankets, they put on heat lamps, uh, and it takes them an hour or two hours to get these patients to stop shivering, to bring them back up to... So we say, "Ah, it's a trivial problem." No, it's a hard problem. It's a hard problem because when you're under anesthesia, you're vasodilated. When you come out of anesthesia, you're hypothermic and you vasoconstrict. That makes it very difficult to get heat into the body. So we got the idea that, well, if we could just take one appendage, like an arm, and we put it in a, uh, environment wrapped in a heating pad and a, a negative pressure, you know, suction, uh, that would pull more blood into that limb. That blood would get heated, and it would warm the body up faster. So my colleague built a prototype device. You (laughs) couldn't get such a device into the hospital these days. (laughs) But we were, were with our anesthesiologist friend, we took it into the recovery room, and, and first thing the patient said, (laughs) "No way. (laughs) You're not going to put that on my patient." But he prevailed. And first patient ins- didn't shiver at all. First patient was back to normal temperature, core temperature in, I think it was eight minutes.

Andrew Huberman 1:09:28 Amazing.

Craig Heller 1:09:28 Eight or nine minutes.

Andrew Huberman 1:09:29 Is this now standard practice in hospitals?

Craig Heller 1:09:31 No, no, no.

Andrew Huberman 1:09:32 So this is another example-

Craig Heller 1:09:33 No, no, no.

Andrew Huberman 1:09:34 ... where I, I don't get upset about the f- although it, it's upsetting to know that it's not. But I think that it's yet another case where a fundamental problem exists. There's a, a science-based solution that makes sense at the level of physiology, engineering, and practice, and yet it's not being done.

Craig Heller 1:09:56 Right.

Andrew Huberman 1:09:56 And I mean, we could t- we, that's a whole other discussion as to what the limitations are. Well, perhaps in, and I know a number of our listeners are in the healthcare and medical-

Craig Heller 1:10:04 Yeah.

Andrew Huberman 1:10:04 ... profession, as well as military athletes, and just also standard other types of jobs, civilians, uh, uh, doing other types of work. Uh, it would be wonderful if people understood this. So, um, once again, is there a, uh, is there a homegrown technology that people could use? If somebody is hypothermic, what is going to be the best way for them to warm up? Is it going to be holding a, a nice warm, um, mug of cocoa or something like that, but not, not too hot, I guess, is-

Craig Heller 1:10:31 Yeah, sure.

Andrew Huberman 1:10:31 ... again, the idea?

Craig Heller 1:10:31 Yeah, um, well, actually, you can go hotter on the, on the glabrous skin, the-

Andrew Huberman 1:10:37 Oh, because they don't dilate.

Craig Heller 1:10:38 ... bec- because it takes the heat away faster.

Andrew Huberman 1:10:41 Mm-hmm.

Craig Heller 1:10:41 Okay? But back to the a- anesthesia, what you can do is you can use, uh, warm pads. They have them in, uh, all hospitals. They have circulating water-

Andrew Huberman 1:10:51 Mm-hmm.

Craig Heller 1:10:51 ... perfused pads. Put-

Andrew Huberman 1:10:52 Hot water bottle type stuff.

Craig Heller 1:10:53 Put them on the feet. Put them on the feet.

Andrew Huberman 1:10:54 So typically, they'll slide them under your lower back or-

Craig Heller 1:10:57 Yeah.

Andrew Huberman 1:10:57 ... something like that.

Craig Heller 1:10:57 Yeah, put them in, put them on the feet. Okay, sure. That, that will do it. But, uh, turns out that, uh, we discovered through this work that it had nothing to do with the whole arm. It was only the hand, and that's when we came to the realization of these special blood vessels. We didn't discover the blood vessels. They're described in Gray's Anatomy, but nobody knew what they were for.

Andrew Huberman 1:11:21 Are... And you mentioned bears earlier and other hairy animals. Um, do they have these AVAs-

Craig Heller 1:11:28 Oh, yeah.

Andrew Huberman 1:11:28 ... as well? Oh, and I suppose we haven't defined AVAs. We've been pretty good about the no acronyms rule. AVAs is?

Craig Heller 1:11:33 Arteria venous anastomoses, so a connection between the arteries and the veins. Yeah.

Andrew Huberman 1:11:40 I actually use this technology. I have a bulldog, bulldog mastiff.

Craig Heller 1:11:43 Uh-huh.

Andrew Huberman 1:11:43 He has a very high, um, propensity for overheating.

Craig Heller 1:11:47 Mm-hmm.

Andrew Huberman 1:11:47 Because they, they're terrible at dumping heat, and bulldogs are great at pushing themselves-

Craig Heller 1:11:52 Yeah.

Andrew Huberman 1:11:53 ... to the point of exhaustion or death. It ha- it happens. And so now we do what we call palmar cooling.

Craig Heller 1:11:59 (laughs) Ah.

Andrew Huberman 1:11:59 Sorry, I couldn't help myself. Where I'll take Costello and lower him into a cool body of water, just the, just the bottoms of his paws. Although I think animals-

Craig Heller 1:12:07 Mm-hmm.

Andrew Huberman 1:12:08 ... instinctually know to do this, and will go and stand in-

Craig Heller 1:12:12 Yeah, yeah.

Andrew Huberman 1:12:12 ... bodies of water. They don't often lie down all the way.

Craig Heller 1:12:15 Yeah.

Andrew Huberman 1:12:15 Some do.

Craig Heller 1:12:16 Yeah.

Andrew Huberman 1:12:16 Um, but they seem to know that's a great-

Craig Heller 1:12:19 Yeah.

Andrew Huberman 1:12:19 ... way to cool themselves off.

Craig Heller 1:12:21 Mm-hmm. Yeah. Oh, absolutely, yeah.

Andrew Huberman 1:12:23 And they get the advantage that their palm, that their palms and their feet are essentially the same thing, so.

Craig Heller 1:12:27 We, we actually built devices for dogs-

Andrew Huberman 1:12:30 Did you really?

Craig Heller 1:12:30 ... and tried them on Iditarod sled dogs, and worked beautifully. They had little backpacks with the equipment and pads on all their feet and, and, uh, it worked beautifully. (laughs)

Andrew Huberman 1:12:42 Amazing, amazing. Along the lines of

Andrew Huberman 1:12:45 heating, deliberate heating, wearing a knit, um, cap is something that you see more of that on the East Coast. You know, people running around Boston and New England-

Craig Heller 1:12:55 Yeah.

Andrew Huberman 1:12:55 ... you know, with a, with a knit cap. Uh, I've always done that at the start of my runs to try and warm up-

Craig Heller 1:13:01 Yeah, yeah.

Andrew Huberman 1:13:01 ... more quickly, and then I take it off. I shed layers as I go. Um-Is that a rational practice the way I just described it?

Craig Heller 1:13:09 Oh, sure. Yeah.

Andrew Huberman 1:13:09 Yeah. 'Cause warming up is important too. Y- you know, there's a certain amount of, uh, quote-unquote, warming up that's required to l- lubricate joints or at least to get the sense that joints are lubricated and, and to be able to move more easily.

Craig Heller 1:13:21 Yeah.

Andrew Huberman 1:13:21 Do you still recommend that people warm up?

Craig Heller 1:13:24 Yeah. Uh, but I think we're misled by the term warm up, as if the major purpose is to raise temperature. Um, I don't, I'm not aware of any data on this, but I, I do think that the major contribution is increasing flexibility. Uh, so you're going to avoid having damage, uh, of joints and, and tendons and ligaments and so forth. Um, but, uh, also, um, the ability of the mitochondria to produce, uh, energy, uh, can be impaired at low- lower temperatures. And you have to keep in mind that we say our body temperature's 37 degrees. But that's not true.

Andrew Huberman 1:14:06 Yeah. It varies across the day. It's-

Craig Heller 1:14:08 It, it, well, it varies in parts of your body. I mean, my hands and arms are not at 37 degrees right now. They're much lower. (laughs)

Andrew Huberman 1:14:16 So that, that raises an interesting question. What is the best way to measure core body temperature?

Craig Heller 1:14:22 Well, the best core temperature is the, what we use is esophageal. So we put a thermocouple up the nose, about two feet down the esophagus, (laughs) so that it's about the level of your heart.

Andrew Huberman 1:14:34 Not gym or home practical. Although-

Craig Heller 1:14:37 (laughs) No.

Andrew Huberman 1:14:37 I don't know, some of those COVID swab tests go pretty far.

Craig Heller 1:14:40 Too far. (laughs)

Andrew Huberman 1:14:40 I can't even imagine going any further.

Craig Heller 1:14:42 Too deep.

Andrew Huberman 1:14:42 I felt like my brain was getting tickled.

Craig Heller 1:14:44 (laughs)

Andrew Huberman 1:14:44 Um, and it was really unpleasant.

Craig Heller 1:14:46 But tympanic, uh, tympanic is a pretty good...

Andrew Huberman 1:14:48 So the ear.

Craig Heller 1:14:49 The ear.

Andrew Huberman 1:14:49 Yeah.

Craig Heller 1:14:50 Uh, it's not foolproof because you have to actually have it aimed properly at the tympanum. And frequently what you're getting is you're getting sort of a mixture of tympanic plus ear canal temperature.

Andrew Huberman 1:15:02 And the, and for those listening and for those watching, the tympanic is not gonna be the pinna, the, this part of the ear, the outer part of the ear. The tympanic is gonna be near the tym-

Craig Heller 1:15:10 All-

Andrew Huberman 1:15:10 ... headed towards the tympanic membrane. And yes, I'm sticking my finger in my ear, because that's where it, the laser would actually have-

Craig Heller 1:15:16 Right.

Andrew Huberman 1:15:16 ... to go to measure your temperature.

Craig Heller 1:15:18 Right, right.

Andrew Huberman 1:15:18 So when we're walking into restaurants and other places nowadays and they're shining the laser at our forehead, that's probably giving a pretty crude readout of temperature.

Craig Heller 1:15:25 Y- it is, but there's much less insulation between your brain and your forehead skin than there is between your biceps and your arm skin. So if you're going to measure a surface temperature, that's where you would do it. And, uh, y- we do temperatures in the infrared. We d- we take infrared videos of athletes and, and our, our subjects. And of course, the face lights up.

Andrew Huberman 1:15:49 Mm-hmm. Okay. So if we're no- I imagine there's gonna be a technology coming soon where you can point your, um, smartwatch or your smartphone at yourself and you're gonna get a heat map.

Craig Heller 1:15:58 Right, right.

Andrew Huberman 1:15:59 That's got to... If, if somebody out there hasn't already invented this, p- for the typical folks outside military, somebody please invent that, because, um, I think there is growing interest in temperature, uh, based on the work that you're doing and also for sake of, um, something I do want to touch on, which is sleep and metabolism, although we don't want to open up, uh, those portals all the way, because we'd need, uh, several days to cover it. Um, okay, so w- putting on the, the, the cap, um, what about some of the helmets and gloves that are used in typical sports? Do you think that those can be improved in order to m- improve performance in terms of their ventilation ability or keeping palmar surfaces, um, open, for instance?

Craig Heller 1:16:40 Well, you mentioned about the, the knit cap in, in cold weather especially, and that is significant because you do lose a lot of heat from your head. Uh, but it's a constant heat loss. It's not variable like your glabrous skin. So, uh, if you decrease that heat loss, you're going to be warmer. Uh-

Andrew Huberman 1:17:02 Okay.

Craig Heller 1:17:02 ... so sure, that, that, that has an impact. Uh, now in terms of helmets, uh, they should be, uh, ventilated. I mean, they should have enough, uh, space in them and holes in them so that air can circulate. Uh, you don't want to insulate, uh, thermally insulate your, your scalp. That's going to decrease heat loss quite considerably. You know, just for a resting individual, the brain is about 20% of your metabolism. So that's, that's a lot of heat production.

Andrew Huberman 1:17:32 Yeah, absolutely. Um,

Andrew Huberman 1:17:35 I realize there was a question that I failed to ask earlier, um, that is y- burning in my mind now, and I think is likely burning in the minds of, of some of the listeners which is, so y- if you do this cooling in between sets in the gym-

Craig Heller 1:17:49 Mm-hmm.

Andrew Huberman 1:17:49 ... you get this performance enhancing effect.

Craig Heller 1:17:51 Mm-hmm.

Andrew Huberman 1:17:52 You don't get the delayed onset muscle soreness-

Craig Heller 1:17:55 Mm-hmm.

Andrew Huberman 1:17:55 ... which is great.

Craig Heller 1:17:56 Mm-hmm.

Andrew Huberman 1:17:56 So presumably, the body is adapting.

Craig Heller 1:17:59 Mm-hmm.

Andrew Huberman 1:17:59 You're getting better as a consequence-

Craig Heller 1:18:00 Yep, yep.

Andrew Huberman 1:18:00 ... of being able to do more work per unit time-

Craig Heller 1:18:03 Yep, yep.

Andrew Huberman 1:18:03 ... or to go harder in some way-

Craig Heller 1:18:05 Right.

Andrew Huberman 1:18:05 ... of course. Um, 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?

Craig Heller 1:18:17 Yes.

Andrew Huberman 1:18:17 So for instance, let's say I can do 10 sets of 10 dips which I, I like to think I can. (laughs) Maybe I need to go try. I don't know if I've done that recently. I do the cooling. I, I cool for three minutes between sets. And let's say I, uh, get to the point where I can do, you know, 20 for 10 sets, n- um, 10 sets of 20 repetitions, and then I don't cool.

Craig Heller 1:18:37 Mm-hmm.

Andrew Huberman 1:18:38 Will I be able to m- match or approximate my new better performance?

Craig Heller 1:18:42 You keep your gains. It's a true conditioning effect. You respond to the increased work volume by all of those mec- mechanisms you mentioned.

Andrew Huberman 1:18:52 Amazing.

Craig Heller 1:18:52 You increase the number of contractile elements in your muscles.

Andrew Huberman 1:18:56 Amazing.

Craig Heller 1:18:56 Your muscles get bigger.

Andrew Huberman 1:18:57 Amazing.

Craig Heller 1:18:58 Uh, we had an experiment that involved some of our, uh, uh, female, uh, students, not athletes, but just regular, they were freshmen actually, and, uh, the experiment was, uh, 10 sets of push-ups to muscle failure with or without cooling.

Andrew Huberman 1:19:15 Same regimen, three minutes of r- of cooling in between sets of push-ups?

Craig Heller 1:19:18 Right.

Andrew Huberman 1:19:18 Okay.

Craig Heller 1:19:19 Some of those young ladies-... reached over 800 push-ups.

Andrew Huberman 1:19:25 Now, the total duration of the workout could be getting much longer as a consequence-

Craig Heller 1:19:28 No.

Andrew Huberman 1:19:28 ... of doing more work.

Craig Heller 1:19:29 No. No. It doesn't take you longer. Well, minor. I mean, a push-up is pretty fast.

Andrew Huberman 1:19:34 Yeah, it's pretty fast.

Craig Heller 1:19:35 Yeah. So, you do 10 sets to the maximum, uh, and 45 minutes total. Most of it-

Andrew Huberman 1:19:40 That's a lot, that's a lot of push-ups.

Craig Heller 1:19:41 That's a lot of push-ups.

Andrew Huberman 1:19:43 Yeah. Yeah.

Craig Heller 1:19:43 (laughs) And so the interesting thing is they came in one day and they said, "Dr. Haler, you cost us a lot of money." "Why?" "Well, we had a formal dance this weekend. We all had to buy new sleeveless dresses." (laughs)

Andrew Huberman 1:19:53 Nice.

Craig Heller 1:19:54 (laughs)

Andrew Huberman 1:19:54 It's a good

Andrew Huberman 1:19:55 problem to have. Good problem to have. Um, let's talk about steroids, anabolic steroids. Um, we're heading into an Olympics.

Craig Heller 1:20:04 Mm-hmm.

Andrew Huberman 1:20:04 Um, every time the Olympics rolls around, you hear about these cases of people getting popped, as they call it, or caught for anabolic steroids. There are some accusations out there now. There will be more. They'll, this will get, um, you know, handled in the press and in the various organizations. Clearly, athletes and non-athletes use anabolic steroids, and typically, anabolic steroids are of the testosterone variety. There are derivatives, et cetera, and those derivatives do different things and anabolic versus androgenic, et cetera, but typically, the idea is, at least as I understand it in talking to some of these individuals, um, is that they allow people to train more because they recover faster. They are able to synthesize more protein because they're basically getting a second puberty because as we all know, during puberty, there's a lot of growth of the body, um, and of course, there are a lot of negative effects of abuse of these things, and they are banned from, from various sports organizations, especially I should mention in combat sports, it's, this is especially concerning because in combat sports, a performance enhancement means that you can harm somebody more than you would be able to otherwise.

Craig Heller 1:21:19 Mm-hmm.

Andrew Huberman 1:21:20 As opposed to in other s- sorts of sports. Just to conceptualize it and, um, and I'm not taking a moral stance on any of this. I just want to ask you, when you compare palmar cooling to anabolic steroids in terms of gym performance, what do you see?

Craig Heller 1:21:38 Well, we do not do research on steroids, (laughs) but there is a lot of research in the literature. Uh, a lot of that re- research in the strength