Dr. Craig Heller

Well, first of all, you get a tremendous shock.

And what that's going to translate into is a bit of a shot of adrenaline.

And I think this is really the so-called benefit, but it doesn't necessarily translate into any benefit in terms of your physiology or performance and so forth.

Now, if you take a cold bath or a cold shower, a couple of things are happening.

One is you're going to stimulate vasoconstriction.

So if anything, it's going to make it a little bit more difficult for your body to get rid of heat because you're shutting off your avenues of heat loss.

If you're in a true cold bath, the overall surface area of your body is so great that it doesn't matter if you've acid constricted, you're still going to lose heat.

The primary sites of heat loss, which we're going to get into, are the palms of your hands, the soles of your feet, and the upper part of your face.

And the reason these are avenues for heat loss is they're underlain by special blood vessels.

And these blood vessels are able to shunt the blood from the arteries, which are 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.

Well, there are differences that are more physical than anything else.

So if you are in a cold bath and you're still, you develop a boundary layer.

It's best to explain it in terms of a hot bath because everybody's experienced that.

You get into a hot bath and, oh, my God, it's really hot.

almost painful.

And then you sit down and eventually it doesn't feel so hot anymore because the still water, which is close to your skin, is coming into equilibrium with your skin.

So it's like having a blanket on you or an insulator on you.

And then if you move around, you disturb that still water layer, you feel the hot temperature again.

Got it.

Yeah.

But I think getting back to your original question about benefits, you have to keep in mind whether you're talking about aerobic activity or anaerobic activity, if you're referring to performance 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.

I see.

Sure.

It'll take them longer to get to the sweat point and to heat up.

And what will that translate to in terms of a performance benefit?

Well, it could increase your speed or it depends on how you use that benefit.

Some people are pacers.

They will go at the same pace and then they will go farther.

Or some people are forcers.

They will take that advantage and use it up as fast as they can.

So they will go faster, but not necessarily farther.

For the anaerobic athlete, and let's say they're doing several sets, their core temperature is not going to rise that fast because it's only certain muscles which are being used.

But the temperature of those muscles will go up.

So it's a local effect.

Right.

And then during rest, that heat will leave the muscle, but it's not fast.

And certainly the heat can't leave the muscle very fast while you're working out because when the muscle contracts, it squeezes the blood vessels.

And the only way heat gets out of a muscle is in the blood.

And your muscle metabolism can go up 50 or 60 fold during anaerobic activity.

That means the heat production in the muscle goes up 50 or 60 fold.

The blood flow to that muscle cannot go up 50 or 60 fold.

So you literally have the capacity to cook your muscles.

So to keep you from damaging your muscle,

by hyperthermia, we have fail-safe mechanisms.

And one of those fail-safe mechanisms is an enzyme which is critical for getting fuel, in other words, the results of metabolism of glucose, getting that fuel into the mitochondria, which is making our major coinage of energy exchange, ATP.

So that particular enzyme is temperature sensitive.

So when the muscle temperature gets above 39 or 39.5, it shuts off.

And that essentially shuts off the fuel supply to the mitochondria.

That's when you cannot do one more rep.

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

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

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

It's one of them.

And it's a quick one.

Because your body surface is a very good insulator.

The skin, the fascia, the muscles underneath, they're all very good insulators.

And that's why I said earlier that the way the heat gets out of the muscle is in the blood.

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

And you can't continue drinking liters of ice water.

You're going to dilute your blood and have other problems.

But yes, it'll help.

Sure, it will help.

But it doesn't have the full capacity you will need.

Well, you have to understand something about our thermoregulatory system.

We have a thermostat, just like you have a thermostat in your house, and that thermostat is in the brain.

It's called the preoptic anterior hypothalamus.

It does many things in terms of physiological regulation, but it serves as a thermostat.

Now, that thermostat has to have information.

It has to have input.

Where does that input come from?

It comes from our overall body surface where we sense temperature.

So one of the things that can happen when you're overheated

is that you can send in a cold stimulus to your thermostat.

And that's sort of like wanting to cool your house by putting a wet washcloth over your thermostat.

It's doing the wrong thing.

So we've actually had experiences where we've had people exercising, getting overheated, and then cooling the body surface.

And they say, it feels great.

This is fantastic.

And their core temperature is going up.

So what can happen if you, let's say, cool the torso with an ice vest, you can actually cause vasoconstriction of your portals, your heat loss portals.

So that's what impairs the rate at which you're losing heat.

It feels good.

Now, back to the head.

That's really interesting.

The major blood flow to the brain comes up four arteries through the neck.

There'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 cooled the thermostat.

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

Interesting.

Yeah, you can feel great and have a dangerously hyperthermic temperature.

But I should say that when you get into the danger zone, things get bad fast.

What are some of the symptoms that people could be on the lookout for, for hyperthermia?

Essentially, it's almost ironic that if individuals are transitioning into heat stroke, they actually vasoconstrict and they stop sweating.

And that's a pathological situation.

I couldn't begin to explain it.

But essentially, you are just feeling exhausted.

You're feeling miserable.

The heart rate is very high.

Your heart rate goes up as your core temperature goes up, called cardiac drift.

So you just feel rotten.

It's not a danger signal that you can translate immediately into, nope, I'm going into heat stroke.

That's why people can overcome their bad feeling with motivation to continue going, to work harder.

So there have been a number of high-profile athletic deaths due to heat stroke that were during practice.

Not in competition when people are really trying to do it, but in practice, which shows they were just motivated to push forward.

Where the portals are, are in the glabrous skin.

Big word, okay?

Glabrous just means no hair.

So it's the hairless skin.

You say, well, most of my body is without hair.

No.

No.

Most of your body has hair follicles.

We are mammals.

Mammals have fur.

We've lost the fur, but we still have that hairy skin phenotype all over our body, except for those skin surfaces where our mammal relatives didn't have fur.

So the pads of the feet.

And for the primates, upper part of the face.

For rabbits, no portions of the ears, the inner surface of the ears.

I never thought about that.

Our mammalian relatives can't lose heat over their overall body surface.

So probably very early on in mammalian evolution...

They evolved these special blood vessels in the limited surface areas that don't have fur.

And as I said, what these blood vessels are, are shunts between the arteries and the veins.

Arteries and veins are both low resistance vessels.

So you can have high flow rate.

Capillaries, which normally are between arteries and veins, are high resistance because they're very tiny.

If you are warm and you look at the palms of your hands, they are fairly red.

The backs of your hands aren't.

You don't have these vessels in the backs of your hands.

Now, if you take a glass, like a water tumbler, right, and you grab it, you can see if you squeeze a little bit, the hand goes white.

that's because you've shut off that blood flow.

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... Well, this is important.

Well, gloves definitely impede heat loss from the hands, just as socks impede heat loss from the feet.

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.

Interesting.

Let me introduce one more thing because you asked earlier about the pouring of water on the head.

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,

And that blood then returns in the venous supply to the heart, but it actually does it in a very strange way.

We go through the skull, okay?

And that's why the scalp bleeds a lot if you cut the scalp.

And these blood vessels were...

primarily thought to be ways that blood is leaving the brain.

But when you're overheated, the direction of flow in those blood vessels reverses.

So the 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 pouring water on your head.

Yeah, it's one of the natural mechanisms for cooling the brain.

I'm aware of those ideas, but they're controversial.

One of the things that you want to do for injury to the brain is to decrease swelling.

And one of the ways that you decrease swelling in many parts of the body is to cool.

It decreases inflammation.

It decreases the blood flow.

So...

I think it's a really interesting topic, and it's something that should be investigated.

It's kind of hard to investigate.

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.

So the word got over, I think, to the 49ers camp.

And one of their players, Greg Clark, who was a tight end at the time, he had been tight end at Stanford, he decided to come over and check it out.

So, Greg came over and we said, Greg, what are you good at?

What activity do you like to do?

He said, dips.

I can do a lot of dips.

I can do 40 dips in a first set and I can probably do five sets.

That's a usual workout for me.

And we said, okay.

So he came over to the gym one day and that's exactly what he did.

He did 40 dips, the first set, and then maybe 25 and 15 and down from there.

Can you recall roughly what kind of rest periods he was taking between sets?

So several days later, he came back, and his first set he did, I think, maybe 42.

Then his second set was, I don't remember the numbers, but very much above the second set on the control day.

This was after we cooled his armor surface.

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

Yeah, that's what we were doing.

We standardized the interval for resting or cooling.

The point is he got to his fifth set, and all of the sets were above what he had done on the previous day.

And he said, you know, I'm not tired.

I can do another set.

And then I can do another set.

I can do another set.

I can do another set.

So from one day to two or three days later with cooling, he doubled the total number of dips.

Right.

So then he kept coming back for four more weeks, twice a week.

And by the end of that month, he was doing 300 dips.

So he tripled.

He tripled.

He essentially tripled.

Here's a professional athlete at peak physical conditioning, and he triples what he can do.

We haven't done a lot in the field.

I mean, outdoors, most of our endurance has been in a hot room with treadmill work and so forth.

So the very first experiment, we had, I think, maybe 18 subjects just off the street.

For this group, with one trial, with and without cooling, we could double their endurance.

Walking on the treadmill, walking uphill on the treadmill in the heat, like maybe 40 degrees ambient temperature, 40 degrees centigrade.

They're doing it continuously.

I see.

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

Well, the company is Arteria, A-R-T-E-R-I-A, and the website is www.coolmit.com.

So coolmit is just C-O-O-L-M-I-T-T, coolmit.com.

The new version of the technology is sort of in beta test versions.

We got it into the hands of people who had used the technology before.

So there's

NFL teams that are using, there's college teams, there's Olympics, there's the Navy SEALs, Major League Baseball, the NBA, the National Tennis Association.

They have locations where now they are trying this out and reporting back, how's it working?

How could you change it?

How could you improve it?

Just cool.

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.

So you stick your hand in cold water.

When it comes out, it's cold.

You just sealed up all the heat in your body.

Yeah, right.

We, once again, had just standardized on three minutes.

And part of the reason for that is that the rate of heat loss is an exponentially declining curve.

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.

You know, it would be experimental.

Sure.

Your idea of frozen peas is a good idea.

After you hold the cold peas in one hand and you switch it to the other hand, if someone then comes and feels your hand, is it warm or cold?

If it's cold, it means you vasoconstricted.

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

And the key is for it to not vasoconstrict.

Or could I put my feet on them?

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.

So that decreases its efficacy.

But once again, it depends on the surface area to get any benefit at all.

We have a study that we published, which was investigating the standard treatment for hyperthermia in the field.

And the standard treatment that's recommended by medical organizations is you take cold packs and you put them in the axilla, the groin.

The armpits and the neck.

Mm-hmm.

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

The cooling rate was double.

Wow.

You keep your gains.

It's a true conditioning effect.

You respond to the increased work volume.

by all of those mechanisms you mentioned.

You increase the number of contractile elements in your muscles.

The muscles get bigger.

It was fun.