Hey everyone, welcome to the Drive

Podcast. I'm your host Peter Attia.

>> [music]

>> Peter, welcome to another AMA. How you

doing? I'm doing very well. Thank you

for having me back. Always welcome to

have you. I see every time we do these

you bring something more and more to

each recording.

>> [laughter]

>> What what have what have I brought this

time? I don't know. I'm not even aware.

Nothing you can think of? Nothing jumps

out? No new additions to the body? No,

but given that we've now introduced

carve outs at the end of these

I've it's made me that much more aware

of

um how much I am the perfect target of

YouTube and Instagram ads because

I could

I could create an entire podcast called

the carve out where I just talk about

you know

the things that I buy when they're uh

served up to me as ads that I end up

liking.

Have you bought one thing today?

Uh not today, but I did get something

really awesome 2 days ago.

Uh it arrived 2 days ago.

Anything you'd like to share with the

group? Heck no, I'm saving it for a

carve out uh

maybe next month. I want to I want to I

put these things to the test. Let me

tell you, I am a

I am I'm a serious tester of product.

So, the thing that I got so far, I've

already tested it once. It was insanely

good.

So, I just need to I need a few more

reps with it and if if I'm still digging

it in a month, it might it might make it

to the carve out list.

That's great. Uh it's exciting because I

don't think people realize

what you're talking about could be a

legitimate thing that is actually

beneficial to health and longevity.

And it could be the dumbest $20 gadget

that has ever existed.

And we have no way of knowing which one

it is when it comes to that spectrum.

>> [laughter]

>> Well, I'll give you a hint. It was

served up on a YouTube ad, so it's

definitely not the former

but I will say it's also not the latter.

>> [laughter]

>> Leaving people hanging. There there's a

lot of daylight between those two, so.

Yes, you you just tend to live on the

spectrums though, right? Like you kind

of go one or the other.

Uh

you know, that's like the only thing you

do in moderation is moderation, which

turns out is the same with engaging in

YouTube and Instagram ads. You like to

go all in.

>> [sighs]

>> So, with that said

what we're covering today

one topic, cardiorespiratory fitness in

simpler terms for people zone two VO2

max. So, this is a topic we have talked

about over the years on different

podcasts, different guests, different

articles

but it's also a topic that we get asked

about by far the most

partly because of the interest in it and

also I think because of how open you are

on how it is the

biggest and strongest modifiable

predictor of both health span and life

span. Meaning

it's the biggest impact that someone can

do something about it. So, that's why we

decided to kind of dedicate this AMA

gather all the questions and try to make

it a one-stop shop for everything

relating to how to measure, track,

improve zone two VO2 max through

training. We'll cover how this relates

to people who have a lot of time to work

out, people who have a little time to

work out. We'll look at how it relates

to people who are just starting

training, people who have been training

for a long time, older adults, if

anything changes for women in

particular, and more. We'll also look at

if your opinion has evolved around some

recent debates and discussions around

zone two, lactate, how to balance

volume and intensity with the goal of

not having your best exercise month ever

and then stopping, but more so long

term. So,

with all that said anything else you

want to add

before we get started? Yes, um this was

an idea that when the the team pitched

it to me

um my initial response was I don't think

this is worth it. We've already

generated plenty of content on this.

It's probably one of the things I talk

about more It's It certainly would be

within the top five things that I talk

about. Um and the team I think was able

to get me uh convinced and I and I

believe rightly so by saying, "Yeah,

Peter, that's kind of the point is if

someone were to try to go out there and

aggregate everything you've said on this

topic, it would be a full-time job and

it would and I think someone even shared

with me how many hours and hours of

content it would be and it was, you

know, triple digit hours.

Um and they said that's great for the

person with an encyclopedic memory who

is a lifelong you know, devotee who

doesn't have a job. Um but most people

aren't going to fit into that category

and it would be really helpful to have a

practical guide, not just a theoretical

guide to this.

Um and so that that kind of won me over.

Um and so I guess I would just say kind

of kudos to the team for convincing me

that this was this was the way to do it

and and I'm I'm really kind of happy

with the with the um the way they've

kind of crafted a story around this, so

let's dive in.

Before we do, quick question. Do you

think if the team started to put their

arguments in forms of videos that we ran

as Instagram or YouTube ads, you'd be

more willing to listen? I mean, if you

could be good enough, but you you have

to catch me within the first 10 seconds

of the ad or I'm skipping it, right? So,

you've

like I don't know that that's a skill

set that exists on our team. We don't we

don't practice that skill of catch you

in the first 10 seconds. No, we practice

more of we will get you at the end of 2

hours

after explaining in rigor. All right, so

with that said, I think what would be

helpful to start is

looking at real quick why is

cardiorespiratory fitness

a central pillar

in not only your approach to life span,

how long you live, but health span.

Yeah, so again, if you've if you've been

listening to me talk about this for for

years, you can literally go to your

podcast player and hit forward for a

couple of minutes. You don't need to

hear this.

Um but but I do want to spend at least a

minute on this idea that that

cardiorespiratory fitness is is one of

the most important and modifiable. It's

very important that we're talking about

modifiable predictors of both how long

you're going to live and how well you're

going to live. Um and so if you look at

all the predictors of all-cause

mortality, which remember that's the

holy grail metric of longevity

cardiorespiratory fitness outperforms

every other variable we can measure.

This includes blood pressure. This

includes cholesterol. This includes BMI,

smoking. It even includes age, which

just blows my mind.

Um

so

cardiorespiratory fitness CRF represents

how efficiently your heart and lungs and

blood vessels and muscles can work

together to deliver and utilize oxygen.

Um so the more efficient that system is,

the more physiological reserve your body

has. And it's this reserve that allows

you to tolerate stress. This stress can

come in the form of an infection, a

surgery,

uh or just, you know, frankly the

day-to-day demands of living.

Now, this has been most typically and

most repeatedly measured using a test

called VO2 max. You've heard me talk

about this, of course,

um and it's become a very popular thing

that people talk about. It's the maximum

rate at which the body can utilize

oxygen tested, of course, during maximal

efforts, which require exercise. Um so

this number is expressed in milliliters

of oxygen per kilogram of body weight

per minute. Um but it can be estimated

using something called METs or metabolic

equivalents, where one MET is equal to

3.5 ml per kilogram per minute of oxygen

uptake or utilization.

Um

so

I would say that the reason that VO2 max

has become such a popular way to do this

is because it is a standardized test.

That doesn't mean it's always done

correctly and we've got plenty of

examples of how this can be done

incorrectly, which is why for our

patients, we actually do the test. We

got sort of tired of relying on other

labs to do it. Um but for the most part,

a well-trained technician can do this

consistently um and that makes it easy

to study and that's why in the

literature you're going to see so much

discussion where it comes down to METs

or VO2 max. The two can be used

interchangeably.

Um and you won't, for example, see that

when it comes to zone two. So, we're

going to talk a lot about that today,

but I just want to point out zone two is

a much more difficult area to navigate

because it's not a maximal effort. It's

an in between effort. Um VO2 max is a

maximal effort. So, when you tell

somebody to basically floor it until

they're going to keel over,

um that's that's actually much easier to

achieve. Now, to put some context around

the importance of VO2 max in mortality,

again because it's been studied, um if

you're in the bottom

quartile or um quintile, so bottom 20 to

25% of the population with respect to

your VO2 max, you've got a

four-to-five-fold

higher risk of mortality, all-cause

mortality in any given year than those

in the top 3%, two to 3%. Um so that's

that's a that's a pretty big jump, but

keep in mind even tiny little jumps, um

you know, say moving from uh the uh

second quartile to the third quartile

will still have uh easily a 50 to 75%

improvement in in all-cause mortality.

So so why is this such a powerful

relationship?

And I think it comes down to not just

what the number represents, which is

everything I've talked about vis-a-vis

oxygen delivery and utilization,

but I think it's it's and I've I've said

this before, but it but I think it bears

repeating.

It's that measures like VO2 max, just

like strength, they're actually

integrators of work done. So

if a person has a VO2 max that is low

and their aspiration is to have a very

high VO2 max, they can, but it will take

potentially years and countless hours of

work done. And that work will be done at

the level of their cardiovascular

system, their pulmonary system, their

hematologic system, muscular system,

metabolic system. And all of those

things will have to work and work and

work for

hundreds of hours to get a desired

outcome. And if you think about that,

that's much more

frankly impressive from a physiological

perspective than taking a pill that

lowers your cholesterol.

And it's not to say that taking a pill

that lowers your cholesterol doesn't

improve outcomes, but it's not going to

come close to improving outcomes as much

as this does on average. There are edge

cases. There are some individuals with

familial hypercholesterolemia where, you

know, that pill that lowers their

cholesterol will have an outsized

benefit. But by and large, this is why

uh

things that improve cardiorespiratory

fitness or strength tend to have such an

impact on mortality.

And then beyond mortality, can you also

talk about the healthspan benefits? So

what you refer to is not only how long

it can help you live, but how well it

can help you live. Yeah, I think the

argument here is just as strong. Of

course, we just don't have the same

uh the the data are not quite as

objective because healthspan is not as

objective. So what what I might aspire

to to be able to do that would define

good healthspan for me might not be the

same as you, Nick, and is not going to

be the same as every person that is

listening to us right now.

But what we do know, and and I think

we'll show at least one figure to that

effect today, is that VO2 max declines

quite predictably with age at about 10%

per decade.

Um

but

you know, oxygen cost of doing things

doesn't change. So whether it be

climbing stairs or

lifting something up or chasing your

kids around or playing a sport, those

things don't change. So if you have a

declining capacity to deliver and

utilize oxygen in the in the presence of

constant demand, at some point those

curves cross

and what that effectively means is you

start losing the ability to do these

things. And again, we'll we'll talk

about this in much more detail when we

when we get there, but

as I as I as I think a figure can

represent better than what I'm saying

necessarily,

our objective is to be able to maintain

optionality around being physical for as

long as possible. And that is tantamount

to having as high a VO2 max as possible

in addition to being as strong as

possible.

And when talking about cardiorespiratory

fitness in the past to kind of help

people understand it in a similar way,

you've often talked about the base and

peak model.

Can you just walk through a little bit

more about that framework and how

different exercise and intensities can

contribute to each component of that?

Yeah, so I talk about this

cardiorespiratory fitness triangle and I

can't take credit for this at all. It

was one of my cycling coaches that came

up with this.

So so the idea was that you you have a

picture a triangle with a with a base

and a peak.

And the base is is what we think of as

your capacity to do sustained submaximal

effort over a long period of time.

So think of something you could do for

hours. And then the peak is is

represents your maximum aerobic output.

So what you could sustain for, you know,

5 to 10 minutes.

Obviously, there are, you know,

so many gradations here, right? Your

functional threshold power, which is

what you could obtain for an hour, is

obviously much narrower is, you know, is

a smaller number than the than the than

the peak and a shorter number than the

base. So

anyway, the goal here, if if if you're

trying to maximize your total aerobic

capacity,

is is to maximize the area of this, you

know, cardiorespiratory triangle. And of

course, to do that, you want to have the

widest base and the highest peak

possible. Um and these require different

forms of training. So if you just

trained at one intensity level the whole

time, you would increase both of these

things. I want to be clear on that point

because it creates so much confusion. If

you only parked yourself at one level of

training, you would, through enough

volume, increase both of these. But

that's not the way to maximize the

problem and it's certainly not the most

time-efficient way to do it, nor is it

necessarily

the best way to do it. In fact, it's

almost assuredly not given the fact that

no high-level athlete trains that way.

So

the the base is ideally built through

adaptations that help you utilize oxygen

more efficiently to convert fuel, but

mostly fat

into ATP. So what this is really geared

towards is improving mitochondrial

density and efficiency and optimizing

fat oxidation and lactate utilization.

Conversely, the peak, which again is

that VO2 max, represents the ceiling for

oxygen delivery primarily, but

utilization.

Um

and it's driven by how well this system

can deliver oxygen to the mitochondria.

That's primarily the bottleneck. It's

how much oxygen can you deliver to

mitochondria, right, versus the base,

which is how much can you

utilize substrate efficiently. So when

it comes to delivering oxygen

[clears throat] to the mitochondria,

there are really four big drivers,

right? So there's there's the diffusion

of oxygen from the lungs into the blood.

There's cardiac output, so that's heart

rate and stroke volume. Then there's the

oxygen carrying capacity of the blood,

namely hemoglobin.

And then there's the muscles' ability to

extract this. But as I said a moment

ago, it's the cardiac output that is the

main driver here and it is the one we're

most sensitive to in reduction. So

again,

what what drives cardiac output?

Primarily is stroke volume, how much

blood comes out of the heart with each

pump, and heart rate. And of course,

when you're at a VO2 max effort, you're

getting to maximum heart rate. So

somewhere between 70 and 85% of the

variability in VO2 max is accounted for

just by this one variable.

In the show notes, we'll include a whole

bunch more detail on this if anybody

kind of wants to nerd out on this stuff.

I love this stuff, but I don't want to

spend any more time on it right right

here.

So

as I kind of alluded to,

it's it's very tempting to and I want to

take I want to apologize if I've ever

created

the impression or oversimplified this

and it's possible that I have.

Um

that

you know, zone two is what you do

exclusively to build your base and

high-intensity workouts is the only

thing you do to build your peak.

As I said,

these systems work together and if all

you did was zone two, you would

absolutely get a wider base. You would

also raise your peak.

Similarly, if you did, you know, higher

intensity training, you would increase

your peak, but you would also widen your

base a little bit.

The key, as we'll get into in the

nuance, is what is the optimized way to

utilize time

around different volume and intensity

requirements. So

um

how much total work can you do? How much

cardiorespiratory

fitness training can you do? Um

that's probably the single biggest

determinant.

But that involves a min-max problem,

which is a big part of what we're going

to talk about today. So that's that's

how I think about the triangle. And when

talking about zone two, you've often

talked about fat oxidation,

mitochondria, lactate.

Often times, I think these terms can be

a little confusing for people, and so I

think it's always helpful to kind of

like re-look at them and explain it. So

do you mind just spending a few minutes

walking through like the cellular

mechanisms that are involved in

cardiorespiratory fitness just so

everyone is kind of familiar with the

terms you may or may not use throughout

here. Yeah, so it's really funny because

I've noticed some amazing memes on

Instagram where you basically have

people that are making fun of anybody

that uses the word mitochondria. So

somehow and I because I don't really pay

attention to the the the wellness

influencer

health space, apparently the word

mitochondria is now just one of those

buzzwords that you should throw around

as much as possible. And so, you know,

if you're if you're playing sort of

wellness influencer bingo, you're going

to get a lot of points for mitochondria.

Um, I can't remember some of the other

awesome words that are just basically

pathognomonic for buffoonery. Uh, can

you I'm sure you've Have you seen any of

these memes? They're amazing. It's like

mitochondria, inflammation,

uh, gut biome. Like they've got all the

buzzwords, right? So,

um, Protein?

Protein. I'm sure, right? So, so you've

set me up now to to to trigger a bingo

card. Um, but I guess you're right.

There you can't have this discussion

without doing this. So, so hopefully I'm

going to get an exemption for my use of

the word mitochondria here. So,

um,

at the foundation of your

cardiorespiratory system,

um, are these organelles called

mitochondria. And of course, all of you

who took a high school class in biology

will remember that they're referred to

as sort of the little power units of the

cell. And the majority of our ATP is is

produced by them. And again, ATP is the

currency for energy. Um,

and I just because I can't resist giving

one more lay level level of detail, the

way the way ATP work is they donate ATP

phosphates. They donate one of those

phosphates, and it's that liberation of

energy that comes from that chemical

bond uh, that creates energy. So,

you know, the mitochondria can generate

ATP from either fatty acids or pyruvate.

Pyruvate is is is the breakdown is a is

a intermediary breakdown product of of

uh, glucose uh, via a process called

glycolysis. And both of these processes

are constantly occurring. Um,

it's just the question is what's the

balance in which they're occurring? And

of course, are these both equal? No,

they're not, right? Each process has a

tradeoff. So, the tradeoff would simply

be stated this way.

If you are optimizing for efficiency,

and you don't care as much about the

speed with which you can deliver ATP,

you want to take that more aerobic

pathway. Meaning, utilizing oxygen and

shuttling the breakdown product of fatty

acid or glucose, um,

either in the form of pyruvate or

acetyl-CoA into the mitochondria, uh, to

use an oxidative pathway to generate

lots of ATP per units of carbon that go

in.

The problem with that is,

as the demand for ATP accelerates,

you have to make a tradeoff. You have to

make a sacrifice. The body says, "I'm

sorry, I can't do this anymore. I have

to go down this quicker path using

glycolysis, where I turn glucose into

pyruvate, ultimately into lactate.

I don't get nearly as many ATP for it,

but I can do this I can deliver much

more ATP to the muscle." Now, I can't do

this indefinitely. There's a whole

problem associated that which we'll talk

about, but that's effectively at the

high level the tradeoff. So, another way

to think about this is through the lens

of the fibers that are involved. And

again, these are terms we've used on the

podcast before, but this the goal of

this podcast is kind of tie this all

together. So, at lower intensities, you

have these type one or slow-twitch

muscle fibers. And again, I think the

term slow-twitch, it's um,

uh, it it it it it does to some extent

reflect the speed with which they

twitch, but I think a more important way

to think about them is they're slow to

fatigue, um, and they're more

endurance-based fibers. So, again, at

lower intensities, they're the ones that

are doing all the work, very rich in

mitochondria, deep red. Uh, they excel

at oxidizing fat, um, and they're very,

very efficient. As the intensity

increases, we have to start recruiting

more of the type two fibers. These are

fast-twitch fibers, which again are more

contractile in their force, but they're

also fast to fatigue. They have less

mitochondria, and they're going to

recruit uh, and rely more heavily on

glycolysis,

um, that's happening outside the

mitochondria.

So, um, initially, lactate, which again

kind of gets a bit of a bad rap, but

again, we've done an entire podcast on

this, and we'll we'll link to the

podcasts on this topic. But the most

important of these is definitely the one

with George Brooks. Um, initially, the

lactate gets recycled locally. Um, so

it's shuttled, um, to neighboring type

one fiber. So, a type It gets generated

in the type two fiber, it gets shuttled

to a type one fiber, it gets converted

back into pyruvate, and then the

pyruvate goes into the mitochondria to

produce more ATP. Um, that's called the

lactate shuttle.

Um, but again, these things are

constrained by demand, and therefore,

as output increases and demand

increases, lactate production in the

type two fibers begins to exceed the

capacity

uh, for for what can be done locally,

right? In the in the mitochondria

adjacent. And at that point, lactate

spills into the bloodstream. So, if you

were measuring lactate in the

bloodstream with a continuous lactate

monitor, which by the way, these things

are uh,

easily in prototype, and there's some

that are probably in the market. This

would be something you can appreciate in

the future. You might start out an

exercise session where your lactate is,

you know, resting at 0.5 millimole,

um,

everything I just described up until

this point would not increase that, even

though locally lactate levels are

rising.

Um,

but once it starts spilling into the

bloodstream, now you actually have to

rely on other tissues in the body. The

heart,

other other muscles that are not being,

you know, utilized at this point in

time, they have to start clearing it

using lactate as fuel, as we've even

learned from George Brooks. The brain

will do this as well. The liver also can

convert that lactate back into glucose

via gluconeogenesis.

Um, and this basically allows the body

to maintain certain levels of lactate,

um, at a new baseline that is above the

original baseline. Um, this is usually

referred to as the first lactate

threshold. And again, for a

metabolically healthy individual,

um, and someone who's metabolically

flexible, meaning they can go back and

forth between utilizing glucose and

fatty acids, this falls at about two

millimole of lactate.

Um,

that is what we refer to as zone two.

Now, again, if some of those conditions

aren't met, if you're not a

metabolically flexible person, using

that uh, first threshold of lactate,

um, at two millimole is not going to

happen. There are people who walk around

at rest with a lactate level above two.

Okay, but the point here is you can

maintain you're now at a new steady

state, where if you remember, the first

steady state is where the local tissues

are able to

uh, offset lactate production at the

rate that um,

uh, it's being produced, right?

Consumption and production are equal

locally. Then you have this sort of

second level, which we refer to as the

first lactate threshold, cuz it's the

first one we're measuring in the plasma,

and that's where now the systemic

tissues are able to balance it. But now

we get to a third level, um,

uh, of lactate, which is really called

the second lactate threshold, and that's

at higher and higher levels. And at this

point, once the body gets above that

level, um, and this level varies quite a

bit by individual.

Um,

I'm not going to Maybe maybe if we have

time, I'll go into how you can measure

that. I I talked about this at length in

the first podcast with um, uh, with with

um,

uh, Olaf Alexander Boo. Um, but um,

but we can come back to that. But but

anyway, at these higher levels of

output, glycolytic lactate production in

the working muscles completely sup- um,

surpasses the body's ability to clear

it. At this point, blood lactate starts

to rise much more sharply. Um,

it accompanies um, it's accompanied by

hydrogen ion, right? Because the the

lactate, um,

is is negatively charged, the hydrogen

is positively charged, so they're

balanced kind of one to one.

Um,

you have this acidity that occurs,

um,

and the it turns out that the it's the

hydrogen ion and not the lactate that is

effectively poisoning the muscle. It it

actually prevents the actin and myosin

filaments in the muscle from being able

to relax. Um, again,

for most people, that second lactate

threshold, or really third one,

depending on how you're counting them,

um, occurs somewhere between four and

five millimole of lactate. Again, that

can be That's that's that's a much more

variable number. Okay. [snorts] So,

I'm going to I'm going to stop there.

There's a lot we could talk about there,

but but I hopefully that kind of sets

the sets the groundwork.

Very much so.

>> [snorts]

>> I think maybe worth clicking on to zone

two

before we get further in a little bit of

a different way, because

that seems like there's been a lot of

discussion lately on whether it has

unique benefits, whether it's just

better to focus on higher intensity work

only.

So, how do you think about this

question? I think it comes down to

context. I think there's a lot of

confusion around this. So, so I I

hopefully I'll do my best to dispel

that. Um, there's there's ideas out

there challenging the idea that zone

two,

um,

is is special or magical or there's

anything that's that's good about it.

Um, and there are certainly people who

would assert that high intensity work

produces the same or even greater

adaptations. Um, and I think honestly,

in the framework that some people are

proposing that, it is true. Okay? So, so

let's now sort of think through this

um,

if you are uh, so so so for for the

proponents of high intensity exercise,

people who say don't waste your time

doing zone two,

um,

the shorter the amount of exercise time

that a person has, the more true that

is.

Because remember something I said a few

minutes ago, which is

if you really want to maximize the area

of your triangle, nothing beats volume.

Now, can't be volume like walking won't

do it. So, you have to have some you

have to get to zone two, this first

place where you have some adaptation. Um

but the more time you spend there, the

better.

And so, if we're going to talk about

a professional athlete or even a

recreational athlete, if you're going to

talk about uh the way I trained 10 or

you know, 10 to 15 years ago, the way I

trained, where by some miracle I still

was managing to spend 14 to 16 hours a

week on a bike, um then we can get into

the nuance of how that time should be

divided. So, now let's turn this over to

kind of someone who's going to adhere to

the general guidelines. So, the general

guideline says you should exercise uh

ideally 150 minutes per week. So, that's

2 and 1/2 hours per week. Um and I'm

sure the guidelines would be happy if

you did more, but that's what we're

trying to get people to, right? Most

people are not exercising 2 and 1/2

hours per week.

And truthfully, if if that's all you can

adhere to, then zone two is not going to

be an efficient use of your time because

it doesn't provide a sufficient enough

training stimulus to drive the

adaptations to make the triangle bigger.

And remember, that 150

minutes is total exercise.

Well, part of that's going to have to be

some resistance training. So, even if

you said, "I'm going to carve out an

hour

uh for two 30-minute resistance training

workouts a week." Then you've got an

hour and a half for cardio.

You know, truthfully, I would say then

all of that time should be done at high

intensity. You should probably have two

45-minute high intensity workouts.

Um

but when I talk about training, I'm not

and maybe I should be, but I'm generally

not talking to that population. When I'm

talking to my patients in that

population, it's a different story. And

we do. We're very clear that you know,

if you've only got 2 and 1/2 hours this

week to exercise, we're going to craft

your program around that. Um but but I'm

sort of talking to a person who is

really thinking about how to optimize

and achieve their best results over, you

know, both lifespan and healthspan over

decades. And if that's the case, then

you're going to need more volume than

150 minutes a week. And then that means

you're going to have to utilize

different levels of intensity. So,

because zone two is this point at which

lactate rises to the level where it's

now in the bloodstream.

Um so, local tissues can't clear it, uh

but your body is able to clear it.

You're stressing this system. This is

the first place where you're now really

stressing the system enough to recruit

more glycolytic fibers.

But what's nice about this is the

intensity is low enough that you can

keep going for a long enough period of

time.

And this is why endurance athletes who

are training for

you know, 15 to 20 hours a week are

indeed spending basically 80% of their

time in this zone because the intensity

is low enough that they can do it for so

long, and yet they are still getting a

training adaptation. So, if you are

training in zone two, while you're not

getting as much adaptation as you're

getting at zone five, uh you're still

applying a strong a strong enough

training stimulus to activate muscle uh

sorry, both fuel systems, right? So,

you're you know, you're not maximal, but

you're near maximal for fat oxidation.

You have some glycolysis. You have

lactate shuttle, but you don't have the

wear and tear of the acidity and the

fatigue that comes when lactate

production completely overwhelms

clearance uh systemically.

So, again, you can pack in volume of

training

um in a way that you can't with very

high intensity.

Um

there are other benefits to zone two, by

the way, if you're an athlete, which is

it comes with the improved um with the

benefits of improved movement

efficiency. Um I discussed this um you

know, on a on a on a podcast as well.

So, um I I guess I hope that clarifies

kind of the context around uh one versus

the other.

And in looking in terms of like spending

more time than the bare minimum when it

comes to exercise,

how does then exercise intensity

play a role into the relationship of

volume and sustainability?

So, once you're not constrained by that

150 minutes per week, and and honestly,

that's my hope. My hope is that

everybody listening to us right now,

even though once in a while they might

be constrained by that, but that they

can find more time to exercise. Um

the limiting factors start to become

fatigue and recoverability, uh and even

to some extent adherence. And I think

that that's especially as you get older,

fatigue and recoverability become real

limiting factors. So, again, higher

intensity workout uh

workout in zone five uh very important,

um

and should always be a part of your

training. You can't do that much of it

once you get into your 40s and 50s. Uh

again, when you're in your 20s and and

even into your 30s, you can still hammer

these workouts. Um

but I

you know, I can't do those workouts

three or four times a week anymore.

Um

and and I don't think most people

listening right now can, either. So, um

if you're going to be able to devote

more time to your training, you're going

to have to be able to um do so at a

lower physiologic cost. And and again,

volume drives adaptation. That's the

thing to remember. It's volume above all

else that's driving adaptation, provided

that volume is at least at zone two,

where you start to um undergo all those

changes we discussed. So, um

basically, there's there's a you know,

uh

you know, there's a cost of doing high

intensity work. And by the way, part of

that is adherence-based. Um it's it's

more painful, it's more fatiguing, and

it's harder to sustain. Um

so, uh

you know, one of the things I tell

patients who are bored when they're

doing zone two is, "Look, use it as an

opportunity to get really caught up on

your favorite podcast or your favorite

audiobook or something like that." Um

something that frankly is a little bit

harder to do during a high intensity

workout, where you're probably not as

not as able to to to concentrate better.

So, taking it back to, you know,

basically the critics of zone two, um

they're correct in a narrow sense in

that per unit time, high intensity

training delivers more physiologic

adaptation,

um but they're kind of wrong in the way

that that it matters. It's not that zone

two is magical, it's that it's

practical. And it becomes more and more

uh valuable as your volume increases.

So, in short, um I think zone two is the

cornerstone that lets you do enough

work, enough volume safely and

consistently, so that you get the

adaptations you need to be an athlete

for life.

Moving on now to look at how someone can

measure zone two and VO2 max, understand

what they are.

Um

when is it useful? How do you go about

measuring it? And let's start with zone

two, just because we were on that

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