[@PeterAttiaMD] A guide to cardiorespiratory training at any fitness level to improve longevity (AMA 79 sneak peek)

Link: https://youtu.be/yisfGtcV5xk

Duration: 38 min

Short Summary

This episode presents a comprehensive guide to cardiorespiratory fitness, with Peter Attia explaining VO2 max as the strongest modifiable predictor of health span and life span, outperforming even age, blood pressure, and cholesterol in predicting mortality. He introduces the cardiorespiratory triangle framework—Zone 2 training building the base of mitochondrial adaptations while high-intensity work elevates the peak VO2 max—ultimately optimizing both for longevity. The episode also clarifies lactate metabolism misconceptions, explains why hydrogen ions (not lactate) cause acidosis, and provides practical training recommendations based on available time.

Key Quotes

1. "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." (00:01:47)
2. "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%." (00:04:42)
3. "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." (00:05:30)
4. "VO2 max declines quite predictably with age at about 10% per decade." (00:11:35)
5. "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." (00:36:15)

Detailed Summary

ThinkingBlock(signature='beffb2fb00a6d2c95c06d0ff8a2a04c43913cda7110977a565f2a2cde6d13fbe', thinking="The user wants me to write a final detailed markdown summary for a long-form transcript. I need to use only the supplied structured summary and section digests. I must not invent facts, transitions, quotes, motives, or context.\n\nLet me review what I have:\n1. A short summary about cardiorespiratory fitness and VO2 max\n2. A detailed structured summary with 8 sections\n3. Section digests JSON with the same content\n\nThe user requirements are:\n- Markdown only\n- At least 8 section headings using '##'\n- Each section should start with 1-2 narrative sentences\n- Include at least 24 bullets total across the document\n- Bullets must focus on substantive claims, disagreements, mechanisms, examples, chronology, names, numbers, and outcomes\n- Avoid sponsor copy, banter, repeated praise, meta commentary, and filler unless substantively relevant\n- Prefer concrete details over generic abstraction\n\nLooking at the detailed structured summary, it already has 8 sections with '##' headings. I need to convert these into a more bullet-rich format while maintaining the narrative introduction for each section.\n\nLet me check:\n1. ## VO2 Max: The Cardiorespiratory Fitness Framework\n2. ## VO2 Max as a Mortality Predictor\n3. ## The Four Drivers of Oxygen Delivery\n4. ## Zone 2 Training: Building the Base\n5. ## Lactate Metabolism and Thresholds\n6. ## Muscle Fiber Types and Energy Systems\n7. ## High-Intensity Training: Building the Peak\n8. ## Practical Recommendations\n\nThat's exactly 8 sections. Now I need to add bullets to each section to meet the requirement of at least 24 bullets total. I'll aim for about 3-4 bullets per section to ensure I have at least 24 total.\n\nLet me structure this:\n\n1. \n\nI'll start by introducing the cardiorespiratory triangle's core concept, focusing on its structure and physiological significance. The base represents sustained submaximal effort, while the peak indicates maximum aerobic output for brief periods. Cardiac output's critical role in VO2 max variability becomes clear, with substantial percentages indicating its impact on aerobic performance.\n\n2. \n\nMortality prediction research reveals VO2 max as an extraordinary health indicator. Low fitness levels dramatically increase mortality risk, with those in the bottom fitness quartiles facing 4-5 times higher all-cause death probability. Modest fitness improvements can significantly reduce mortality risks, making even incremental increases in aerobic capacity meaningful for long-term health.\n\n3. \n\nOxygen transport involves a complex, multi-stage physiological process. Lungs, heart, blood, and muscles collaborate to deliver oxygen, with cardiac output - determined by heart rate and stroke volume - playing a pivotal role during maximum exertion. Maximum heart rate becomes a critical factor in determining oxygen delivery capacity.\n\n4. \n\nZone 2 training offers a scientifically nuanced approach to metabolic adaptation. Distinct from simple lactate thresholds, it represents the first point of physiological adaptation where metabolic processes begin shifting. Elite endurance athletes spend approximately 80% of their training time in this intensity zone, optimizing fat oxidation and lactate management.\n\n5. \n\nMetabolic thresholds define an individual's aerobic and anaerobic performance zones. Resting lactate levels and lactate accumulation points provide insights into metabolic flexibility and endurance potential. The lactate shuttle mechanism reveals how the body efficiently recycles metabolic byproducts between different muscle fiber types.\n\n6. \n\nMuscle fiber composition determines metabolic and performance characteristics. Slow-twitch fibers demonstrate exceptional fatigue resistance and metabolic efficiency, while fast-twitch fibers prioritize rapid energy generation. Mitochondrial function bridges these fiber types, enabling flexible energy production strategies.\n\n7. \n\nHigh-intensity training targets the peak performance ceiling through oxygen delivery optimization. Elite athletes systematically vary training intensities to maximize cardiorespiratory adaptations. Time-constrained training protocols can still generate equivalent or superior physiological improvements through strategic high-intensity approaches.\n\n8. \n\nTraining volume and intensity interact as primary drivers of physiological adaptation. For individuals with limited time, concentrated high-intensity workouts provide efficient performance gains. Zone 2 training remains critical as overall training volume increases, establishing a foundational metabolic base that supports more intense training protocols.\n\nEmerging continuous lactate monitoring technologies promise to revolutionize personalized training optimization, enabling real-time metabolic tracking during exercise sessions.", type='thinking')

VO2 Max: The Cardiorespiratory Fitness Framework

This episode provides a comprehensive guide to optimizing cardiorespiratory fitness through the cardiorespiratory triangle framework. The triangle has a base representing sustained submaximal effort (Zone 2) and a peak representing maximum aerobic output achievable for 5-10 minutes (VO2 max).

• The triangle metaphor visually represents how aerobic fitness has both a foundation (Zone 2) and a ceiling (VO2 max)
• Cardiac output accounts for 70-85% of the variability in VO2 max, making it the most sensitive variable for reduction
• VO2 max measures the maximum rate at which the body can consume oxygen during intense exercise

VO2 Max as a Mortality Predictor

VO2 max outperforms every other variable in predicting all-cause mortality, including blood pressure, cholesterol, BMI, smoking, and even age.

• Individuals in the bottom 20-25% of VO2 max have a 4-to-5-fold higher all-cause mortality risk compared to those in the top 2-3%
• Moving from the second to third quartile yields a 50-75% improvement in all-cause mortality
• VO2 max declines predictably with age at approximately 10% per decade after age 25
• This makes VO2 max the single strongest modifiable predictor of both health span and life span

The Four Drivers of Oxygen Delivery

Oxygen delivery to mitochondria is driven by four factors that must all function optimally for peak aerobic performance.

• Diffusion from lungs into blood represents the first critical step in the oxygen transport chain
• Cardiac output (heart rate multiplied by stroke volume) is the primary driver at VO2 max effort
• Hemoglobin oxygen-carrying capacity enables the blood to transport sufficient oxygen to tissues
• Muscle extraction refers to the ability of working muscles to pull oxygen from the blood
• Maximum heart rate is reached during VO2 max testing, making stroke volume the final adjustable component

Zone 2 Training: Building the Base

Zone 2 builds the base of the cardiorespiratory fitness triangle through mitochondrial density, fat oxidation, and lactate utilization.

• Zone 2 is defined as the first place where physiological adaptation occurs during exercise
• Specifically, it is the point where lactate rises to levels that local tissues cannot clear but the body as a whole can still clear systemically
• Endurance athletes training 15-20 hours per week spend approximately 80% of their time in Zone 2
• Zone 2 training allows near-maximal fat oxidation without overwhelming lactate clearance mechanisms
• The sustained nature of Zone 2 work drives mitochondrial biogenesis and capillary density improvements

Lactate Metabolism and Thresholds

The episode clarifies common misconceptions about lactate metabolism and explains why hydrogen ions (not lactate) cause acidosis.

• Resting blood lactate is approximately 0.5 millimole in a metabolically healthy individual
• The first lactate threshold (equivalent to Zone 2) occurs at approximately 2 millimole
• The second lactate threshold occurs between 4-5 millimole, at which point glycolytic lactate production surpasses clearance capacity
• At the second threshold, blood lactate rises sharply because production exceeds what can be cleared
• The lactate shuttle recycles lactate locally: generated in Type 2 (fast-twitch) fibers, shuttled to neighboring Type 1 (slow-twitch) fibers, converted to pyruvate, and processed in mitochondria to produce ATP
• Hydrogen ions (not lactate itself) cause muscle acidosis by preventing actin and myosin filaments from relaxing
• This distinction is critical because lactate is actually a valuable fuel source and signaling molecule

Muscle Fiber Types and Energy Systems

Type 1 (slow-twitch) and Type 2 (fast-twitch) fibers have fundamentally different metabolic capabilities and疲劳 characteristics.

• Type 1 fibers are slow to fatigue, rich in mitochondria, deep red in color, and excel at oxidizing fat efficiently
• Type 2 fibers are more contractile but fast to fatigue, have fewer mitochondria, and rely more heavily on glycolysis
• Mitochondria generate ATP from both fatty acids and pyruvate (from glucose via glycolysis)
• Both aerobic and glycolytic pathways occur simultaneously depending on metabolic demand
• The aerobic pathway optimizes for efficiency (more ATP per unit of carbon) but cannot meet high ATP demands alone
• At accelerated demand, the body switches increasingly to glycolysis to meet energy requirements

High-Intensity Training: Building the Peak

High-intensity training increases the peak of the cardiorespiratory triangle through oxygen delivery and utilization improvements.

• No high-level athlete trains at only one intensity level; varied intensities maximize the cardiorespiratory triangle more efficiently
• Proponents of high-intensity-only training argue it produces equivalent or greater adaptations than Zone 2 under certain time constraints
• High-intensity work drives improvements in maximum cardiac output, stroke volume, and capillary density
• The peak represents the maximum aerobic output achievable for 5-10 minutes of sustained effort
• Combining both training modalities optimizes both the base and the ceiling of aerobic capacity

Practical Recommendations

The episode provides actionable guidance for individuals with varying amounts of time available for cardio training.

• For individuals with limited time (2.5 hours weekly for cardio after resistance training), two 45-minute high-intensity workouts are more efficient than Zone 2 training alone
• However, as training volume increases, Zone 2 becomes more valuable—it is the cornerstone that enables sufficient volume safely and consistently
• Volume drives adaptation above all else, provided intensity is at least at Zone 2 threshold
• The goal is to maintain physical optionality as long as possible, as oxygen demand remains constant while capacity declines with age
• Continuous lactate monitors are in prototype or early market stages and will allow real-time lactate tracking during exercise
• With adequate time (5-10 hours weekly), Zone 2 becomes the dominant training modality for building the aerobic foundation

Full Transcript

Show transcript

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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