summarize "Most treatments of exercise are either very specific (e.g., how to
train for your first marathon) or overly vague (e.g., “Just keep moving!”). Or
they emphasize “cardio” over “weights,” or vice versa. In this chapter, we are
seeking to optimize our exercise regimen around the principle of longevity.
What combination of modalities will help us delay the onset of chronic
disease and death, while simultaneously maintaining healthspan for as long as
possible?
This question turns out to be more complicated than how to lower your
risk of cardiovascular disease, because there are more variables, and more
choices within each variable. It is not a one-dimensional problem but more of
a three-dimensional one. The three dimensions in which we want to optimize
our fitness are aerobic endurance and efficiency (aka cardio), strength, and
stability. All three of these are key to maintaining your health and strength as
you age. (And as we’ve seen, they also extend lifespan.) But both cardio and
strength are far more nuanced than most people realize—and stability may be
the least understood component of all.
When we say “cardio,” we are talking about not one thing, but a
physiologic continuum, ranging from an easy walk to an all-out sprint. The
various levels of intensity all count as cardio but are fueled by multiple
different energy systems. For our purposes, we are interested in two particular
regions of this continuum: long, steady endurance work, such as jogging or
cycling or swimming, where we are training in what physiologists call zone 2,
and maximal aerobic efforts, where VO2
 max comes into play.
The strength side of the equation seems simpler, at first: if you use your
muscles to counter some resistance, in the form of weights or other forces
(e.g., gravity, or elastic bands), they will adapt and grow stronger. That’s how
muscle works, and it’s really quite wonderful. There are a few specific
movements that I consider to be foundational, but here our most important
goal is not only to build strength and muscle mass. It’s equally important that
we avoid injury in the process.
This is where stability comes in. We will talk about it in much more detail
in the next chapter, but I consider stability to be just as important as aerobic
fitness and strength. It’s a bit hard to define, but I think of stability as the solid
foundation that enables us to do everything else that we do, without getting
injured. Stability makes us bulletproof. Sophie was relatively fit for her age,
but she likely lacked stability, making her vulnerable to injury. Many people
are in the same boat without even realizing it—even me, in my twenties. It
almost doesn’t matter how fit you are; you can still be at risk. This is why our
approach to exercise must increase not only our conventional measures of
fitness, such as our VO2 max and our muscular strength, but above all our
resistance to injury.
In the sections to follow, we will be building a framework around each of
these, to help you craft your training program for your own Centenarian
Decathlon.
Aerobic Efficiency: Zone 2
Notice that one word has been missing in our discussion of exercise thus far:
calories. Most people think that one of the primary benefits of exercise, if not
the primary benefit, is that it “burns calories.” And it does, but we are more
interested in a finer distinction—not calories, but fuels. How we utilize
different fuels, glucose and fatty acids, is critical not only to our fitness but
also to our metabolic and overall health. Aerobic exercise, done in a very
specific way, improves our ability to utilize glucose and especially fat as fuel.
The key here are the mitochondria, those tiny little intracellular organelles
that produce much of our energy. These cellular “engines” can burn both
glucose and fat, and thus they are fundamental to our metabolic health.
Healthy mitochondria are also important to maintaining the health of our
brain, and to controlling potential bad actors like oxidative stress and
inflammation. I am convinced that it is impossible to be healthy without also
having healthy mitochondria, which is why I place a great deal of emphasis
on long, steady endurance training in zone 2.
Zone 2 is one of five levels of intensity used by coaches and trainers in
endurance sports to structure their athletes’ training programs. It can get
confusing, because some coaches define training zones in terms of heart rate,
while others focus on different levels of power output; adding to the
confusion, some models have five zones, but others have six or seven.
Typically, zone 1 is a walk in the park and zone 5 (or 6, or 7) is an all-out
sprint. Zone 2 is more or less the same in all training models: going at a speed
slow enough that one can still maintain a conversation but fast enough that the
conversation might be a little strained. It translates to aerobic activity at a
pace somewhere between easy and moderate.
I had done plenty of zone 2 workouts in my cycling days; this type of
training is foundational for any endurance sport. But I had never fully grasped
the importance of zone 2 training to our overall health until I happened to
meet a very bright exercise scientist named Iñigo San Millán in 2018. I had
flown to the United Arab Emirates for a meeting, and shortly after landing, at
11 p.m. on a cool December evening, I was introduced to San Millán, an
assistant professor at the University of Colorado School of Medicine who had
recently been hired as director of performance for the UAE Team Emirates
professional cycling team. He was there to do preseason testing of some of
the UAE team riders, and when he found out I was a former cyclist, he put
me on a stationary bike right then and there, in the middle of the night, to do
a VO2
 max test. My kind of guy.
A native of Spain and a former professional cyclist himself, San Millán
has worked with all kinds of athletes and coaches in many sports, including
hundreds of top professional cyclists. He is also the personal coach of 2020
and 2021 Tour de France champion (and 2022 runner-up) Tadej Pogačar.
Despite his impressive sports résumé, San Millán’s true passion is studying
the relationship between exercise, mitochondrial health, and diseases such as
cancer and type 2 diabetes. As he explained, he hopes to use his insights into
the fittest people on the planet, professional cyclists and other elite endurance
athletes, in order to help the very least fit people—the one-third to one-half
of the population with metabolic diseases or derangements.
In San Millán’s view, healthy mitochondria are key to both athletic
performance and metabolic health. Our mitochondria can convert both
glucose and fatty acids to energy—but while glucose can be metabolized in
multiple different ways, fatty acids can be converted to energy only in the
mitochondria. Typically, someone working at a lower relative intensity will be
burning more fat, while at higher intensities they would rely more on glucose.
The healthier and more efficient your mitochondria, the greater your ability to
utilize fat, which is by far the body’s most efficient and abundant fuel source.
This ability to use both fuels, fat and glucose, is called “metabolic flexibility,”
and it is what we want: in chapters 6 and 7, we saw how the relentless
accumulation and spillover of fat drives conditions such as diabetes and
cardiovascular disease. Healthy mitochondria (fostered by zone 2 training)
help us keep this fat accumulation in check.
A few years ago, San Millán and his colleague George Brooks published a
fascinating study that helps illustrate this point. They compared three groups
of subjects: professional cyclists, moderately active healthy males, and
sedentary men who met the criteria for the metabolic syndrome, meaning
essentially that they were insulin resistant. They had each group ride a
stationary bicycle at a given level of intensity relative to their fitness (about 80
percent of their maximum heart rate), while the scientists analyzed the
amount of oxygen they consumed and the CO2
they exhaled in order to
determine how efficiently they produced power—and what primary fuels they
were using. The differences they found were striking. The professional
cyclists could zoom along, producing a huge amount of power while still
burning primarily fat. But the subjects with metabolic syndrome relied almost
entirely on glucose for their fuel source, even from the first pedal stroke. They
had virtually zero ability to tap into their fat stores, meaning they were
metabolically inflexible: able to use only glucose but not fat.
Obviously, these two groups—professional athletes and sedentary,
unhealthy people—were as dissimilar as could be. San Millán’s insight was
that the sedentary subjects needed to be training in a manner similar to the
Tour de France–bound cyclists he worked with. A professional cyclist might
spend thirty to thirty-five hours a week training on his or her bike, and 80
percent of that time in zone 2. For an athlete, this builds a foundation for all
their other, more intense training. (The catch is that a professional rider’s
zone 2 output feels like zone 5 for most people.)
As fundamental as zone 2 training is for professional cyclists, however,
San Millán believes that it’s even more important for nonathletes, for two
reasons. First, it builds a base of endurance for anything else you do in life,
whether that is riding your bike in a one-hundred-mile century ride or playing
with your kids or grandkids. The other reason is that he believes it plays a
crucial role in preventing chronic disease by improving the health and
efficiency of your mitochondria, which is why training aerobic endurance and
efficiency (i.e., zone 2 work) is the first element of my Centenarian Decathlon
training program.
When we are exercising in zone 2, most of the work is being done by our
type 1, or “slow-twitch,” muscle fibers. These are extremely dense with
mitochondria and thus well-suited for slow-paced, efficient endurance work.
We can go for a long time without feeling fatigued. If we pick up the pace,
we begin to recruit more type 2 (“fast-twitch”) muscle fibers, which are less
efficient but more forceful. They also generate more lactate in the process,
because of the way they create ATP. Lactate itself is not bad; trained athletes
are able to recycle it as a type of fuel. The problem is that lactate becomes
lactic acid when paired with hydrogen ions, which is what causes that acute
burning you feel in your muscles
[*1] during a hard effort.
In technical terms, San Millán describes zone 2 as the maximum level of
effort that we can maintain without accumulating lactate. We still produce it,
but we’re able to match production with clearance. The more efficient our
mitochondrial “engine,” the more rapidly we can clear lactate, and the greater
effort we can sustain while remaining in zone 2. If we are “feeling the burn”
in this type of workout, then we are likely going too hard, creating more
lactate than we can eliminate.
Because I am a numbers guy and I love biomarkers and feedback, I often
test my own lactate while I am working out this way, using a small handheld
lactate monitor, to make sure my pacing is correct. The goal is to keep lactate
levels constant, ideally between 1.7 and 2.0 millimoles. This is the zone 2
threshold for most people. If I’m working too hard, lactate levels will rise, so
I’ll slow down. (It’s sometimes tempting to go too hard in zone 2, because the
workout feels relatively “easy” on good days.) I make a point of this because
lactate is literally what defines zone 2. It’s all about keeping lactate levels
steady in this range, and the effort sustainable.
If you don’t happen to have a portable lactate meter on hand, like most
people, there are other ways to estimate your zone 2 range that are reasonably
accurate. If you know your maximum heart rate—not estimated, but your
actual maximum, the highest number you’ve ever seen on a heart rate monitor
—your zone 2 will correspond to between approximately 70 and 85 percent
of that peak number, depending on your fitness levels. That’s a big range, so
when starting people out, I prefer they rely on their rate of perceived exertion,
or RPE, also known as the “talk test.” How hard are you working? How easy
is it to speak? If you’re at the top of zone 2, you should be able to talk but not
particularly interested in holding a conversation. If you can’t speak in
complete sentences at all, you’re likely into zone 3, which means you’re going
too hard, but if you can comfortably converse, you’re likely in zone 1, which
is too easy"