Category Archives: Thinking in Systems

What is the aerobic threshold, and why does it matter?

The aerobic threshold is the point where exercise intensity increases enough that the body can no longer supply enough oxygen to cover its total fuel utilization.

(The anaerobic threshold is totally different: it is the point where the rate of anaerobic activity exceeds the body’s ability to keep it in check.)

As work rate increases, the body’s big muscles (let’s call these “exercise muscles” for short) start working harder and harder, increasing the fuel and oxygen demand. More oxygen has to be pulled in, and so the breathing muscles—diaphragm, muscles around the ribcage and various shoulder muscles—also have to work harder.

But these breathing muscles have their own oxygen demand. So the more they (and the exercise muscles) work, the more the overall demand for oxygen rises.

This can’t go on forever: if the overall demand of oxygen rises, the breathing muscles have to work even harder to meet it. What’s happening? The harder the body works to meet its oxygen demands, the greater they become. 

At the point at which these demands start to rise in tandem, it’s essentially impossible for the body to cover all of its fueling needs with oxygen. The body then has to start consuming fuel without mixing it with oxygen (also known as anaerobic activity).

This means that there’s a sweet spot just before this tandem increase where the exercise muscles are working somewhat hard—but not hard enough that the breathing muscles have to work significantly harder and dramatically increase their own oxygen demand.

This sweet spot is the aerobic threshold.

Note that this is nowhere near the maximum ability of the body to supply and utilize oxygen (also known as VO2Max). The body can still increase the breathing rate, expanding and contracting the lungs much more and much faster, and it can still increase the heart rate to pump oxygen-laden blood everywhere it needs to go.

Conceivably, it could be pulling in and transporting oxygen at twice the rate (and using it to burn twice the fuel). But doing so would itself have extraordinary oxygen requirements. The body can’t approach its VO2Max and still be spending less oxygen than it is requiring (a.k.a. still aerobic).

The aerobic threshold is critical from a physiological perspective—much more important than the anaerobic threshold, for example—because it is the point where the body has the first reason to worry about its oxygen supply. Anywhere from resting to the aerobic threshold, the body is A-OK. It can essentially continue doing whatever it is doing ad infinitum: it has enough fuel and oxygen going to all of its systems (brain, organs, muscles, etc.) that they are at no risk of shutdown.

Above the aerobic threshold, the game changes: the further you get, the less the body is able to sustain that rate of activity indefinitely. The further above the aerobic threshold, the farther the body is from the conditions that allow it to remain alive over the long-term (e.g. oxygen to cover its entire fueling needs).

Above the aerobic threshold, you’re on Everest. You’re in the Death Zone. You literally don’t have enough oxygen to just keep on doing whatever you’re doing. It’s OK to be up there for a while (and there’s benefits to doing so), but if you don’t come down, you’re gonna die.

(And just like on Everest, if you go up there more often than you can recover from, you’re going to get sick).

If the body is doing anaerobic stuff too often, it just won’t be able to recover—and keep on breaking down.

Training under the aerobic threshold has all kinds of benefits that you just can’t get training above it. To stay under the aerobic threshold, the body has to be able to bring oxygen all the way into the muscles to cover every bit of its energy demands.

While this may seem too obvious to mention, it actually hides a critical point: in order for oxygen to make it all the way into the muscles, it has to get handed down a long ladder of systems, organs, and processes. The lungs have to fill up, and they have to hand the oxygen off to the red blood cells in the bloodstream, which then have to get pumped through the bloodstream and through the capillary networks into the muscles.

(This chain is the aerobic system).

The amount of oxygen that makes its way down to the muscles at any given time is determined by the weakest system in the body (and not the strongest). Let’s say that the lungs have capacity for lots of oxygen, and the red blood cells can carry all that oxygen, and the heart is powerful enough to pump all that blood around the body, but the breathing muscles aren’t very strong. It won’t matter how big the heart or the lungs are, or how much red blood cells are in the body. The body will have to drive those lung muscles extremely hard in order to get the oxygen it needs. (And its oxygen requirements will go up, and boom it’s above the aerobic threshold).

The more you train under the aerobic threshold, the better the body gets at handing oxygen from the nose all the way down to the muscles.

In technical terms, this means that aerobic training strengthens the vertical integration of the body’s aerobic system—“vertical” as in all the way up and down the oxygen ladder.

If there’s a really strong part, it won’t develop much until the weaker parts (that were constraining oxygen flow) catch up. So aerobic training really evens out the body in terms of its ability to transport and utilize oxygen.

Anaerobic training does exactly the opposite. Anaerobic activity literally starts because the body’s rate of exercise exceeded the oxygen transport capabilities of the weakest system.

Training anaerobically means that you’re committing to run the body harder than it has the oxygen for. So the systems that are already strong enough to take the body above the aerobic threshold get stimulated. They get trained, and they get even stronger, while the other systems lag behind. The asymmetry grows, and the athlete grows less resilient, not more.

If you keep doing this too long and too often, and without making sure to train the vertical integration of the aerobic system, you’ll eventually train yourself into a situation where the least capable part of the body gets neglected, and the most capable part of the body gets powerful.

And since that less-capable part was a critical piece of the oxygen puzzle, the body’s ability to use oxygen remains exactly that neglected.

When the whole oxygen chain is strong, aerobic training is awesome. But when there’s one really weak part, aerobic training can be super slow and super boring. But that’s also why it’s so important.


PS: In my next post I’ll discuss how muscle mitochondria—the body’s tiny aerobic motors—relate to the aerobic threshold and to aerobic training in general.


In defense of the endurance running hypothesis, part 1: how we think about evolution.

The endurance running hypothesis is the idea that humans evolved primarily as endurance runners. The argument goes that the human physique evolved and took its shape and function from the primary adaptive pressure of persistence huntingthat of chasing down our prey until its body shuts down.

However, this hypothesis is not without its detractors. A significant amount of scientists provide an array of counterevidence to the endurance running hypothesis. (And the debate continues.)

Take for example the case of the human gluteus maximus (butt muscle). Lieberman et. al. (2006) claim that the human gluteus maximus evolved its shape and size due to endurance running.

However, another article in the Journal of Comparative Human Biology finds that the gluteus maximus grows much more in high-force sports (weightlifting) and high-impact sports (such as soccer), than it does in endurance running. In fact, they also show that the butt muscle in endurance runners is no larger than in the non-athlete population.

What I disagree with is their conclusion, which is paraphrased in the “What does this mean?” section in the image below:

“The human gluteus maximus likely did NOT evolve through endurance running, but through varied explosive and forceful activities.”


My disagreements with the article (and the image) are primarily about how and why we interpret the science to mean a certain thing.

At first blush, the fact that endurance running doesn’t enlarge the gluteus maximus as much as other sports seems to detract from the idea that the muscle takes its shape from endurance running. But I think it actually adds to it.

By my analysis, these findings show that the basic, untrained shape and size of the gluteus maximus—it’s “factory specifications,” if you will—assume that it’s going to do the amounts of cutting, jumping, weightlifting, and sprinting that a habitual endurance runner might need to do. But it requires aftermarket modification to meet the (literally) outsize power and stability requirements of soccer or weightlifting.

Let’s say that a muscle evolved under a particular adaptive pressure. This means that its shape and size literally evolved to do that thing. If you take a muscle that usually doesn’t do a thing for which it evolved to do, and you ask it to do that thing, you are asking it to do something that it has prepared to do for millions of years of evolution.

In order to fit a function that it has been designed to do, the changes in shape and size that the muscle should have to undergo should be smaller, not larger. You would expect a muscle to change far more if you ask it to do something that is less aligned with its evolutionary job description.

Let’s illustrate this by looking at the arm and hand.

We probably all agree that one of the things that specifically sets us apart from our hominid cousins is the ability to coordinate the thumb with the rest of the fingers in order to grasp and manipulate objects to a high degree of dexterity. In its simplest form, this is the capability to oppose the thumb and the fingers—to make an “OK” sign with the thumb and each of the fingers of each hand.

Now let’s take a snapshot of the people who take this unique human ability to its very pinnacle: string musicians, graphic artists, etc. Their livelihood depends on the degree to which they can explore the potential of one of the major evolutionary functions of the human hand.

Compare the forearm muscles of a violinist or painter with that of a weightlifter. The weightlifter’s arms, hands, and shoulders will be much larger and more powerful. (I trust I need not cite a scientific, randomly-controlled study on the matter.) Why? Quite simple: weightlifters engage in activities that develop the body to phenomenal proportions.

But if we go by the conclusions of the article, the fact that the arm and hand get bigger through weightlifting would mean that it didn’t evolve for the kind of fine motor control that you produce in the arts. (Or that lifting heavy objects is its primary evolutionary role). A particularly ambitious version of this argument would be to suggest that one of the core functions of opposition is to become better able to lift heavy objects. But all these suppositions break down when you realize that our primate cousins were not only quite able to grasp branches and use them ably, but that opposition emerges at the same time that hominid arms were becoming smaller (and less powerful), not larger (and more powerful).

Of course, the human hand (and upper extremity in general) still needs to be able to grow and develop in order to be able to lift heavy objects—and can indeed grow to a huge degree to exhibit that function. But its core evolutionary function is to produce the unparalleled dexterity of the human being.

Furthermore, the fact that the non-painter’s hand remains relatively unchanged in size compared to the painter’s hand means that the non-painter’s hand is already relatively set up to perform that kind of dextrous function—because that’s what it presumably evolved to do. This should serve as evidence (not counterevidence) that the hand is primarily for painting (and other fine motor tasks), not for weightlifting.

We should think the same of the gluteus maximus.

Let me conclude by saying that nothing I’ve written here means that the gluteus maximus evolved exclusively for endurance running. Indeed, there is ample evidence suggesting that the architecture of the gluteus maximus is uniquely multifunction as far as muscles go. (In future posts, I’ll delve more into the nuanced view of the gluteus maximus that I proposed above: that it owes its shape and size to the fact that it is a muscle designed for the kinds of “varied explosive and forceful activities” that a bipedal, primarily endurance running animal expects to have to do.)

But what we can say is that the fact that the gluteus maximus gets bigger through a particular stimulus has no bearing on its core evolutionary role, (or on the evolutionary story of the organism as a whole).

A training logic in 4 basic steps.

In recent posts I’ve outlined some of the difficulties that runners face when training—a phenomenon I call the runner’s catch-22: people want to start running, but they either don’t get fast, or they become overtrained and their health deteriorates.

This is because running is relatively physiologically demanding: the minimum requirement for being able to run at all is far more rigorous than (say) for cycling. Most of the time, the reason people experience the Runner’s Catch-22 is because they’re physiologically not ready to train for their chosen sport. They need to develop more fitness on multiple levels before they’ll be genuinely ready to begin running.

In this post, I provide the basic concepts I use to develop a training plan. This is not just for runners, but for anyone that hopes to increase fitness in a safe, structured, and predictable way. My goal for this article is not just to provide a bird’s eye view of the “how-to,” but also to give the reader a framework to understand why it might not be a good idea to run some race or get into some other sport until certain requirements have been met. To do so, I divide this process into 4 basic steps: Training for (1) the person, (2) the sport, (3) the event, and (4) competition.

At the end of each step, I provide several questions whose answer will help you figure out the duration, frequency, and type of exercise that is best suited to helping you develop towards your athletic goals. (Keep in mind that in practice, these steps are far less discrete than I make them out to be.)

If you skip one step, you’ll have a very difficult time meeting the next. And the problem isn’t that you’re flaky, or that you’re not an athletic person, or that you’re not determined. No amount of determination will be enough to overcome the fundamental problem: That you skipped a step.

 Step 1. Training for the person:

 Even before you pick a sport to train for, it’s crucial to consider your overall situation: physical, physiological, psychological, nutritional, etc. If you’ve been sedentary all your life, hoping to suddenly be able to run and lift things over your shoulders will be damaging at best and impossible at worst.

Take a long, hard look at your particular body: all the muscle imbalances, digestion problems, moods, energy levels. Typically, any body is well-suited for its present activity levels: what, how long, and with what intensity you do whatever it is that you do. But the less activity you do (or that any part of your body does), the harder it is to change.

The best strategy is NOT, for example, to become a runner despite insulin resistance or a severe muscle imbalance. You’ll just hurt yourself in obvious and non-obvious ways. Instead, any training program should first address the constraint—muscle imbalance, insulin resistance, etc.—(and eliminate it) in order to bring the body back to a relative baseline of physical and physiological competency. What does that baseline look like? In a basic sense, when you go searching for odd pains, sorenesses, various symptoms of sickness, and you just can’t find any.

Keep in mind that while the process of doing so might include some “running” (for example), the fact that you’re “running” doesn’t mean that you’re actively training the running movement, or that you’re explicitly training for the running sport.

Ask these questions about yourself, and train according to the answers:

  1. At present, how (and how much) are you physiologically able to train?
  2. In the simplest terms, what is the biggest barrier to growth?
  3. Considering the answer to question (1), how can you train to remove it?

Note how question #3 is about training yourself out of the constraint, rather than mitigating the constraint through other means. NOT training yourself out of the need for orthotics (to the extent possible), means that it will be more difficult to get faster and perform more consistently. In systems terms:

“Any long-term solution must strengthen the ability of the system to shoulder its own burdens.”

This is how I start.

Step 2. Training for the sport:

 When I say sport in this context, I mean “the specific movement or movements required for participation in the sport.”

There are minimum basic requirements that must be met to even be able to participate in any given sport. (Training for proficiency at a sport comes later.) Any conceivable sport has minimum participation requirements in at least 5 domains of human motor expression: mobility, stability, skill, power, and endurance. However, for all sports, one or two key requirements reign above all others. For example:

  1. Deadlifting: The most salient requirement for deadlifting is more transparently understood as a mobility requirement: to perform a clean toe-touch. While standing upright with feet together and knees straight, to be able to reach down and tap your toes with the tips of your fingers without having to strain (read: while breathing continuously). If you can do this, it’s a good bet that you’re going to be able to consistently grow and develop in the deadlift.
  2. Running: The requirement for running is more transparently understood as a power requirement: To be able to accelerate into a cadence in the ballpark of 180 steps per minute (spm). This ensures that the critical neuromuscular processes necessary to efficiently maintain the running movement are developed enough to carry your weight.

(I say that a “salient requirement” is “more transparently understood as X” because if you really pick apart the toe touch or the ability to hit 180 spm, you’re going to find mobility, stability, skill, power, and endurance components for each.)

For some people, a cadence as low as 175 spm works just fine. I’ve yet to meet the person who hits peak efficiency below 170 spm. Keep in mind that a cadence of 180 spm is brisk as hell.

In order to meet that requirement, your joint stacking (the alignment of your ankles, knees, hips, and shoulders) has to be excellent—and has to stay excellent for the minimum amount of steps that it takes to accelerate into 180 spm. (And that’s just for starters. Maintaining a cadence of 180 spm for any kind of distance is much more difficult).

If you don’t have the requisite mobility in a given area (say, you have a hip restriction), movement becomes more awkward. That means you probably can’t produce stability: your abs can’t keep your upper body steady, making it difficult to control the arcs of motion of your arms and legs. So you can’t develop a high level of skill (the ability for your entire body to move in the best possible way given its structure and capabilities).

This means that it takes a lot more power to accelerate into a cadence of 180 spm. So, training for just about any event (short or long) becomes inordinately difficult—and as a result, you might just end up coming to the (wrong, wrong, wrong) conclusion that you’re “not athletic.”

A few guiding questions:

  1. What are the minimum requirements for your chosen sport (mobility, stability, skill, power, and endurance)?
  2. How (and how much) do you need to train to meet them?

 Step 3. Training for the event:

 I define event as: “the minimum planned volume of sports-specific activity.”

If the deadlifting competition starts at 100 lbs, then you better be able to meet the minimum requirement for deadlifting when loaded with a weight of 100 lbs. What does this mean? That you have to be able to perform the equivalent of a clean toe-touch—no straining—with 100 lbs on you.

It’s similar for running. If you want to run 100 yards, you have to be physiologically capable of accelerating into a cadence in the ballpark of 180 spm for 100 yards. If you want to run a marathon, you have to keep a cadence of 180 spm for the entire marathon.

This is why training for the event is s Step 3 in my list (and not Step 1). I’m well aware that a lot of people would like to pick from a menu and “choose” to run a marathon instead of a 5k because they “like” the marathon better. It doesn’t work that way. That would be like a novice “picking” to enter a deadlifting competition that starts at 250 lbs instead of 150 lbs, because they “like” 250 lbs more. For obvious reasons, you don’t do it.

What we don’t realize is that distance must be earned as surely as weight. Weight, is volume. Distance, is volume. They may not be the same kind of volume, but they’re both volume. They both deserve the same respect: they’ll both break you (in different ways) if you don’t train accordingly.

If you haven’t earned a certain distance (read: if you can’t physiologically meet the sports-specific requirement for the entire duration), pick a shorter distance. Here’s 2 questions to help you in this process: 

  1. What are the sports-specific requirement at the planned volume (duration, weight, speed, etc.)?
  2. How (and how much) do you need to train to meet them?

Step 4. Training for competition:

I define competitiveness or competence as “being able to exceed the sports-specific requirement for a particular event.”

It has nothing to do with being particularly good (that would be “elite-” or “semi-elite competitiveness.” It’s just about being better than the minimal physical and physiological requirements the event requires.

Training for competition, then, occurs when you can already meet the sports-specific requirement for the event, and now you want to exceed it. This is also a great way to gauge whether you’re ready for a more demanding event. Once you can hit 190 spm for 100 yards, you’re pretty sure you can train for 200 yards at 180 spm (and expect to make good gains). Same with deadlifting: if you are able to do 2 reps at 100 lbs, you can probably start training (say) for 1 rep at 150.

An important caveat: None of this means that the best, or the only way to train is to increase reps first, or increase power first (or whatever). Training is always strategic and multileveled, and you always approach it from as many angles as there are people in the world. The above only means that exceeding the sports-specific requirements at a given event is a decent gauge of whether you’re ready to train for a more challenging event.

  1. Can you exceed the event-specific requirements?
  2. How (and how much) do you need to train to exceed them for . . .
    • Greater competitiveness at the same event?
    • Participation in a more challenging event?

Final thoughts:

In future posts, I’ll break down these steps further and provide concrete examples of what they look like in training. I’ll discuss how to use the 4 steps together to design a more comprehensive training plan.

Runners: “Aerobic training” is not the same as “Endurance training.”

It’s common that training which develops the aerobic system is equated with training that increases the body’s endurance. It’s understandable: the aerobic system burns fats in the presence of oxygen in order to provide long-term energy for the body—exactly what it needs for endurance. But the problem is that a powerful aerobic system isn’t the only thing necessary for increase endurance.

The most important difference between “aerobic training” and “endurance training” is this: the former trains a critical supersystem of the human body (the aerobic system), while the latter improves the product of the successful interaction between the aerobic system and many other parts and functions of the body (endurance performance).

What runs isn’t the aerobic system—it’s the entire body. While the aerobic system can be powerful, it can’t perform on its own. Whenever we talk about “performance,” even when the subject is endurance performance, we’re talking about how (and how well) the body uses its aerobic power to create one particular kind of athletic movement.

Roughly, endurance means: “how long the body can produce a particular movement or action without falling below a minimum threshold of performance.”

Another way to say this is that the aerobic power is general, and endurance is specific. Geoffrey Mutai (elite marathoner) and Alberto Contador (Tour de France cyclist) both have extraordinary aerobic systems. In both athletes, all the parts that enable their muscles to be fueled for long periods of time are extremely developed.

It should be noted that in both athletes, we are talking about developing essentially the same parts, developed to comparable levels and talking to each other in very similar ways. Both these athletes also obtain fundamentally the same general physiological benefits—a greater ability to recover, better health, longer careers—all despite competing in wildly different sports.

However, their endurance in specific sports varies wildly. We can expect Mutai to be a proficient cyclist, and Contador to be an able runner, but we can expect neither to have world-class endurance in the other’s field. In other words, Mutai’s endurance is specific to running, and Contador’s is specific to cycling. This is because:

  • Both sports use different sets of muscles: runners use a larger set of muscles for stability than cyclists, since the latter have so many more points of support. Cyclists have the handlebars, pedals, and seat, whereas runners have at most 1 foot on the ground.
  • They load joints in different ways, and use very different ranges of motion: cyclists keep their waist and hips relatively flexed, while runners keep the same joints extended.
  • They use different neuromuscular mechanisms to facilitate endurance: running economy depends on a powerful stretch-shortening cycle, while cycling economy does not.

In my opinion, the stretch-shortening cycle is the most important piece of the running puzzle (and also one of the most overlooked). Running shares a lot of pieces with just about every sport—and developing them is very important if you want to become a good runner. But without an increasingly powerful stretch-shortening cycle, all the power that you develop in any other system (cardiovascular, respiratory, etc.) doesn’t translate into actual running performance increases.

As discussed above, the aerobic system is responsible for sustaining endurance. The best way to exclusively train the aerobic system is by running at a physiologically intensity (below the aerobic threshold).

This is a problem for less aerobically-developed runners: it takes a lot of juice to run the stretch-shortening cycle effectively. In previous posts I discussed how the minimum requirement for running properly is to be able to produce a (very fast) cadence of around 180 steps per minute (spm). This is because the muscles’ stretch-shortening cycle hits peak efficiency around that cadence.

So, these runners often need to run at a higher intensity: they’ll use the maximum output of the aerobic system at max and engage some of the anaerobic system in order to produce a cadence of 180 and properly activate their stretch-shortening cycle. If they fall below their aerobic threshold with the goal of doing “aerobic training,” their cadence falls and the stretch-shortening cycle will largely deactivate.

When I talk about hitting 180, I mean hitting 180 at an average step length: It’s possible for a weaker runner to shorten their stride to artificially increase their cadence without going above the aerobic threshold. But I consider this a rather useless hack, since in my experience it doesn’t really get runners the performance benefits expected of reaching “the magic 180 mark.” (More on this in a future post.)

For a workout to be “running performance training” (endurance or otherwise), it needs to train the key pieces necessary to improve running performance. So whenever you’re not actively training the stretch-shortening cycle, you’re not really doing “running performance training” in my book. “Running endurance training” would be about teaching the body how to run for longer, at a lower intensity, while maintaining a reasonable cadence.

So, whenever an aerobically weak runner trains under the aerobic threshold, I consider it to be quality aerobic training but NOT “running performance training.”

It’s not that their running performance won’t increase—it will. Let me illustrate with a rather extreme example: If playing checkers is the only active thing someone does, playing checkers is better for their running performance than not doing so. But because it doesn’t train the critical systems for running, I don’t think of it as “running performance training.”

Of course, running at a low cadence shares a lot more with running at a high cadence than playing checkers does. But the idea here is to set the highest possible bar for what “running performance training” should mean: training the key systems that running performance rests on. And running without substantially activating the stretch-shortening cycle really doesn’t meet that criteria.

(We can say that running without the stretch-shortening cycle still helps you to improve your running—to a point. But you can’t hope to maximize your performance gains without it.)

For a competent runner (someone who can engage their stretch-shortening cycle at low physiological intensity), “aerobic training” and “running endurance training” become identical: just about all of their training provides all the benefits they need to maximize their running endurance.

What is a less-powerful runner to do with all this information? If I could say only one thing:

Jump rope! Jumping rope (on both feet, alternating feet, on one foot, spinning around, crossing the rope, etc.) is training primarily the stretch-shortening cycle up and down the body, almost identically to the way it’s used in running. IMO, if a runner does only one other thing besides running, it should be to explore and master the jump rope to its fullest potential.

UPDATE Nov 18, 2016: Another (great!) article on the mechanics of running, also touting the potential of jumping rope.

But there’s a lot more than this. Now that I’ve covered all the theoretical ground I absolutely need to cover for my following posts to have any real substance, I can begin to discuss concrete strategies that the runner can use.

Addendum (for the curious): Why do I focus so much on fleshing out the principles (and, more importantly, taking so long to get to the processes)?

Because the idea, of course, isn’t to “balance” aerobic training with performance training. (That’ll only increase endurance.) The idea is to potentiate aerobic training with performance training. (That’ll maximize endurance.) And to turn balance into potentiation, it’s necessary to already have understood the “why.”

Endurance: the ultimate test of physiology.

For a beginner runner to get into running because in 6-12 months they want to run an ultra-endurance race (or even a marathon) is—to put it mildly—folly.

There’s a reason the marathon is the final event in the Olympics: It’s by far the hardest. A recent The New Yorker article reports on one athlete trying to describe the experience of running a 2:10 marathon: “You feel like you will die. No, actually die.”

There are fundamental differences between the endurance sports and the power sports. Oftentimes, when discussing these differences, people think about what gives an athlete a competitive edge: for power sports, it’s higher concentrations of Type I muscle fibers. For endurance sports, it’s more mitochondria, and a greater oxygen carrying capacity.

This is important, but it’s not what I’m talking about. I’m talking about understanding the endurance sports by attempting to discuss what “endurance” is—not human endurance, or endurance at sports, but rather what “endurance” means in a fundamental sense. And for that, I find it best to discuss extremes.

Take a power sport: the 100 meter sprints, for example. Usain Bolt is a phenomenal athlete. There’s no question about it. And there’s no question that there’s a certain glory to be had in being the fastest human being on the planet—glory that is simply not available to the marathoner. Let’s set that aside. What would have to happen for Bolt to be unable to continue competing?  In other words, what would “catastrophic system failure” mean for Bolt?

My answer is: an ACL injury, or a torn hamstring, probably. In other words, something breaks.

Now let’s look at the marathon. Rarely does something break in that way in the endurance sports. There’s plenty of microdamage—achilles tendinitis, stress fractures, chronic fatigue, etc. But when something breaks, truly breaks to a point where the person cannot compete (in the “catastrophic system failure” sense discussed above), what does that look like? It’s typically the entire system that fails. Take a gander at a list (compiled off the top of my head) of the quintessential ailments you see in a marathon:

  • Extreme dehydration
  • EAH/EAHE (Exercise Associated Hyponatremia/Hyponatremic Encephalopathy)
  • Heart attack
  • Kidney failure
  • Heatstroke
  • Respiratory infections

What these issues all have in common is that they’re systemic failures—they’re what happens when the body as a whole, rather than a specific part (say, the hamstring) can’t cope with the event. In other words, they’re what you get when the body starts to come apart at the seams.

The best way to think of this difference is that when you bust a hamstring (or even break your spine in certain places) you can still use your body as a whole except for the part you broke. But when you get any of the illnesses that typically occur during a marathon, it’s the entire body that is put out of commission—sometimes permanently.

To put it simply, we can think of speed and power as a question of how powerful the body is. And while speed and power have tons of importance in the endurance sports, we can say that endurance is primarily a question of how good the body is at holding itself together. In other words, endurance is a test of the body’s fundamental integrity: of how much stress can you subject it to for how long without any substantial collapses in any critical processes.

And this is the main difference between the endurance and the power sports. In the power sports, the body has to be very, well, powerful, but it doesn’t have to be all that good at holding itself together—at least not in ways that relate to the ailments described above. After all, the power sports only ask the body to perform for a few moments: it stops before it becomes dehydrated, or before enough lactate builds up that the kidneys fail, or before the lungs become stressed enough that they become susceptible to infection (etcetera, etcetera).

But that’s not the case in the endurance sports. The body is going to be in activity for a very long time. If any of its systems (respiratory system, cardiovascular system, etc.) are working at different rates, some of those systems are going to get tired first. This is a problem: those systems were only active in the first place is because they were providing a critical service to the body’s endurance performance.

When one of those systems fails, some critical process associated with it also stops. If the body continues activity in this state, critical processes start falling like dominoes. And the body starts coming apart at the seams.

It’s not that endurance sport are “better” or “more of a sport” than power sports. But it is the case that being highly successful at an endurance sport takes much more time, much more consistency, and much more athletic maturity than to be highly successful at a power sport. This is why, for example, it is not uncommon to see 19 and 20 year old athletes competing in power sports at the Olympic level—the 400m, the 1500m, etc.

It’s usually those very same athletes who, 10 or 15 years later, are running marathons. Once their athletic career was already taking off, it took their body an additional 10 to 15 years to be physiologically organized and cohesive enough to run a marathon.

On the other hand, any athlete who is seriously contending for a medal at an endurance sport at 20 years of age, is a unicorn. Either they’re already so athletically mature that they’ll have a wildly successful career ahead of them, or they have already pushed themselves so far, so fast, that decades of chronic illness and overtraining are already on the horizon.

Strengths and weaknesses of analytic and synthetic thought, explained through tacos: The real “about this blog.”

About a year ago, Craig Payne from Running Research Junkie leveled a (fair) criticism at my blog in the comment section of another article: that I don’t do “analysis.”

Craig is right: I don’t (and I don’t claim to). Judged as analysis, much of my thought process on this blog is indeed poor. One of the reasons I don’t is because too many people in the run-o-blogosphere already offer excellent analytic thought—of which the highest expression might be Craig’s own blog.

But another reason I don’t offer analysis is because of an emerging field that is very dear to my heart: systems science (and specifically systems thinking).

So what is it that I offer here?

I offer synthesis.

Systems thinking—and other emerging fields that depend on its tenets (such as psychoneuroimmunoendocrinology, or PNIE)—are synthetic sciences. What they do is best is tell a coherent story about a system or supersystem by making sense of all of its features and bugs, strengths and weaknesses, to postulate an argument about its functional purpose: why it does what it does.

Run PNIE through tests that establish whether a particular form of analysis has value, and it will be found wanting.

It joins seemingly unrelated domains—the mind and the immune system, society and hormones—by telling a story about why it makes sense that they interact.

It factors in phenomena that create turbulence in the system (but by themselves have no lasting impact on the system at large) by suggesting how they could conceivably be interconnected through a  long line of effects on parts and properties of the system—some, like thoughts, emergent; others, like killer T cells, not.

(I imagine analytic sciences staring with incredulity at PNIE, thinking: “Are you insane?!”)

While a field like PNIE can produce a consistent narrative, what it cannot do is reconcile every specific variable with every other specific variable. Evolution, for example, is imperfect at best. It gerrymanders structures that performed one function at some point into structures meant to perform a different one.

Modern accounts of biology observe this basic evolutionary reality: human physiology, for example, is far from the physical consummation of the divine form, or the expression of cherry-picked mathematical constants (as alleged by the Classical paradigm). The human body is best described as a hodgepodge of systems and parts, twisted and tweaked by evolution to perform a specific function (or series of functions) at the expense of countless others.

We can’t rely on analysis of specific strengths and weaknesses to come to conclusions about what structures do. It just isn’t possible for the (decidedly imperfect) tales told by PNIE, systems thinking, and other synthetic sciences to have fewer imperfections than the gerrymandered biological structures they examine.

What analytic sciences ask for, synthetic sciences simply cannot give. For analysis, the devil is in the details (but so is everything else). For synthesis, while the details must be addressed, imperfections in the story do not always mean that the story is imperfect in and of itself. Instead, as long as the gestalt remains intact (in the face of newly discovered details), imperfections in the story may speak to corresponding imperfections in the structure it describes. 

Here’s a great example: tacos. As most of us know, the filling falls out of tacos all the time. Sometimes it falls out the ends. Sometimes the tortilla gets soggy and breaks apart. Even then, the general consensus is that the purpose of a taco is to hold stuff in (despite the fact that it can only do so imperfectly).

The story we tell about the taco—that its functional purpose is to hold stuff in—is imperfect: in just about every instance of eating a taco, stuff falls out of one. (To analysis, this seems paradoxical: these two realities about the taco seem to be contradicting the idea that the taco is meant to hold stuff in.) But synthesis shows us that the reason the story is imperfect is not because the purpose of a taco isn’t to hold something in. It’s imperfect because the taco is only imperfectly capable of performing its functional purpose.

This tells us something very important: just because a structure is meant for a particular function does not mean that it can (or should be able to) produce it perfectly. Trade-offs and inefficiencies do not mean that the structure was meant to produce a different function.

In other words, there are better ways to hold in the filling. For example, we can fold in the edges of a taco, but doing so alters its essential nature: we’ve turned it into a burrito. But it also isn’t the case that the burrito is the better taco, and that as such, taco vendors are just behind the curve. There are (at least) 2 specific advantages to preserving a food’s “taco-ness”:

  1. Versatility: By tolerating the disadvantage that a taco has a hole at either end, you gain the advantage of being able to stuff it with more veggies and sauce from end to end and still being able to pick it up without getting dirty. (Try re-folding a burrito that is already filled to capacity.)
  1. Modularity: By putting up with the fact that your basic taco shop will give you nothing but meat on a tortilla, you are able to go to the veggie and salsa bar and build it however you like. Depending on how good you are harnessing the (imperfect) modularity of the taco, you’re also able to (imperfectly) swap out any ingredients you may not like.

Similarly, the fact that an imperfect structure produces any given function with some degree of difficulty does not entail that the structure is not meant to produce some particular function in some particular way: A taco isn’t completely versatile, excellently modular, or perfect at holding stuff in.

Furthermore, the advantages that the taco holds over the burrito—versatility and modularity—were bought at a steep price: it’s ability to effectively contain cheap meats and vegetables pales in comparison to that of a burrito. But all those disadvantages and compromises don’t mean that those aren’t intended features of the taco, or that there aren’t gastronomical situations to which the taco is better suited than the burrito.

For the taco (like for the human body), convenience and function—instead of the pursuit of efficiency in a few arbitrary parameters—drive evolution. As Noam Chomsky said about human communication, “languages do best what people do most.”

(What they don’t do is what’s most efficient.)

In order to explain the cobbled-together, evolutionary Frankenstein monster that is the human body, we need to rely on a mode of thought that is not allergic to paradox—and attempts to reconcile it instead of simply describing it. (While plenty of paradoxes have been reconciled successfully within analytic sciences, doing so has always been the result of synthetic thinking.)

We need to become storytellers of physiology and bards of biomechanics. To describe what human bodies have been observed to do is as dour as it is noble. To spin a story of what this depressingly imperfect, infinitely complex machine is attempting to do—in all its flawed glory—is the endeavor I want to be a part of.



A much-needed disclaimer:  I recognize that Craig does not need (and probably doesn’t want) my opinion that his blog is the “highest expression of analysis.”

A second, much-needed disclaimer: I embark on this post sequence only because (1) I deeply care for these themes, (2) I believe that there exists a functional, coherent story to be told about running, (3) that’s what synthetic thought is built for, and therefore (4) it is my opinion that analysis par excellence is simply is not enough in our collective attempt to give a complete, functional account of the running human body.

The fact that most of what I do here is synthesis (and not analysis) is an issue aside from whether my attempts at synthesizing information—or anyone else’s—make any sort of sense. (But that’s a different issue.) But if, having read this post, you still tell me you believe that synthetic thought (or science) should play no part in explaining the human body’s function, I bid you a good day.

Speaking the body’s language: simplifying training stimulus.

As your understanding of athletic training becomes more sophisticated, one of the first concepts you come across is that of training stimulus. In simple English, training stimulus refers to what the body gets out of a particular workout.

Discussion of training stimulus abounds in circles that use MAF (Maximum Aerobic Function)—also known as the Maffetone Method—as their main framework for training.

The overarching mandate of the MAF Method is to protect the body. That is the best way for it to tolerate stresses, grow from training, and produce a great race performance. The party responsible for these functions is the body’s aerobic system, which oxidizes fats (burning them in the presence of oxygen) to provide a stable and long-lasting energy supply.

In endurance events, “protecting the body” means that the aerobic system must provide almost all the energy utilized during exercise. In power events, the aerobic system should be buttressing the function of the anaerobic system—which provides vast amounts of quick energy by burning sugars without oxygen—and still be strong enough to take charge for the duration of the recovery period.

For those who have already committed to developing their aerobic systems (by training at a low relative intensity), an issue inevitably arises: in long workouts that should occur theoretically at a low intensity, people accidentally (and often) end up rising above the desired intensity for a few seconds.

This brings up a crucial question: does this change the training stimulus?

There are several ways of answering this question. We can observe whether our speed at the aerobic threshold decreases after a month of training. We can go out and get a heart rate variability app that tracks our body’s autonomic readiness. We can even go get lab tested to see if our VO2 Max has decreased.

(If these terms mean nothing to you, don’t worry. Unless you’re an elite athlete who redlines for a living, they don’t need to. That’s the point.)

The body isn’t a black box. Action and circumstance affect it in ways that we can readily experience (when we know what to look for). A critical caveat: In this post, I’m only discussing the interpretation of experience before and after a workout. Using our subjective experience to measure and manage training stimulus in real time brings a whole other level of complexity.

Let’s abstract away from training for a second, and leave all that exercise terminology behind. Suppose you are on a long, leisurely birdwatching hike. You stop every few minutes to take notes, and you loiter every now and then with your binoculars as you try to make out the species of a bird in the distance. But 4 times over the course of this hike, you saw a novel bird just around the bend. Excited, you raced to take a picture.

How do you return from that hike? You are energized, renewed, invigorated. In spite of those few short sprints, the hike was a “low-intensity” experience.

Here’s another example: you’re back in your hometown after 5 years on a family visit. There’s been parties and get-togethers every day, and you’ve had ample time to catch up with all your friends.

But two things happened: the second day, you had the great misfortune of being mugged. And then the day after that, a former business partner caught up to you at a stop sign. He’s had a spell of bad luck—and in that short encounter, saw fit to threaten you and your family (over what you had thought was water under the bridge).

99% of the time, everything was pleasant and relaxing. But, for 10 minutes, the ground shook. That was enough for you to leave town with a new and unexpected wariness. Even the language—“two things happened”—tells you what the primary experience was.

This is also the case in athletic training. Put another way, the same body that has to glean meaning from that unexpectedly stressful visit (in order to be able to adapt to the next threat) is the same one that you take to the gym or out on the trails. That same body has to figure out whether it makes more sense to treat a particular training event as an “endurance workout” or a “strength workout.”

When a run feels “rejuvenating”—it’s very likely that’s exactly what it’s doing for your body. (The opposite holds true as well.)

You can break down the experience of being mugged in ever finer detail, and identify sensory and psychological stressors, and observe their physiological and neurological effects . . . but you don’t really have to.

Don’t get me wrong—you’ll get far more data about the effects of a divorce or a family vacation if you go get an fMRI every time something happens. That is a fact. (You can probably make better lifestyle choices when you know for sure whether your amygdala lights up when you see pictures of your former spouse.) But you don’t need an fMRI to be spot on—in a general sense—when asked what either experience did for your mental and physical health.

You can say the same about phenomena such as autonomic readiness (of the nervous system), which contributes to produce our subjective feelings of readiness for a wide variety of tasks.

Our experience of readiness doesn’t just happen to co-occur with our physiological readiness. Look at it from an evolutionary point of view: we didn’t have heart rate variability apps or monitors “waaay back when.” Our experience of readiness has to emerge from the fact that our nervous system, metabolism, hormonal system, and motor capabilities are actually ready for whatever it is we feel ready for. This is essentially the same line of argument that Tim Noakes (in his immortal book Waterlogged) uses to argue that the best measure of physiologically relevant dehydration is the subjective experience of thirst.

(In the same book, Noakes also argues that the fact that this even needs to be argued shows just how disconnected from the obvious we’ve become.)

If the subjective and the physiological weren’t part and parcel of the same system (to say that they’re “linked” is a gross misrepresentation), we’d all be dead. In other words, our heart rate variability monitor isn’t really going to change until we feel ready—and if it does change but we still don’t feel ready, we can be quite sure that there’s some other measurable physiological parameter out there that explains why.

The biggest mistake we can make is to listen to our pet parameter while disregarding the conclusion of a built-in measuring device capable enough to have outcompeted every other life form on the savannah—a device without which Neil Armstrong would have made it to the orbit but not the surface of the moon.

Is there really a difference between “injury-prevention” and “training specificity”?

A lot of us are familiar with sports specificity: you tailor your training to achieve greater performance in individual sports. Some of us go as far as being “event-specific.” We train trails for trail running events. We practice running the inclines and hill lengths we’re likely to encounter during the event.

But I think that we can take the concept of training specificity a lot further: particularly as it pertains to the realm of injury prevention.

What does an injury mean from the perspective of athletic competency? It means that there was some stress, supposedly germane to the sport, that the body simply could not tolerate. Presumably, this is a stress that the body can (and should) adapt to.

I’m not talking about obscene stresses such as the micro-concussions that have been shown to cause brain damage in football players. I’m talking about simpler things: dehydration and hypoglycemia after a marathon, shin splints, etc.

Let’s take shin splints, for example. Shin splints are reputed to occur due to the repetitive stress associated with running. Shin splints—and the subsequent stress fracture—cause people to lose training time and training quality, increase the overall stress of training, etc.

My point is this: an inability to cope with a particular stress (resulting in an injury) is a bottleneck to development.

If an injury prevents a runner from improving, or puts their athletic future at risk (and it does), then injury-prevention should be at the very top of the priority list. Put another way, injury-prevention is the ultimate sports-specific training: it means training the body not just to get better at the sport, but to train the body to handle the basic stresses associated with the sport.

This is a difficult proposition for many people: it is different on a case-by-case basis. The same symptom (shin splints) can have a multitude of causes. When the issue is the amount of stress, increasing lower-leg strength by itself can solve the problem. But others may need to fix an imbalance between the front and back muscles of the lower leg, for example. Others yet may be erroneously unburdening the big calf muscles by giving the job of knee flexion entirely to the hamstrings.

Failure to address any of these issues can dramatically reduce the training response: tighter muscles and less mobility means less neuromuscular feedback. But a higher heart rate is necessary to drive stiff (and weak) muscles. This means more stress. And because some muscles are stiff, the body geometry is disadvantageous: it isn’t going to align itself (or remain aligned) with the primary vectors of force.

Fixing any of these issues will allow the body to learn from and adapt to the sport. Ultimately, I believe that the runner who “paradoxically” spends time correcting muscle imbalances or strategically strengthening bone, muscle, tendon, and connective tissue—and running less miles because of it—will need to run far fewer miles to observe the benefits of training.

We need to make the choice to not merely roll out our tight quads or hip adductors after the fact. I think we need to address the underlying cause of that tightness (a process which may or may not include myofascial release). And I think that we need to put this within the larger context of our training and racing: in no way does injury prevention or rehab constitute “taking time off” from training.

Preventing injuries and doing the rehab is a much better—and more honest— example of “training the body” than going out and slogging miles that are just going to put us back on the table. In every way that matters, we’re doing the training that our body needs, right now.  Tomorrow, we’ll be able to go out and do the training we want, and achieve the effects that we want.

And how much happier, faster, and healthier would we end up if we can trick ourselves into wanting to do the training our body needs?

Shoulder (T-Spine) training for runners: Completely overlooked, and absolutely necessary.

The benefits of lower-body training have always been obvious for runners. For the past few years, we’ve seen that the ill-defined and ill-understood “core” has come into its own as a legitimate focus of attention for runners who want to better their athletic situation.

The shoulders are just as important as the core—and yet almost completely neglected.

Most of us who are a little bit studied in the science of running know that arm swing is largely passive—a way for the body to contralaterally balance the movement of the legs. So why should we even worry about the shoulders?

We should care because of how they are connected to the body and how they affect the areas around them. The shoulder region is also known as the “T-Spine”—the T-shaped structure created by the backbone, the shoulder blades, and the collarbone (and of course, the hugely complex array of muscles, tendons, and ligaments that contribute to its function).

If any one of the muscles implicated in T-spine function is impaired, functionality of the entire structure goes down the drain.


Developing T-Spine functionality is important not only because the shoulders and arms are part of the body (and are needed for running well) but because in that immediate vicinity is the ribcage—and the ribcage houses the lungs and the heart, which are the main facilitators of the aerobic system (a.k.a. the distance runner’s main engine).

Bad T-spine function isn’t isolated to runners—it’s one of the biggest motor problems in the general population. In this sedentary world, our brains never had to understand how to use this complex (yet astonishingly elegant) interface between the arms and the torso.

Think about what happens when someone has bad general stability (they are “klutzy”), and their stability is challenged by walking on a balance beam or a raised log: they tense up and are unable to complete the task—or alternately, grossly underperform relative to someone with better motor control.

The same thing happens to the T-spine, particularly in a dynamic, repetitive-impact sport such as running. (Imagine, if you will, the same log or balance beam shaking repeatedly).

When faced with this kind of challenge, any impairment in function causes the T-Spine to seize up and refuse to move.The arms stop being able to swing freely. The “natural” arc that the arms would follow passively (if there was total freedom of movement) gets altered. Because the arm swing directly counterbalances the movement of the legs, either the legs move differently to match the different arm-swing, or the movement of the body stops being in sync with the forces traveling through it.

As is the case with Mr. Shutterstock here.

These are the building blocks for a running injury. (But it gets worse).

Since the shoulder blades sit on top of the ribcage (and the rest of the T-spine mechanism is literally all around it), the ability of the ribcage to expand and contract is immediately impaired. The diaphragm must work harder to make the lungs expand. Less oxygen permeates the body (with more effort), resulting is less aerobic development. In the long-term, improvement stagnates.

A mechanical problem can have far-reaching consequences: it can (indirectly) impair the body’s ability to utilize energy.

Or it can force a hopeful distance runner to think that they “aren’t made for endurance.”

The problem becomes exacerbated for broader-shouldered runners (like me) who lose upper-body mass due to the natural emphasis running places on the lower body system. These runners have comparatively more bone mass up top, which means that they need comparatively more muscle mass in order to keep that heavier structure mobile and stable.

When the T-Spine is neglected, muscle strength may drop to the point that it takes a lot more effort to keep this structure stable. Adding distance (or increasing power) may cause the weakened structure to seize up.

A seeming conflict of interest arises here: stockier runners have an increased need to lose weight to improve running economy. Keeping the muscle mass necessary to stabilize the T-Spine may mean that they won’t be as fast, at least in the short term.

The thing is, it’ll open up oceans of future potential. Usually, the main bottleneck for the development of a distance runner isn’t their weight. As Gray Cook said in a recent interview on T-Nation, “Technique is always the bottleneck of limitation.” This is true even when applied to something as basic as T-spine mobility. If the body—or a part of it—can’t move right, that athlete is never going to fulfill their potential.

T-Spine function is not the only problem plaguing runners. But how many runners may be plateauing because of this—and don’t know it?

UPDATE: While we can’t pinpoint the origin of Mr. Shutterstock’s problem from a picture—the problem may originate in the pelvis, for example—it is plainly evident that the shoulders, arms, and the entire T-Spine isn’t moving correctly.

UPDATE 10/22/15: Matt Whitehead from Oregon Exercise Therapy shared an excellent article about many of the specific postural imbalances associated with T-Spine dysfunction. He makes a great point about the “dos” and “don’ts” for correcting these kinds of problems: “[Nike athlete Mary Cain’s] coach can drill her over and over about swinging her arms straight forward and back, but it just won’t happen until her upper body posture is improved.”

High-intensity fitness culture, explained in systems: Physiology, evolution, overtraining in ultrarunners, and what it means for the rest of us.

In the modern approach to training and fitness, the idea that you should (or need to) train at a low intensity is utterly neglected. This neglect is a huge problem. It benefits the few, and harms the many. And even when this philosophy works, it only does so up to a point.

A recent article in Outside Magazine bit into this issue with great abandon. The Outside article discussed the extreme example: Overtraining Syndrome (OTS) in ultrarunners. Many elite ultrarunners have become seriously overtrained, finding that their legendary competitive and running ability evaporates almost overnight. And we see this sort of thing across the board: in crossfitters who get exertional rhabdo; in recreational runners that start too hard. But why does this happen?

Our present fitness culture has an extremely damaging “more is better” and “no pain, no gain” mentality. If your favorite sport is HIIT or CrossFit, you’re prompted to increase the intensity, to “feel the burn,” and to “not feel your legs after leg day.” You name it, it’s out there. If your favorite sport is running, everything around you tells you to collect miles like they were baseball cards—the more the better.

The problem is this: whether you’re an elite ultraunner or someone who is just looking to shed some pounds, the amount (or type) of training that society pushes you towards typically means a lot of stress. It’s not that you won’t get quick results with that high-intensity training program (or by going out and clocking as many miles as you can). It’s that in doing this, a majority of people cross a stress threshold beyond which it’s impossible to keep these gains. It happens to Joe Smith at the gym, and it happens to the ultrarunner.

But in order to understand why it happens (and why you can’t cheat your way around it) we have to discuss a critically important biological system known as the Hypothalamic-Pituitary-Adrenal, or HPA axis.

The HPA axis is the system that creates the autonomic stress response (ASR)—which kicks up the organism’s stress levels (think: alertness) in order to survive a challenge to its existence. Let’s put this in a real-world example: alertness alone isn’t enough for an antelope to escape a lioness. There are two more components to ASR: First, the antelope’s heart rate has to go through the roof in order to bring a high volume of blood to the muscles. Second, the antelope’s anaerobic energy system—which burns sugar without the presence of oxygen, kicks in.

There’s another energy system available to the antelope: the aerobic energy system. It burns a much more plentiful resource—fats—but it takes some time. The fats have to be broken down into sugar, transported through the bloodstream to the muscle fibers, and combined with oxygen inside the mitochondria, before they can be converted into energy. Typically, it takes the aerobic system 15 minutes to get to full burn. But the antelope doesn’t have 15 minutes. It doesn’t even have a few seconds for the initial gulp of oxygen to reach the muscles through the bloodstream. There’s a lioness charging towards it at 40 mph. It needs energy now.

lion hunt
Or towards a water buffalo.

Stress, a high heart rate, and the anaerobic system are hardwired together in every animal. This wiring has to be absolutely reliable. If it wasn’t—if, given certain conditions, you could get a high heart rate and stress but no spike in anaerobic activity—you will die. As far as your body is concerned, in a “real-world scenario” the price for not having these three things occur together every time, with utter certainty, is death.

That’s what your body is thinking—thanks to your HPA axis—every time you get too stressed. Your HPA axis has to assume that there’s an imminent threat to your life, and make all of your internal systems react accordingly. If not, you will die.

The anaerobic system takes over to ensure the immediate survival of the organism. It doesn’t just happen to burn the fuel we use in the short term (sugar). We are wired so that when our bodies are thinking and acting in the short-term (that is, prioritizing escape from a threat over long-term health) we use the anaerobic system.

On the other hand, when our bodies are behaving with the long-term in mind, we use the aerobic system. In the long-term, it doesn’t matter if all the energy isn’t available right now—we’re not running away from anything. On top of that, we have fats, which is a more reliable and plentiful energy source. Sure, it takes a little bit more time to get energy from fats than from sugar, but time is something we have.

But that’s not all: there are reasons to NOT use the anaerobic system in the long-term. Burning sugar without the presence of oxygen wears down the engine: it accumulates protons—hydrogen ions (H+)—which cause the body’s pH to fall, becoming more acidic. (The idea that lactate is the culprit of muscle acidification is a misconception: the presence of lactate predicts, rather than causes, proton-based acidosis in the body).

In the short-term, the antelope’s body doesn’t care about its pH balance. If it doesn’t move, NOW, that lioness will take it down. The temporary acidification of the body is a small price to pay for escape. If everything goes as planned, 45 seconds from now, the antelope will have a chance to calm down. Its stress levels will drop, it’s heart rate will slow down, and a powerful aerobic base will kick in and all the lactate will get churned through the muscle mitochondria and converted into more energy. The proton build-up that happened during the chase will be quickly negated. In that process, a final acidic by-product will come out in a form that the body is designed to quickly and competently expel: CO2.

As soon as the body’s short-term survival has been secured, and it starts thinking in the long-term, it uses its aerobic system.

But if you are under chronic stress, your body never gets a chance to think in the long-term. Remember that stress, an elevated heart rate, and anaerobic function cannot be untied. If you are under stress all the time (even if it’s work stress), you’ll have at least some anaerobic function. Your body will be burning more sugar and less fat. As you use the aerobic system less and less, it will grow less inclined (and less capable) of fueling your daily activities with fat. You’ll have to rely on dietary sugar to keep your energy levels up. You’ll burn even less fat. You’ll slowly and steadily gain weight. But your body will also have a higher proton concentration than it should. It’ll remain more acidic. You’ll wear it down, putting yourself at risk of chronic disease.

Just look at how this snowballs. The media (and your peers) are kind enough to pelt you with exercise programs that promise quick, short-term gains! You can see where this is going. You’re piling acute stress on top of chronic stress. Your problem wasn’t the excess fat itself: it was that your long-term energy system—the aerobic system—was compromised. And those quick, short-term gains that you’re promised? You might get them, but at the cost of keeping them.

Yet again, you’re using the short-term energy system. Yet again, you’re training your body to think in the short-term. The energy system that is responsible for your body’s long-term upkeep is incompetent. By definition, you’ll be unable to maintain that level of activity in the long-term. You’ll lose those short-term gains.


The problem isn’t that you’re flaky, or that you’re not an athletic person, or that you’re not determined. No amount of discipline or determination will be able to overcome the fundamental problem: that you trained for the short-term instead of the long-term.