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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.


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.”