The Analytic Fitness™ Dictionary – Cardiovascular Fitness

This entry of the Analytic Fitness™ Dictionary looks at a misunderstood physical quality: cardiovascular fitness. (About 3.300 words, estimated reading time: 13-15 minutes.)

If I had to pick a fitness-related topic that everybody should get right but most people get wrong anyway, cardiovascular fitness would be my first pick.

And indeed it was my first pick in the Training From Scratch Series and this post on the Tabata protocol, the first being my contribution to getting it right, and the second a contribution to not getting it wrong. This entry of the Analytic Fitness™ Dictionary develops some points touched in those two.

Before I get there, I need something out of the way: cardiovascular exercise for fat loss is both the #1 fitness industry cash-cow and epic-level science-based bullshit. Cardio-for-fat-loss is science-based because cardiovascular exercise relies in principle on an energy pathway that uses fat for fuel. It’s also bullshit because whether the pathway is activated in practice depends only marginally on exercise modalities (and it’s typically not elicited by cardio-for-fat-loss programs/classes).[1]

In truth, the only valid reason to indulge in cardiovascular exercise is to improve cardiovascular fitness. In fact, if you are not an athlete, it should be your primary fitness goal (if you are, I’ll make the case in future posts that it should be second only to the main quality for your sport). You may have seen that coming if you read the first two entries of the Training From Scratch Series about Cardio and Strength. Otherwise, this entry is reasonably self-contained, so you might as well keep reading it: ignore references to previous posts and check them when you’re done reading it.

Cardiovascular Fitness and Longevity

Cardiovascular Fitness (CVF) leads the race for being elected Best Predictor of Longevity with a serious head start on its two outsiders, Strength and Lean Body Mass.

In fact, the outsiders are stooges. First, strength in old age prevents the age-related decline of CVF: it delays age-related muscle loss (sarcopenia), enables higher levels of physical activity, and elicits positive cardiovascular adaptations (some details here). Second, there’s a primary among Lean Body Mass indicators, but the Muscle Mass Index (see here) has a solid lead. Obviously, the higher the muscle mass in old age, the lower the sarcopenia (duh), and from there it’s the strength-in-old-age thing all over again: muscle mass in old age prevents the age-related decline of CVF.

The race for second is marginally interesting in its own right because Strength and Lean Body Mass are composites and there’s some leeway on how to analyze them and define indicators accordingly. Then again, the issue will probably be settled by answering the question: which index of Strength /Body Mass best predicts a slower decline of CVF? or something like that. Of course, we need more data to settle all this empirically, but when we have it, I’ll be standing on my soapbox saying “Duh, I told you so”.

I told you so

Back to the topic of the day, cardiovascular fitness is a composite too, which entails the proverbial issue of devils-over-details ratio. On the big picture side, there really is just one way only to analyze CVF and only one component of CVF that seems to matter for health and longevity. On the details side, there seems to be a ‘falling domino’ effect that makes the other component relevant.

The Analysis of CVF

‘Cardiovascular fitness’ is a composite of two different physical qualities: aerobic cardiovascular fitness and anaerobic cardiovascular fitness.

The first is commonly equated with the ability to extract oxygen from the environment and to distribute it across the musculoskeletal system, and the second with the ability to function under oxygen debt when the cardiorespiratory system is outpaced. In layman’s terms,

  • anaerobic CVF determines performance in any task you have to breathe through but which would get you quickly out of breath, and thus matters for sprinting or running away from predators, and in general any all-out effort lasting longer than 15 seconds but no more than 2-3 minutes;
  • aerobic CVF determines performance in any task that you have to breathe through but which wouldn’t get you out of breath if you pace yourself, and thus matters for running back from a hunt carrying fresh meat, and in general any sustained-but-paced (aka not all-out) effort lasting longer than 2-3 minutes.

There is a universally adopted index of aerobic CVF: VO2max, where ‘V’ stands for Volume, ‘O2‘ for oxygen, and ‘max’ for maximal. The VO2max index is thus a measure of maximal oxygen uptake, which is just a fancy way to say “the ability of the cardiorespiratory system to extract oxygen from the environment”.[2]

There is no equivalent to VO2max for anaerobic CVF. To make a long story short, however ‘anaerobically fit’ someone is, anaerobic efforts cannot be maintained more than 2-to-3 minutes. Directly observable gains, therefore, amounts to seconds or fractions-of-seconds, so the only reliable way to measure them is through biopsy (measuring the by-products of anaerobic metabolism).

This issue is however not of utmost interest for health purposes, since unlike with Body Mass (and to an extent, with Strength) there is little ambiguity about the relevant indicator of CVF for health purposes: when it comes to risks of premature death, there’s VO2max, and that’s it. Well, almost, because of the causal link between avoiding sarcopenia and maintaining CVF, but I covered it in the previous section.

Fortunately, VO2max is directly correlated with the ability to maintain aerobic effort for a longer period. In fact, there is a simple VO2max test that everybody can take with a cell phone (the beep test, with free cell phone apps for Android and iPhone).

So why bother with anaerobic CVF? Well, because anaerobic CVF comes back with a vengeance when it comes to training aerobic CVF, as we’ll see in the next section. Below is a quick aside on the aforementioned difficulties of measuring anaerobic CVF (and why they may not matter that much) as a preliminary.

Anaerobic fitness and the anaerobic-lactacid pathway. The companion state of sustained anaerobic effort is metabolic acidosis and there is a minor scientific controversy as to what causes it. The ‘standard model’ holds the byproduct of anaerobic effort (lactate) responsible, but more recent research seems to indicate that lactate may actually delay acidosis (see here). All this is duly addressed in the Energy Systems entry of the Analytic Fitness™ Dictionary. I also strongly suggest that you peruse this post by Chad Waterbury which breaks down the science nicely (it’s on the reading list for the Energy Systems entry anyway). The absence of consensus about the cause of metabolic acidosis does not preclude the measurement of anaerobic fitness, but in view of the recent research, the ability to sustain activity while in effort-induced metabolic acidosis (aka anaerobic fitness) seems to matter less than the ability to delay the onset of metabolic acidosis (that would be part of aerobic fitness) through adaptations that make one more efficient at dodging metabolic pathways that induce acidosis. Again, I’ll discuss this topic at length in the Energy Systems entry, but you can check this article about strategies for triathletes to push through effort while delaying acidosis (note: the article still adheres to the ‘lactic acid’ narrative, but its recommendations are valid notwithstanding).

Why Bother With Anaerobic Capacity?

Some training protocols combining aerobic and anaerobic training but prioritizing the latter boast gains in VO2max that seem unmatched by protocols based on aerobic training alone.

Beginning in the 1990s, sports scientists established that the dose-response relation between aerobic exercise and VO2max gains could be manipulated dramatically by adding anaerobic exercise, even when the actual dose of aerobic exercise was dramatically low. The infamous Tabata study stands out as a landmark and the catalyst of attention to this phenomenon.

I have given a detailed analysis of this study (and its associated bullshit) which I’ll sum up here briefly. In a nutshell, the study pitted two groups of moderately-trained young males, training them on stationary bikes for 6 weeks:

  • The participants with the highest initial VO2max (7) constituted the Endurance Training (ET) group and cycled 60 minutes, 5x/week at 70% of their initial VO2max throughout the study (they were not tested for progress and intensity was never adjusted during the 6-week period).
  • participants with the lowest initial VO2max (also 7) constituted the Intermittent Training (IT) group and cycled for either:
    1. 10 minutes at 70% of their initial VO2max (usually not mentioned), followed by up to 8 intervals (20 second-on/10 second off), 4x/week, at 170% of VO2max (intensity was adjusted during the 6-week period: if a participant completed 8 rounds at the prescribed intensity, resistance would be cranked up on the next session).
    2. 30 minutes, 1x/week, at 70% VO2max followed by 4 intervals at the same intensity as their last session, as active recovery (never mentioned).

The surprise finding was that the IT group improved their VO2max 1.4x more than the ET group with less than 25% of the dose of aerobic exercise performed by the ET group (70 minutes for IT, 300 minutes for ET). The graph below represents visually the relative proportion of aerobic exercise (in green) and anaerobic exercise (in red) performed by each group.


The Tabata study was a bombshell and in the following years, everybody jumped the bandwagon of intermittent anaerobic exercise. As often, this was accompanied by a catchy acronym, HIIT, for High-Intensity Interval Training and inflated promises of same-fat-loss-as-regular-cardio-in-a-fraction-of-the-time.

The cardio stuff is bullshit, as previously mentioned, and I debunked the myth around the Tabata study elsewhere so I will not reiterate. But performance-wise, everybody was all too quick to forget a few things, namely that the IT group had actually performed aerobic exercise, and that the ET group had improved in spite of performing just above what usually counts as ‘active recovery’ for 6 weeks.

When I said that everybody was all too quick to forget this, I also mean researchers, with subsequent research and publication biases kicking in, leading to a relative deficit in the research on ‘traditional’ endurance training. And that’s too bad because there are also principled reasons to suspect that repeated bouts of anaerobic training are detrimental to health and thus ultimately for performance (a sick athlete does not compete). And they were forgotten, too.

Cardio That Makes You Sick

The same HIIT protocols that can increase your VO2max could very well make you sick.

And I mean literally sick. HIIT protocols have trainees alternate between two energy pathways, the anaerobic-glycolytic and the aerobic-oxidative that have very different metabolic effects. Anticipating on the Energy Systems entry, tapping into the anaerobic-glycolytic system induces a state called metabolic acidosis. The picture below should convince you that metabolic acidosis is not a good thing.


Of course, some nuance is in order here: acute, exercise-induced acidosis is not chronic acidosis caused by underlying conditions (chronic kidney failure, diabetes). A comparison should immediately come to mind with acute, exercise-induced inflammation, which is known to protects against chronic inflammation (one of the reasons to promote resistance training for healthy aging, as I mentioned here, although dosing yourself with baking soda is just as good for that particular purpose).

Then again, most pathological onsets of metabolic acidosis are acute, one-time things (dehydration, methanol poisoning, or the hosts of pathological causes for lactic acidosis, including exercise) rather than chronic, on-going things. And unlike resistance training, we lack longitudinal data about the long-term consequence of repeated phases of exercise-induced acute metabolic acidosis.

It is very likely that exercise may eventually cause adaptations to acidosis, but the Law of Adaptation has a built-in limitation: the state where all stimulation ceases may also be a state where all stimulation ceases because there’s nothing left to be stimulated. So, if repeated acidosis kills us, it’s still adaption. Not the best kind of adaptation and certainly not biological adaptation, although the difference does not matter if we’ve already spread our genes. But it’s adaptation nonetheless.

Wrapping Up: In the Long Run…

Our current best evidence suggests that, from a health standpoint, one should prioritize aerobic CVF, with resistance training coming a close second.

Barring performance-enhancement purposes, anaerobic CVF should come third if it comes at all. This does not mean that occasional higher-intensity cardiovascular exercise has no place for health purposes. For instance, testing one’s VO2max with the ‘beep test’ implies pushing oneself to the point of oxygen debt (and the associated metabolic acidosis).

In the long run, we are all dead.

John Maynard Keynes

There are some indications that unsavory side effects of regular HIIT, such as depressed immune system and chronic inflammation may be indirectly protective in the long run. I’ll review this evidence in an entry of this dictionary (Intensity most likely, but you can work your way from here and here). Then again, as pointed out by John Maynard Keynes, in the long run, we are all dead (hence, adapted to everything).

Put together, these indications, the known benefits of protocols à la Tabata, and the willingness to roll the dice and subordinate health to performance entail that HIIT for athletic performance enhancement is almost an open-and-shut case. Then again, athletes should not program HIIT for extended periods (and usually don’t), and regular Joes and Janes who partake in HIIT classes at commercial gym certainly do not “train like athletes”.

Honesty commands to mention that the case for or against HIIT for health remains pretty much open. Same as the case against it, depending on whether you are a half-full or half-empty type of person. The reasons are the in-the-long-run reasons as with athletic performance and with the same John-Maynard-Keynes caveat.

Then again, in practice, you don’t need to ditch your favorite ‘Tabata’ workout or skip your HIIT classes at the gym if you enjoy them. Odds are that you don’t perform it at Tabata-intensity level anyway. There is no way anybody could maintain a 170%-of-VO2max intensity for up to 30 minutes (yes, some ‘Tabata workouts’ are that long). More often than not, the label ‘Tabata’ is either cardio-for-fat-loss bullshit, a term of endearment, or good old plain ignorance (I suspect the latter two in the example linked).

Now, there are viable alternatives to HIIT that promote similar VO2max adaptations, if not even better. I mentioned research and publication biases in favor of HIIT and these protocols are somewhat less researched, and consequently, arguments for them are mostly analytic. But they are really solid. Practical examples include the triathlon program I linked already or suggestions for recreational trainees laid down by Chad Waterbury (again) in that post which also breaks down very nicely the science supporting them.



[1]^Just to be clear, the one thing that promotes fat loss is caloric deficit: your body does not care how you burn calories, it just cares that you get less in than you get out. As for cardiovascular exercise, high-intensity exercise, commonly recommended for fat loss, does not elicit the fat-for-fuel pathway (aerobic-oxidative) but the sugar-for-fuel pathway (anaerobic-lactacid), and your body cannot make sugar out of fat (it can free sugar trapped in your fat stores, but you have to be in a fasted state for that, and high-intensity cardiovascular exercise in a fasted state is not a good idea). There is more about all that in the Energy Systems entry of this very Analytic Fitness™ Dictionary. Furthermore, given the Law of Adaptation, and the fact that adaptations are not always optimal, prioritizing cardiovascular exercise under a caloric deficit might end up making you lose weight, but not fat, without actually improving your cardiovascular fitness. The reason why it is so is sketched out why in this post and I’ll get back to it eventually, possibly in the Diet entry of the Analytic Fitness™ Dictionary.

[2]^ Yuri Verkhoshansky has proposed (here) that the efficiency of muscles at using oxygen provided by the cardiorespiratory system would be a better predictor of performance than the ability to extract it from the environment. Verkhoshansky’s arguments are supported by recent research on the role of lactate (and the absence of role of lactic acid) in effort metabolism, but they predate that research and are, by Verkhoshansky’s own light, ‘deductive’ (which means that they are based on the same principles as Analytic Fitness™). The dust has not settled yet and Verkhoshansky’s position is still in need of empirical validation. Then again, I’d put my money on it. In fact, I may already have, since the way I train (myself and a few others) closely parallels Verkhoshansky’s recommendations.

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