VO2 Max... The Perfect Example Of Goodhart's Law?

*** This post is geared towards endurance enthusiasts who are a little confused with the pendulum swing in the fitness space right now, between things like zone 2 and VO2 max training. Hopefully this helps challenge some misconceptions.

VO2 max is the maximal integrated capacity of the pulmonary, cardiovascular, and muscular systems to uptake, transport, and utilise oxygen.

VO2 max has had a bit of a rise in popularity recently. Lots of coaches are talking about what it is, how to improve it and why it is important to train it. However, when a measure becomes a target for control or manipulation, it ceases to be a good measure of the underlying process or goal it was originally intended to reflect.

The performance outcome is the context that we should be concerned with. Not a number on a lab report that actually tells you very little about what's happening under the hood (economy, thresholds are more informative and can help guide your training more appropriately).

I think people have forgotten that VO2 max is just a descriptor of maximal oxygen uptake, not a training target, or even a marker of progress for those that are already well trained endurance performers. Ultimately, VO2 max can be a useful measure, but I'm not sure we should be striving for it in performance contexts, especially for those who already have a decent amount of endurance training under their belt. Because of the hyperbole many have also made a category error, where in order to improve VO2 max they advocate for more VO2 max type sessions. This of course isn't inherently wrong, but it is missing the woods for the trees.

Below are some key misconceptions and errors that I have seen online over the last few months.

1) VO2 max can only be developed via specific intervals.

To improve VO2 max I should do more work at VO2 max, right? Well, not really. There are two issues with this; First, the assumption that only high intensity intervals can improve VO2 max. Second, if VO2 max is our goal, that we can actually achieve a really high VO2 max with only this approach, or that this works realistically in a programme for long periods of time.

The first part is an assumption rooted in the oxygen delivery model of VO2 max, which identifies cardiac output as the primary limiter. People intuitively think if I spend more time at maximal cardiac output then that will improve my VO2 max. However, as stated “VO2 is the maximal integrated capacity of the pulmonary, cardiovascular, and muscular systems to uptake, transport, and utilise oxygen”. This definition highlights that multiple subsystems contribute (pulmonary ventilation, hemoglobin, cardiac output, utilisation at the muscle). Therefore, for example, peripheral adaptations can be limiting in some cases (e.g capillary density, mitochondrial content, substrate etc). When we think about this we can start to see VO2 max intervals alone provides insufficient volume and duration of stress to remodel peripheral tissue and metabolic systems. This should also be intuitive, because if it were sufficient, then we wouldn't see high training volumes correlating with better endurance performances. It would all save us a lot of time training.

Consider this analogy;

Think of the aerobic system as a transport network. The motorway represents central oxygen delivery (heart, lungs, blood volume, haemoglobin, cardiac output). The local roads and side streets represent peripheral diffusion capacity (capillary density, mitochondrial density, oxidative enzymes). Traffic congestion does not occur because the motorway is too small but it occurs because traffic cannot leave the motorway and be absorbed fast enough by the side streets. In physiological terms, this congestion reflects a limit in oxygen extraction and utilisation, not a failure of delivery (heart and lungs, it rarely is the pulmonary system).

The idea that VO2 max then is best improved by repeatedly prescribing VO2 max workouts reflects a misunderstanding of endurance adaptation (or even what contributes to elite performance). VO2 max is not a discrete trait you train directly, but an emergent property of a system whose peripheral components are overwhelmingly trained in a volume dependent manner. High intensity work can help yes, but it cannot build the infrastructure required to sustain high rates of aerobic metabolism, why you ask? Because time doing is the most important factor to attaining elite endurance performance and we can't train much when intensity is always high.

2) Research applied to the real world. The 12 week problem.

Intensity is a flame that burns bright but dies quickly. Short term upticks in VO2 max results found in 8-12 week studies don’t provide us with long term training solutions. Whilst intervals should likely always be a part of VO2 max development, drawing conclusions from this research (namely that VO2 max intervals out performs low intensity high volume work) fails to consider real world viability and time frame adaptation considerations.

Ultimately, cumulative peripheral and structural changes that keep moving VO2 max upward for years requires high volumes of training. Intervals are costly: high neuromuscular strain, high stress, long recovery time. You cannot accumulate 10–20 hours/week of interval work. This is why 80/20 approaches exist and why high volumes are the hallmark of elite endurance performance.

3) VO2 max is the most important performance metric to chase and therefore improvements in this metric will see improvements in performance outcome.

As mentioned in the opening VO2 max ≠ Performance. If VO2 max directly dictated performance then the individual with the highest value would always win. This is not the case. Whilst it is one factor, elite performers can have lower VO2 max values than their competitors but still outperform them due to superior lactate threshold, critical power, efficiency, economy, psychological and tactical factors. It is necessary but not sufficient. So maybe we shouldn't make it the goal...

Putting VO2 max in perspective

All of these assumptions then are examples of component level thinking rather than thinking about system integration. Instead VO2 max emerges from multiple interconnected subsystems. Intervals are a powerful tool, but high volume low intensity training is what helps build the central and peripheral adaptations that ultimately makes VO2 max gains and, more importantly, usable in performance contexts.

So the most important question remains here, what are you trying to improve (not VO2 max but performance), and is this relevant / a potential scenario that could be limiting you e.g. previous training history can help guide you or physiological testing data (VO2 along with RER, thresholds, substrate utilisation, fractional utilisation, critical power, NIRS).

What helps answer that question, and whether you need to worry about it - what are you goals? And how much time can you actually dedicate to training? I think when it comes to programming, this post still sums it up - if you have loads of time to train you should be cautious how much VO2 work you're putting in. If you only have 5 hours to train then you do probably want to leverage some more intensity to make up the gap, however you will have to accept you won't become the next Tour de France winner.

You can't find a substitute for time.