A common saying when it comes to health is to “know your numbers,” but what do you really need to know when it comes down to it? If you had to ask which one number had the biggest impact on health and longevity, it technically wouldn’t be your blood pressure, your cholesterol, or your blood sugar (even though all of these matter, a lot)… it would be your VO2 max. There’s a lot going around nowadays about this number and how important it is, but to many it still feels pretty abstract as to what it means. Let’s dive into what it is, why it is so important, how you can track it, how you can improve it, and more.
The term “VO2 max” is basically short-hand for the maximum rate at which you can utilize the oxygen you breathe. Without going too far in the weeds, let’s just think about what this means. When we take a breath in, we need clear airways that will help that air make its way through our lungs. At the end of our lungs, in little sacs of tissue called alveoli, we need efficient gas exchange from the air to our bloodstream, maintaining the oxygen concentration of our blood. From there, we need a strong heart and cardiovascular system to pump that fresh oxygen-rich blood to every tissue in our body effectively. Lastly, we need well-functioning mitochondria, which will use all of that oxygen efficiently in the process of producing energy to sustain life.
Think for a moment about every step of that cardiorespiratory system. If one single step goes wrong, our VO2 max will suffer as a consequence. Every part needs to be in working order to sustain a high utilization of oxygen, from our respiratory tract to the mitochondria of our cells. That is why this metric is so important: it is an integral of the entire system, a way to gauge its total function. If we maintain a high VO2 max, we can be confident that all of this–our core system to supply an essential molecule for life–is functional. For what it's worth, if you don't buy the theory, this is also true in practice. Countless studies such as this one in JAMA have shown VO2 max to be among the strongest associated metrics with overall longevity. So, we have observational, empirical evidence to support it, we have a mechanistic explanation for why it makes sense… but why is more not made of it? That is to say, why is it not regularly tested?
The problem is it’s not all that easy to test, but there are effective strategies to at least get a sense of where you stand. Most wearables, including the Apple Watch, actually do provide an estimate of your VO2 max. However, the true validity of these numbers has been brought into question, as the algorithms they use are virtually entirely dependent on patterns in heart rate response to exercise. This is a pretty crude way to approximate a complex metric like VO2 max that doesn’t correlate all that well, not to mention the heart rate accuracy of most wearables is far from perfect in the first place. The number you see produced by your wearable might not be that accurate to understand where you fall on an absolute basis, but it can still probably be useful to see how you’re doing relative to yourself and your baseline.
Unfortunately, the best way to actually test it is in an exercise physiology laboratory, or with a costly face mask device. Either of these will essentially measure concentrations of oxygen and carbon dioxide in the air you breathe in and out, and based on the quantities and ratios of those two, one can actually calculate quite accurately the total oxygen utilization, and even the type of fuel one is primarily utilizing (i.e. carbohydrates in glycolysis, fats in mitochondrial oxidation, etc.). While this is nowhere near common to see as a routine test in the doctor’s office every year, we firmly believe it should be a regular component of the annual physical exam, and are hoping to see its implementation become more widespread in clinical practice.
It may be frustrating that arguably the most important number in determining our long-term health is so difficult to obtain, but luckily, it’s still easily actionable to improve your VO2 max, even if you don’t know with certainty the exact number it may be. A lot has been looked at for the most effective strategies to improve VO2 max, and historically it has been thought that high-intensity training, perhaps in certain short-length intervals to maximize output, would help most with this sort of measure of peak performance. Though it is still almost certainly the case that this sort of training is highly beneficial for VO2 max, it may not be the only way. In fact, in our most recent newsletter, Nick shared a large-scale meta-analysis that highlighted the similar benefits in VO2 max improvement from both high-intensity exercise and moderate-intensity training like zone 2. There are likely still strong benefits to training both sorts of energy systems, but it appears our body’s adaptation is more flexible to different kinds of training than we previously thought. Also, and possibly most importantly, the meta-analysis demonstrated that larger increases in VO2 max resulted from greater training frequency. The takeaway? Consistency of any cardiovascular training is the key to improving the strongest predictor of your longevity.
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