Simple plain English explanation of VO2 MAX

Question

What is VO2 MAX and how is a measurement taken? By how much can VO2 MAX be increased in the average person?

Answer 1

VO2 Max refers to the maximum volume of oxygen that an individual can use at maximum levels of intense aerobic exercise. It is usually reported as as milliliters of oxygen used in one minute per kilogram of body weight, though sometimes you see liters of oxygen per minute with no adjustment for body weight. The former measurement is more useful in exercise and sports science since it allows the measurement to be compared among athletes of widely different weights.

It is usually measured in a fitness lab setting using either an exercise bike or a treadmill. The test subject wears a mask and heart rate monitor. The mask is connected to a device that collects and measures of the volume and oxygen concentration of inhaled and exhaled air.

At some point below maximum effort the body switches from aerobic to anerobic processes to generate energy. Exercise intensity is increased gradually until the subject is at a maximum aerobic effort - beyond which there is not or only negligible increase in oxygen uptake. That is the VO2 Max point.

I don't know how much it can be increased in any individual, and there are both genetic and exercise components. This page lists that:

The average for a sedentary individual is close to 35 ml/kg/min. Elite endurance athletes often average 70 ml/kg/min. One of the highest recorded VO2 max results (90 ml/kg/min) was that of a cross country skier. Cyclist Lance Armstrong's VO2 max was reported at 85 ml/kg/min.

For even more detail, including the associated math, see Wikipedia: V02 Max.

Answer 2

Vo2 Max is a measure of 2 things:

1. Physical lung capacity -- This a measurement of the actual cubic feet of airspace available in your lungs. This is a genetic factor, which cannot be trained up.
2. Ability to transfer oxygen in your blood stream. Increased red blood cell counts mean more carriers available to transport oxygen to the active muscles in your body. This can be increased through exercise or drugs. The latter course, drugs, while common will bar you from any competition, and is both dangerous and illegal.

The combination of the 2 gives you your oxygen consumption rate, which is also known as Vo2 Max.

VO2 max (also maximal oxygen consumption, maximal oxygen uptake, peak oxygen uptake or maximal aerobic capacity) is the maximum capacity of an individual's body to transport and use oxygen during incremental exercise, which reflects the physical fitness of the individual. The name is derived from V - volume, O2 - oxygen, max - maximum. VO2 max is expressed either as an absolute rate in litres of oxygen per minute (l/min) or as a relative rate in millilitres of oxygen per kilogram of bodyweight per minute (ml/kg/min). The latter expression is often used to compare the performance of endurance sports athlete

Answer 3

In studies on health, VO2max is an indicator of cardiorespiratory health. It might be used to predict some important outcome. For example, better VO2max is very strongly linked to longevity. Many readers will probably have heard this from popular media.

Alternatively, researchers might see if some exercise program affects VO2max, either in the general population or in trained athletes. It is an important indicator of athletic potential. However, it isn't the be-all indicator. In cycling, your threshold power is also important, and people may hit their threshold at a lower or a higher fraction of their VO2max.

Last, the body uses oxygen to produce aerobic power, so the volume of O2 you are burning right now is a measure of power, like the watts from your power meter. You could interpret VO2max a bit like a car's maximum rated horsepower (but even world-class athletes have <1 hp)¹. Your maximum 5 minute cycling power can be used as a proxy for VO2max, or even as an estimate of VO2max, with caveats. However, some of us can sustainably work at a higher fraction of VO2max than others. Also, this omits anaerobic power, and efforts under 3 minutes, a lot of the power is anaerobic.

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VO2max as an indicator of cardiovascular health and athletic ability, which are different things

Take caution that my background is not clinical or exercise science. I haven't reviewed the full body of literature related to these topics.

VO2max is a widely accepted measure of cardiovascular fitness in the general population. There is a standard process to measure it, and universities have the equipment.

Higher VO2max is consistently associated with lower mortality in the general population. For example, this Finnish cohort study (Laukkanen et al, 2016) found that people with a lower decline in VO2max over the several-year study period (i.e. they maintained their aerobic fitness better) had lower all-cause mortality. Or in this study by Chiaranda et al, on a population with cardiovascular disease (CVD), higher VO2max was associated with lower probabilities of readmission to hospital. (Actually, VO2max was estimated in the study from a submaximal treadmill test for health reasons.) Or Mandsager and colleagues (2018) show that the relationship between VO2max and longevity is non-linear. It's particularly important to improve a low VO2max, e.g. in the bottom quartile.

In trained endurance athletes, the meaning of VO2max changes slightly. Your power at VO2max is a ceiling on your threshold power. However, some athletes can work sustainably at higher percentages of VO2max than others. In training, it's possible to improve other aspects of performance without necessarily improving VO2max. For example, you might improve your threshold (which means a higher fractional utilization) or time to exhaustion at threshold. Higher VO2max should directly correspond to higher short-term power (e.g. 3-8 mins). Highly-trained endurance athletes might need high-intensity intervals to improve their VO2maxes.

One example study is Helgerud et al (2007), who found that

High-aerobic indensity endurance interval training is significantly more effective than performing the same total work at either lactate threshold or at 70% HRmax, in improving VO2max.

Or Rønnestad et al (2012) tested 2 VO2max workouts per week versus a block periodization scheme: do one week with 5(!!) VO2max workouts, then back off to a single interval session per week. The block periodization group saw a bigger gain in VO2max than the baseline group. The average VO2maxes in both studies were high, 55-60 in the first study and a bit over 60 in the second.

Last, actual performance, e.g. maximum mean power for a set time, or average power over a set distance, is measurable and it's another potential outcome. Interestingly, one recent meta-analysis by Rosenblat and colleagues showed that including at least some HIIT (or at least training above threshold) is associated with VO2max gains, but not with improvements in time trial performances, at least not within the study periods. Perhaps it might take more training for a higher VO2max to produce higher performance. At the limits of human performance, sports scientists debate if there is a tradeoff between VO2max and gross efficiency (an average of about 22% of the power produced by the body goes to the cranks and becomes cycling power). That is, past a certain limit, if you increase your VO2max, you may decrease your efficiency this Outside article discussed the debate in sports science and talked about a case study of one athlete who raised his VO2max from 77 to nearly 97 (not a typo, and the authors went and checked their equipment calibration after that reading), but his efficiency decreased as his VO2max increased. Thus, his actual cycling power may not have improved much. Anyway, casual readers should probably not be too concerned about this.

HIIT, VO2max, and the popular media

Consumers might have heard of high intensity interval training (HIIT). It was definitely a trend at one time. For example, this 2019 Vox article discusses some of the science behind it. Anyway, that article mentions VO2max as an outcome, the fact that VO2max is a strong predictor of overall health, and the fact that HIIT leads to gains in VO2max. In fact, as I write this, I think VO2max is hitting a trend in the popular media or at least among some social media influencers, like Peter Attia (physician and longevity researcher/influencer). He characterized VO2max as being affected by your athletic activity over your whole life, meaning that it is hard to radically improve it in a short timespan.

In the general population, if you don't already exercise, I suspect that any aerobic activity may be sufficient to improve cardiovascular health. That includes long slow distance work (aka zone 2 rides, endurance rides). If you're starting from literally playing video games on the couch, then starting to walk a few times a week would probably raise your VO2max and improve your health outcomes. If your fitness is poor, then it is probably advisable to start with long slow distance anyway. Attia has said on his podcast that he feels that everyone should get their VO2max measured because of how predictive it is of mortality (remember, his thing is longevity). Perhaps that gives rise to questions like the original one and also this one.

If you're on the Bicycles Stack Exchange, you are pretty likely to ride your bike regularly. I suspect this is pretty much sufficient. You could do it more. I suspect that the fitter you are, you are more likely to require some dedicated VO2max work to actually move the needle. For those interested in adding VO2max sessions, Attia reports that he does 1 VO2max session a week, and I think that's likely fine for general purpose fitness and longevity. Remember that if you do them correctly, they are pretty strenuous. 2 a week is probably too much for the average person. What should you do? You probably want to warm up and then do 2 to 5 minutes at a nearly all-out pace, then rest for the same amount of time, then repeat. I would start with aiming for at least 12 minutes of working time if possible, i.e. start with something like 6x 2 mins. Less if you can't manage, more if you can. Pace yourself so that you can maintain similar output across all your intervals. Your power/speed can decline a bit, it mainly matters that you're working above threshold, but if you go much too fast on the first few intervals, you'll burn out.

I am not saying that the general population should avoid high intensity intervals barring some sort of medical contraindication. They take less time! Also, I haven't reviewed the literature, and they might give greater VO2max gains than the alternatives. I think the most important point is that you should do a routine that you can enjoy and that you can do sustainably. You can start with long slow distance, build up fitness a bit, then think about adding harder workouts. Long, slow distance work / zone 2 work produces a somewhat different set of physiological adaptations that I bet still benefit health. In athletes, an aerobic base built by lots of zone 2 is considered essential to support you doing more high intensity work.

I don't know that I agree with Attia that everyone should go measure their VO2max. That said, you can; private testing labs exist, usually charging US$150-300 or so to measure your VO2max and perhaps some other information. Or your local university may have a sports science lab that decides to rent out its equipment.

It is possible to estimate, with caveats, your VO2max from a max cycling effort of 5 minutes plus or minus a few minutes without going into a lab. See here for details.

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VO2max and VO2 are measures of power

Last, our bodies burn oxygen to produce power. Thus, VO2 (not VO2max) is a measure of aerobic power your body is currently generating. As explained more below, our bodies also generate anaerobic power, and in many cycling contexts, you are generating both aerobic and anaerobic power. In a 100m track sprint or a final sprint in a road race, you're mostly drawing on anaerobic power.

Also, note that VO2 is not cycling power. Our bodies do not convert all the aerobic power to cycling power. So, VO2 could be converted to watts, but not all those watts make it to your crank. Most are dissipated as heat, which is why in cold weather they tell you to just keep moving. Your power meter measures cycling power, but that power will have some anaerobic contribution in some hard efforts. 3 to 8 minute max efforts will usually get you up to or near to your VO2max, but you also have some anaerobic contribution.

Consider the graph below from Trainer Day. This graph is based on an individual athlete (i.e. the height and the slope will vary by person, but the graph conveys generalizable information). The red line is the total measured power output for a max effort of duration on the x-axis (note the scaling isn't linear).² The blue line represents the estimated anaerobic power and the green represents estimated aerobic power at each effort duration.

That is, for a 35-minute max effort, most of the power is aerobic. For an 8-minute max effort, a small but significant fraction of the power comes from anaerobic glycolysis. But the aerobic system produces roughly the same total power - that is, it's at its maximum output (VO2max). For a 1-2 min max effort, you're at roughly 50:50 between anaerobic and anaerobic power.

Devices that measure VO2 consumption when on the bike (or in another activity) exist but are not widely used³. In the graph above, the company measured cycling power with a power meter. It applied a proprietary model to estimate anaerobic and aerobic power contributions at various effort durations. In a discussion with an exercise scientist on Attia's podcast, the scientist said that actually these portable devices are accurate at measuring O2 consumption.

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Footnotes

1: Actually, the horsepower is a measure of total work done, rather than oxygen consumed, and it's not normalized for weight. The VO2maxes of a sample of racehorses ranged from 123 to 172 mL O2/kg min, so their relative VO2maxes are higher than us. And they're a lot bigger, so their absolute VO2maxes are much higher, which illustrates how important horses were to building human civilization.

2: The total power-duration curve (the red line) in the graphic is actually estimated using 2-4 maximum efforts and a mathematical model. Usually you need to do one 3-5 min effort and one 10-15 min effort, or similar. The Critical Power model is one such model.

The aerobic and anaerobic power contributions (blue and green lines respectively) are estimated from what I believe is Trainer Day's proprietary model. They are not directly measured.

3: These guys sell a portable VO2 analyzer, which requires you to put a mask over your face like you would in the lab. There may be competitor companies.

Answer 4

One note about VO2 max, is that it is becoming more and more an academic interest number, as studies are increasingly showing that it is a poor predictor of actual performance. The two numbers that are becoming more important/relevant are vVO2max, and tlimvVO2max.

vVO2max is the minimum running/cycling speed at which your VO2 max level is attained, and after a few minutes of which, additional power has to come from anaerobic sources. This number is receiving increased attention (especially in running) as economy of motion is becoming a factor. A more efficient athlete will be traveling faster when they hit VO2max, so their vVO2max is higher than a less efficient athlete. In cycling (especially for TT), aerodynamics and proper fit will increase economy (Getting more speed out of the same effort). In aerodynamics I include losing weight, as a larger person presents a larger wind profile, efficiency would be enhanced through a proper fit, and comfort/familiarity on your bike.

tlimvVO2max is simply the time limiter for VO2 max, or how long you can continue to keep your pace once you've hit your VO2 max. If two cyclists both hit their VO2 max at 26mph, but cyclist A has a tlim of 10 minutes, while cyclist B has a tlim of 15 minutes, cyclist B will win. (Assuming the finish line isn't 10 minutes away :p)

Both tlimv and vVO2 can be increased through greater efficiency and training, while VO2 is a relatively static number, and really only indicates potential, so while VO2max is an interesting number to know, simply knowing it won't really help you change anything in your training.