The Triathlete Blueprint Newsletter #129- VO2max: Simply Explained — What It Is, Why It Matters, and How to Train It

Yan Busset
23 minutes ago
7 min read

Read time: 5min.

By Coach Yan Busset

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VO2max Demystified: A Simple Breakdown for Smarter Training

You’ve worked on your VO2max, you’ve heard it from your coach, seen it in training programs, and you probably think you know what it is. But do you really? Only a few athletes actually take the time to understand what it really means, what it measures, and why it matters. You know it’s about oxygen, but usually not much more than that.

So let’s go a bit deeper, because the more you understand about your training sessions, the more likely you are to do them the right way. And once you understand the logic behind your workouts, training becomes more enjoyable and more rewarding. I always want my athletes to be as educated as possible about what they’re doing, because when you know the “why,” you’re far more likely to get the most out of every session.

What VO2max really means

At its core, VO2max is about how much oxygen your body can use during intense exercise. Think of it as the size of your engine. A bigger engine can deliver and process more oxygen, which means more aerobic power. But engine size isn’t the only thing that matters. Fuel consumption does too. That’s your aerobic efficiency, how economically you use that oxygen. You need both. VO2max is about the engine size, while efficiency is about how far you can go with each drop of fuel. Another way to think about it is as the size of your house. Working on your VO2max is like raising the ceiling so you have more room to grow.

Scientifically, VO2max is defined as the maximum volume of oxygen your body can consume per minute relative to your body weight.

The formula is:

VO2max = Q × (CaO2 − CvO2) / body weight

In simple words. Your heart is the pump that moves blood. Blood carries oxygen to your muscles. Your muscles use that oxygen to create energy. The more oxygen your body can deliver and use, the higher your VO2max. We usually talk about it as either absolute (the total oxygen you can use) or relative (oxygen use per kilogram of body weight). For endurance sports, the relative number matters more because you’re moving your body weight through space.

Can you improve your VO2max?

There is a genetic part to VO2max ( studies show a wide range from 20- about 50% of your VO2MAX die to genetics), but don’t let that discourage you. Some people are born with a bigger engine but there is a trainable part of it so you have room for improvement.

And how much can you really improve it?

With consistent endurance training, sedentary adults can typically increase their VO2max by about 15 to 25%, with some “high responders” improving up to around 40% ( again depends on genetics).

For well-trained athletes, the margin is smaller, often around 5 to 10%, but at that stage, VO2max training is still super important to slow the decline, improving oxygen kinetics, and increasing the time you can sustain close to your maximum.

Your Future health benefits of training VO2MAX

VO2max starts to drop after your mid 20s. Without training it falls roughly 8 to 10 percent per decade and the decline accelerates with age. With consistent training you can slow this down by a factor of 2 or 3! This is not only about racing. VO2max is one of the strongest predictors of longevity. Classic and modern cohorts show higher cardiorespiratory fitness is linked to much lower mortality, with no clear upper limit to the benefit. In real life terms, as you get older and move into the later stages of life, once VO2max drops below about 18 ml/kg/min for men and 15 ml/kg/min for women, even daily tasks get hard. Getting up from a chair without help can become impossible.

VO2 kinetics and why it matters

To understand VO2max training, it helps to understand VO2 kinetics. This is how quickly your oxygen use ramps up when you start working hard. Faster kinetics means you reach the target zone sooner and accumulate more useful time there. Slower kinetics means you need longer efforts to get the same stimulus. Fitness, age, training history, and prior exercise all influence this. A thorough warm up with a few accelerations shortens the delay and helps you hit VO2max earlier in the main set.

How to train VO2max

VO2max sessions are intense. Think Zone 5, roughly around 120 % of FTP on the bike for many athletes. These efforts are short and hard. Think " Best effort" intensity.

If you are new to VO2max training, or you simply have not done it for a while, start with shorter intervals like 30 seconds on and 30 seconds off, or 1 minute on and 1 minute off ( HIIT High intensity Interval Training style). As your fitness adapts, progress to 2 minute intervals and then to classic sets like 4×4 or 5×4 minutes. High intensity aerobic intervals have repeatedly been shown to improve VO2max more than steady endurance or threshold work, and the 4×4 model is a proven option.

What matters most is the total time you spend near VO2max in the workout. A practical target is to build from about 8 to 12 minutes of total time at or near VO2max up toward 15 to 20 minutes as you get stronger. Beyond that, quality often drops and fatigue rises with limited extra benefit . It is normal if your power or pace fades toward the end of a proper VO2max session. That is often a sign you are hitting the right system.

How often should you do VO2max? One session per week to maintain your fitness, and up to two per week in a dedicated, time limited block if your goal is to improve it ( if no other interval training sessions same week ), more than that usually adds fatigue without providing extra gains.

A more advanced approach with Critical Power and W′

If you use Critical Power, you can individualise VO2max sessions with W′, your anaerobic battery above CP. The W′ balance model lets you track how much of that battery you are spending in each work bout and how much you have reconstituted during recovery. Many athletes like to repeat efforts until W′ is substantially drained, then recover until W′ is mostly back before going again. This is a way to match interval and recovery to your physiology rather than using a one size fits all prescription.

Other factors that influence VO2max

It is not only about brutal intervals.

Zone 2 endurance training. A strong aerobic base increases stroke volume and mitochondrial density and supports VO2max. Even continuous endurance training improves VO2max, while intervals tend to improve it more and also speed VO2 kinetics.

Body composition. Because VO2max is expressed per kilogram, reducing excess body fat directly raises your relative VO2max for the same absolute oxygen use.

Sleep and recovery. Adaptation happens after training. If you are not well rested, you will not hit the right intensities and you will not adapt properly. Simple as that.

Measuring VO2max

The gold standard is a gas exchange test with a metabolic cart where you wear a mask and the device measures oxygen in and carbon dioxide out while you exercise.

You can also estimate VO2max with field tests like a Cooper test, VAM, Critical Power, or CSS. Most wearables, like Garmin, Polar, or Apple Watch, provide estimates too. They are less precise than gas analysis, but they are getting better and are useful to track trends over time. What matters most is not the exact number on any given day but the direction where the trend goes.

Final thoughts

VO2max is a key part of endurance performance, but it is not the whole story. Think of it as the size of your engine. If your fuel economy is poor, you will still run out of gas before the finish. Two athletes can have the same VO2max but very different race results if one is more efficient aerobically. Aerobic efficiency is often even more decisive than VO2max itself.

You still need to work on your VO2max. Push that ceiling higher. But remember, endurance sport is a mix of engine size and efficiency. And the best part is that VO2max training is not only about your next race. It is an investment in a healthier, stronger, more independent future self.

Here are some interesting studies to look at if you want to develop this topic:

-Bouchard C. et al. (1999). Familial aggregation of VO2max response to exercise training. Journal of Applied Physiology. Read the study

-Fleg J.L. et al. (2005). Accelerated longitudinal decline of aerobic capacity in healthy adults. Circulation. Read the study

[-Blair S.N. et al. (1989). Physical fitness and all-cause mortality in healthy men and women. JAMA. Read the study

-Mandsager K. et al. (2018). Association of cardiorespiratory fitness with long-term mortality: No observed upper limit of benefit. JAMA Network Open. Read the study

-Shephard R.J. (2009). Maximal oxygen intake and independence in old age. Sports Medicine. Read the study

-Poole D.C. & Jones A.M. (2012). Oxygen uptake kinetics. Comprehensive Physiology. Read the study

-DeLorey D.S. et al. (2004). Effects of prior heavy-intensity exercise on pulmonary O2 uptake kinetics. Journal of Applied Physiology. Read the study

-Helgerud J. et al. (2007). Aerobic high-intensity intervals improve VO2max more than moderate training. Medicine and Science in Sports and Exercise. Read the study

-Midgley A.W. & McNaughton L.R. (2006). Time at or near VO2max during continuous and intermittent running. Journal of Sports Medicine and Physical Fitness. Read the study

-Daussin F.N. et al. (2008). Effect of interval versus continuous training on cardiorespiratory and mitochondrial functions. American Journal of Physiology. Read the study