VO2max: What It Is, What It Isn’t, and Why It’s Not the Whole Story

VO₂max: What It Is, What It Isn’t, and Why It’s Not the Whole Story

In 2012, Norwegian cyclist Oskar Svendsen recorded a VO₂max of 97.5 ml/kg/min — the highest value ever measured in a human being. He turned professional in 2013. By 2014, at age 19, he had retired from competitive cycling. The athlete with the greatest recorded aerobic engine in human history couldn’t sustain a career at the top.

This story is not an anomaly. It is an illustration of one of the most important and widely misunderstood truths in exercise physiology: VO₂max is a ceiling, not a guarantee. Understanding what it actually measures — and what it doesn’t — changes how you think about endurance training, performance prediction, and the science of human limits.

What VO₂max Actually Measures

VO₂max is the maximum rate at which the body can consume oxygen during maximal aerobic exercise, expressed in milliliters of oxygen per kilogram of body mass per minute (ml/kg/min). When you run or cycle to exhaustion in a laboratory setting, VO₂max is the plateau — the point at which increasing workload no longer produces a corresponding increase in oxygen consumption.

Average untrained adults: 35–45 ml/kg/min. Recreational endurance athletes: 50–60 ml/kg/min. Elite marathoners: 70–80 ml/kg/min. Elite cross-country skiers and cyclists: 80–90 ml/kg/min. Svendsen’s 97.5 ml/kg/min sits far beyond all of them.

The measurement itself is straightforward in principle: the athlete breathes through a metabolic cart while exercising at progressively increasing intensities until maximum effort is reached. Oxygen consumption is calculated from the volume and composition of exhaled air. Heart rate, power output, and ventilation are measured simultaneously.

Cardiac Output: The Primary Limiter

What limits VO₂max? This question has generated decades of scientific debate. The short answer: primarily the heart.

Oxygen delivery to working muscles depends on two things: how much blood the heart can pump per minute (cardiac output) and how much oxygen the muscles can extract from that blood (arteriovenous oxygen difference, or a-vO₂ diff). The Fick equation captures this elegantly:

VO₂max = Maximum Cardiac Output × Maximum a-vO₂ diff

Maximum cardiac output is the product of maximum heart rate and maximum stroke volume (blood pumped per beat). Elite endurance athletes develop enormous stroke volumes — up to 200 ml per beat — through years of training that literally enlarges the heart’s left ventricle. The resulting “athlete’s heart” can deliver 30–40 liters of blood per minute at maximum effort. An untrained person might manage 18–20 liters.

This is why VO₂max responds to endurance training: training volume and intensity drive cardiac remodeling, increasing stroke volume and therefore maximum cardiac output. When athletes report improvements in VO₂max of 10–20% over a training program, they are largely reporting improvements in cardiac output.

The peripheral side — how much oxygen muscles extract — also matters and is trainable through mitochondrial adaptation. But the consensus from decades of research, including the landmark studies of Saltin, Rowell, and others, is that the cardiovascular system is the primary ceiling, with peripheral factors playing a secondary but significant role.

Heritability: The Genetic Ceiling Above the Ceiling

The most sobering fact about VO₂max is its heritability. Twin studies and family studies consistently find that genetic factors account for approximately 50% of baseline VO₂max and up to 50% of the trainability of VO₂max — the degree to which it responds to training.

The HERITAGE Family Study, which subjected over 700 sedentary individuals from 110 families to an identical 20-week aerobic training program, found that VO₂max improvements ranged from less than 5% to more than 40% — and family membership predicted much of this variance. Some families were “high responders”; others were “low responders.” The training was identical. The outcomes were not.

This has profound implications. Two athletes training identically may reach fundamentally different VO₂max ceilings — not due to effort or commitment, but due to genes they were born with. Oskar Svendsen’s 97.5 was, in large part, an inheritance he received at conception. His early retirement suggests it was a necessary but insufficient condition for sustained elite performance.

Why VO₂max Predicts Less Than You’d Think

Here is the paradox: VO₂max correlates strongly with aerobic performance across broad populations. But among elite endurance athletes — who are already selected for high VO₂max — it predicts performance poorly.

Studies of elite distance runners have found that VO₂max explains only 25–40% of performance variance within the elite tier. Athletes with similar VO₂max values can differ in marathon performance by 10–15 minutes. Among a group of runners all with VO₂max values between 70–75 ml/kg/min, the one who wins isn’t necessarily the one at 75.

Three additional variables pick up the explanatory slack:

1. Lactate threshold (LT)
The lactate threshold is the exercise intensity at which blood lactate begins to accumulate significantly — typically defined as 2 mmol/L (LT1) or 4 mmol/L (LT2, also called the anaerobic threshold or OBLA). This threshold, expressed as a percentage of VO₂max, is one of the strongest predictors of endurance performance.

An athlete with a VO₂max of 70 ml/kg/min who can sustain 85% of VO₂max before lactic acid accumulates may outperform an athlete with a VO₂max of 78 ml/kg/min who can only sustain 70% of VO₂max. The threshold determines how much of the ceiling you can use, and for how long.

2. Running economy (RE)
Running economy is the oxygen cost of running at a given submaximal speed — how efficiently the aerobic engine converts fuel to forward motion. Two athletes with identical VO₂max values may differ substantially in economy: the more economical runner uses less oxygen per stride, meaning their same engine delivers more performance output.

Economy is influenced by biomechanics (stride length, contact time, limb stiffness), muscle fiber type distribution, and tendon elasticity. The Achilles tendon’s energy storage and return — which can recover 35–40% of the energy loaded during ground contact — is a key contributor. Elite Kenyan runners often display exceptional running economy even at VO₂max values not dramatically higher than European competitors.

3. Durability
A concept that has received increasing research attention is “durability” — how well an athlete maintains their lactate threshold and economy over time during a long race. Some athletes show significant deterioration of threshold and economy after 90–120 minutes of racing. Others maintain their physiological parameters much longer. This latter quality, which may relate to glycogen management, mitochondrial fat oxidation capacity, and neuromuscular fatigue resistance, is what separates ultramarathon performers from those who simply have high VO₂max.

How to Actually Improve VO₂max

Despite its ceiling being partly genetically determined, VO₂max is trainable. The research is clear on which approaches work best:

High-intensity interval training (HIIT): Intervals at 95–100% VO₂max (roughly 3–4 minutes hard, recovery, repeat 4–6 times) are the most direct stimulus for VO₂max improvement. This is sometimes called “VO₂max training” and represents the physiological stress closest to the maximal cardiac output that drives adaptation. Classic examples: 4×4 minute intervals (Helgerud et al., 2007), 8×3 minute intervals.

Large training volume: Elite VO₂max is not built solely through intensity. The cardiac remodeling that drives stroke volume adaptation responds to volume — hours of aerobic stimulus at all intensities. Elite Nordic skiers and cyclists training 900–1,000 hours per year have VO₂max values that reflect decades of cumulative cardiac stimulus. There is no shortcut that fully replaces volume.

The polarized model: Research by Stephen Seiler and colleagues suggests optimal VO₂max development comes from spending ~80% of training time below the first lactate threshold and ~20% at or above the second — with the “gray zone” between thresholds minimized. This counterintuitive model (more easy, more very hard, less moderate) appears to produce superior adaptations to purely moderate-intensity approaches.

Altitude training: Chronic altitude exposure (2,000–3,000 meters) stimulates erythropoietin production, increasing red blood cell mass and therefore oxygen-carrying capacity. This raises the blood oxygen delivery component of cardiac output — effectively pushing the VO₂max ceiling. The “live high, train low” (LHTL) model is the most researched approach, though access remains a limiting factor for most athletes.

The Threshold vs. Ceiling Framework

The most practically useful way to understand VO₂max is through the lens of the ceiling-and-floor framework:

VO₂max is your aerobic ceiling — the maximum power output your cardiovascular system can sustain. It determines the upper bound of your performance. Raising it matters, especially at lower training levels where it correlates strongly with performance.

Lactate threshold is the floor of elite performance — the fraction of that ceiling you can sustain in a race. An athlete with a modest ceiling but a very high threshold-to-ceiling ratio (95% of VO₂max at threshold) will outperform an athlete with a higher ceiling and a lower ratio (70% of VO₂max at threshold) in most real-world endurance contexts.

Running economy adds a third dimension: the conversion efficiency from oxygen consumed to speed produced.

Training that raises all three simultaneously — or strategically prioritizes whichever is the limiting factor for a given athlete — will produce the best race performances. For most athletes past their first year of training, improving lactate threshold and running economy will outperform focusing exclusively on raising VO₂max.

Svendsen’s Lesson

Oskar Svendsen had a ceiling higher than any measured human. But cycling performance also requires the ability to recover between training sessions, sustain motivation through years of structured training, manage the physical and psychological demands of professional life, and translate physiological capacity into race tactics and consistency. A 97.5 VO₂max is remarkable and irreplaceable. It is also not sufficient.

The exercise scientist’s temptation is to reduce performance to physiology. The reality is more complex — and more human. VO₂max is one chapter in a longer story.

Conclusion

VO₂max remains one of the most useful single metrics in exercise physiology. It establishes the aerobic ceiling, responds predictably to training, and is a reliable comparative benchmark across populations. But understanding its limits — genetic heritability, poor performance prediction within elite tiers, and the competing roles of lactate threshold and economy — is what separates a superficial grasp of exercise science from a practical one.

Your VO₂max is not your destiny. It is a starting point, a boundary, and one variable among several that determine endurance performance. The science of pushing that ceiling — and using more of it — is what separates exercise physiology from armchair analysis.

For a comprehensive exploration of VO₂max, lactate threshold, and the integrated science of endurance performance, see THRESHOLD: On Fatigue, Endurance and the Limits of the Human Body.