VO2max or maximal oxygen uptake, is a key physiological measure of cardiovascular fitness.

Along with fractional utilisation and running economy or cycling efficiency, VO2max determines endurance performance.

A high VO2max indicates a high level of aerobic fitness and can help to explain differences in performance between individuals. A high VO2max is important for success in endurance sports like running, cycling, triathlon and duathlon.

What does VO2max mean?

V stands for volume; O2 for oxygen; max is for 'maximum'. Technically we should place a dot over the V, and the 2 in VO2 should be superscripted. However, this is not practical in non-science writing.

So VO2max is the maximum rate at which oxygen can be absorbed, transported, and used during exercise.

VO2max is normally expressed as the volume of oxygen that we can use per kilogram of body weight per minute (ml/kg/min), often abbreviated to ml/kg.

It can also be expressed in absolute terms, ie. Without a weight element, in litres per minute or millilitres per minute (l/min or ml/min). Knowing and using both is useful when comparing previous tests and planning training, particularly if your weight.

**How Does VO2max Influence Performance?**

An athlete with a higher VO2max has a greater capacity to absorb, transport and use oxygen during exercise. This is the ceiling to an athlete’s aerobic potential. You cannot perform at greater than VO2max work rates for more than a few minutes (4 - 8min typically depending upon training status).

All exercise intensities have an oxygen requirement. Let’s take a 10km runner as an example who wants to beat 40min.

Roughly speaking, a runner will require ~ 45ml/kg/min of oxygen to run a 40min 10km. Depending on their running economy, this could be a little higher or lower.

If the athlete’s VO2max is 45ml/kg/min, clearly running a 40min 10km is not going to be possible. So this athlete has to improve VO2max in order to be able to meet their goal. On the flip side of this, if the athlete has a VO2max of 60ml/kg this is more than sufficient to beat 40min if economy and fractional utilisation are ‘normal’. Therefore, if the runner cannot beat that time, then the limitation for the athlete is either in their ability to sustain a high enough percentage of VO2max or their economy is poor.

This enables the athlete or coach to begin developing a plan to improve performance.

VO2max is influenced by a number of factors, including:

The capacity of the lungs to oxygenate your blood. Structures called alveoli in the lungs transport oxygen into the bloodstream.

Athletes with higher VO2max values usually have greater quantities of alveoli, therefore enabling more oxygen to be extracted in the lungs.

The capacity of the blood to transport oxygen

Athletes with higher VO2max values usually have a greater volume of red blood cells and haemoglobin mass. These are what the oxygen binds to, allowing more O2 to be transported.

The capacity of the cardiovascular system (heart, arteries, capillaries etc) to transport the oxygenated blood to the muscle.

Athletes with a higher VO2max usually have larger heart chambers and thicker arteries to pump a greater volume of blood per beat, thus carrying more blood to the working muscles.

The capacity of the working muscles to accept the delivered oxygen

This is dependent on factors such as:

the proportion of slow-twitch muscle fibres,
the number of mitochondria,
aerobic enzymes and capillaries.

Well-trained endurance athletes tend to have a greater quantity of type 1 and type 2a muscle fibres, increased density and quantity of mitochondria and enhanced capitalisation of the muscle.

Some of these are trainable, but most have a genetic starting point and limit. So, as the saying goes, you can’t turn a cart horse into a racehorse, but you can make the cart horse go faster or limit the racehorse's potential.

Velocity or Power at VO2max (pVO2max/vVO2max)

This is the power or speed at which VO2max occurs. There are several protocols for establishing this, and the scope of this article is not to discuss the merits of each, just the concept.

This is arguably a more valuable metric, as it can be directly measured or used in training planning, prescription, and analysis.

Using lab data, it is calculated using economy/efficiency data and VO2max, therefore only leaving fractional utilisation out of the equation and making it a stronger predictor of performance than VO2max or economy individually.

It's Not Just About VO2max

In some arenas, VO2max is considered to be a poor predictor of performance, and it is, when looked at in isolation. VO2max is one of the three components influencing endurance performance, so if you only use one to predict performance, the likelihood of an accurate prediction is reduced.

For example, three runners all with a VO2max of 60ml/kg/min

1. Achieves a 40min 10km – sustains 92% of VO2max, with a poor running economy.

2. Achieves a 37min 10km – also sustains 92% but has a ‘normal’ running economy

3. Achieves a 35min 10km – also sustaining 92% but with an exceptionally low (good) running economy.

VO2max cannot predict this result, but knowledge of all three physiological variables can. In this example, running economy is the defining characteristic.

There is an example of a runner called Derek Clayton, who set a world record marathon time of 2:09:36 in 1967. He was tested in a lab and found to ‘only’ have a VO2max of 68ml/kg/min. With a ‘normal’ running economy, he would have needed to sustain ~95% VO2max for 2hrs, which is not possible. Some authors attribute an unrealistic fractional utilisation capacity to his performance. However, they are missing out on the crucial running economy stats.

This is one of the earliest examples of the interaction of VO2max, economy and fractional utilisation, and is often misrepresented to show that VO2max is not important. Imagine what he might have been able to achieve with a VO2max of 80ml/kg/min.

I had the pleasure of coaching and testing an athlete with one of the highest-ever recorded VO2max figures in the BASES-accredited Performance Lab at Loughborough University. This experience provided further insight into the interaction of these variables.

On several occasions, the athlete achieved a VO2max of ~91-ml/kg/km. However, his running economy was extremely poor, at 250ml/kg/km. At the time, he was an elite triathlete, but after this career, he went on to run marathons seriously, with a best of 2:17:45. Assuming he was holding ~83% VO2max, this would mean he would have had to sustain 62ml/kg/min for the duration. Not far off DC’s VO2max!

The Importance of Interpreting Research Appropriately

You will find research that concludes that an increase in VO2max doesn’t necessarily improve performance in a particular event. However, it is all in the interpretation and application of the research. As a coach, I know that changing one variable in a short space of time won't necessarily improve performance. However, what it can do, is provide the platform upon which to build training to influence other aspects of physiology that will in the end result in improved performance. In many cases, research studies have provided a higher ceiling but not trained the athlete to be able to use that new capacity, and therefore, the performance doesn’t change.

Other studies and anecdotal evidence show that elite athletes’ VO2max doesn’t change much during the course of a season or over their career. So how can VO2max be relevant?

Again, this is a valid point. If you are truly an elite athlete and have spent many years training, including VO2max specific work, then it is possible you have ‘maxed out’ your capacity in training to improve VO2max. However, you will know that doesn’t mean it is not relevant. It just means you might not be actively trying to increase it. However, the power or speed at VO2max does change during a season. Why? Changes in efficiency or energy availability.

If you are not an elite athlete, and you have not been training correctly to improve VO2max then there are many ways in which training can facilitate a greater capacity and therefore potential to improve.

What is a Good VO2max Value?

VO2max values can vary greatly between individuals, with untrained individuals typically having a VO2max in the range of 25-45ml/kg/min and elite endurance athletes having values in the 80s or even 90s. Males tend to have higher values than females, and VO2max will decrease with age, although appropriate training can slow this decrement.

Factors affecting VO2max

Several factors affect an individual's VO2max including:-

Age
Gender
Genetics/physiology
Altitude
Body type/body composition
Training status
Exercise type

Age

VO2max is usually highest at age 20-30. It decreases by ~0.5ml/kg/min per year (due in part to the age-related decline in max HR and stroke volume.

Training, particularly high-intensity training, can help to delay decrement.

Gender

Male athletes are higher than the equivalent level female athlete – due to %body fat, muscle mass, blood volume, and haemoglobin levels.

Genetics/physiology

10-30% of variability due to genetics influencing cardiac output, muscle fibre composition, body size, muscle mass, body fat %, mitochondrial density, aerobic enzyme levels, capillary density, lung capacity, the viscosity of the blood and the concentration of red blood cells. Genetics also influences how well we adapt to training.

Altitude

Decreased air pressure at altitude reduces the availability of oxygen = lower VO2max. As altitude increases, VO2max decreases. Wide individual variation in the effect of altitude - larger decreases typically being observed in athletes with a higher sea level VO2max.

HOWEVER, training at altitude can cause adaptations that lead to increased VO2max at sea level.

Body type/body composition

VO2max is normally expressed relative to body weight. So any variation in body weight affects VO2max. Large body mass (even if it is lean body mass) = lower relative VO2max compared to smaller athletes.

Higher % body fat = lower VO2max than a similarly sized athlete with a lower % body fat.

Training status

The extent of any increase varies greatly between individuals and depends on current fitness, previous training history and existing training regime.

Highly trained elite athletes are unlikely to see further significant improvements in VO2max.

Exercise Type

Type of exercise is known to affect VO2max, with greater values generally recorded in weight-bearing exercises (e.g. running) than in non-weight-bearing exercises (e.g. swimming). Another factor here is that athletes tend to record higher VO2max values in the mode of exercise they use in training. As an example, you would expect to see a runner score higher during a running test compared with if they underwent a cycling VO2max test.

Is VO2max Trainable?

The good news is that VO2max is trainable in most athletes, for more on that see our article on how to train to improve VO2max.

Is Your VO2max Limiting Your Triathlon Performance