VO2 max is widely regarded as a gold standard of aerobic fitness. It shows up on watches, in training apps and across social media as a benchmark for comparison. But the number that you’re seeing might not present your fitness level as accurately as assumed.
Research questions whether the most common way that we measure VO2 max – that is, based on bodyweight – actually provides the best way to compare aerobic efficiency across different body types. For runners, this raises an interesting follow-up: is VO2 max skewed by your weight and if so, what should you do about it? Let’s dig into things.
How do you measure VO2 max?
First, it helps to understand the difference between the two common ways that physiologists report VO2 max.
Absolute VO2 max measures your maximal oxygen uptake per minute, usually displayed in litres per minute.Relative VO2 max takes that number and divides it by your total bodyweight, commonly expressed in millilitres per kilogram per minute.
Relative VO2 max is the measure that you see most often. Its purpose is to level the playing field and provide a comparative measurement, because heavier people generally consume more oxygen than smaller people and will have higher absolute VO2 max readings, says Kate Baird, CSCS, running and metabolic testing coordinator and exercise physiologist at the Hospital for Special Surgery in New York City.
The problem with accounting for weight
The traditional relative VO2 max score treats all bodyweight the same, whether it’s lean muscle or fat. Why might that be an issue? Muscle dominates your body’s oxygen consumption during exercise, explains Baird, while fat – also known as adipose tissue – does not contribute to oxygen utilisation at all.
Way back in 2015, researchers examined the relationship between VO2 max and body composition and size. After a series of exercise tests on young subjects, researchers did not see a linear relationship between total bodyweight and VO2 max, but did see one between lean body mass (muscles) and VO2 max. They concluded that it makes more sense to factor in lean body mass, rather than total bodyweight.
A review from 2021 argues in favour of these findings, saying that the common relative VO2 max formula (milligrams per kilogram bodyweight per minute) assumes that VO2 max scales directly with total bodyweight, when evidence suggests that the relationship is not linear. (It’s also worth noting that more recent research shows a link between lean muscle mass and higher VO2 max, which may be particularly important for older adults to keep in mind.)
Basically, research agrees that the current formula for relative VO2 max (dividing absolute VO2 max by total bodyweight) isn’t as accurate a measure of fitness as it may seem.
What does this mean for runners?
Although these findings originally surfaced over a decade ago, the conversation around this metric is more relevant now than ever. As Baird points out, with wearable technology putting VO2 max estimates directly on our wrists and alerting us to apparent changes, it’s easy for runners to treat the number as a definitive measure of overall fitness.
That’s why it’s important to know the nuances involved in this metric.
For one, your bodyweight can influence how your VO2 max appears on your watch, says Baird. ‘If you gain weight of any kind and nothing changes with your fitness, your relative VO2 max is going to go down,’ she explains. ‘If you lose weight and nothing changes with your fitness, it’s going to go up. That’s just how the maths works.’
However, this doesn’t mean that your aerobic capacity has necessarily worsened or improved. It just means that the calculations shift based on your weight.
This helps to explain why athletes in different sports can look very different in terms of relative VO2 max, continues Baird. Elite marathoners tend to have high relative VO2 max values, partly because of their smaller, lighter frames. Meanwhile, athletes like rowers, who typically carry more muscle mass, often post lower relative VO2 max numbers than marathoners, even though their absolute readings may be larger.
This limitation is exactly why the researchers above suggested using lean mass – or a more complicated scaling model – instead of total bodyweight in relative VO2 max calculations.
‘If the question is how much oxygen you’re able to consume per kilogram of muscle mass, or lean mass, I think that’s a good way to compare athletes,’ says Baird. ‘I just don’t know if it’s that personally discerning on a day-to-day level.’ On paper, these approaches do offer more physiologically accurate relative readings. In practice, they don’t change how runners should think about their fitness, weight or training strategy, she explains.
No matter if your relative reading is calculated using total bodyweight or muscle mass, VO2 max is only one piece of the performance puzzle. Distance runners also need to zero in on lactate threshold, running economy and durability in order to achieve their best times.
When it comes to overall health and ageing, VO2 max is strongly associated with long-term health outcomes, such as decreased risk of cardiovascular disease and improved longevity.
But Baird still cautions against obsessing over the number. ‘Your aerobic engine is not the only consideration,’ she says. ‘Sleep, mental health, musculoskeletal health – there’s more to [a healthy lifestyle] than VO2 max.’
In other words, chasing a higher relative VO2 max score – whether by dropping weight or changing the calculation entirely – doesn’t automatically lead to improved health.
The takeaway
Yes, evidence suggests that the traditional way that we calculate relative VO2 max has its limitations, as it may underestimate cardiovascular fitness in heavier or more muscular individuals. However, switching to a more precise formula isn’t going to change the way that you train, says Baird. The VO2 max workouts that you know and love still help to raise your aerobic ceiling, regardless of how the number is calculated.
If your goal is to improve aerobic fitness, the same fundamentals always apply:
Prioritise consistent, easy running that builds a strong foundation.Work in structured interval workouts that challenge your cardiovascular system.Progress gradually over time.
As an exercise physiologist herself, Baird stresses that for most people, runners included, simply being active and maintaining a well-rounded routine is far more important to both your aerobic fitness and your overall health than trying to optimise this metric – or trying to manipulate your way to a better score.
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