VO2: The number on your smartwatch you should pay most attention to

What number do you think is the best measure of your health? Your BMI is a fair suggestion, given that it categorises your weight and can hint whether you might fall victim to weight-related complications. A blood sugar reading can reveal whether you’re hurtling towards diabetes, while cholesterol levels can flag if you’re at risk of a heart attack or stroke, so can also be vital pieces of the jigsaw.

But VO2 max is another metric that could reveal whether you’re in good health. And if you’re one of the around 24 million people in the UK who own a Fitbit, Garmin or Apple watch, or other fitness band – a figure that’s nearly doubled over the last five years – you’re likely already logging it.

What is VO2 max?

VO2 max refers to the maximum volume of oxygen that the body can take up and use in a single minute of intense exercise.

Therefore, it reflects the limits of your cardiorespiratory system – how well the body inhales oxygen, transfers it to the bloodstream and delivers it to muscles.

“It is a good measure of the function of your heart, blood vessels, lungs and muscles,” says Stuart Gray, a professor of muscle and metabolic health at the University of Glasgow.

Generally, a higher VO2 max is better as it means the body is better at using oxygen and able to physically perform at a higher level. High scores have also been linked to longevity and a lower risk of disease.

It is measured in millilitres of oxygen consumed in a minute per kilogram of body weight (mL/kg/min). For a man in his 40s, a good score would be around 42, while below 38 would be poor and higher than 52 would be superior. For a woman of the same age, 36 would be good, lower than 33 would be poor and more than 45 would be excellent.

The Norwegian cyclist Oskar Svendsen is thought to have achieved the highest ever recorded VO2 max, when he measured 96.7mL/kg/min in 2012.

How can you find out your VO2 max?

Completing a VO2 max test in a lab is the gold-standard option.

Jonathan Robinson, an applied sport scientist at the University of Bath, conducts these tests on Olympic athletes and professional footballers, as well as the health-conscious who want to find out their reading.

It involves exercising, usually running or cycling, at increasing levels of intensity until a person can’t keep going – a point typically hit around 10 minutes in. While doing this, Mr Robinson and his team measure the concentrations of oxygen and carbon dioxide that participants breathe in and out to calculate their VO2 max.

Mr Robinson says members of the public are increasingly coming forward to get tested ahead as part of their training regime for marathons, triathlons and cycling events. For this group, the ideal is to get VO2 max checked at the start of their training and a follow-up a few months later to see how it has changed.

“Do the second test early enough that you’ve got enough time prior to your event to make any more changes that you need to make,” he recommends.

Others are interested in the links between VO2 max and longevity and just want to know what their score is and log it over time, he adds.

“If you’re just doing it to monitor your health and wellbeing, you could get tested at any point really,” Mr Robinson says. “Then obviously, the idea is that you come back and retest it – annually or up to twice a year. But obviously, it depends on people’s plans and budgets.”

At his Sport Science Lab the test costs £135, which he says is at the cheaper end of the scale. Some labs charge up to £250, according to Mr Robinson.

For those reluctant to fork out this sum, their smartwatch can provide a decent guide. Instead of measuring oxygen levels, the devices provide a VO2 max estimate based on pace and heart rate. Garmin users can find their VO2 max data under the “health and performance” tab on the app, or it flashes up on the watch after exercise. Those with an Apple watch can find their data on the “cardio fitness” section of the Health app.

“They’re quite accurate at the moment. If you asked me five years ago, I would have said that they’re okay as a guide, but they’re not really particularly close, whereas now they’re much closer,” Mr Robinson says. “If you’ve got a VO2 max of 55, people’s watches might say 50 to 57 – a little bit higher or lower. Very occasionally, I’ll get one which is off.”

However, Prof Gray is more sceptical. “The consensus is they are highly variable and not a good replacement for direct measurement in the lab,” he says. “They rely on several assumptions such as someone’s maximal heart rate, the HR-work rate and HR-VO2 relationship, in which there is a high level of variability that then comes into the calculations.

“For example in the lab my VO2 max is around 45 but my Garmin says 58 – I would love to believe my Garmin.”

The traditional beep test can also provide a guide to VO2 max levels. “Many years ago, hundreds of people were put through the VO2 max tests in the lab, then did the beep test – a fitness test that gets progressively faster – and the results were correlated into a table that people can read their results from as a bit of a guide,” Mr Robinson says.

There’s also the Cooper Test – you run as far as you can in 12 minutes and that can be equated to a VO2 max score – and the Rockport Walk Test, which matches up the time taken to walk one mile to a score, he adds.

How does VO2 max influence your fitness and health?

VO2 max acts as a proxy of our physical fitness. “Our ability to take up and use large volumes of oxygen means we have the capacity to perform exercise at a higher intensity,” Prof Gray explains.

“So it is very important for endurance exercise performance. It is not the only factor though and things like how efficiently we use that oxygen are also very important.”

The metric can also reflect the state of our health. Research from Prof Gray and his colleagues, published in the British Journal of Sports Medicine, revealed that those with better scores were more likely to live longer and faced a lower risk from cardiovascular disease, respiratory disease and colorectal cancer.

“It is also a good predictor of how well people will cope with major surgery, and their prognosis after. Often if VO2 max is too low people will not be given the surgery,” he adds.

How can you improve your VO2 max?

Any aerobic exercise – those that get the heart pumping – can improve VO2 max scores.

This can be anything from a low intensity longer duration workout, such as cycling or running at 70 per cent of your maximum effort at least four times a week, to higher intensity interval exercise, which typically involves four minutes of maximum effort followed by four minutes of low effort, completed four times in a row, Prof Gray suggests.

“Really whatever form of aerobic exercise you prefer – you might get a little bit of a gain from some strength training too,” he says.

“However, there are some things we can’t change that affect VO2 max, such as our sex and our genetics – we inherit about 50 per cent of our VO2 max ability,” he says.