Sports watches used to tell us how far we’d run. These days, however, fitness trackers can do everything from alerting our nearest and dearest when we trip over a pothole to measuring our stress levels and the quality of our sleep.

But if you really are using your tracker for fitness, there’s one number that always pops up after a run: your VO2 max measurement. Even after years of running, I’ve never really understood what this is or why it’s significant. Some watches rate your VO2 max on a traffic-light system, so while you might ascertain that your number is healthy (or not), what are you supposed to do if you want to improve it? 

Personal trainer Aimee Pearce explains: “At a very basic level, VO2 max is an indicator of fitness level. The definition of VO2 max is the maximum or optimum rate at which the heart, lungs and muscles can effectively use oxygen during exercise.” V = volume, o2 = oxygen.

Put simply, VO2 max is a scientific way of measuring aerobic fitness. According to BUPA, aerobic fitness is “your body’s ability to deliver oxygen to your muscles for movement […] the more efficient this process is, the fitter you’re thought to be, as you’re likely to be able to continue working for longer”.

Dr Jim Pate, senior physiologist at Marylebone Health, explains that VO2 max is a measure of aerobic capacity within exercise. “A person’s aerobic fitness score can be compared to their peer group based on measures of age, sex and body mass, and VO2 max is another of these predictors,” he tells Stylist. “Changes in the score over time represent an increase or decrease in aerobic capacity and therefore similar changes in exercise performance.”

Unless you’re an elite athlete, Pearce says that VO2 max is “more of a nice-to-know rather than a need-to-know” for the average person who is regularly exercising.

That said, it is important for athletes as an indicator of where marginal gains can be made. “An awareness of VO2 can be used to compare fitness during competition seasons and see where improvements can be made,” says Pearce.

So, if you’re determined to improve that Parkrun PB, you might want to start analysing the VO2 readings. But whatever your fitness goal or ability, understanding VO2 max will always benefit your training. 

The higher your VO2 max reading, the more efficiently you’re converting oxygen into aerobic energy, so the faster, further and harder you will be able to train, whether this is walking up a hill comfortably, or competing in an ultra-marathon. 

Gender

According to Pearce, several factors can affect a person’s VO2 max score. “Women tend to have lower VO2 maxes than men because of the differences in physiology between the genders. Men tend to be larger and have a higher percentage of muscle mass.”

Age

“Age has a part to play, so the younger we are the better our scores tend to be,” says Pearce. “Our peak VO2 max scores tend to be around age 18-25 (in men and women) and after that there is a gradual decline as we age.”

Location

“The altitude of where your test takes place will have an impact on your score because there is less oxygen available at higher altitudes,” says Pearce. Probably one for those elite athletes!

The good news is that those VO2 max readings can be improved. Pearce explains that it’s possible to increase VO2 max simply by regularly working out at a level close to your own personal maximum heart rate. She recommends working out your maximum heart rate by using use the sum 220 minus your age.

That means for someone who’s 32, 188 should be the maximum heart rate they aim to work out at. But, as with everything, it’s a measurement worth taking with a pinch of salt. You might have a naturally high heart rate, for example, or be recovering from a bad cold – meaning you’ll exceed your max heart rate easily. In those cases, it’s better to go by feeling; a few times a week, try to push for 80-90% of your maximum effort for a few minutes. That might mean sprinting at your top speed on a treadmill for 400m, or doing a minute on an assault bike, rower or doing as many burpees as you can in one minute.

“Fundamentally, the most direct route to improving VO2 is to increase aerobic muscle tissue mass,” says Dr Pate. “This requires training at or above your VO2 max intensity, best achieved through high-intensity interval training to fatigue.”

Studies show that interval training in particular can improve a VO2 max reading, as opposed to endurance training alone.

While your fitness tracker may well have a VO2 max function, Pearce stresses that “the most accurate way to find your VO2 max is in a laboratory with specially trained sports and exercise scientists”, but as a general rule, the higher the number, the better.

“The higher the score, the more oxygen uptake/used per minute there is, leading to more energy production which ultimately means a better performance in endurance activities,” she explains.

So, while you shouldn’t lose any sleep over it, knowing your VO2 max might just pique the interest of any exercise-mad scientists out there. 

Images: Getty