When you think about how fit you are, you might think about how far you can run or how many push-ups you can do. Or maybe you think about health metrics like your resting heart rate or heart rate variability, or the time gaps in between each heartbeat.
With a fitness tracker, you’ll have access to a variety of these health metrics—but there’s one that is key to determining your cardiovascular fitness that you may be ignoring: your VO2 max.
What is VO2 max?
VO2 max is a score that quantifies how much oxygen your body absorbs and uses while working out, says sports medicine doctor and professor of orthopaedic surgery Dr. Alexis Chiang Colvin. V stands for volume, O2 for oxygen, and max indicates the amount of oxygen used at maximum effort, measured in milliliters of oxygen consumed per kilogram of body weight per minute (mL/kg/min).
“It’s pretty important,” Colvin tells Fortune. “It is giving a good measurement of your aerobic capacity,” or how efficiently your body can use oxygen during exercise.
How do you measure VO2 max?
Colvin says to measure VO2 max you’ll need to be in an exercise medicine lab or a doctor’s office that offers the test. The test requires wearing a face mask over your mouth to measure your oxygen consumption and carbon dioxide production during cardiovascular exercise, like running on a treadmill.
The test isn’t very comfortable—you’ll be working at maximum effort for 10 to 20 minutes, Colvin says.
When it’s over, you’ll get a score: The higher your score, the higher your level of fitness, Colvin says.
According to the Cleveland Clinic, these are the average VO2 max scores for men ages 18 to 45 based on activity level:
- Sedentary: 35 to 40 mL/kg/min
- Active: 42.5 to 46.4 mL/kg/min
- Very Active: less than or equal to 85 mL/kg/min
And for women ages 18 to 45:
- Sedentary: 27 to 30 mL/kg/min
- Active: 33 to 36.9 mL/kg/min
- Very Active: less than or equal to 77 mL/kg/min
Colvin says the number isn’t as important as what you do with it. She emphasizes that it should be used in tandem with other metrics, to give you information about your fitness and overall health trends over time.
“It has different value for different groups,” Colvin says. For people invested in their fitness, it can be used for measuring progress and setting performance goals. Others may use it to better understand their overall well-being. Colvin says a score under 20 could be an indication that you need to focus on your cardiovascular health.
Is your fitness tracker’s VO2 max accurate?
Many fitness trackers like Apple Watch, Garmin, Fitbit, and Coros will provide you a VO2 max score based on the exercise data you’ve logged—but Colvin says that the most accurate way to get your VO2 max is in a lab setting. A 2024 study found that the Apple Watch underestimated VO2 max of those with excellent fitness levels, while it overestimated VO2 max for people with poor fitness levels.
While your tracker’s number should be taken with a grain of salt, Colvin says it could be helpful to determine overall trends in health and fitness over time—especially alongside other metrics.
How to improve your VO2 max
Aerobic exercise is key to improving your VO2 max, Colvin says. “Anything pretty vigorous,” she says. Running, cycling, swimming, cross-country skiing, and the elliptical are all forms of aerobic exercise, but how you exercise is also important.
“It depends on your baseline,” Colvin adds. For someone who doesn’t exercise at all, walking could be enough to increase their VO2 max, she says. But for someone who exercises more regularly, variation in your workouts is important, Colvin says.
If you’re doing most of your cardio at a steady, easy effort, you should think about incorporating interval sessions—short bursts of hard effort with rest or low-intensity periods in between intervals, Colvin says, like high-intensity interval training (HIIT).
Switching up your routine is particularly important once your body has adapted to the exercise you’ve already been doing, she says.
“Your body adapts to whatever you give it, so if you can change around what you’re doing more that helps to challenge it,” Colvin says.
Colvin says that even if you can’t control your VO2 max decreasing as you age—just as it’s hard to control losing lean muscle mass and cardiovascular fitness with age—you should try to see if you can keep it steady by keeping up with an exercise routine that progressively challenges you.
Regardless of fitness level, consistency is crucial, she adds. The American Heart Association (AHA) recommends at least 150 minutes of moderate-intensity aerobic activity 75 minutes of vigorous aerobic activity, or a combination of both, each week—preferably spread throughout the week. That should be the bare minimum to shoot for, especially if you’re looking to improve your VO2 max, Colvin says.
In addition, the AHA recommends adding two days of muscle-strengthening workouts to your routine—which Colvin says can also help boost your VO2 max by creating more efficient oxygen respiration and improving your overall fitness. Strength training may also help you maintain lean muscle mass and lose fat, something the Cleveland Clinic says can help improve your VO2 max as well.
For more on fitness:
- 4 ways to make sure your workout habits last all year long
- The workout routine that leaves this 82-year-old fitness instructor feeling like he’s 50
- Pilates dominated fitness trends this year. 4 health benefits of the workout that will make you a convert
- Here’s the right way to start running
