VO2 max is considered to be the gold standard measurement of cardiorespiratory fitness or aerobic fitness. While many people know the concept of V02 max, how to measure VO2 max in a practical way is generally not well understood by recreational athletes.
However, if you find a VO2 max measurement you can do on your own, you can use V02 max to help inform your training.
So, how is VO2 max measured? How does the Apple Watch measure V02 max? What is the best way to measure V02 max outside an exercise physiology lab?
In this guide, we will discuss some of the methods for how to measure VO2 max both in terms of a lab setting as well as field tests and Apple Watch VO2 max estimations.
We will look at:
- How Do You Measure VO2 Max?
- How to Measure VO2 Max Outside of a Lab
- How Does The Apple Watch Measure VO2 Max?
Let’s get started!
How Do You Measure VO2 Max?
So, how is VO2 max measured?
The only real way to measure VO2 max is in a laboratory setting using a metabolic cart and specific VO2 max protocols that have been developed; otherwise, you can calculate VO2 max based on various VO2 max protocols that estimate VO2 max using heart rate.
Graded Exercise Test
The gold standard for measuring VO2 max is performing a VO2 max test in an exercise physiology laboratory or some clinical setting.
There are different VO2 max protocols, but generally, you will be walking or running on a treadmill or using a cycle ergometer.
Each of the VO2 max protocols has various stages that get increasingly more difficult as time goes on.
While you perform the VO2 max test, you wear a specialized face mask that is hooked up to a metabolic cart.
This metabolic cart analyzes the composition of your expired respiratory gasses and compares the exhaled air to the percentage of gasses in the inhaled atmospheric air.
This allows for a detailed evaluation of how much oxygen you are consuming versus how much carbon dioxide you are exhaling.
The relative proportion of these gasses is called the respiratory exchange ratio, or RER.
Based on your RER, exercise physiologists can determine the relative percentage of each fuel source you burn: carbohydrates vs fats.
The closer the RER gets to 1.0, the higher the relative percentage of carbs you are burning, which means that you are hitting your max effort, whereas an RER closer to 0.7 indicates that you are burning primarily fat for fuel and have not reached your VO2 max.
Note that at maximum-intensity exercise, your body relies almost solely on blood sugar and stored glycogen to fuel ATP production rather than body fat or circulating triglycerides.
The metabolic cart can also calculate the volume of oxygen you are consuming by how much air you are inhaling.
Because VO2 max is a measure of how much oxygen you can consume and use per minute per kilogram of body weight, this is a key factor in the VO2 max measurement protocol.
Simultaneously, your heart rate is recorded and also used as an indicator of when you are likely reaching your maximum aerobic capacity.
Various VO2 max test termination criteria indicate if you’ve reached your true VO2 max.
How to Measure VO2 Max Outside of a Lab
There are various field tests to estimate VO2 max outside of a lab.
Examples of VO2 max estimation protocols include the Rockport Walk Test, the 1.5-Mile Test, the Cooper VO2 Max Test, the Bruce Treadmill Test, and the YMCA Cycle Ergometer Test, step tests, among others.
Let’s look at a few of these:
#1: VO2 Max Running Test (Field Test)
There are field tests to measure VO2 max, such as the 1.5 Mile Run.
This specific way to measure VO2 max is a true max effort test and has only been validated for college-aged populations.
After running 1.5 miles on level ground as fast as possible, the time is converted into a decimal and then inserted into a VO2 max equation for this VO2 max measurement test as follows:
- Males: VO2max (ml/kg/min) = 88.02 + 3.716 – (0.0753 x body weight in pounds) – (2.767 x time for 1.5 miles in minutes and fractions of minutes)
- Females: VO2max (ml/kg/min) = 88.02 + – (0.0753 x body weight in pounds) – (2.767 x time for 1.5 miles in minutes and fractions of minutes)
Accuracy of Prediction. This test has a R = 0.90 and an SEE = 2.8 ml/kg/min
#2: Bruce Treadmill Test
This is a submaximal VO2 max test, which means that your VO2 max will be predicted based on the trend in your heart rate at various workloads at a lower exercise intensity.
An equation and specific protocol have been created and validated that then use that data to extrapolate your estimated maximum aerobic capacity if you were exercising at max intensity for a true VO2 max test.
This is essentially how any VO2 max measurement that doesn’t require maximal effort exercise works:
A protocol and algorithm/equation have been designed with decent accuracy and reliability for predicting V02 max based on the linear increase in heart rate at different stages of aerobic workload.
Because the percentage of max heart rate is strongly associated with the percentage of VO2 max, your heart rate data can, in an incremental exercise test, be used to estimate your VO2 max.
The Bruce protocol is a progressive treadmill test, which involves walking on a treadmill for three minutes per stage and progressing through specific established stages that get progressively harder.
This VO2 max test protocol is stopped when the individual has reached 85% of their age-predicted maximum heart rate or if the heart rate exceeds 115 bpm for two stages.
After completing the test, VO2 max calculations are performed using a formula that takes into consideration your sex and the total time that you lasted while performing the Bruce treadmill test.
Here are the formulas for Bruce Protocol VO2 max prediction:
- Men: VO2 max = 14.8 – (1.379 x T) + (0.451 x T²) – (0.012 x T³)
- Women: VO2 max = 4.38 x T – 3.9
T represents the total time on the treadmill and is written as a fraction of minutes and seconds. For example, a total time of 8 minutes and 45 seconds would be written as T = 8.75.
For example, if a woman did the Bruce Protocol stress test and lasted 8 minutes and 45 seconds, this would result in the following VO2 max:
VO2 max = 4.38 x 8.75 – 3.9 = 34.425 ml/kg/min.
#3: The Rockport Walking Test
The Rockport Walking Test is one of the most popular submaximal VO2 max tests that predicts your maximum aerobic capacity based on walking 1 mile at an even pace; jogging is not allowed. The test has been validated on subjects between the ages of 30 and 69.
The key to improving accuracy with this VO2 max estimation protocol is taking the heart rate immediately after finishing the mile without waiting more than a couple of seconds at most.
Then, count the pulse for 15 seconds and multiply by four to get your heart rate in beats per minute.
Convert your fastest mile walking time into a decimal, so 14:30 would be 14.5.
VO2max calculations are then done by using the formula:
- Males: VO2max (ml/kg/min) = 132.853 – (0.0769 x weight in pounds) – (0.3877 x age) + 6.315 – (3.2649 x mile walk time) – (0.1565 x ending heart rate)
- Females: VO2max (ml/kg/min) = 132.853 – (0.0769 x weight in pounds) – (0.3877 x age) – (3.2649 x mile walk time) – (0.1565 x ending heart rate)
Based on research, there is a correction factor for individuals between 18-24 years old: You subtract 6 ml/kg/min from the value obtained from the regular VO2 max equation above.
Accuracy of Prediction. This equation has an R= 0.88.
#4: The YMCA Submaximal Bicycle Test
The YMCA Submaximal Bicycle Test is a popular submaximal test for VO2 max. You ride a bicycle ergometer following a specific protocol regarding resistance and a cadence of 50 rpm.
You perform a couple of stages of exercise (3 minutes per stage), to obtain two heart rates between 110 bpm and 150 bpm to estimate VO2 max. A graph is made plotting the heart rate at the different workloads with a line of best fit inserted.
Then, this line is extrapolated up to your age-predicted maximum heart rate to estimate V02 max.
There are even non-exercise assessments that can predict V02 max based on your answers to questions regarding your physical activity along with other demographics better than inserted into a VO2 max equation.
An example is the Jackson Non-Exercise VO2 max test.
As can be surmised, any submaximal or predictive way to measure VO2 max is not a true VO2 max measurement and will have a margin of error.
Accuracy of Prediction. This test has R= 0.86, SEE= 10% of the predicted VO2 max.
How Does The Apple Watch Measure VO2 Max?
As the utility of and interest in measuring VO2 max for competitive and recreational runners, cyclists, triathletes, and everyday athletes has increased, some of the best fitness watches and GPS running watches have started implementing a VO2 max feature so that you can estimate VO2 max on your watch.
For example, the VO2 max Apple Watch feature allows you to see an estimate of your VO2 max based on your workout history.
But how does the Apple Watch measure VO2 max, and how does Garmin measure VO2 max?
Your VO2 max on Apple Watch is calculated by evaluating the relationship between your pace and heart rate.
An algorithm is used that looks at how fast you can run at various percentages of your age-predicted max heart rate.
The faster you can run at a relatively lower percentage of your heart rate, the higher your Apple Watch VO2 max score will be.
However, the Apple Watch VO2 max is determined based on submaximal exercise intensities, so it is a prediction of your VO2 max rather than a true measurement.
In addition to the Apple Watch VO2 max capabilities, some of the premium GPS running watches also offer V02 max estimations, including:
- Garmin watches such as the Garmin Forerunner 45, 55, 245, 745, 945, all Garmin Fenix watches, Garmin Vivoactive 4/Venu watches
- Polar Pacer GPS running watch
For more information about another assessment of your cardiovascular fitness, check out our article about heart rate recovery here.
To learn more about how to improve your VO2 max, check out our article here.