Estimate Your VO2 Max With The Bruce Protocol Treadmill Test

There are several useful metrics for assessing overall health and fitness, including resting heart rate, heart rate recovery, body fat percentage, one-rep max (1RM) for strength exercises, and anaerobic threshold.

For endurance athletes in particular, VO2 max is one of the most valuable indicators of aerobic capacity and cardiovascular performance.

Among the various ways to measure VO2 max, the Bruce protocol treadmill test remains a classic and widely used method.

In this guide, we’ll explain the background of the Bruce protocol stress test, how it’s performed, what insights it offers, and how it can help you determine your VO2 max and monitor aerobic fitness over time.

What Is the Bruce Protocol Treadmill Test?

The Bruce protocol treadmill test¹Sarma, S., & Levine, B. D. (2016). Beyond the Bruce Protocol. Cardiology Clinics, 34(4), 603–608. https://doi.org/10.1016/j.ccl.2016.06.009 is one of several tests that can be used to assess cardiovascular health and fitness by estimating VO2 max.

The name for the Bruce Protocol treadmill test comes from the last name of the cardiologist who created it, Robert A. Bruce.

Dr. Bruce designed the Bruce treadmill protocol in 1963 to serve as a non-invasive assessment of cardiovascular health and function for patients with suspected heart disease. 

Even though healthy athletes may use the Bruce treadmill protocol to estimate VO2 max and aerobic fitness level, the most common application of this test is to serve as an exercise tolerance test or stress test.

In either application, this test is an incremental treadmill test with different stages. 

The test’s results will be used to provide an estimated VO2 max, a measure of aerobic capacity, as well as an indication of cardiovascular risk based on how many stages the athlete or patient can complete before the test must be stopped due to failure to progress according to the protocol.

How To Preform The test

The Bruce protocol is an incremental treadmill test, which means that it involves walking on a treadmill and progressing through specific, established stages that become gradually more challenging.

Unlike incremental VO2 max tests on the treadmill, the Bruce protocol only estimates your VO2 max because, to assess VO2 max precisely, a metabolic cart must be used that can measure expired respiratory gases.

Instead, the Bruce treadmill test only requires participants to wear a heart rate monitor.

Because the percentage of max heart rate is strongly associated with the percentage of VO2 max, the heart rate data can then be used to estimate VO2 max.

The test is stopped as soon as the participant has reached 85% of their age-predicted maximum heart rate, if the heart rate exceeds 115 bpm for two stages of the cruise protocol, or if the patient or administrator decides that the test should be stopped due to discomfort or distress.

Generally, each stage of the Bruce treadmill protocol lasts three minutes.

The reason this time is used for each stage is that it should be long enough for the participant’s heart rate to reach a steady state, but not excessively long, so that it would not be exhausting for unconditioned individuals and prevent them from progressing to the next stage.

However, the caveat with three three-minute stages is that if the individual’s heart rate increases or changes by more than six beats per minute between minutes two and three of any given stage, that stage is extended another minute.

That means that the participant will continue walking at the same speed and incline for an additional minute (for four minutes total).

Note that there are a few additional important considerations or “rules“ when doing the Bruce treadmill test.

For example, do not hold onto the handrails on the treadmill during the test.

Additionally, it requires clearance from your physician and supervision by a trained professional administering the test. 

You should never attempt this test on your own if you have any underlying health conditions or suspected cardiac issues.

However, if you are a healthy, fit individual who exercises routinely, has recently had a thorough medical check-up with no detected issues, and is under the age of 40 for men and 50 for women, you can try the Bruce treadmill test to estimate your VO2 max.

Please ensure you understand that you are assuming the risks associated with near-maximal exercise and are comfortable with these risks.

The Bruce Protocol Test Stages

As mentioned, each stage of the Bruce protocol lasts three minutes, unless the test must be stopped or the participant does not reach a steady state (as evidenced by the average exercise heart rate changing by more than six beats per minute between minutes 2 and 3). 

In the case of the former, the test is stopped, while in the case of the latter, the stage is continued for an additional minute.

Each stage has a set incline and speed for the treadmill.

Here are the stages for the Bruce protocol stress test:

How to Calculate Your Results

Your VO2 max is used as a biomarker for your aerobic capacity, as it measures your ability to take in, circulate, extract, and utilize oxygen to generate ATP (energy) aerobically.

VO2 max is measured in milliliters of oxygen consumed and used in one minute per kilogram of your body weight (ml/kg/min).

Measuring VO2 max directly requires collecting and analyzing both inspired and exhaled air (gases) to determine the relative percentage of oxygen and carbon dioxide during incremental exercise. 

However, this method is somewhat invasive and cumbersome, requiring sophisticated laboratory equipment and specialized technicians. 

For these reasons, indirect VO2 max measurements can be more practical and accessible.

You can estimate VO2 max from the Bruce protocol 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 the 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 were able to last 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.

Once you have carried out the VO2 max calculations from the Bruce Protocol, you can use tables with established norms to compare your VO2 max to those in your age range, sex, and fitness level.

You can read more about what a good VO2 max is based on your age and sex in our article here.

If your doctor has ordered the Bruce Protocol stress test to evaluate your cardiovascular health, the provider will then make recommendations for further evaluation or treatment, if necessary.

Remember, if you experience any concerning symptoms or want to stop the test, please alert the technician right away.

You should discuss any concerns about taking the test with your healthcare provider. There may be alternatives if this test does not seem like a safe or good fit.

For more information about another assessment of your cardiovascular health and risk status, check out our article about heart rate recovery:

References

• 1
  Sarma, S., & Levine, B. D. (2016). Beyond the Bruce Protocol. Cardiology Clinics, 34(4), 603–608. https://doi.org/10.1016/j.ccl.2016.06.009