There are various metrics that can be useful for providing information about your health and fitness. Examples include your resting heart rate, heart rate recovery, body fat percentage, one-rep max (1RM) for different weightlifting exercises, and your anaerobic threshold.
For endurance athletes, particularly, your VO2 max is a helpful indicator of your aerobic fitness.
While there are different ways to measure your VO2 max or estimate your VO2 max, the Bruce protocol treadmill test is one of the classic assessments for cardiovascular health and VO2 max.
So, what does the Bruce Protocol stress test entail? What specific data can you get from the Bruce Protocol treadmill test, and who should consider doing it?
In this article, we will discuss the background of the Bruce protocol stress test, how the Bruce treadmill protocol is performed, the benefits and information you can get from it, and how to use this test to determine VO2 max.
We will cover the following:
- What Is the Bruce Protocol Treadmill Test?
- How Is the Bruce Protocol Performed?
- Bruce Protocol Stages
- How to Calculate VO2 Max With the Bruce Protocol
Let’s jump in!
What Is the Bruce Protocol Treadmill Test?
Note that VO2 max is a measure of your aerobic capacity.
The Bruce protocol treadmill test is often referred to as the Bruce Protocol treadmill stress test or Bruce treadmill protocol stress test.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.1
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 (thus the name Bruce protocol stress test).
In either application, the Bruce Protocol treadmill test is an incremental treadmill test with different stages.
The test’s results be used to provide an estimated VO2 max, which is a measure of aerobic capacity, as well as an indication of cardiovascular risk based on how many stages the athlete or patient can get through before the test must be stopped due to failure to progress according to the protocol.
How Is the Bruce Protocol Performed?
The Bruce protocol is an incremental treadmill test.
This means that the protocol involves walking on a treadmill and progressing through specific established stages that get gradually harder.
Unlike incremental VO2 max tests on the treadmill, the Bruce protocol treadmill test only estimates your VO2 max because in order to assess V02 max precisely, a metabolic cart must be used that can assess expired respiratory gases.
Instead, the Bruce treadmill test only requires that the participant 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 Bruce protocol stress 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.
In general, each Bruce treadmill protocol stage lasts three minutes.
The reason this time is used for each Bruce protocol stress test stage is that it should be long enough for the participant’s heart rate to reach a steady state but not excessively long such that it would be exhausting for unconditioned individuals such that it would prevent progressing to another 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, you should not hold onto the handrails on the treadmill when performing 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.
Just ensure you understand that you are assuming the risks of doing near-maximal exercise and are comfortable with said risks.
Bruce Protocol 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 (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:
|Bruce Protocol Stage||Treadmill Speed||Treadmill Incline|
|1||1.7 mph||10% grade|
|2||2.5 mph||12% grade|
|3||3.4 mph||14% grade|
|4||4.2 mph||16% grade|
|5||5.0 mph||18% grade|
|6||5.5 mph||20% grade|
|7||6.0 mph||22% grade|
How to Calculate VO2 Max With the Bruce Protocol
The Bruce treadmill protocol can be used as an indirect measure of VO2 max, which is a measure of maximal oxygen uptake and utilization during high-intensity or maximal-effort exercise.
Your VO2 max is used as a biomarker for your aerobic capacity since it measures your ability to take in, circulate, extract, and use 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 inspired and exhaled air (gasses) and analyzing the relative percentage of oxygen and carbon dioxide while performing incremental exercise.
However, this method is somewhat invasive and cumbersome, and it requires sophisticated laboratory equipment and 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 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 was 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 the VO2 max for 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 are feeling any concerning symptoms or want to stop the Bruce stress test, alert the technician right away.
You should discuss any concerns about taking on the Bruce Protocol treadmill 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 here.