With our Bruce protocol METs calculator, you'll learn everything you need to know about the Bruce protocol stress test. It is a non-invasive stress test to assess cardiovascular fitness and aerobic endurance or detect weak heart conditions. This article also explains the concepts of the metabolic equivalent of task, and how to interpret your treadmill test results.
What is a metabolic equivalent of task (MET)?
Before we dive deeper into the Bruce protocol METs calculator, we first have to understand what a metabolic equivalent of task is. METs is a unit that estimates the energy used by our body during physical activity. To learn more about the energy our body consumes, see the calorie calculator. One MET is defined as:
- 1 kilocalorie per kilogram of body weight per minute of activity (kcal/kg/min); or
- 3.5 milliliters of oxygen per kilogram of body weight per minute of activity (ml/kg/min).
Due to its standardized nature, METs can be used to compare activities over a range of body weights and intensities. As we see in the definition, METs is directly related to the amount of oxygen our body needs, and therefore the often used metabolic measure VO2. This calculator helps you find your VO2 max for various physical activities.
One MET equals the energy cost of sitting quietly. The more demanding the physical task is, the more oxygen your body consumes, and the higher the METs:
- Under 3 METs: Light-intensity activity
- 3-6 METs: Moderate-intensity activity
- Over 6 METs: Vigorous-intensity activity
What is the Bruce protocol stress test?
The Bruce protocol METs calculator allows you to interpret the results of the Bruce protocol stress test. Also known as the exercise tolerance test, it is used to estimate endurance athletes' overall fitness or to detect weak heart conditions. By gradually increasing the intensity of the physical activity, a person's maximum METs is measured. Cardiologist Robert A. Bruce developed the test in 1963 as a non-invasive test to examine patients with suspected heart disease, such as a previous heart attack or a ventricular aneurysm. Even early signs of coronary artery diseases in healthy patients can be detected. For subjects with existing or suspected heart diseases, this test should only be performed under medical supervision.
Additionally, the test can measure an athlete's capacity to perform sustained exercise. It finds the maximum METs and VO2 an athlete can maintain in physical exercise. The latter metric expresses the capacity of your body to utilize oxygen when exercising.
We show the stages of the Bruce protocol in the table above. The runner is exercising on a treadmill, with the activity intensity increasing gradually. Every 3 minutes, the treadmill's speed and inclination are raised, for a maximum of 7 stages. A pulse watch or an electrocardiograph (ECG) monitor the runner's heart rate. Additionally, the blood pressure and perceived exertion are recorded at the end of every stage. The Bruce protocol stress test ends when the subject cannot continue due to fatigue, or the medical staff decides to end it due to blood pressure or heart rate values going beyond healthy limits.
There are numerous methods to find the maximum heart rate. For further information, see our heart rate calculator. The maximum heart rate can be determined with the Oakland non-linear formula:
Max heart rate = 192 - (0.007 * age²)
This maximum heart rate serves as one main criterion to stop the Bruce protocol stress test. The maximum METs value is then defined as:
- For women:
METs_max = (4.38 * T - 3.9) / 3.5
- For men:
METs_max = (14.8 - (1.379 * T) + (0.451 * T²) - (0.012 * T³)) / 3.5
T is the time the subject spent on the treadmill running. The maximum oxygen volume VO2 max can then be determined as:
VO2_max = METs_max * 3.5
For elderly or frail patients, a modified Bruce protocol METs exists. The modified Bruce protocol stress test adds a stage 0 and 1/2 at the beginning. They are performed at 1.7 mph (2.7 km/h) and 0% and 5% treadmill inclination. After those initial stages, the modified Bruce protocol METs follows the normal Bruce protocol from stage 1. This calculator is not suitable for interpreting the results of the modified Bruce protocol stress test. Please consult a medical expert in that case.
The Bruce protocol METs test's main strength is that it allows a calculation of maximum METs and VO2 max without directly measuring the oxygen the person uses during exercise. This direct measurement requires an oxygen mask, which complicates the procedure significantly.
What are good maximum METs values?
The maximum METs a person can achieve depends heavily on age and gender. On average, men have larger hearts than women, therefore pumping more blood through the body, providing oxygen to the muscles. Furthermore, the maximum METs peaks naturally in the 20s, and from this point on declines by 10% per decade. Hereditary aspects also impact your peak performance. And if you exercise at a high altitude, the lower air density will lower your maximum METs (see our air density calculator for a closer insight).
But most importantly: your training status has a massive influence on your maximum METs!
- Average non-trained women have a maximum METs of around 8 and non-trained men 10.
- A good maximum METs value for a 30-year-old woman is 14 and for a man 15.
- Elite athletes can reach maximum METs of up to 22 (women) and 25 (men).
Do not fret if your current maximum METs is not perfect. You can easily increase it with a good training schedule.
And on the other hand, rest assured that the highest METs won't make you the best endurance athlete in the world. A massive share of athletic performance depends on technique and experience.
Why is this relevant for me?
After all this talk about METs and peak physical performance, you might think: why do I care? My maximum METs value is a bit lower than the average. So what? I am not planning to become a professional athlete. I feel great the way I am.
In that case, I am sorry to say, but there might be advantages in stepping up your workout routine a bit. A scientific article from 2018 found that cardiorespiratory fitness measured via VO2 max, and therewith also max METs, "has been shown to be a strong and independent predictor of all-cause and disease-specific mortality." Poor cardiorespiratory fitness is directly associated with a higher risk of cardiovascular disease and cancer.
To provide a reference on how much you should exercise, the WHO recommends "150 to 300 minutes of moderate to vigorous aerobic activity per week for all adults", and also emphasizes that "every move counts".
And don't you worry, we at Omni Calculator are here to support you. Whether you want to know how many calories you can burn running, how much longer you on average life if you cycle regularly, or what your bench press rep maximum is, we got your back – those and many other tools you can find in our Omni Calculator sports section.
How to use the Bruce protocol METs calculator?
Now that we've learned about the metabolic equivalent of task and the Bruce protocol stress test, we have all the knowledge needed to use the Bruce protocol METs calculator.
- Provide the Bruce protocol calculator with your personal information, namely sex and age. Let's assume you are female and 30 years old.
- Your maximum heart rate is 185.7 bpm based on the Oakland non-linear formula.
- Insert the information on how long you could perform the Bruce protocol stress test, in minutes and seconds, for example, 12 min 30 sec.
- The calculator determines your VO2 max as 50.85 ml/kg/min and your METs max as 14.53 kcal/kg/min. This is a good result for your sex and age. Congratulations!
- The table below gives you an overview of the meaning of your result in the context of average results for your sex and age group. The source for those values can be found in this article about VO2 Max Charts.
So that's it. Now you know the metabolic equivalent of task, the Bruce protocol, and the meaning of METs max and VO2 max, and how to use the Bruce protocol calculator to determine your cardiovascular fitness state.