- Much conflicting information exists about how long on the treadmill equals how many METs
- There is a formula for the Bruce Protocol (we’ll explain it below)
- Use our online Bruce Protocol METs calculator for more precise calculations
The Formula for Our Bruce Protocol METs Calculator
Our Score Calculator is a useful tool for estimating your metabolic equivalents (METs) during an exercise tolerance treadmill test. The calculator takes into account the speed, incline, and duration of your treadmill exercise.
The precise formula is different for men & women.
Formula for Men
METs = (14.8 - (1.379 * t) + (0.451 * t²) - (0.012 * t³)) / 3.5t = time completed in decimal form. For example 10:30 = 10.5
Formula for Women
METs = (4.38 * t - 3.9) / 3.5t = time completed in decimal form. For example 10:30 = 10.5
These formulas are generally accurate above 2 minutes of exercise
Understanding Metabolic Equivalents
Metabolic equivalents, are a unit of measurement used to quantify the energy expenditure of physical activities. One MET represents the amount of energy expended at rest, which is approximately 3.5 milliliters of oxygen consumed per kilogram of body weight per minute
For example, if an individual is performing an activity that requires 4 METs, it means they are expending four times the amount of energy compared to being at rest. This measurement allows healthcare professionals to recommend specific activities or exercise intensities based on a person’s fitness level and health goals.
For the average adult, 150 minutes of moderate-intensity aerobic activity per week, which is equivalent to 3-6 METs, is recommended for maintaining good cardiovascular health.
Higher MET activities, such as running or intense sports, can contribute to more significant health benefits, including improved heart function, reduced risk of chronic diseases, and increased calorie expenditure for weight management.
Metabolic Equivalent of Tasks
Activity Intensity | Range
Resting | 0.9
Light activities (e.g., walking) | 2-3
Moderate activities (e.g., biking) | 3-6
Vigorous activities (e.g., running) | >6
It’s important to remember that the intensity of an activity and the resulting MET value should be considered in conjunction with an individual’s fitness level, health status, and specific goals.
Technical Aspects of The Bruce Protocol
Stages: Treadmill Speed, Incline & Approximate METs
The treadmill increases the speed and incline every 3 minutes (until you must stop due to symptoms or the patient’s request).
To get the best measurement of a patient’s fitness, the test should usually be symptom-limited. It should stop due to patient request, fatigue, or other symptoms. Achieving 85% of the patient’s MPHR is generally not advisable as a reason for termination.
Here’s a breakdown of the settings for each stage:
| Stage | Minutes | Speed (mph) | Incline (%) | Approx METs |
|---|---|---|---|---|
| 1 | 3 | 1.7 | 10 | 3 |
| 2 | 3 | 2.5 | 12 | 4-5 |
| 3 | 3 | 3.4 | 14 | 7 |
| 4 | 3 | 4.2 | 16 | 10 |
| 5 | 3 | 5.0 | 18 | 14 |
| 6 | 3 | 5.5 | 20 | 17 |
| 7 | 3 | 6.0 | 22 | 21 |
As you advance through each stage, pay close attention to your heart rate and monitor signs of fatigue.
Remember to consult with a healthcare professional before attempting the Bruce Protocol, especially if you have any existing medical conditions or concerns.
Reasons for Terminating an Exercise Tolerance Test
During an exercise tolerance test (ETT), there are certain indications or situations in which it may be necessary to terminate the test to ensure the safety and well-being of the patient. These indications may vary depending on the individual’s specific health condition, but some common indications for terminating an ETT include:
Chest pain or discomfort: The development or worsening of chest pain during exercise is a serious sign that could indicate underlying heart disease or angina. It is necessary to stop the test and evaluate the patient’s condition further.
Severe shortness of breath: If the patient experiences extreme difficulty in breathing, becomes excessively short of breath, or exhibits signs of respiratory distress, it is essential to halt the test immediately.
Abnormal heart rhythm: Certain abnormal heart rhythms, particularly those that pose a risk to the patient’s health or can lead to cardiac arrest, may warrant terminating the test. These can include ventricular tachycardia, ventricular fibrillation, or excessively rapid or irregular heart rhythms.
Significant drop in blood pressure: A substantial drop in blood pressure during exercise may lead to feelings of lightheadedness, dizziness, or fainting. It is important to stop the test if there is a significant decrease in blood pressure to prevent potential falls or injuries.
Signs of cardiovascular instability: Such as signs of shock (pale skin, rapid weak pulse, low blood pressure), or exhibits other concerning symptoms like profuse sweating, nausea, or confusion, the test should be terminated promptly.
Patient’s expressed desire to stop: Patients have the right to voice their discomfort or request to stop the test at any point. It is crucial to respect their wishes and closely monitor their condition.
Aside from these specific indications, there are others.
Refer to the ACC/AHA Guidelines for Exercise Testing: Executive Summary if you are conducting Exercise Tolerance Tests.
Estimating VO2 max
VO2 max is the maximal oxygen consumption, which represents the maximum amount of oxygen that an individual can utilize during intense exercise. Expressed in ml/kg/min, it is considered one of the best indicators of cardiorespiratory fitness and overall cardiovascular health.
You can estimate VO2 max by a simple formula:
VO2_max = METs * 3.5VO2 max is typically expressed in milliliters of oxygen consumed per kilogram of body weight per minute (ml/kg/min). The higher it is, the more oxygen an individual’s body can utilize, indicating better aerobic fitness. Values can vary based on age, sex, fitness level, and other factors. Here are some general ranges based on various demographics:
Adults:
Poor: 15-20 ml/kg/min
Fair: 20-30 ml/kg/min
Good: 30-40 ml/kg/min
Excellent: >40 ml/kg/min
Athletes:
Highly trained athletes: >70 ml/kg/min
Elite endurance athletes: >80 ml/kg/min
Older adults:
Average sedentary adults: 17-24 ml/kg/min
Healthy active older adults: 25-34 ml/kg/min
Highly fit older adults: >35 ml/kg/min
Children and adolescents:
Boys (aged 6-17): 40-50 ml/kg/min
Girls (aged 6-17): 35-45 ml/kg/min
It is important to note that these values are approximate and can vary depending on the reference population used.
Assessing VO2 max accurately requires specialized equipment and testing procedures, typically conducted under controlled laboratory conditions. However, estimating VO2 max is a practical and widely used approach.
History of the Bruce Protocol
Developed by Dr. Robert Arthur Bruce, it has become the most prominent stress test protocol.
Born in Boston in 1916, Robert Bruce developed an early interest in cardiology and internal medicine. He completed his medical degree from the University of Rochester and continued his internship and residency at the University of Oregon Medical School. During his time there, he carried out his groundbreaking work in exercise cardiology, a field in its infancy at the time.
Originally published in 1951, “Evaluation and significance of physical fitness for moderate work; a study of patients with cardiovascular or pulmonary diseases” was a groundbreaking paper by Dr. Bruce.
In 1963, he published his signature work, “Exercise Testing of Patients with Coronary Heart Disease: Principles and Normal Standards for Evaluation,” in the Annals of Clinical Research. This paper laid out the Bruce Protocol as we know it today. The protocol became a standard measure in clinics and hospitals worldwide to evaluate the functionality of the heart and lungs during exercise.
The Bruce Protocol remained the most widely used exercise test for diagnosing ischemic heart disease for decades. Today even though several modifications and alternatives to the protocol have been developed, it remains a substantive benchmark in exercise testing. Recognized for his contributions, Robert Bruce has been termed ‘the father of exercise cardiology’.
Robert Bruce passed away in 2004, but his legacy continues in the widespread use of his protocol and in the field of exercise cardiology that he helped pioneer. His work revolutionized cardiac care, and the impact of his protocol remains evident in diagnostic procedures today.
Frequently Asked Questions
Age, fitness level, body composition, and your overall health.
Your performance on the treadmill and the stage at which you feel fatigued or need to stop the test also play a key role. It is essential to communicate any discomfort or issues you face during the test to the test administrator to ensure accurate results.
Your score indicates your exercise capacity and aerobic fitness. A higher score means better fitness. Generally, a score below 5 METs indicates a low fitness level, while a score above 10 suggests an above-average to excellent fitness level. However, it is crucial to consult with your healthcare professional to understand your specific score in the context of your health status and individual factors.
Achieving 10 METs on a stress test signifies a good level of fitness. In the context of the Bruce Protocol, reaching this level suggests that your heart can effectively pump blood and your body can efficiently utilize oxygen during physical activity.
A higher score, such as 10 or above, is often associated with a lower risk of cardiovascular disease and better overall health outcomes.
Yes, scores can be calculated using various stress tests, such as the treadmill test, cycle ergometer test, or the Individualized Ramp Treadmill test. Each stress test has its protocol for measuring exercise capacity and can provide insights into your fitness. However, the Bruce Protocol is the most widely used and well-established protocol.
Citations:
BRUCE RA, LOVEJOY FW Jr, YU PN, McDOWELL ME. Evaluation and significance of physical fitness for moderate work; a study of patients with cardiovascular or pulmonary diseases. AMA Arch Ind Hyg Occup Med. 1951 Sep;4(3):236-50. PMID: 14867936.
Bruce RA. Exercise testing of patients with coronary heart disease. Principles and normal standards for evaluation. Ann Clin Res. 1971 Dec;3(6):323-32. PMID: 5156892.
ACC/AHA Guidelines for Exercise Testing: Executive Summary, 1997 TA – Circulation, 345-354 VI