The Bruce Protocol Treadmill Test

The Bruce protocol treadmill test was designed by cardiologist Robert A. Bruce in 1963 as a non-invasive test to assess patients with suspected heart disease. In this capacity, is perhaps more widely known as a stress test or exercise tolerance test.

Now, the Bruce protocol test is commonly used to help identify a person's level of aerobic endurance. It does this by providing an estimated maximal oxygen uptake or VO2 max. V02 max is a measure of an athlete's capacity to perform sustained exercise and is linked to aerobic endurance.

Bruce Protocol Stages

The Bruce protocol involves getting on a treadmill with the speed and incline increasing every three minutes (in stages). The test stops when you've hit 85% of your maximum heart rate, your heart rate exceeds 115 beats per minute for two stages, or it is deemed that the test should no longer continue.

If your heart rate changes more than six beats per minute between the second and third minute of any given stage, you are kept at the same speed and incline for an additional minute. The reason for this is because your heart rate has not achieved a steady state.

The length of time you spend on the treadmill is your test score and can be used to estimate your VO2 max value. During the test, blood pressure and ratings of perceived exertion are often also collected.

Measuring VO2 Max With the Bruce Protocol

Maximal oxygen uptake (VO2 max) refers to the maximum amount of oxygen that an individual can take in and use during intense or maximal exercise. It is measured as milliliters of oxygen used in one minute per kilogram of body weight (ml/kg/min).

The Bruce treadmill test is an indirect maximal oxygen uptake test. It is considered indirect because it estimates VO2 max using a formula and the person's performance on a treadmill as the workload is increased.

Other methods of measuring VO2 max are more cumbersome and require the direct collection and measurement of the oxygen volume and oxygen concentration of inhaled and exhaled air the athlete uses while running. Direct testing requires far more elaborate and sophisticated equipment and data collection than the formula based on time on the treadmill.

When the Bruce protocol formula is used, T stands for total time on the treadmill and is measured as a fraction of a minute (a test time of 10 minutes 15 seconds would be written as T=10.25); and this formula changes based on sex.

• Men: 14.8 - (1.379 x T) + (0.451 x T²) - (0.012 x T³) = VO2 max
• Women: 4.38 x T - 3.9 = V)2 max

Bruce Treadmill Test Cautions 

Because the Bruce treadmill test is a maximal exercise tolerance test, it requires a physician's clearance and expert supervision. In an untrained individual or an athlete with an underlying heart condition, exercising to a maximal effort can lead to injury or heart events.

While performing the test, clinicians monitor the patient's vital signs continuously and stop the test at any sign of trouble. If you take this test, be sure that your testing facilitator has the appropriate clinical expertise and has conducted such tests many times before you step on the treadmill.

Alternatives to the Bruce Protocol

The Bruce protocol is not the only treadmill test that can be used to assess your cardiorespiratory fitness. Two other options include the Balke & Ware treadmill exercise test and the Ebbeling single-stage treadmill test.

Balke & Ware Treadmill Exercise Test

Like with the Bruce protocol, the Balke & Ware treadmill exercise test is done in stages; however, these stages range from one to three minutes each. Another difference is that the speed is kept constant with the incline being the only thing that changes.

If this exercise test is used, the goal is also to get the heart rate to 85% of its max, this time by beginning at a 0% incline and increasing by 2.5% every three minutes. Again, if any symptoms develop that warrant termination, the test is stopped.

Ebbeling Single-Stage Treadmill Test

The Ebbeling single-stage treadmill test is designed for individuals who are low-risk and otherwise healthy, yet not physically active. As its name implies, it has only one stage and that stage is just four minutes long. The speed remains constant with the incline raised to 5% after warming up.

The speed is determined by the person's heart rate, generally falling somewhere between 2.0 and 4.5 mph (but this can be adjusted after the first minute if needed). If the heart rate varies by more than five beats per minute, the test can be extended another minute to get the final score.