Before the development of the Bruce Protocol there was no safe, standardized protocol that could be used to monitor cardiac function in exercising patients. Master's Two-Step test was sometimes used, but it was too strenuous for many patients, and inadequate for the assessment of respiratory and circulatory function during varying amounts of exercise. Most physicians relied upon patients' complaints about exertion, and examined them only at rest.
To address these problems, Bruce and his colleagues began to develop a treadmill exercise test. The test made extensive use of relatively new technological developments in electrocardiographs and motorized treadmills. A Bruce exercise test involved walking on a treadmill while the heart was monitored by an electrocardiograph with various electrodes attached to the body. Ventilation volumes and respiratory gas exchanges were also monitored, before, during and after exercise. Because the treadmill speed and inclination could be adjusted, this physical activity was tolerated by most patients. Initial experiments involved a single-stage test, in which subjects walked for 10 minutes on the treadmill at a fixed workload. Bruce's first reports on treadmill exercise tests, published in 1949, analyzed minute-by-minute changes in respiratory and circulatory function of normal adults and patients with heart or lung ailments.
In 1950 Bruce joined the University of Washington, where he continued research on the single-stage test, particularly as a predictor of the success of surgery for valvular or congenital heart disease. Later he developed the multistage test, consisting of several stages of progressively greater workloads. It was this multistage test, a description of which was first published in 1963, that became known as the Bruce Protocol. In the initial paper, Bruce reported that the test could detect signs of such conditions as angina pectoris, a previous heart attack, or a ventricular aneurysm. Bruce and colleagues also demonstrated that exercise testing was useful in screening apparently healthy people for early signs of coronary artery disease.
Typically during a Bruce Protocol Heart Rate and Rating of Perceived Exertion are taken every minute and Blood Pressure is taken at the end of each stage (every three minutes).
There are Bruce Protocol Tables available for Maximal and Sub Maximal (more practical with the majority of the non-athletic or competitively athletic population) efforts (see below).
Bruce Protocol (Sub Maximal Table)
The Modified Bruce protocol starts at a lower workload than the standard test and is typically used for elderly or sedentary patients. The first two stages of the Modified Bruce Test are performed at a 1.7 mph and 0% grade and 1.7 mph and 5% grade, and the third stage corresponds to the first stage of the Standard Bruce Test protocol as listed above.
The test score is the time taken on the test, in minutes. This can also be converted to an estimated VO2max (maximal oxygen uptake) score using the calculator below and the following formulas, where the value "T" is the total time completed (expressed in minutes and fractions of a minute e.g. 9 minutes 15 seconds = 9.25 minutes). As with many exercise test equations, there have been many regression equations developed that may give varying results. If possible, use the one derived from a similar population and which best suits your needs.
- VO2max (ml/kg/min) = 14.76 - (1.379 × T) + (0.451 × T²) - (0.012 × T³)
- Women: VO2max (ml/kg/min) = 2.94 x T + 3.74
- Women: VO2max (ml/kg/min) = 4.38 × T - 3.9
- Men: VO2max (ml/kg/min) = 2.94 x T + 7.65
- Young Men: VO2max (ml/kg/min) = 3.62 x T + 3.91
ref: ACSM's Health-Related Physical Fitness Assessment Manual
Underlying Heart Rate Formulas
Maximum Heart Rate (MHR) is typically calculated with the formula 220-age. This formula is a bit controversial because it doesn't reflect the differences in heart rate according to age. The underlying heart rate formula most often used for the Bruce is the outdated Karvonen formula (below).
A more accurate formula, offered in a study published in the journal, Medicine & Science in Sports & Exercise, is 206.9 - (0.67 x age) which can also be used to more accurately determine VO2 Max, but may produce significantly different results.
A diagnostician (e.g., personal trainer, doctor, athletic trainer, nurse, medical professional, dietitian, etc.) may be best served to conduct the test twice using both parameters and formulas.
The Karvonen method factors in resting heart rate (HRrest) to calculate target heart rate (THR), using a range of 50–85%:
- THR = ((HRmax − HRrest) × %Intensity) + HRrest
Example for someone with a HRmax of 180 and a HRrest of 70:
50% intensity: ((180 − 70) × 0.50) + 70 = 125 bpm
85% intensity: ((180 − 70) × 0.85) + 70 = 163 bpm
- Robert A. Bruce, Frank W. Lovejoy, Jr., Raymond Pearson, Paul N. G. Yu, George B. Brothers, and Tulio Velasquez (November 1949). "Normal respiratory and circulatory pathways of adaptation in exercise". J. Clin. Invest 28 (6 Pt 2): 1423–1430. doi:10.1172/JCI102207. PMC 439698. PMID 15407661.
- Robert A. Bruce, Raymond Pearson, Frank W. Lovejoy, Jr., Paul N. G. Yu, George B. Brothers (November 1949). "Variability of respiratory and circulatory performance during standardized exercise". J Clin Invest 28 (6 Pt 2): 1431–1438. doi:10.1172/JCI102208. PMC 439699. PMID 15395945.