How this calculator works
The standard Bruce protocol starts at 2.74 km/h and a 10 percent grade and raises both every three minutes. The time at which the test stops is the main result. Two regressions are used here. The Foster equation turns time into an oxygen uptake estimate with a cubic curve, and dividing by 3.5 converts millilitres of oxygen per kilogram per minute into METs. The Bruce equation uses time in seconds and a sex term. The predicted maximum heart rate is the common 220 minus age value.
Formula
Foster VO2 (mL/kg/min) = 14.8 - 1.379T + 0.451T squared - 0.012T cubed, where T is time in minutes. METs = VO2 / 3.5. Bruce VO2 = 6.70 - 2.82 x sex (1 male, 2 female) + 0.056 x time in seconds. Predicted maximum heart rate = 220 - age.
Worked example
A 40-year-old man stops at 9 minutes, or 540 seconds. Foster VO2 = 14.8 - 12.411 + 36.531 - 8.748 = 30.17 mL/kg/min, which is 8.62 METs. The Bruce equation gives 6.70 - 2.82 + 30.24 = 34.12 mL/kg/min. The predicted maximum heart rate is 180 bpm.
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Frequently asked questions
What does a MET on the Bruce protocol mean?
One MET is resting oxygen use, about 3.5 mL of oxygen per kilogram per minute. A result of 8.6 METs means the estimated peak effort was 8.6 times resting metabolism.
Why do the two equations disagree?
They were fitted to different groups and use different inputs. The Foster equation uses time alone, while the Bruce equation includes sex. Neither replaces a direct measurement, and the difference of a few mL/kg/min is expected.
Is the predicted maximum heart rate used in the test?
No, it is shown for context. A clinical test may stop at a target heart rate, but the MET estimate depends on the time completed, not on the predicted maximum.
Can I use this without a treadmill?
No. The protocol is defined by its speed and grade stages. Without a treadmill you cannot know the time completed under those conditions.