How this calculator works
The Keytel equation was published in 2005 after measuring steady-state exercise in 115 regularly exercising adults. It predicts energy expenditure from heart rate, body mass, age and sex, and does not need a VO2 max test. Heart rate rises with effort, but the relationship differs between people, between exercises and with fitness, temperature and caffeine. The equation was fitted at about 57 to 90 percent of maximum heart rate, roughly 90 to 150 beats per minute for a young adult, so values outside that range are extrapolations. It also estimates gross energy use, including the energy you would have used at rest.
Formula
Male: kcal/min = (-55.0969 + 0.6309 x HR + 0.1988 x mass + 0.2017 x age) / 4.184. Female: kcal/min = (-20.4022 + 0.4472 x HR - 0.1263 x mass + 0.074 x age) / 4.184. HR is in beats per minute, mass in kg and age in years. Total calories = kcal/min x duration in minutes.
Worked example
A 30-year-old man with a body mass of 80 kg and an average heart rate of 150 beats per minute: -55.0969 + 94.635 + 15.904 + 6.051 = 61.493, divided by 4.184 gives 14.70 kcal/min. For 30 minutes that is 440.9 kcal. A 40-year-old woman, 60 kg, 140 beats per minute for 20 minutes: 37.588 / 4.184 = 8.98 kcal/min, or 179.7 kcal.
Advertisement
Frequently asked questions
Why does the equation ask for sex?
At the same heart rate, men and women tend to differ in body composition and stroke volume, so the fitted coefficients differ. Using the wrong column shifts the estimate.
Can I use my maximum heart rate here?
No. Use the average heart rate during the exercise. A peak value overstates the average and pushes the estimate above the range where the equation was fitted.
Why is the result different from my fitness tracker?
Trackers use proprietary equations, personal history and motion data. The Keytel equation is a population model, so it will not match a device that has been calibrated to you, and neither is a measurement of your actual metabolism.