How do heart rate monitors estimate calories burned?

February 26, 2006 6:44 PM

How do heart rate monitors estimate how many calories you burn while exercising?

I ask partly out of intellectual curiosity, and partly because I wonder if I should believe the number the monitor spits out.

I would like to know how the algorithm works and how accurate the estimate is. Are there differences in accuracy between heart rate monitors from different companies?

posted by betterton to Health & Fitness (2 answers total)

I believe they make assumptions about how much oxygen your blood can carry; the increase in heartrate is to ensure a steady supply of oxygen and blood-sugar to muscles and whatnot. I think that for an average heart of known age & gender, you could fairly accurately calibrate a curve of heart rate (and therefore flow rate) vs energy consumption. That only works because the energy consumed is directly related to the amount of oxidation your metabolism is doing. You could probably get a better idea of energy by looking at CO₂ emissions but that's a lot harder than counting electrical pulses.

As to actual accuracy, I don't know.
posted by polyglot at 3:16 AM on February 27, 2006

My polar monitor seems to calculate a lot higher calories than I would guess for my bike rides. Here's a Google groups thread that has similar conclusions, using bike calculators that estimate wind resistance, etc. Maybe it depends on what exercise and your efficiency, too.
posted by jjj606 at 12:45 PM on February 27, 2006