How does HRM calculate calories burned?

[CardioFan]

Hi,
Does anyone know how a heart rate monitor calculates the calories burned during a workout? My treadmill and heart rate monitor disagree. Thanks!

[2Scoops]

HR monitors (depending on make) estimate calories burned on your height/weight/age/RHR/MHR and any other details you put into it - in particular its built-in fitness tests, once you do them, e.g. Polar's "OwnZone Index".

Treadmills use the speed/grade and your weight to predict a general energy expenditure but totally ignores economy.

Neither are perfect, but I'd go with the HR monitor.

[CardioFan]

That was helpful. Thank you!