The Basis of Heart Rate and Energy Expenditure

There is a common assumption regarding the ability of heart rate monitors to predict energy expenditure. This is partly because there are many consumer products available that attempt to do just that, for example heart rate chest-strap monitors with wrist watches or software that estimate calories burnt. Plus there is literature that describes accurate energy expenditure estimation from heart rate recordings. However a closer look at the products and the literature shows that predicting energy expenditure (EE) from heart rate (HR) is 1) only appropriate for certain activities and 2) only accurate after a lengthy and complicated calibration processes has been performed for each subject. This means that it is inappropriate to use HR to estimate EE in free living situations (those outside of controlled settings and activities) and for unseen subjects