Gentleman,
Is there such a thing as a Fat burning Zone Based on the percent of MHR?
Doug
Doug,
Thanks for the post and I hope you’re well 
There is an heart rate that corresponds to physical activity intensity where the predominant fuel being used is fat- though other fuels will ALSO be used at the same time.
That said, this is of little practical importance because the more important factor is how much fat is being burned daily, which is more a function of volume and intensity than heart rate while doing the activity.
In short, high intensity intervals can work for fat loss just as well as low intensity cardio.
-Jordan
Thanks Jordan,
and happy holidays!