What is the optimal heart rate percent for fat burning? I read some places 60% to 70% is good and other places I read that 65% to 85% is optimal. Then some sat that 85% is too high and is more aerobic that fat burning. Could someone help me with which is the better of the two. Will I basically get double the results with staying at a HR% for one hour as opposed to a 30 mins or is there an time limit?