1) I'm pretty sure you're exaggerating. 3% body fat is only sustainable for a few hours before you die. Most long distance runner are in the 7-9% body fat range. it's VERY hard for any endurance athlete to go below this point due to dietary changes (ie: carb restriction and cycling) needed which would be VERY detrimental to endurance performance. There is a reason why most bodybuilders who compete at 3% gain 30lbs the day after contest. They are so tired and depleted they have nothing left in their body. There is zero chance for any serious athlete of ANY sport who could be competitive at 3% body fat.Aerobic or in oxygen exercise puts the body into a state of burning FAT as fuel. So long slow but at the same time slightly getting towards 60% of your max HR will burn FAT and require you to go longer in order to burn more calories. Going all out for 10 minutes is not the way to burn fat effectively.
10 mins at 190HR = 1900 beats in the outut category. and not in oxygen thus not buring fat!
60 mins at 125HR = 7500 beats in the output category but well utilizing fat as fuel.
Lowest resting HR is in the sleeping and earliest awaken AM hours vs highest in mid to late day before bed.
Seems pretty simple to me how and when to exercise to lose weight.
I am a former National Class distance runner and practiced this to daily hitting a body fat percentage at one point of 3%. Its all input VS output and eating right. Lets not make this anymore complicating then it has to be.
2) You're wrong about steady state. While it has its uses and is perfect for beginners to exercise, it's not the optimal way to lose fat by far. This article explains better than I. Enjoy.