fat oxidation

In a nutshell, the higher the rate of work, the more calories you will burn, but at a smaller rate for fat calories.

Your body's energy efficiency is just like a car. if you are cruising 5 miles in fifth gear at 50mph then you will be at say 30 miles per gallon, if you raced it as fast as you could and used each gear to the red line and tooped 80mph then you would probably get that down to 20mpg.

Your body is exactly the same. You would use less fuel at a slower speed but at a higher concentration of fat.

You need to condition your body to burn fat cells, even when not exercising and this is ultimately performed through working off your base levels! 50-65% of your maximum heart rate.