Now that I’ve started studying for my state-licensed exam (“Fitnessinstruktorin mit eidg. Fachausweis”), I’m starting to realize how many unscientific half-truths we use without thinking about it.
For instance, a lot of customers work out to “burn fat”. However, few people actually mean they want to improve the efficiency of lipolysis. This would be the goal of, say, a long distance runner who needs a (slow but steady) energy source of almost unlimited availabity. Most people, however, simply want to reduce their body fat.
As can be seen on the chart, the higher the energy expenditure, the less it has to do with “burning fat”. Fat is a fairly slow source of energy and, in percentage (not absolute numbers!), the less you do, the more your body relies on fat. Sleeping, for example, can be done mostly by burning fat. But, by morning, you might have burned the calories of about one glass of milk.
To reduce body fat, you want to expend high calorie levels. The chart shows that high energy expenditure means relying on fast energy sources that are only available for limited periods at a time.
To return to running: try sprinting for 1-2 minutes followed by easy jogging or walking for 1-2 minutes. Including warm up and cool down, around 20-30 minutes in total. This will allow you to burn lots of calories for a short period of time during your sprint. Also, it will allow you to replenish your quick and quickly depleted high energy sources during your jog or walk.