Running is not the most effective way to burn fat. The most effective way to burn fat is keeping a specific target heart rate for a period of time. You see the body needs oxygen to oxidize the fat to get rid of it. So when you run your body needs more oxygen and at a specific heart rate you will need enough oxygen to keep up that your body will shut down the oxidation process to conserve needed oxygen. You actually burn fat when you are sitting or sleeping. The problem is that you need to be at the top of your fat burning range. You can do virtually any exercise to achieve the peak for fat burning. There is a formula you can do to determine the best heart rate to keep you in an optimal fat burn zone. The formula is 220-age=? then take your answer (?) and multiply it by .6 for your low end of optimal fat burn. Take the same number (?) and multiply it by .75 for the top of the fat burn zone, low and high end answers are beats per minute. So here's my range done with the formula.
220-42=178
178x.6=106.8 bpm low end
178x.75=133.5 bpm high end
Happy fat burning!