Watch your heart rate, not your speed. Heart rate formula: 220- 15 (age) =205. This is your highest heart rate. The heart rate of fat loss should be controlled at 65%-75% of the maximum heart rate, that is, your heart rate during running should be controlled within the range of 135- 155 within one minute. Do aerobic exercise 3-4 times a week and run for 35 minutes each time. Don't care too much about speed.