Running is one of the most convenient and inexpensive forms of cardiovascular exercise. In general, running for any sustained period of time longer than two minutes burns calories mostly from fat. However, it takes a more holistic approach of diet combined with individualized prescriptions of exercise intensity and duration to reduce body fat content and increase muscle mass.
The body uses a mixed energy system to fuel physical activity. Quick bursts of exercise such as a sprint draw energy mostly from carbohydrates while a three mile run burns mostly fat combined with some carbohydrates and protein for fuel. How much fat a person burns from running three miles is specific to the intensity of the run, your starting weight and other metabolic factors.
One way to gauge energy expenditure and stay in a fat-burning zone while running is to use a heart rate monitor. Running with a monitor provides an individualized overview of the amount of calories burned and heart rate. Use these readings to adjust intensity and keep target heart rate in a fat-burning zone, or between 65 to 85 percent of maximum. Calculate your maximum heart rate by subtracting your age from 220 and then aim to reach 65 to 85 percent of that. For example, a 32 year old should aim to stay between 122 to 160 beats per minute.
Fitness experts such as those at the American College of Sports Medicine recommend combining strength-training with cardio activities. While aerobic activities like running provide many benefits for the cardiovascular system and burn calories for weight loss, resistance training helps to build muscle and reduce body fat content through boosted metabolism. A leaner body means more efficient metabolism and fat-burning for runners. The ACSM recommends doing 8 to 10 strength-training exercises with 10 to 15 repetitions, two to three times per week.
While running is a good way to burn fat, engaging in any physical activity that repeatedly uses the same muscles can increase the risks for injury. A weekly running schedule should provide days of rest in between bouts of activity. Another consideration is that nutrition plays an important part in fueling physical activity. When combined with exercise, lean diets based on heart-healthy fats, moderate calories, lean protein, whole grains and fruits and vegetables account for long-term maintenance of reduced body fat.