Carbohydrates provide the major energy source for your muscles. Your body converts this macronutrient -- found in starchy vegetables, sugar, fruits and grains -- into glucose, which it then transports to cells for energy or stores for later use. Once your glycogen stores are full of this glucose -- after about 300 to 400 grams -- the body stores the excess as fat. Prolonged cardio activity performed at an intense level is best for working through your carbohydrate stores. Once you've stored carbs as fat, they don't burn as efficiently.
Maintain a high-carbohydrate diet. Make carbohydrates consist of 60 to 70 percent of your daily calorie intake to get your body accustomed to burning carbohydrates primarily for fuel. Adequate carbohydrate intake also ensures your body has carbs, or energy, to burn.
Work out at a high intensity for an extended period of time, such as running a half-marathon or biking for several hours. High-intensity means a level you can maintain for the duration of the event but that still feels challenging. The American Council on Exercise describes it as about 80 to 95 percent of your maximum heart rate. Train over time to be able to hold this intensity for 90 minutes or longer.
Perform a quick all-out set of pushups for a minute, a 400-meter running sprint, 50-meter swimming sprint or a set of eight to 12 repetitions of a strength exercise using a weight that is hard to complete. These types of intense movement that you can only maintain for a minute or so are examples of use of the glycolytic energy system, which uses carbohydrates almost exclusively for energy. You'll burn through carbs quickly with such activity, but because they're so intense, you can't maintain them for long periods of time and won't burn a large net amount of carbohydrates.
You can train your body to use different energy systems for endurance activity. Your body reaches for carbohydrates first during submaximal endurance exercise, the point at which you work at 80 to 95 percent of your heart rate, but if you've trained your body to burn fat during exercise by performing fasted workouts and consume a diet rich in protein and fat, you'll use more fat for fuel.
Intervals of glycolytic exercise may burn carbs during the high-intensity portions of the workout, but actually boost your fat-burning capacity post-workout.
Consult with your doctor to ensure you're healthy enough to start a program that includes submaximal endurance exercise or glycolytic intervals.
- Experience Life: All About Your Metabolic Energy Systems
- European Food Information Council: Frequently Asked Questions
- Clinics in Sports Medicine: Role of Carbohydrate in Exercise
- American Council on Exercise: High-Intensity Interval Training
- Journal of Obesity: High-Intensity Intermittent Exercise and Fat Loss