The fat-burning potential of your 30-minute cardiovascular workout depends on your heart rate and exercise intensity. When your heart rate reaches 60 to 80 percent of its maximum, you are in your fat-burning zone. How quickly you reach the fat-burning zone depends on your exercise intensity. Adding intervals to your half-hour cardio workout puts you into the fat-burning zone sooner. Consult your doctor before making any dramatic changes to your exercise regimen.
Cardio workouts fall into the aerobic exercise category. Aerobic exercise can reduce your body fat. During aerobics, your body needs a steady supply of oxygen. The need to replenish your oxygen supply constantly causes the lungs to work harder and your heart to pump faster. When your heart rate goes up, the amount of fat you burn increases.
Your body burns fat for energy. During a half-hour cardio workout, the body needs a constant supply of energy to keep the heart pumping. In response to the need for energy, your body will begin to break down fat. Exercise intensity determines the amount of fat burned during a 30-minute cardio workout. A greater percentage of energy used during low-intensity exercise comes from fat, University of New Mexico researchers explain, but you burn more fat during high-intensity exercise because the overall need for energy is greater.
Find your fat-burning zone and maximize your fat-burning potential. A person's fat-burning zone falls in the range of 60 to 80 percent of his maximum heart rate; you can find your maximum heart rate in beats per minute by subtracting your age from 220. Your maximum heart determines how fast your heart can pump before it becomes detrimental to your health. If your heart rate reaches the fat-burning zone early in your 30-minute workout, you will burn more fat.
Incorporate interval training into your half-hour cardio routine. Interval training mixes low- and high-intensity exercise periods. For example, during a half-hour cardio interval routine, you walk for 2 minutes then run for 30 seconds before repeating the cycle. Adding intervals into your cardio workout helps you reach your fat-burning zone sooner. Study results published in 2008 in the journal "Applied Physiology, Nutrition, and Metabolism" found increased fat burn for participants who engaged in high-intensity aerobic interval training.