The difference between fat-burning and cardio zones is point of controversy among health and fitness professionals because neither is a scientific term, and different workout gurus use them differently. Some people refer to aerobic exercise as fat-burning or cardio exercise. Others call moderately intense exercise below your aerobic threshold fat-burning because it burns a higher percentage of fat calories than glycogen calories.
If you consider the fat-burning and cardio zones two completely different workout targets, then the fat-burning zone is the less intense of the two. It takes place at roughly 50 percent to 60 percent of your maximum heart rate. At this heart rate, most of the calories you burn come from fat. With aerobic, or cardio exercise, you burn fat and glycogen at a roughly 50:50 ratio, while during anaerobic exercise, such as tennis or sprint intervals, you burn most of your calories from glycogen. In the fat-burning zone, you’ll burn fewer total calories than you do with aerobic exercise or sprint training. If your goal is to burn the most calories and most total fat calories, then an aerobic, or cardio, workout, is a better choice for you. If your goal is to burn calories while you build stamina and endurance to create more intense workouts later, then fat-burning is for you.
Some people refer to any exercise that raises your heart rate during your workouts as cardio exercise. This would include brisk walking, or using a treadmill at speeds of 2.5 mph to 3.5 mph. If you consider cardio exercise to be activity performed in your aerobic heart rate range, you’ll work at a pace similar to jogging, reaching 70 percent to 80 percent of your maximum heart rate. Health experts recommend you take the “talk test” during your workouts to determine if you’re in you’re aerobic heart rate. If you are sweating and breathing hard, but can still talk, you haven’t left your aerobic threshold.
The harder you work, the more calories you burn, which is why even though you burn more calories from fat as a percentage of calories burned during fat-burning workouts, you bun more total fat calories with more intense exercise. For example, walking on a treadmill or outdoors at 2.5 mph, in the fat-burning zone, will help a 160-pound person burn roughly 200 calories per hour. Raising that to a jogging speed of 5 mph, she’ll burn approximately 600 calories per hour. At a 50:50 ratio of fat to glycogen, that’s 300 total calories from fat. The American Heart Association recommends that you perform moderate-intensity workouts for 150 minutes each week, or 75 minutes of vigorously intense each week.
Target Heart Rate
To find your target heart rate for exercise, start by determining your maximum heart rate. The most common method for calculating this is to subtract your age from 220. This is a very general formula, and you should meet with a health professional to find your personal maximum heart rate, taking into consideration your resting heart rate, age, gender and weight. Northwestern Medicine researchers recommend that women subtract 88 percent of their age from 206 to find a more accurate maximum heart rate. Once you know your maximum heart rate, multiply it by .50 and .60 to get your fat-burning target heart rate range. To find your aerobic, or cardio, heart rate zone, multiply your maximum heart rate by .70 and .80. Personal heart rate monitors and exercise machine heart rate monitors help you determine how different exercises and workouts help you burn calories.
Sam Ashe-Edmunds has been writing and lecturing for decades. He has worked in the corporate and nonprofit arenas as a C-Suite executive, serving on several nonprofit boards. He is an internationally traveled sport science writer and lecturer. He has been published in print publications such as Entrepreneur, Tennis, SI for Kids, Chicago Tribune, Sacramento Bee, and on websites such Smart-Healthy-Living.net, SmartyCents and Youthletic. Edmunds has a bachelor's degree in journalism.