Not long ago, every piece of cardio equipment in the gym would have a fat burning heart rate chart on the console, with one range of heart rates labeled for "fat burning" and the other for "cardio." But nowadays, the experts want you to think in terms of moderate or vigorous exercise intensity.
About the Fat Burning Zone
Those once-ubiquitous "heart rate zone" charts are now a relic of vintage — ahem, long-lived — exercise equipment. So where did the charts come from, and where did they go? They cropped up because a relatively small body of research established that you burn more calories from fat when you work out at a moderate intensity, as compared to the calories you'll burn from fat when exercising at a more vigorous intensity.
As explained by Len Kravitz, PhD, an exercise researcher at the University of New Mexico, that's true — but there's more to the story.
If you were to exercise for the same amount of time in the higher "cardio" heart rate zone as in the more moderate "fat burning" heart rate zone, you'd burn a smaller percentage of calories from fat while in the cardio zone. But the total number of calories you burn in the cardio zone is so much higher than in the "fat burning" zone that even that lesser percentage ends up being a bigger number overall.
It's also true that working out at a higher intensity puts more stress on your cardiovascular system, forcing it to adapt by becoming more efficient. But when taken out of context, these two pieces of information gave rise to a false either/or dichotomy: That the only way to burn fat is by staying in that lower heart rate zone, and the only way to build cardiovascular fitness is by staying in the higher heart rate zone.
And that isn't true. For some people, lower-intensity workouts are the only appropriate exercise for building their cardiovascular capacity. When it comes to losing excess fat, take a hint from Kravitz: It's better to focus on overall calories burned than to worry about staying in the "fat burning zone."
Read more: 10 Simple Ways to Improve Your Heart Health
Measuring Your Heart Rate
Even though the fat burning heart rate chart no longer reigns supreme on the faces of all your exercise equipment, measuring your heart rate is still a valid way to measure your exercise intensity.
For many people, the intuitive way to measure their heart rate is with one eye on a clock as they place a couple of fingers at the pulse point in their neck or wrist — or maybe reaching for a favorite fitness-tracking device. Some types of exercise equipment, like treadmills and elliptical trainers, also come with heart rate monitors built into the hand grips.
But the "pause and count" method of taking your heart rate is inconvenient at best and, as Harvard Health Publishing points out, those built-in heart rate monitors on your exercise equipment are notoriously inaccurate. Fitness trackers are somewhat better, and have the advantage of being easy to use. But if you want the sort of accurate heart rate measure that's necessary for a truly accurate gauge of your exercise intensity, you need a chest-strap heart rate monitor that displays its readout on a wristwatch, and some models will pair with your smartphone to give the most accurate readout.
Target Heart Rate Charts
So you've found a heart rate monitoring system that works for you. What number should you be looking for on the screen? First, it's important to note that heart rate monitoring isn't an appropriate way to measure exercise intensity for everybody. Certain medications and medical conditions can skew the results.
If you're not sure whether this warning applies to you, talk to your doctor before tracking your exercise intensity via heart rate. If you're under a medical provider's care for any medical condition, they'll give you specific guidelines about what you can and can't do for exercise, and how best to measure your workout intensity.
However, most healthy adults have a couple ways to determine what sort of heart rate they should be aiming for, and the simplest is to consult a chart that offers estimates for maximum heart rate and target heart rate zone according to your age. The American Heart Association offers a useful one.
The term "maximum heart rate" is a little misleading, because this isn't the number you want to aim for in an intense workout. Instead, most people should aim for a number within the "target heart rate zone," which the AHA defines as 50 to 85 percent of your maximum heart rate. They further subdivide that range into two intensity levels of roughly 50 to 70 percent of your maximum heart rate for moderate intensity, and 70 to 85 percent for vigorous intensity.
Your other option for calculating a target heart rate zone is to use a more complicated mathematical formula. The American Council on Exercise provides an excellent breakdown on several formulas that give you more nuanced heart rate estimates than those used in the recent past. Once you have a target heart rate range to aim for, you can monitor your heart rate using your method of choice and then adjust your exercise intensity as needed to keep yourself within the target range.
But Seriously, What's My Target?
If you're still not sure how much time you should be spending in a moderate-intensity heart rate zone, a vigorous-intensity heart rate zone, or perhaps even the mythical doughnut-eating heart rate zone, don't worry: Every five years, the Department of Health and Human Services issues a set of physical activity guidelines for Americans. Although the nuances of some definitions have changed over the years, the recommendation for how much cardio you should do to maintain optimal health, and at what intensity, remains steady:
- At least 150 minutes of moderate-intensity aerobic activity every week; or
- At least 75 minutes of vigorous-intensity aerobic activity every week
If you can double those amounts — making it 300 minutes of moderate cardio every week, 150 minutes of vigorous cardio or some combination of the two — you'll get even more benefits. And of course you can always do more, as long as you're not working yourself out to the point of overtraining.
- American Council on Exercise: "Advances in Aerobic Training: How to Apply the New Heart Rate Formulas"
- American Heart Association: "Know Your Target Heart Rates for Exercise, Losing Weight and Health"
- University of New Mexico: "Fat Facts"
- Harvard Health Publishing: "Feel the Beat of Heart Rate Training"
- Health.gov: "Physical Activity Guidelines for Americans"