Heart-rate zones are one the best-known yet least understood aspects of exercise. We’ve all encountered them at some point. And in that, you’ve probably noticed inconsistency around names, number of zones and overall information. What you may not know is that there is no governing body of heart-rate zones. Some folks swear there are three zones, some five and others seven. Others argue it’s based on sport — for example, runners get five zones and cyclists get seven. However, there is one heart-rate zone that pretty much everyone knows, especially those of us who frequent the cardio machines at the gym: the fat-burn zone.
What’s not to like about the fat-burn zone? The name alone makes it sound like the ultimate weight-loss hack. And as far as intensity goes, the fat-burn zone falls relatively low on the toughness scale, meaning it’s an easy zone for most of us to hit. Even better news for those of us looking to burn a little belly fat, right?
Unfortunately, that’s not quite how weight loss and fat burning work. To better understand the misconception of the fat-burn zone, we have to look closer at the relationship between body fat and exercise.
To understand how to burn that annoying tummy fat, you must first understand there is more than one type of fat. Among others, there are subcutaneous fat stored under the skin (Think: pesky tummy fat) as well as intramuscular fat stored inside of muscles (Think: marbling in a nice cut of steak). Fat stored under the skin functions as insulation and provides cushioning when we fall (seriously!), but it can build up in excess. Meanwhile, fat stored inside muscle is used for energy. Thus, these two types of fat are used in very different ways.
Unfortunately when it comes to the fat-burn zone, you primarily rely on the fat stored in the muscles, especially for workouts lasting less than one hour. So in reality, that cardio session you thought was melting away those annoying love handles really wasn’t.
Does that mean working out is a waste of time? Certainly not, since exercise burns calories, the driving force behind weight loss. The fat-burn zone may not target belly fat explicitly, but the reality is none of the zones do. So what do we do to get rid of excess fat?
Exercising for fat loss — whether on your belly, back, arms or butt — involves a lot of factors; one of those is burning the optimal amount of calories with each exercise session, not some singular or magical combination of heart-rate zones. A rough rule of thumb is this: The harder you work out, the more calories you burn. For example, a low-intensity 30-minute workout will burn fewer calories than a high-intensity 30-minute workout. Since we all have a finite amount of time we can devote to exercise, in theory we should aim for the hardest zone we can manage every time we exercise. However, this isn’t the best practical approach because working out as hard as possible every day of the week makes us more likely to burn out or get hurt — both of which will work against us in the long run.
A better way to exercise for weight loss is to alternate high-intensity workouts (a 4 or 5 out of 5 on the toughness scale) with more moderate ones (a 2 or 3 out of 5). With this approach, your strategy should be to burn as many calories as possible for the type of workout you’re going for during that exercise period.
At this point you may be asking yourself why we even call it the fat-burn zone if the goal of weight loss (burning fat) is really about calorie burn? Well, because technically you are burning more fat than other fuel sources, like sugar, in the fat-burn zone. It’s just not the type of fat most of us envision melting off.
Muscle moves by burning fuel, primarily derived from fat or sugar. Think of these two as a balancing scale. At low exercise intensity, the scale is heavily weighted toward fat, while at high intensity, the scale is heavily weighted toward sugar. There’s a lot more to the story, but, in short, there is only a finite amount of sugar available for energy in your body. As a result, if you’re doing a very long event, you want to exercise at an intensity that maximizes the balance between fat burn and sugar burn. That, in turn, is typically the fat-burn zone.
You know the saying — if something seems too good to be true, it usually is. The fat-burn zone gets a lot of hype but often for the wrong reasons. Thus, it is not the life hack we all wish it were. Keep these three points in mind the next time you hit the gym for a cardio workout:
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