All of the cardio machines are lying to you. There’s probably some workout on the elliptical that promises to keep you in the “fat burning zone,” and a chart on the treadmill informing you that the zone exists when your heart is beating at a certain rate. Forget it. The fat burning zone is a myth.
Those machines will tell you the zone exists somewhere in the range of 50 to 75 per cent of your maximum heart rate (which it is probably miscalculating anyway). There is nothing special about exercising in this zone, and it certainly won’t make your body burn more fat than exercising any other way.
Fat loss doesn’t depend on your heart rate during exercise
If you’re trying to lose weight, the first factor to look at is how much you’re eating. It should be less than the total calories you end up burning in a day.
But can’t you burn more calories by exercising? Sure. The longer you exercise, the more you burn; the harder you exercise, the more you burn. It’s up to you how you’d like to plan your workouts. An hour’s walk burns about the same calories as a half-hour run.
We burn fat all the time
Your body doesn’t hang on to fat for a rainy day. It’s burning fat all the time, including right now while you’re reading this on the toilet and not exercising at all.
Fat burning is efficient, but it supplies slow and steady energy. If you need to work really hard, really fast (think: a tiger bursts into the bathroom and you have to run) you’ll use other energy sources, including some of the sugar that your muscles store for exactly this reason. Fat is still getting burned in the background, but it’s not the major energy source for this, say, 60 seconds of run-screaming-from-a-tiger effort.
If you’re on a cardio machine at the gym, your body is using a mix of the two fuels: the baseline amount of fat burning has maybe ramped up a little bit, but a good bit of your energy comes from burning other fuels, including that stored sugar called glycogen. (I’m simplifying a lot; here’s a slightly more detailed version if you’d like to geek out.)
Bottom line, we are always burning fat, and sometimes we burn other fuels too.
So why is it called the fat burning zone??
This supposed zone exists at a level that feels easyish — a brisk walk, a light jog, a pace on the elliptical or bike that you feel you could keep up indefinitely. If you’re new to exercise, this is meant to reassure you. You can work out nice and easy, and you’ll still be burning calories.
Here’s the grain of truth: The harder you exercise, the more your body needs those other fuels, like glycogen. So percentage-wise, you’re burning a higher proportion of fat in the fat burning zone. But that’s just because you’re burning fewer calories total.
The real fat burning zone, where we burn the greatest percentage of calories from fat, is the one where we’re not working at all. So, loafing on the couch. Or sleeping.
What is the right zone to exercise in?
Honestly? Whatever strikes the right balance of enjoyment and work, according to your goals and your preferences. Think of the zone labelled “fat burning” as the easy exercise zone, and the zones above that as representing medium and hard exercise.
Exercise in the “fat burning zone” if:
You want a light workout
You’re new to exercise and the idea of a hard workout sounds scary
You’re pacing yourself so you can do a very long workout
Exercise in a higher zone if:
You feel like working hard
You want to get your workout over with as fast as possible
You want to burn more calories in the same time
If you want to improve your overall fitness, spend time in all the zones: some easy cardio, some medium, and some intervals that dip into the highest effort levels. There’s no one single best way to exercise.