What Is the Fat-Burning Zone and Why Should You Care?

What Is the Fat-Burning Zone and Why Should You Care?

It’s gym day. You step into the cardio room and climb onto your favorite treadmill. It’s time to burn big cals. But then, doubt kicks in. Do you pick the fat burn, cardio, or interval setting? Gotta make it count!

If you’ve been fooled by the fat-burning zone on your gym’s cardio machines, don’t feel bad. It’s one of those exercise myths that refuses to go away.

Exercising in the fat-burning zone has been discredited as an effective weight loss strategy by countless fitness magazines, experts, and the American College of Sports Medicine. Yet it’s still with us because it’s partly true.

Yes, the fat-burning zone is real, but it’s not quite helpful for losing significant amounts of fat. And you’re about to find out why.

What Is the “Fat-Burning Zone”?

Your body’s fat burning zone is the heart rate level at which it burns the most calories from fat relative to other forms of fuel. Treadmills, ellipticals, and step machines are common gym contraptions that offer settings like this one, which correspond with exercise intensity.

The fat burning zone setting seemingly takes the guesswork out of identifying the perfect workout intensity at which to achieve the greatest fat loss. Just push a button, keep pace, and be careful not to slip on all of that jettisoned fat as you step off the machine, right?

Wrong. The term and its corresponding setting are fatteningly misleading. To help understand why, let’s take a tour through the different heart rate zones.

The 5 Heart Rate Zones

There are five zones of heart rate activity, which correspond to exertion levels that range from scarcely moving to death by sprinting.

heart rate scale zones

Zone 1: 50-60% of max heart rate (MHR)

This zone governs very light activity. Talking in this zone is easy, with no meaningful increase in your breathing rate.

Zone 2: 60-70% of MHR

Light effort will bring you to this zone, wherein your heart starts to beat slightly faster. You can still talk comfortably, but your breathing becomes heavier.

This is the fat burn zone and, as you can see, there are still three zones remaining, making this an awfully nominal amount of effort when trying to get fat’s attention.

Zone 3: 70-80% of MHR

In this zone, you’re working at moderate effort. Your heart beats harder and faster and, while you can hold a conversation, it takes effort given how hard you’re breathing.

Zone 4: 80-90% of MHR

This is hard effort. You can no longer talk in much more than bursts, and once your heart rate goes above 85 percent of MHR, exercise becomes anaerobic. That’s an important factor in fat loss we’ll discuss later.

Zone 5: 90-100% of MHR

In this zone, you’re exerting maximum effort. Your heart and lungs are now working at full capacity, making talking an impossibility.

The Link Between Exercise Intensity and Fat Burn

Here’s where we tell you why the fat-burning zone exists.

Your body burns calories 24 hours a day regardless of whether you’re moving or not. But when you move — be it fidgeting at your desk, playing tag with your kids, or pounding the pavement in your section of town — you burn more calories, and the extent of that burn is directly related to the intensity of the activity.

Whether those calories come from fat or carbs (in the form of glucose) is also influenced by exercise intensity. Research shows that low intensity exercise, like walking or jogging, burns a larger proportion of fat as fuel (hence the “fat burning zone” on cardio machines). Moderate to high intensity exercise (e.g., running, sprint intervals, and circuit training) causes the body to shift primarily to glucose, which can be broken down to supply energy at a faster rate.

Here’s the catch: The fat-burning zone may help you burn a larger proportion of calories from fat as you work out, but high-intensity exercise keeps your metabolism elevated for longer after you finish. This phenomenon is called the afterburn effect, or excess post-exercise oxygen consumption (EPOC).

Think of it in terms of money. Would you rather have 90 percent of 10 dollars, or 20 percent of a hundred? Low-intensity exercise doesn’t ask much of your body, diminishing the significance of the fat burning heart rate zone’s disproportionate reliance on fat. Exercising at higher intensities burns less fat as a percentage of fuel expended, but it burns far more fat overall.

The afterburn effect explained

When you exercise, your body toggles between energy systems, the aerobic and anaerobic. Once you go anaerobic (85 percent or more of MHR), your body is no longer able to provide oxygen commensurate with the demands being placed on it. So it keeps making up for that deficit for up to 48 hours afterward, helping you burn more calories (and fat) overall during recovery.

That said, always listen to your body — pushing your physical limits won’t feel comfortable, but it shouldn’t be unbearably painful either.

Calculating Your Fat-Burning Heart Rate

Ever confessed your age to an exercise machine? Don’t lie when prompted — your age is used to calculate your fat burning heart rate. If you’re without the necessary gadgetry to determine your precise max heart rate, there’s a handy equation:

208-(0.7 x your age)

From here, you’ll be able to calculate your heart rate in all of the zones by simply multiplying the total from above by the corresponding percentage of MHR.

Fat burning zone chart

Age MHR Fat Burn HR
18-19 195 117-137
20-21 194 116-136
22 193 116-135
23 192 115-134
24-25 191 115-134
26 190 114-133
27 189 113-132
28-29 188 113-132
30 187 112-131
31-32 186 112-130
33 185 111-130
34-35 184 110-129
36 183 110-128
37 182 109-127
38-39 181 109-127
40 180 108-126
41-42 179 107-125
43 178 107-125
44-45 177 106-124
46 176 106-123
47 175 105-123
48-49 174 104-122
50 173 104-121
51-52 172 103-120
53 171 103-120
54-55 170 102-119

Workout Tips for Getting Into the (Real) Fat-Burning Zone

Next time you’re on a cardio kick, use these tips to get more more fat-burning benefits from your workouts.

1. Use the manual setting on workout machines

You can still use the zone settings on a treadmill or stationary bike as a guide, but don’t zone out after that. Assess how you feel during your workout. Is it too hard? Too easy? Manually change speed and elevation to challenge yourself. Hint: If you can carry a conversation while moving, bump up the intensity!

2. Include strength training

Steady-state cardio shouldn’t be your only strategy if you want to optimize fat loss. Indeed, strength training is an even more effective strategy in that regard, because it keeps your metabolism elevated for longer after you work out, helping you burn more calories overall.

And the benefits don’t stop there — especially if you’re a cardio junkie, as resistance training can help increase running speed, economy, and power output. What’s more, studies show that it can increase time to exhaustion and reduce your risk of injury. So try replacing at least one cardio session per week with strength training.

3. Try high-intensity interval training (HIIT)

HIIT is an exercise strategy in which you alternate periods of intense activity (heart rate zone 4) with less intense periods of rest. Circuit training, sprint drills, and stadium stair running are all examples of HIIT. The idea is that you repeatedly push your body to its limits, focusing on workout density and intensity rather than duration. Studies show that HIIT causes the greatest afterburn effect.

Although HIIT is the most effective form of exercise for losing weight, it’s not always the best choice for beginners. If you’re new to exercise, or are getting back into it after a long absence, save HIIT for when you’re built a solid fitness foundation. That way, you can optimize fat loss without increasing your risk of overtraining or injury.

Trinh Le

About

Trinh is a registered dietitian by day, blogger at Fearless Food by night. She loves helping folks develop a better relationship with food, which includes lots of cooking, eating and learning about nutrition. When she’s not snapping mouthwatering shots of (mostly) healthy food, you can find Trinh HIIT-ing it at her local gym. Follow her on Twitter.