189: Facts About Fitness Trackers & Heart Rate Zones

Jun 9, 2016

I’ve been getting a lot of questions about calorie burn during workouts (as reported by cardio machines), wearable fitness trackers and the validity of target heart rate zones for fat burnings. So, of course, we’re diving into those topics today.

In today’s episode I’ll be diving into the myths & facts about fitness trackers, heart rate zones and the accuracy of calorie counters on your workout equipment.

While folks who are working out have awesome intentions, they’re often misguided based on inaccurate or incomplete information. If you are something who uses a fitness wearable, pays attention to the calorie burn on your workout equipment or monitors your heart rate, you do not want to miss this episode!

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Myths & Facts About Fitness Trackers, Heart Rate Zones and Calorie Burn During Workouts

Lots of people use the amount of calories they think they burned during a workout to help them determine how many calories they should consume that day. In most cases, that is highly inaccurate information.

First of all, that approach assumes that the calorie in/calorie out model is the most effective or accurate model for fat loss. It’s not. If you aren’t sure why it’s not, please go no further until you’ve listened to episode 062 of the Primal Potential podcast on why calorie counting is misleading.

Second of all, these calorie counting devices do not collect much of the relevant information that would allow for an accurate determination of calorie burn.

By knowing your pace on the machine and age/weight, you know a little, but not nearly enough to determine calories burned with a reasonable degree of accuracy. Among other things, they overlook:

  • fitness level
  • exertion
  • body composition
  • nutrition status
  • muscle glycogen availability

Even the fitness trackers which obtain more information than the random machine at the gym (these trackers tend to know your gender, age, weight, height, etc) have a high degree of inaccuracy, anywhere from 10-25% . While that might not seem like a lot, if you’re using these burn estimations to determine how much you should eat, being off by 10-25% can absolutely be the difference between significant fat loss and significant fat gain.

Another area of misunderstanding is around target heart rate zones. Don’t miss today’s episode for a full explanation of where these heart rate zones come from and how accurate they are.

In short, here’s the primary issue. These heart rate charts that suggest a particular range so that you’ll burn a higher percentage of fat, they’re based on percentages, not absolute numbers.

Here’s a brief example: let’s say these heart rate charts indicate that in a lower heart rate zone, 60% of the energy you burn during the activity will be fat while in a higher heart rate zone only 40% of energy you burn will be fat.

People see that information and think, “Oh! I want to be burning 60% fat so I’m gonna hit that zone.”

It begs the question: 60% of what??

Seriously. Let’s say, using arbitrary numbers, that in a 20 minute workout in this lower “fat burning” zone you burn 100 calories. 60% of that is supposedly fat, which means you burned 60 calories from fat.

But, if you were working out in a higher heart rate zone you might burn 300 calories in that same 20 minutes. While only 40% of the calories burned were from fat, you still burned far more fat! In fact, you burned 120 calories from fat – twice as much fat burned in the same time, even though the percentage was lower!

Beyond that, these target heart rate zones don’t take into account the “after burn”, or calories burned after the workout. There is little to no after burn with lower intensity workouts. Higher intensity workouts create a significant after burn which adds to the total fat burned during the workout.

For the other major considerations related to heart rate zones and fitness tracking devices, listen to the entire episode!


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074: CrossFit & Weight Loss

125: Fat Loss Basics Part 5

160: Fat To Fit Part 3 – Fitness

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