Growing up you probably saw those burn fat heart rate zone charts plastered to the gymnasium walls at your school. Are these burn fat heart rate zone charts even accurate? Let’s discuss.
What’s the Best Heart Rate Zone for Burning Fat?
According to these burn fat heart rate zone charts it would appear working out at about 60-70% of your maximum rate is optimal for burning fat. Is it?
Max Heart Rate
First, what is max heart rate? Max heart rate is the maximum beats per minute your heart can sustain. As you age, your maximum heart rate decreases. A common rule of thumb for calculating your max heart rate is starting with the number 220 and subtracting your age. For example a 20 year old would have a max heart rate of 200 (220-20), and a 30 year old would have a max heart rate of 190 (220-30).
For example, If you’re a 20 year-old with a maximum heart rate of 200, 60-70% of your maximum heart rate would be about 120-140 beats per minute.
Does it seem like a heart rate of 120 bpm would cause more fat loss than say, a heart rate of 180 bpm? Let dive deeper.
HIIT vs. Steady State Cardio
The answer to the question in the previous paragraph is a little bit tricky. You see, the 60-70% max heart rate zone burns the highest percentage of fat when compared to the amount of glycogen burned. But this doesn’t necessarily mean the most fat calories are burned at that heart rate zone.
A more intense cardio workout at the 80-90% max heart rate zone will burn more calories because the body is doing more work. However, a lower percentage of fat calories are burned at this heart rate zone when compared to the amount of glycogen calories burned.
To summarize, workouts above the 70% max heart rate zone will burn more total calories from fat and calories from glycogen than a workout that is in the 60-70% max heart rate zone. Conversely, workouts within the 60-70% max heart rate zone will burn a smaller amount of calories from fat, but will burn a higher percentage of fat calories compared to calories burned from glycogen.
So there you have it, the more intense the workout the more fat calories are burned. However, maintaining high intensity workout days isn’t so easy. The more intense you workout, the less time you can stay at that intensity. The lower the intensity of the workout, the longer the duration you can sustain. Therefore, there are trade offs between HIIT and steady state cardio.
The Best Way to Burn Fat
It is generally accepted by the fitness community that HIIT workouts are one of the best ways to burn fat But, is this belief true?
According to one study, men who participated in a 20 minute HIIT cycling session achieved as much energy expenditure as a 50 minute steady-state cycling workout.
There you have it. This study shows that HIIT can be a more efficient method to burn calories when considering the amount of time spent performing the workout.
One of the reasons why HIIT is thought to burn so many calories is due to a phenomenon called EPOC. EPOC is an acronym for excess post-exercise oxygen consumption. Basically, during an intense workout, your metabolism raises. The interesting thing about EPOC is even after you have completed the workout, your metabolism still remains elevated for a period of time. The prolonged rise in metabolism is helps to burn more calories.
Is EPOC a Myth?
Some more recent studies show that the EPOC effect might not be as effective as once thought. For example this study found that resting metabolic rate didn’t change significantly after performing interval training.
I looked at the study myself and did notice that participants only completed 4 intervals of 30 seconds max effort sprints on a spin bike separated with a 4 minute break.
Not only is 4 a small amount of intervals, but a 4 minute break between sets is extremely long. Most HIIT protocols call for a 1:1 work to rest ratio or 1:2 at the most. A Tabata HIIT circuit has a 2:1 work to rest ratio and consists of 8 rounds total. Compare that to this study that had a very low work to rest ratio of 1:8.
In addition, a meta-analysis crunched the data of 28 studies that tried to discern whether HIIT or steady state cardio was better. The result: there was no significant difference in fat loss between either.
Which is Better
In my opinion I do believe HIIT is a more efficient way of doing cardio. As referenced previously, one study showed 20 minutes of HIIT was equivalent to 50 minutes of steady state cardio.
When push comes to shove, as long as you are getting some high intensity efforts in your cardio sessions, you should see good recents