The "After Burn" Effect...

debunking HIIT cardio claims

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Moving on...

I spend a significant amount of time on various pieces of cardio equipment in an attempt to fight the cascade of body fat associated with beer and a lackluster diet. 

As a nerd with a degree in nutrition, I'm no stranger to the science behind the process of burning fat, and all of our fat burning efforts should be based in science.

Joe Rogan might tell you to eat a raw caribou every day harvested via rear naked choke, but you should question such recommendations... despite his abs.  

(By the way, if you actually read this newsletter, you might want to click on a link occasionally so that my robots don't eventually remove you due to click-related inactivity.  They are unfortunately aggressive robots.)

It has long been speculated that HIIT (high intensity interval training) is a 'more effective' way to burn fat than traditional steady-state cardio, because of something called "The After-burn Effect... in which your body theoretically continues to burn more calories after the exercise is over. 

So, instead of suffering on a hamster wheel for 40 painful minutes, you could bang out a bunch of sprints, separated by light cardio, and in 15 minutes get the same benefit! 

What a time saver! 

Unfortunately, the "After-Burn Effect" is dramatically overstated (if it even exists at all), which was brought to my attention by a decent article on HIIT training in general.

The article references a study which found that regular old steady state cardio will contribute to an 'after-burn' of an additional 7% more calories after your workout is over... so, if you burn 100 calories during your regular old cardiovascular exercise (not HIIT), you can expect to burn 107 calories total.

The HIIT group in the study was found to have a caloric 'after-'burn of 14%... so if 100 calories were burned during the workout, 14 additional calories would be burned afterwords, for a total of 114 calories. 

A 7% difference in the caloric "After Burn" effect will not have a significant effect on weight loss... and I actually found another study which showed NO difference in the 'after burn' effect between the two groups.

I was not able to find ANY data that supported the claim that HIIT caused a significant amount of calorie burn after the exercise was over. 

And that's not all...

Another drawback of HIIT cardio for 'fat burning' is that it burns more muscle glycogen than it burns fat!

As you shift to an anaerobic state (after burning off all available oxygen and becoming 'out of breath'), your body taps into stored glucose to use as energy... not fat. 

Here's one of many studies on that fact.

So, in addition to not burning more fat AFTER the workout, you're burning less fat DURING the workout... because your body doesn't burn fat effectively when you run out of oxygen.  

So there are two notable takeaways here:

1.  If your goal is to burn fat, your focus should be on the amount of calories that you burn DURING your workout, not afterwards. 

2.  During HIIT training, your body is going to burn more muscle glycogen than fat... making aerobic training a  better option for fat loss in general.

This does not take into consideration MUSCLE GROWTH, or the other benefits of HIIT cardio.  

This is purely for the management of pudge.  

So for those of us who are training in a perpetual effort to shrink our guts, our time is best spent exercising for 40 gentle minutes (bored out of our minds), and doing so consistently.  

Or we could give up the beer and pizza. 

The choice is yours. 

Have a fantastic week!


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