HIIT Afterburn Pro advice if possible !!!

ItsOnlyHonest

So I have been doing HIIT / Tabata training for a couple of years now and I have always been curious about the amount of calories you burn in the afterburn phase. Depending on who you talk to the common consensus has been that afterburn can last up to 72 hours after your workout depending on age gender, weight and type of workout etc.

Some studies of late suggest that maximum calorie burn only lasts up to 3 hours after training.

Last evening, I did a simple test of my own and I was very surprised with the results. I did a HIIT workout and measured my calorie expenditure during and for a total of 4 hours after….see below

I was training on a watt bike pro using a wahoo heart rate monitor. Start time was 18:30 GMT end of afterburn monitoring was 23:00 GMT

I did a 5 minute warm up and a 20 minute HIIT consisting of 4 X 1:1 and 4 X 2:1 then a 5 minute cool down. 30 minutes in total with 17 minutes of HIIT.

My calorie burn on this ride was 395 calories in that half hour.

Afterburn Calorie expenditure

Hour 1 = 806 (+ 411 calories)
Hour 2 = 1079 (+ 273 calories)
Hour 3 = 1360 (+ 281 calories)
Hour 4 = 1608 (+ 248 calories)

So before I did this little test if you told me that a 20 minute HIIT would net me in excess of 1500 calories I would have certanly called you a doctor ...!

Note: During the 4 hour afterburn I was relaxing watching TV for the evening after a shower. HRM was left on at all times even during my post ride shower.

Penny for your thoughts ……….

cwolfman13

My thoughts are that your HRM isn't going to give you anything remotely accurate for epoc. All it's doing is measuring your heart rate. There is no direct correlation between HR and calorie expenditure. HR is used as a proxy for effort and thus oxygen consumption in algorithms used by a HRM in estimating calorie expenditure...these algorithms also assume a steady state cardiovascular event and become less accurate the further away you get from that type of activity. Calorie expenditure for just sitting around wearing a HRM is virtually meaningless...it's just not what the tool was designed for.

yirara

I agree with the wolfman above. An elevated hr has nothing to do with calorie burn here. When I hike for a few hours my HR remains elevated for hours thereafter. Not because of an afterburn effect but because of stress from hiking. It doesn't mean I burn more calories.
Btw, how did you determine the calories of your workout: also based on HR or based on wattage from the bike?

cwolfman13

yirara wrote: »

I agree with the wolfman above. An elevated hr has nothing to do with calorie burn here. When I hike for a few hours my HR remains elevated for hours thereafter. Not because of an afterburn effect but because of stress from hiking. It doesn't mean I burn more calories.
Btw, how did you determine the calories of your workout: also based on HR or based on wattage from the bike?

Also curious about this. My smart trainer is equipped with a power meter and I also wear a chest strap HRM to monitor my HR during training bouts (I don't typically use either outdoors)...my HRM religiously gives me about 130 calories more per hour than what my power meter indicates during a training ride. I would be shocked if a power meter was giving anyone 395 calories for 20-30 minutes of interval work where you'd be shuffling between high wattage work efforts and very low wattage rest. I did 40 minutes with four sets of over/unders (4 minutes per set) and then a 10 minute straight climbing effort to end and my power meter indicated that I burned around 280 calories in 50 minutes due to big efforts, but also easier efforts under threshold and rest periods of very easy efforts between sets. 395 seems like a lot, even if it was a steady effort for 20-30 minutes...I can't do the math right now, but that would seem like laying down some extraordinarily high wattage consistently for the duration.

NorthCascades

ItsOnlyHonest wrote: »

Penny for your thoughts ……….

How did you measure your off time calories? You need something like a metabolic ward to get an accurate number. Reading between the lines it sounds like maybe you wore a chest strap to count heart beats and let something else guess for you based on that?

ItsOnlyHonest

Nice one thank's for all your replies guys.

NorthCascades wrote: »

ItsOnlyHonest wrote: »

Penny for your thoughts ……….

How did you measure your off time calories? You need something like a metabolic ward to get an accurate number. Reading between the lines it sounds like maybe you wore a chest strap to count heart beats and let something else guess for you based on that?

cwolfman13 wrote: »

yirara wrote: »

I agree with the wolfman above. An elevated hr has nothing to do with calorie burn here. When I hike for a few hours my HR remains elevated for hours thereafter. Not because of an afterburn effect but because of stress from hiking. It doesn't mean I burn more calories.
Btw, how did you determine the calories of your workout: also based on HR or based on wattage from the bike?

Also curious about this.

yirara wrote: »

Btw, how did you determine the calories of your workout: also based on HR or based on wattage from the bike?

Ohh it is just the predictive calories from he HR wahoo app, I appreciate there is no accuracy here at all. This is why I’m putting these
questions out there to guys that know more than I on this. I want to gain a true understanding of what’s actually happening and what’s going on pre during and post my training sessions.

ItsOnlyHonest

cwolfman13 wrote: »

There is no direct correlation between HR and calorie expenditure.

You see this is where my understanding is a little hazey here I thought that higher HR = More calories burned not taking
oxygen deficiency into account.

Also yes I hear you in relation to stady state peaks and troughs.

Really good info guys thank you....

cwolfman13

ItsOnlyHonest wrote: »

cwolfman13 wrote: »

There is no direct correlation between HR and calorie expenditure.

You see this is where my understanding is a little hazey here I thought that higher HR = More calories burned not taking
oxygen deficiency into account.

Also yes I hear you in relation to stady state peaks and troughs.

Really good info guys thank you....

No, not really...or more precisely, not directly. Oxygen consumption is the best measure of change in metabolism during exercise, however, this is obviously not easily measured outside of a lab setting. As you begin to exercise, there is an exponential increase in oxygen consumption until a plateau or "steady state" has been reached. This happens relatively quickly with lower to moderate intensity exercise and can be sustained for a prolonged period of time. In this regard (and outside of a lab setting), HR serves as a reasonable proxy...basically, as your HR rises and then levels out...so does your oxygen consumption...not exactly tit for tat, but their is that proxy relationship and in the absence of a lab or being able to measure actual power (cycling) it is generally considered reasonable enough.

The problem is that HR can be influenced by many factors that don't necessarily represent power output and power output is ultimately going to determine oxygen consumption. Heat, humidity, fed or fasted exercise, higher or lower than average resting HR (high HR can be a big factor for people who are out of shape), etc can all influence HR during exercise and can muddy the waters...for example, HR is often elevated in hot conditions...but hot conditions aren't really leading to any kind of additional oxygen consumption (if anything it could lead to greater fatigue and less power generated), so there's really not any meaningful difference in energy expenditure than if you were in a more temperate environment...but your HR is likely to tell you otherwise. This is also one of the reasons a HR isn't really good for much besides measuring your beats when you're at rest or at very low level intensity activity.

Another issue is that if exercise is too intense, it can't be performed long enough for oxygen consumption to actually plateau and steady out, despite the fact that your HR may be through the roof...so in this case, HR becomes and invalid proxy.

One of the reasons that so many studies on calorie expenditure with exercise have been done with cycling is because you can quantifiably measure power with a power meter...and there is a direct correlation between power, oxygen consumption, and energy expenditure. Energy expenditure can be very accurately measured when you can quantify power output...unfortunately, you can't really use a power meter for running or walking or most exercises other than cycling.

In regards to epoc...it exists...but it doesn't really seems to be something that is mentioned a whole lot outside of marketing certain products and exercise programs. As someone who religiously does interval work and lifts, I'd say it's not quite what it's made out to be and I think trying to nail it down is somewhat of a fools errand.

sijomial

Have a read of this from Lyle McDonald - one of an interesting series debunking a lot of the claims about huge EPOC calorie burns,
He puts intense interval training at a more believeable 14% of the calories burned during the exercise session.

https://bodyrecomposition.com/research/epoc-after-exercise


Some oddities about the Wattbike......

It uses a highly accurate power meter for measuring your effort which normally should lead to very accurate and net calorie estimates ideal for use with MyFitnessPal.
BUT for reasons best known to themselves Wattbike choose to apply a frankly bizarre set of maths on your power produced which leads to exaggerated calorie burns. (Maybe they are trying to estimate gross cals, maybe it's just their marketing department getting in the way!)

To get accuracy do not use heartrate for calories which is simply awful for intense interval training, do not use Wattbike displayed calories either.
Take your average power per hour and multiply by 3.6.
e.g. 200watts for an hour is a very accurate 720 net calories.

As an example: Wattbike for a 20min session averaging 217w gave me 322 cals.
In reality it should be 260 net cals.

(I simply link my Garmin to the Wattbike's power meter and it does the correct maths for me.)

NorthCascades

ItsOnlyHonest wrote: »

Nice one thank's for all your replies guys.

NorthCascades wrote: »

ItsOnlyHonest wrote: »

Penny for your thoughts ……….

How did you measure your off time calories? You need something like a metabolic ward to get an accurate number. Reading between the lines it sounds like maybe you wore a chest strap to count heart beats and let something else guess for you based on that?

cwolfman13 wrote: »

yirara wrote: »

I agree with the wolfman above. An elevated hr has nothing to do with calorie burn here. When I hike for a few hours my HR remains elevated for hours thereafter. Not because of an afterburn effect but because of stress from hiking. It doesn't mean I burn more calories.
Btw, how did you determine the calories of your workout: also based on HR or based on wattage from the bike?

Also curious about this.

yirara wrote: »

Btw, how did you determine the calories of your workout: also based on HR or based on wattage from the bike?

Ohh it is just the predictive calories from he HR wahoo app, I appreciate there is no accuracy here at all. This is why I’m putting these
questions out there to guys that know more than I on this. I want to gain a true understanding of what’s actually happening and what’s going on pre during and post my training sessions.

I don't have access to Wahoo's code or anything, but my understanding is: when you use it and feed it HR data, it assumes you're doing some kind of exercise. It doesn't know what, but it assumes you're doing something, and hands out calories based on a generic average calorie burn for a generic activity. If you're sitting on the couch with a recovery drink and a tablet, you're burning a little over BMR. The afterburn effect adds to that, but not a whole lot.

AnnPT77

You might enjoy the article linked below: Very informative, a good basic intro to what you can expect from a heart rate monitor, realistically. (The info about specific devices is outdated because the article is old, but the fundamentals haven't changed.)

https://www.myfitnesspal.com/blog/Azdak/view?id=the-real-facts-about-hrms-and-calories-what-you-need-to-know-before-purchasing-an-hrm-or-using-one-21472

Also, I'm wondering how high your heart rate is staying for several hours after the half hour of exercise, to produce those numbers?

ninerbuff

EPOC is so over exaggerated. As a fitness professional in the business for over 30 years, most of what you hear is anecdotal information with little actual science to support it. Also MOST people DON'T actually do HIIT or Tabata the way the protocols are designed. True Tabata is ONLY 4 minutes long. Hardly anyone does 95%-100% intensity through it. And even with HIIT most people don't hit the 90% range.
As for HRM's, what is displayed isn't that accurate because it's only measuring heart rate. If you watched a scary movie, your heart rate increases. Hell if I could lose weight burning calories that way, it would be a breeze.
If you really want to get more accurate burning info, get hooked up to an indirect calorimeter and have it done.

A.C.E. Certified Personal and Group Fitness Trainer
IDEA Fitness member
Kickboxing Certified Instructor
Been in fitness for 30 years and have studied kinesiology and nutrition

heybales

sijomial wrote: »

Have a read of this from Lyle McDonald - one of an interesting series debunking a lot of the claims about huge EPOC calorie burns,
He puts intense interval training at a more believeable 14% of the calories burned during the exercise session.

https://bodyrecomposition.com/research/epoc-after-exercise

To add to the Lyle estimate - that's 14% of actual calorie burn - not the inflated calorie burn every HRM is going to show for intervals.
OP - for your length of time doing the intervals - the estimated 7% is probably more likely.

As mentioned, Tabata protocol is very specific, actually not even a give it all ya got level like HIIT normally is. But the shorter lack of recovery interval makes it feel harder.

Yep, not worth worrying about.

Better to be concerned about is eating enough carbs after 1 workout to allow the next to be just as beneficial. Though intervals like those every day isn't great idea either.