More calories burned in "fat burning" zone?

smcgrath45

I have a FitBit Alta HR and I guess it uses my heart rate to calc my calories burned (not 100% sure how it works). I've noticed the last two times I took spinning, my time in the "Fat Burning" zone was a lot higher than the two times prior to that, where most of the time was in cardio and peak. As a result, Fitbit gave me 714 calories for the 45 minutes in the Fat zone versus 314 in the non-fat burning zone. That is pretty significant, 400 calorie swing. Logically it does not make sense that my lower heart rate = more calories burned. I thought people burned a lot of calories with high intense workouts.

I know not to track these thing religiously but I'd like to know how to focus my workouts and how to create a calorie deficit. I start with only 1200 calories so I really need the exercise calories.

lynn_glenmont

Ignore the fat_burning zone for purposes of losing fat. It's your overall calorie-deficit that matters. If you deplete glycogen stores while you're inspin class, you'll be burning more fat when your out of class. Why would you care when you're burning the fat, as long as you are?

And if you're only consuming 1200 calories, you've already created a deficit unless you're a very small person who's confined to bed all day.

smcgrath45

Well, it seems my heart rate zones control the amount of calories it says I burn in class. The higher my zones, the less calories I "earn". And no, it is difficult to only eat 1,200 calories. I am not tiny. I'm 5'10 but I'm 45 and that is what it says to eat to create a deficit. I guess that is why everyone packs on pounds as they age.

AnnPT77

No, we don't burn fewer calories at a higher heart rate. In reality, the work we do is the main determiner of how many calories we burn. The heart rate isn't a measurement of calorie burn; instead, it's a proxy that can be used to (imperfectly) estimate calorie burn.

In general, we burn more total calories doing X minutes of a specific exercise at a higher intensity than doing that same exercise for the same X minutes at a lower intensity, assuming we're at the same fitness level (and environmental temperature, and hydration, and a bunch of other minor stuff). The reason we're burning more calories in the higher intensity case is that we do more of the activity in the same amount of time.

Look at an example: Calories from walking a basically level route can be estimated based on one's body weight and the distance. Walking a mile in 20 minutes (3mph) and walking the same mile in 30 minutes (2mph) will burn very close to the same number of calories. But walking for half an hour at 3mph burns more calories than walking for half an hour at 2mph, because we've covered more distance (a mile and a half, instead of just a mile). Other exercises are loosely similar - same amount of time, higher intensity means more calories burned. Typically, walking at 3mph will also result in a higher HR than walking at 2mph.

The fat burning zone is more about what fuel mix your body is using in the moment, a matter that is of potential concern to endurance athletes, but for those of us simply trying to lose weight and get fitter, fuel mix isn't that important. Total calorie burn is. If we're in a calorie deficit over the course of time, then the deficit will eventually be made up, mostly by burning stored fat. The stored fat may be burned during the exercise, or it may be burned later - doesn't matter for weight loss.

That implies that the best exercise and best intensity is accomplished by allocating how much time we can spend on exercise (while still achieving good overall life balance), then exercising at a challenging but not exhausting intensity we can sustain for that amount of time . . . without becoming so fatigued that we drag through the rest of our day, sapping calorie burn from our daily activity and wiping out some of the exercise benefit.

I can't explain why your FitBit is telling you what it is; perhaps someone who uses one will have a theory. I use a Polar HRM when exercising, mainly for training purposes, and take its calorie estimates with a grain of salt, . . . or maybe several tablespoons of salt.


Edited: Had typed "lower" where I meant "higher"!

AnnPT77

smcgrath45 wrote: »

Well, it seems my heart rate zones control the amount of calories it says I burn in class. The higher my zones, the less calories I "earn". And no, it is difficult to only eat 1,200 calories. I am not tiny. I'm 5'10 but I'm 45 and that is what it says to eat to create a deficit. I guess that is why everyone packs on pounds as they age.

I think the estimate is incorrect. An intense spin class of the same length will burn more calories than a less intense spin class of the same length.

The calorie goal MFP gives you is a result of your personal characteristics you put in your profile (weight, age, daily-life activity level, etc.) and your chosen target weight loss rate. Many people automatically select 2 pounds a week as a weight loss goal . . . but that can be risky healthwise for someone who's less than 200 pounds or within around 50 pounds of goal weight. If 1200 is too hard, it's always an option to lose weight more slowly, and it can be a less risky option.

When I started losing (age 59, 5'5", 183 pounds), MFP gave me 1200, too, and it was too low. I lost weight too fast - faster than 2 pounds a week, even, for a brief time, even though based on my estimated TDEE 1200 should've resulted in more like a pound a week - and got weak and fatigued. It took weeks to recover, even though I adjusted as soon as I realized I was losing faster than I should've.

mmapags

For whatever reason, you are getting wonky data from your Fitbit. A few thoughts:
Zones are completely irrelevant for fat loss.
Fuel substrate is completely irrelevant for fat loss.
Calorie deficit is of primary relevance for fat loss.
Getting a 100% accurate estimate of calorie burns is impossible.
Tracking your own data over a couple of months with averaged actual results will be more accurate than your Fitbit. It is just giving an average based on your stats. And it doesn't seem to be capturing your data correctly.

Ann is right, your goal is too aggressive at 1200 calories at 5'10". I'm guessing your have your goal set at 2 or 2.5 lbs per week? I'm a little shorter than you and maintain on 2500 roughly and lose on 2000 at around 1lb per week. You need to be more realistic about your deficit. It is too high at 1200 and 5'10".

New_Heavens_Earth

I find that my Fitbit Charge 2 actually stops recording during periods of high intensity activity, resulting in less calories recorded and therefore looking like a lower calorie burn. This happens during interval training like sprints and Spinning.

It stops recording my heartrate by bottoming out then slowly rising to the level I'm actually working at. It'll look like a huge valley on your calorie and heartrate graph. So you could still be burning a large amount of calories in your cardio or peak zone, it's just not being recorded.

Duck_Puddle

It sounds like something is way off on the one activity where your Fitbit says 714 calories. Are the start and stop times correct? Does the HR chart look normal (no gaps or random time extensions as mentioned above)? Did you edit the activity after it was done? Those are things that have occasionally caused my Fitbit activities to be a little (or a lot) off.

Burning 714 calories in 45 minutes is well...extremely unlikely. I would consider this activity to be some kind of an anomaly/malfunction.

310 seems very reasonable. I think those are the activities that should be viewed as accurate (or as close as we’ll get outside of a lab or power-meter type measurements-which you might get on a spin bike).

I think it’s that the activity in the “fat burning” zone has something very wonky going on.

Sorry-just read that it’s 2 activities with the higher burn and 2 with the lower. So check both of your activities with the higher burn. There’s something funky with those.

And I’m seconding (or 3rding) everything that @AnnPT77 said. I’m just offering some possible ways those Fitbit activities got screwy. My Fitbit records calorie burn as you would expect (higher at higher intensity, lower at lower intensity). If yours continues to record abnormally high burns at lower intensity, I would reach out to fitbit support. It shouldn’t be doing that.

TavistockToad

smcgrath45 wrote: »

I know not to track these thing religiously but I'd like to know how to focus my workouts and how to create a calorie deficit. I start with only 1200 calories so I really need the exercise calories.

1200 includes the deficit already

snemberton

Ii

smcgrath45

Thanks everyone. I did a class today at the gym and Fitbit said I burned 236 extra calories in the hour. It was boxing and TRX, not overly cardio, so I guess the more cardio, the more calories you "earn". I probably should not follow the calories that Fitbit gives me, just pick a number and stick to it for calories each day. The 1,200 does include the 500 deficit, that is to lose 2 lbs a week. I honestly cannot eat that little, I guess I could.......but life would be pretty unpleasant. I'll go for 1,500, even that is difficult to be honest. But I guess that is why we are all here.

mmapags

smcgrath45 wrote: »

Thanks everyone. I did a class today at the gym and Fitbit said I burned 236 extra calories in the hour. It was boxing and TRX, not overly cardio, so I guess the more cardio, the more calories you "earn". I probably should not follow the calories that Fitbit gives me, just pick a number and stick to it for calories each day. The 1,200 does include the 500 deficit, that is to lose 2 lbs a week. I honestly cannot eat that little, I guess I could.......but life would be pretty unpleasant. I'll go for 1,500, even that is difficult to be honest. But I guess that is why we are all here.

How much do you have to lose?

middlehaitch

It is a 1000 deficit to lose 2 lbs a week. You may do better setting yourself to 1lbs a week loss.
How much do you want to lose, and what is your weight now, and goal weight?

Cheers, h.

DancingMoosie

...and you are supposed to eat your exercise calories back since mfp has already created the deficit. 300 seems like a good # to start with for the spinning, a little less for the boxing/trx class. Try 1450 maybe and see how you feel?