Why are calories used similar for light and strenuous exercise?

[NineToTheSky]

When I go for a 30 minute stroll (and I do mean stroll - my heart doesn't go over 100bpm), Fitbit says I have used over 300 calories. When I do 30 minutes on an exercise bike, with my heart rate at my maximum of over 150bpm for the whole time, it records 370-380 calories consumed. Surely that can't be right? (And both results are consistent on many occasions.)

[emili]

Hi Nine. It depends which fitbit you have. I have the HR which monitors my heart rate in real time. I set it to excercise mode (stop watch) so I know exactly how many calories I burned for that iterval. Otherwise, entering your activity manually in the excercise trackering part will give you a more accurate guesstimate on what you are actually burning. Hope this was helpful- happy to help if you have more questions.

[Heybales]

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@NineToTheSky wrote:

When I go for a 30 minute stroll (and I do mean stroll - my heart doesn't go over 100bpm), Fitbit says I have used over 300 calories. When I do 30 minutes on an exercise bike, with my heart rate at my maximum of over 150bpm for the whole time, it records 370-380 calories consumed. Surely that can't be right? (And both results are consistent on many occasions.)

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Dittos to above - need what Fitbit you are using to give useful answer.

I'd say the calorie burn for the walk actually sounds rather high at 10 cal/min for just a walk.

If you have idea of accurate distance (and don't assume the Fitbit is correct, that could be the issue), then take your stats here and confirm it's close for calories and distance.

Use the Gross option since that's what Fitbit is reporting.

http://www.exrx.net/Calculators/WalkRunMETs.html

If you need accurate distance - www.mappedometer.com

If using non-HR model - the bike is badly underestimated.

Oh, your maximum HR is no where near 150 if you are going over it the whole time.

Definition of HRmax is not what you can sustain - but what you can barely reach for a few seconds before your muscles give up.

[NineToTheSky]

Thanks for your replies. I have the Charge HR. I thought your maximum heart rate is 220 minus your age. I am 64, so that makes my maximum heart rate 156. Is this not correct?

[Heybales]

Thanks for your replies. I have the Charge HR. I thought your maximum heart rate is 220 minus your age. I am 64, so that makes my maximum heart rate 156. Is this not correct?

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No, that is not correct. That is a huge rough way to estimate your HRmax. Doesn't mean it's fact.

You have better odds of being more than 10 bpm away from that figure than being within 10 bpm. Huge bell curve you might say.

Most people unless doing specific training, could hold about 85% of the HRmax for sustained period of time - with great difficulty. May 20 min. If you were dying at the end of 20 min, then you might have been about 85% of HRmax. Otherwise, probably 75-80%.

Mine should be 173 by formula. Tested it's 194.

Just genetics, only thing fitness does it keep it from lowering as fast with age it seems.

Some have motorcycle heart, some have diesel heart.

Yours is sounding like motorbike. It can rev high.

Now, that bad estimate on the top end will negatively effect calorie burn calculation. But at least it appears Fitbit uses the resting HR for lower end and that is measured, so not totally off.

If Fitbit was smart - they'd do some estimates of HRmax beyond that standard formula based on length of workout. Would at least improve things.

[emili]

The older you are the lower your starting number would be for calculating mhr. 208 seems to be the magic number for your age group. This would put you around 144. This means at your highest intensity you would be at 144 - which depending on your cardio fit may be higher or lower. This is also the number that you sustain the shortest period of time- this is the number that puts you in that exhausted can't take another step mode. The best thing to do is to reach your almost ready to drop place and see what your HR is on your fitbit. Plus or minus a few beats- you should have a pretty good idea where you fall. I would also try the stop watch feature- it will give you some really good data.

[NineToTheSky]

I do use my Fitbit in stopwatch mode. I have looked back on my logs, and I sustain 140-145 over a period of time, and I have peaked at 150-152 for brief periods.

When I go to the gym tomorrow I will focus on this. But I still don't understand why Fitbit shows such similar calorie expenditure.

[Heybales]

Reread what I wrote above - you need to do some testing.

Several reasons to cause that effect. You just need to figure out which one.