Fitbit versa 2 accuracy - same run, less calories

[Lkd891202]

Hi can anyone help please? 

Today I ran 3.04 miles at the fastest pace I have and burned 229 calories 

I ran the same 3.04 miles last week at a slower pace (approx 1.5 mins difference) and burned 290 calories. 

How can a faster run (by 1.5 mins only) burn significantly less calories than a slower run?? 

[JohnnyRow]

Fitbit provides you all the data to analyze this yourself.  Calorie burn is based on heart rate.  Look at the 2 exercise summaries heart rate charts and calories per minutes.

[Lkd891202]

Appreciate the response but there is not even difference to warrant a loss of 70 calories?! 

Infact I had more active zone minutes on my run today that burned less calories.... 

[Heybales]

What zone the HR is in has no bearing for calorie burn.

You can have more Zone minutes but average is different.

So what was really the avgHR for each run?

If it was elevated HR because of body trying to cool itself, inflated calorie burn. If you were dehydrated tad more, elevated HR and inflated calorie burn. If you had a bad stressful day, can have elevated HR.

When I say elevated, I mean above what would normally be needed for that level of effort. It's why formula for calorie burn has some caveats.

Also - are you still within the first 2 weeks of having the device, or first 2 weeks of starting up exercise again?

The calculations for calories from HR (it's not measured, it's formula) get to be a better estimate the longer it sees how many workouts you are doing and frequency. It may be it's honing in on better estimates now, or you are exercising more.

So the latter would be better estimate if avgHR is the same.

Or did your logged weight change?

That's in the formula too.

[shipo]

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@Lkd891202 wrote:

Hi can anyone help please? 

Today I ran 3.04 miles at the fastest pace I have and burned 229 calories 

I ran the same 3.04 miles last week at a slower pace (approx 1.5 mins difference) and burned 290 calories. 

How can a faster run (by 1.5 mins only) burn significantly less calories than a slower run?? 

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I have a few runs of just over three miles I do on a semi-regular basis, typically when I'm under the weather or recovering from an injury or something.  One of the runs is about 3.2 miles and is quite hilly (with about 300' of climbing), and another one which is pretty flat; both are primarily on dirt trails.

For the hilly run, I've done it quite slowly (about 41 minutes), most notably after getting my COVID-19 vaccine, and other times I've run it at a pretty good clip (about 35 minutes), typically when I'm pressed for time.  Looking at a sampling of five slow runs on the hilly course, I see an average calorie burn of about 550, however, on the faster hilly runs my average calorie burn in more like 465; yeah, a significant difference.  Then there is the flat course, I'm lucky to burn even 400 calories when I do that run.

[Baltoscott]

As others have said, bodyweight change and changes in average heart rate will affect the total calorie burn over a given course. And sometime changes reflect errors in heart rate readings or the length of the course detected by your GPS.  So to measure progress, pay attention to averages over several exercise sessions rather than looking at just two sessions. 

Also, in general, you get a higher calorie burn for slower runs over a set course simply because it takes longer when you run slower and your calorie burn includes your BMR (i.e, the daily calories needed to keep you alive -- pump blood, cellular repair, grow hair, digest food, fuel your brain so you can obsess over your calorie burn ;0) -- not just additional calories attributable to the exercise.