The faster I run, the fewer calories I burn?

[jarmenia]

I'm not sure where the best place to put this is so please feel free to move it if necessary.

I've noticed that days I run slower, my Fitbit indicates I burned more calories running than on days when I run at a faster pace despite the same total distance both days.  This is counterintuitive to me.  The only way I can make sense of this is that the calories burned during exercise also include calories burned because of my BMR and therefore working out longer burns more overall calories.   

[USAF-Larry]

@jarmenia, on the Exercise Details, what does it show for "cals/min" for the different exercises? Since the time is different for each run, as well as the number of steps counted, the cals/min is important number to determine the total calories burned.

[MrMarv · Accepted solution]

@jarmenia - 

In addition to what @USAF-Larry said which is totally true, make note of the minutes in each heart rate zone if your tracker supports heart rate monitoring to possibly help mitigate the difference you are seeing.

Plus I suspect I can calculate your calories burned per minute, or at least come pretty close.

While I am not currently running, I am currently spending a fair amount of time on the treadmill. Depending on the time of day and whether I start out tired or not, my time in the different heart rate zones are sometimes loaded towards cardio on the shorter walks than the longer ones. Heck, maybe phase of the moon makes a difference, I don't know; I just know it is a fact. Anyway the more time in cardio, as a percentage during the exercise period, more calories per minute burned for the exercise. Another reason for @USAF-Larry's question.

If you don't already know this, the fat zone is called that because more fat, as apposed to stored carbs are burnt in that zone. In the cardio zone, a little more fat is burned but a lot more stored carbs than in the lower zone, therefore a larger number of total calories.

Speaking of calories a minute, using your lap times:

16.84 calories a minute for the top exercise 

17.22 calories a minute for the bottom exercise

A difference of only .38 calories a minute. Easily explainable if your device has a heart rate monitor.

Also, if I am remembering clearly back 40 years ago when I was a young Marine, my faster times were when I was able to easily stretch out my stride and I actually felt less strain and recovered easier afterwords. I had some of my best runs during Physical Fitness Tests when I actually felt like I wasn't running hard at all. And I'm sure that with the ease at which I ran and a lesser heart rate, I burned fewer calories per minute.

******** edit ********

Re-reading my post after pressing "Post" I had a "Duh" moment.

Just like me - your faster times had you stretching out your stride; 5,268 for the first run and 4,811 on the second run a difference of 457 steps or 91 steps a mile. Less physical effort to run the same distance equals a little less calories burned.

********* end edit *********

BTW, BMR is included in each individual calories per minute, so while it may add about 4 to 5 calories to the longer period run's totals, it isn't that much of a factor as far as the totals go and noting for the average per minute.

Just my thoughts.