Curious about calories burned at different fitness levels

Jwildeboer

I'm curious about something. I figured I'd give some background first, before asking my question.

I've been running pretty much all my life. It used to be shorter distances like a mile or two. If I kept consistent, I'd get to 3 miles. It was always at a slower pace, over 10 minute miles. sometimes slightly under 10 if I were to be running consistently enough. If I took an extended period of running off, i would obviously do a slower pace and shorter distance. I was able to lose weight with this pace. It was enough to get my heart going and since I was waaaay overweight, it was a good pace for me.

Fast forward to the past couple years and a loss of around 30 lbs. I've been running and training to get my time down. I joined the running team of the company I started working for in 2011 and while I did not initially enjoy the thought of running a 5k, I got instantly hooked when I did it. I had a time of 30:59. I've really got into the competition of it after that, and now I'm running in the lower 20's, my PR being a 22:20. Over the winter, I've been training on the treadmill training to get under 20 some time this summer. I can do a 5k on the treadmill in 21 minutes if I'm really pushing it, which historically looking at my treadmill times vs real life times, I should be close to the 20 minute mark if I were to run in a 5k.

I will run outside 1 night a week, with the running group from work. I live in Michigan, we only run if it is at least 10 degrees outside, and it's usually right around that temperature. It's hard to run a pace like I do on the treadmill because of snow ice, and it's hard to breath in the cold. Our pace is right around the 9:30-10 minute mile, maybe a bit slower. We also talk during this time, and run for just over 4.5 miles, so that attributes to the slower pace, as well.

It seems as though I don't burn calories during the outdoor run. At least not as much as calculators will say. Now, I know these calculators are not accurate. I also know that weight isn't instantaneously lost when I weigh in the next day. However, I do weigh in every day knowing there will be fluctuation. When I have a run in on the treadmill, then weigh in the next day, I can see that the weight is lower than usual. I'm assuming that might be part water loss, but I am drinking a lot of water on those days to make up for that.

When I run outside, the next morning, I don't see that same type of change and I sometimes will actually see the weight is higher.

****MY QUESTION****

Is it possible that as I have my fitness level up to the fact that I do around 20-25 minutes of hard running on a treadmill several times a week means that running at a slower pace will not allow me to burn calories, even if doubling the time/distance?

Maybe the cold has to do with it, but I usually end up warming up as I'm wearing a hoodie, etc. Maybe it's the fact that my heart rate isn't as high as I'm running the slower pace?

What do you think? Am I still burning calories on these slower runs? Or are they not really worth much other than a good way to loosen up with a slower run?