Huge reduction in calorie burn...

DavidRocketts

Hi all,

Returned to MFP a month ago with a goal to get fitter and lose about 30 pounds. Lost 5 in my first month and happy with that. My diet is 90% paleo (low carb no grains). Measuring exercise with a Polar HRM. Here's the thing: a month ago I was burning 150+ calories per mile walking. Today that has dropped to 90. I walk about 5 miles a day (not difficult as a dog owner). Does anyone know the biological science behind such a change in calories expended through exercise..?

Thanks, David

wendsg

The calculation has likely changed because you are physically moving less mass around, which takes less energy (calories). That's the explanation I have for it; dunno if it's right, but this is how my brain logics it out. :P

Cylphin60

wendsg wrote: »

The calculation has likely changed because you are physically moving less mass around, which takes less energy (calories). That's the explanation I have for it; dunno if it's right, but this is how my brain logics it out. :P

Same here. Moving less mass requires less energy.

I don't know that would account for a difference like the OP is showing, but it's all I got lol.

CyberTone

A five pound change in weight in itself should not cause that much of a difference. The more likely explanation is a change in the algorithms used by the activity tracker (Polar). Did you recently have a birthday? Many trackers use different age ranges to apply slightly different algorithms. Another possibility is that Polar recently updated their algorithms based on data collected from all of their users and tightened up the estimates provided by their trackers. Who knows?

Edited to add: MFP recently updated their algorithms for iOS users in the last update; that could also be a contributing factor if you use iOS.

ninerbuff

Metabolic adaptation. You do something long enough, your body becomes efficient at using energy for a physical activity. The fitter you get, the EASIER it gets to do something physical that was harder before. Your heart doesn't beat as fast or as hard.

A.C.E. Certified Personal and Group Fitness Trainer
IDEA Fitness member
Kickboxing Certified Instructor
Been in fitness for 30 years and have studied kinesiology and nutrition

bbell1985

There shouldn't really be a change after 5lbs. Maybe 10. Look at your "active" minutes.

sbrandt37

That seems like a suspiciously large change. Have you changed the batteries in your HRM recently?

As you get fitter, your body does become more efficient. Muscles don't work as hard, you burn a few less calories, and your heart rate stays lower. Even though the actual physical work your body is doing remains almost the same (except for carrying a little less weight), the lower heart rate will cause the calorie calculations based on your HRM readings to be lower, because it looks like you are doing an easier workout.

aubned92

I agree with @ninerbuff It's less about weight change and more about your body adapting. I had a similar thing happen to me a year ago and my weight hadn't changed an ounce. The fitter we are, the easier it is on our heart, etc.

DavidRocketts

Thanks for the helpful replies. The monitor is quite new, batteries ok. I used to exercise a lot before a bit of a slump, so maybe my system has remembered that, and yes, my heart rate is quite a bit lower. I will carry on walking but mix things up more in the gym and see if that helps meet my exercise calorie target (500 a day).

trigden1991

You weigh less and you're probably experiencing metabolic adaptation.

lemurcat12

It's probably that you are in better shape and your heart rate isn't overreacting to the exertion of walking, which is a good thing. It's also why a HRM probably isn't as great a measure of calories for someone not fit as people sometimes think. The formulas for calories burned while walking are probably better, really (although the best ones would deduct calories you'd burn during the same time anyway, which always leaves a sad number).

That said, the new numbers are probably good and more accurate.

emilysusana

lemurcat12 wrote: »

It's probably that you are in better shape and your heart rate isn't overreacting to the exertion of walking, which is a good thing. It's also why a HRM probably isn't as great a measure of calories for someone not fit as people sometimes think. The formulas for calories burned while walking are probably better, really.

I'd love to get ahold of said formulas. A formula for calories burned while running was suggested to me on here, but I've yet to find a similar one for walking. Do you know it?