Increased fitness and calories burnt

becnaffine

I'm just curious. If you get better (fitter) at doing an activity like a step class, do you burn less calories as your heart is not working as hard? I've just noticed a decrease in my burn level on a few activities the last few weeks even though I go for the same mount of time and the same pace.

underwater77

In short, yes.

johnkernmusic

I think that your body would get used to the movements and figure out easier ways to do them. So, yes less calories burned.

xilka

Yup.
Also, as you lose weight, there is less weight for your body to move around, thus less effort is made.

RunFarLiveHappy

This is my life!!! Lol. I'm so happy to be healthier and more fit, but I miss those high burns! Haha.

heybales

In long - no.

Your HR as a measure of your calorie burn is ONLY tied together by your VO2max - ability of your body to provide oxygen, to burn fuel, to power you.

As you get more fit, you improved your lungs, heart, blood flow, muscle uptake, ect to all get the same amount of needed oxygen with the heart beating less, and even you breathing less.

It's why when you start out your heart was racing and you were breathless.

And if 3 weeks later you weighed exactly the same and did the exact same pace on the steps - you burned the exact same calories. But no longer heart racing and out of breath.
Moving your mass against gravity did NOT change the amount of energy needed to accomplish that (does the energy needed to lift 5lb off the floor against gravity ever change?).
Your body supplying the required oxygen to burn the fuel to do so did improve.
And along with that, the type of fuel changed too, more carbs at first, more fat later.

Some types of exercise have a lot of difference in efficiency though, and if that improves you'll burn slightly less. Like P90X or similar. That's why they go for "muscle confusion", to throw you in to inefficiency again. If you are quick to make the change, you get less positive effect from that. But that is very minor.
Steps, walking, jogging, bike - those have no changes in efficiency, you've been doing them or similar your whole life.

You being lighter, so there is less mass to move - now that makes a difference.

Now, with your HR lower to do the same workload for your muscles, does mean 1 muscle is not being worked out as hard.
If 10 lb dumbbell started to be easy to lift, you'd have to move to 15 lb to still make it a workout, right?
If the HR lowers, your heart isn't getting as good a workout, that's the muscle.
So gotta increase the pace or intensity. Now you've increased the calorie burn compared to before too.

Oh - cheap HRM like Polar FT4/FT7 have no stat for VO2max. The base it on BMI - bad BMI, bad fitness level.

So as you get fit, they'll assume that lower HR means you aren't working out as hard, and if the same weight and same pace or intensity, you are working exactly as hard, it'll just underestimate your calorie burn.

Sorry so long, but that's the correct answer.