Exercise Efficiency vs. Calorie Expenditure

Basically no (not to a meaningful extent).

Personal example of efficiency of my heart and lungs etc. versus calorie burns using power output as the measurement. (i.e. What I'm doing rather than what I'm feeling.)

Fit for my demogrpahic and also in relation to lifetime fitness levels:
Resting HR around 60bpm
Maximal sustained power for an hour 170watts / 612 net calories.

Very high CV fitness after a long period building up my capabilities:
Resting HR 48bpm (20% reduction).
Maximal sustained power for an hour 210watts / 756 net calories.

So the same exercise in sense both were maximal efforts at my maximum sustainable HR.
But that's also reflected all the way through the intensity range. What was hard is now moderate, what was moderate is now easy.
I could of course choose simply to ride same speed / distance in which case it would feel easier and my HR would be lower for the same calorie burn.
Extreme example would be professional long distance cyclists who burn fantastic amounts of calories due to their astronomical power outputs and have to eat huge amounts of food/calories to avoid losing weight.

Remember that HRMs are being used as a proxy for oxygen uptake which is difficult to monitor outside a lab. It's an indirect relationship and there is no universal "this pulse = this oxygen uptake". Your heart is a muscle and as you train it it's able to pump more blood per beat.

If your workout is strength training then please don't use HR as a meaningful metric (primarily because it's not an aerobic exercise) but the same capability improvements apply. If the you are shifting more weight during your workout you are burning more calories whether it feels same or easier as your strength goes up.

In any meaningful sense, no. Same objective amount of work, same calorie burn. Fitter body makes it feel easier (maybe lots easier), may make a heart-rate-based calorie estimating device give you a lower estimate (but there's more than that to modern devices that use heart rate among other things to estimate).

There can be small differences, but nothing major, for most common exercises. Sure, if your heart rate goes down, you're spending a zillionth of a calorie per second fewer on heart pumping, but that's trivial in comparison to the calories spent actually using muscles to do running, biking, etc., at a given pace for a given amount of time.

Estimates from exercise machines can be tricky, in this context. They're measuring the effort that goes into making the machine do what the machine wants you to do. I see people at the gym using the Concept 2 rowing machine in ways that probably burn somewhat more calories than the machine is registering, because they're spending a fair amount of energy in useless motion that doesn't accelerate the flywheel. How much more? No way to know.

So, efficiency in that sense - wasted energy - can matter to calorie estimation of some types. But, for a large range of common exercise types, the range of real efficiency is likely to be pretty small. The perceived difficulty difference (with fitness) can be pretty large, and coupled with the heart rate monitor problem can convince people that they're burning fewer calories doing the same thing at the same bodyweight, when they actually aren't.

The whole "muscle confusion" or "switch workouts to keep your body burning" rhetoric helps Beachbody and their ilk keep selling new programs and equipment, though. Elite swimmers, cyclists, rowers, runners, etc., have high TDEEs. If efficiency cancelled out calorie burn in some significant way, that wouldn't be true. Yes, their volume is huge compared to most of us, but no enough to justify the "efficiency = lower burn" for a constant objectively-measured intensity at constant bodyweight, in per minute terms.

I think there can be some cases where calorie burn decreases as the exercise becomes more efficient, especially if there is a skill involved.

I've seen some discussions citing swimming as an example. Someone with terrible form will burn more calories to cover x number of meters vs someone with perfect form.

MsCzar wrote: »

Thanks for the answers, all. I love my daily rebounder workouts, but they no longer have me panting and sweating like they once did. Not looking to be any sort of buff athlete; but I was concerned that perhaps I wasn't burning as many calories now that it feels like a casual stroll to my heart and lungs.

I'd expect something like that to keep burning about the same number of calories at the same bodyweight, no worries.

I'm sure you realize this, and I'm not saying it's a problem at all, but if you reach a point where the activity isn't as challenging (feels easy), it will be the case that you're not continuing to *improve* your cardiovascular capability so much, but rather maintaining it at the good level you've achieved. (Same for muscular benefits, but it seems like much of the rebounder benefit would be on the CV side.) If that fits with your goals, that's absolutely fine IMO.

However, if continued fitness *improvement* is a goal, then increasing intensity, frequency, duration or even changing exercise mode (to something more challenging, or adding something new to the mix in addition) would be necessary, to keep improving.

Congratulations on your fitness progress - that's great!

Theoldguy1 wrote: »

I think there can be some cases where calorie burn decreases as the exercise becomes more efficient, especially if there is a skill involved.

I've seen some discussions citing swimming as an example. Someone with terrible form will burn more calories to cover x number of meters vs someone with perfect form.

This is absolutely the case. 🙂 Nordic skiing is another example. Cycling can be, too. But it's a different thing thing on, where you learn how to do less work which obviously requires less energy, and get the same results for it.