So if 2 riders similar size but say 25 pund weight difference both ride for an hour at 170 watts average who would burn more calories heavier or lighter?
They would burn more or less the same. The work required to ride at 170W is the same. If outdoors, speeds would be different.
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Depends on their efficiency in terms of EPOC etc. The work is the same.
Yeah i didn’t think that through. A buddy of mine is really kicking ass this year and he weights less than me but on his rides he is burning nearly 30% more calories so his ftp must be huge. Unfortunately he doesn’t have a power meter for outside rides so thats what threw me off.
Depends on their relative efficiency, which won’t depend on weight but stroke volume, blood volume, haemoglobin, capillary density of muscles, whether one is working tempo and the other Z1, genetics etc.
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If he doesn’t have a power meter, calories burned will just be a guess based on HR data and speed and will be less accurate.
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If he doesn’t have a power meter for those rides, ignore any calorie burned metric….they are junk.
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Apart from his calorie measurement being just a wrong estimate, some added thoughts about this situation:
As said above, if the two riders ride at the same power, they will burn the same amount if calories.
If they ride at the same speed, it is likely that the heavier rider burns more calories, because they need more power whenever the road is going up. They are also likely to be a bit less aerodynamic. If the two ride in a bigger group, drafting can really change the power they need (and thus calories burned).
Also you don’t automatically burn more calories with a higher FTP. You might even burn less, because the load on the rest of your body might be different. Having a higher FTP just means you are more likely to ride at higher power, which burns more energy. (For example if your endurance ride is at 200W compared to someone else’ endurance at 100W, you would burn twice the amount of calories).
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It depends on which is heavier a pound of feathers or a pound of marbles
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Calories on a device are measured using HR. Try doing the workout at a similar intensity with and without power and you’ll get a similar value.
Therefore both riders would have different calories because their HR relative to max/LTHR would be different.
Garmin used activity type, age gender, height and heart rate (if available).
A rider with a25% efficiency would burn approx 1000 cals on 1000kj ride as opposed to approx 1300cals if he was only 19% efficient ie me
The calorie estimate based on HR are horribly flawed. You won’t get similar results….often hundreds of kcal in difference.
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I agree, relying on device data is not worth it.
That said, I know that at a certain intensity, I’ll hit 600 calories anywhere between 55-65 minutes. Easier will be longer and harder will be sooner.
Yeah, that is usually what I will use as a general estimate for my rides at a steady effort.
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Almost certainly the heavier rider!
The calorie burn from the ride would technically be the same (barring huge differences in normalized power or biomechanical efficiency). But the heavier rider is likely to have a higher basal metabolic rate unless the difference is all fat, so the total burn would be higher 
Sorry, I know that’s not the spirit of the question 
Nope, unless their efficiency was exactly the same which is doubtful
Power is just energy per time unit. 1 W = 0.86 kcal/h Efficiency doesn’t come into that.
Extra calories might be burned because high metabolic load, which could include low efficiency in fuelling your muscles, but if you just look at the measured power output per hour, you get exactly the same energy use.
Not between different riders you don’t. Even with the same rider. Let’s say when fresh they produces 170 watts at a steady 101 bpm, then as they fatigue they produce 170 watts at 127 bpm. Is the rate of energy expenditure of the rider the same at the end as at the start?
170W for an hour is always 146kcal. That is just physics. There might be other things going on, that also need energy, like rapid breathing, extra high heart rate, stopping your eyelids from closing, but just pressing the pedals for 170W uses 146kcal.
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But that’s not biology, it’s not asking what do you get multiplying 170W x 3,600 second = 612,000 Joules. It’s not a 1:1 relationship. How much energy did the individual expend to produce that output at the pedal?
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