How many calories does cycling actually burn?

Logged on to a website earlier that calculated calories burned for different activities and it said that for a man of my weight, 95kg, cycling at 15.5 mph for 80 minutes would burn about 1400 calories. I read somewhere else that cycling burns 300 cal/hour. Which is more like the truth? Thanks in advance to those that may know.
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As a very rough estimate it's probably around 400-800 calories per hour, again, depending on fitness and intensity.
I reckon 300/hour is about right for recreational cyclists at a relatively slow pace, and 700-1000 a reasonable ball-park for anyone who puts some effort in.
Disclaimer: I am not a boffin.
For a brisk, hilly commute I assume 350 calories "extra" per hour. This is worth remembering with the numbers that it is the "extra" amount that's of interest. Sitting watching TV uses 50 calories per hour.
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As the 'average' male burns between 2000 and 2500 calories a day just by being alive, that translates into roughly 160-200 calories an hour. I say roughly....but I suspect sitting around watch TV burns off more than 50 calories an hour.
By the same token - if you are burning off 200 cals an hour just by being awake, I would think that even recreational cycling will burn off more than 300 calories an hour.
I RIDE A KONA CADABRA -would you like to come and have a play with my magic link?
you estimator was most likely way wrong, unless you require ~ 290 watts to ride at 15.5 mph. which might be the case if going up a long climb of say ~ 2.5% for 80 minutes.
Is it linked to HR or Power? i.e. 20 = Max possible HR sustainable for 1hr, or 20 = Max power sustainable for 1hr?
How would temperature affect these numbers? Regulating your body temperature uses quite a bit of energy - outside the sauna I go to, it says on the wall that you burn 10 Calories per minute in there! When climbing in hot weather, I can sometimes overheat like crazy!
It is a measure of mechanical work done (power x time) divided by our efficiency level (typically 19-24% - with the rest being dissipated as heat) to get the total energy metabolised, multiplied by the conversion factor of joules to kcal.
The very top pros can do close to 6 watts/kg for about an hour.
6 watts for an hour = 6 x 3600 seconds = 21.6kJ/hour (per kg)
Efficiency and the conversion to calories happen to nearly cancel each other out, so that equates to roughly the same number of calories per hour.
Hence suggesting 20 Cal/hour/kg is about an upper limit and attainable only by a Pro for about a hour, or for the rest of us mere mortal riders, for a few minutes if we are lucky or somewhat less than a minute if we are untrained recreational riders.
But your Heart pumps in anticipation of work being required, and doesn't immediately drop back to rest when work is no longer required. So calories used is not a simple relation to Heart Rate.
Yes, making your body work to cool yourself will burn calories, you'll burn more calories making your body actively warm itself, so sitting in a freezer would do more. However more than either of them would be doing some exercise.
2. There are a number of things that can elevate HR without burning a lot of calories, for example a ride that is highly variable in intensity can make for a relatively high overall HR but have a relatively low average power and hence work performed (kJ burned).
It may not be as accurate, but pumping blood burns calories. And to pontificate that HR is completely irrelevant to caloric consumption is just plain wrong.
If I may butt in...
It's a bit misleading to suggest that power produced is a 'factor' in determining calories burned; since a calorie is a unit of energy, calories burned per hour (or whatever unit of time you care to use) is exactly the same thing as power.
As you were.
From my somewhat limited understanding...The heart rate is an indication that you are working harder but the actual calories burned by the heart in doing this is negligible to the work performed by the rest of your body in moving your bike.
This seems logical in my head at the moment.
If it weren't then you could answer this question:
Two riders who both weigh 70kg and with a Max HR of 180bpm ride an hour with an average of 160 bpm. How many calories are they burning per hour?
A: you can't tell me because you have to know how much power they are producing. Their HR is irrelevant.
By the same token, two people sitting around doing nothing, but one is... let's say in the sauna (to go back to the start of this arguement). The one person in the sauna has a higher heart rate than the one sat outside. Both sat around not exerting any energy.
Are they both burning the same amount of calories?
There would be a little variation due to extra perspiration but nothing worth measuring
You don't know, I don't know and from that information no one would ever know if they are burning the same amount of calories
We could play this game all day long
Let's suppose that by some freak of nature the same person had the same weight and the same physical condition and was doing the same quality of exercise on two occasions. At time a) he had a lower heart rate than at time b) then it would be strongly likely that he was using more calories at b) than a)
However there are a lot of conditions there and no actual numbers for the calories
Also in this example how would you know that the person had exactly the same physical condition?
For an individual I believe that you could calibrate a HR monitor to give a calorie read out that gave useful information. But you would have to use some other means (invovling a power meter probably) to work out what the HR readings meant
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Just ride the bike and ride it hard.
Depends what you are hoping to achieve....As someone pointed out earlier a mid-low intensity tempo ride will burn fat as you ride....if you increase the intensity too much then different energy pathways wil be used with varying percentages of fats being used