Accurately measuring calories spent

[Reardy Mister]

The Garmin Edge 200 this morning claimed that for our 25mile ride, averaging 15.3mph (it was windy!) with an elevation difference of 1325ft, for a rider at 78kg, that we burnt about 1400 calories.

That seems optimistic and further, how does the computer know how much resistance we encountered to achieve those figures? Wind? Tyre pressure? Rolling resistance of the surfaces etc?

Should we disregard the calorie count function or does that seem about right?

[okgo]

Just go with around 600 an hour and you'll be probably near enough.

You need a hrm really if you want to be very accurate. Sadly I think you've bought a garmin that cannot do heartrate stuff?

[Watchman]

The only accurate way is to measure the amount of force applied to the pedals - for that you need a crank-based strain gauge.

[okgo]

I think you can do it fairly accurately without having to buy a powermeter. And the point of a power meter is nothing to do with calories.

Does it have to be that accurate? I think it's fairly pointless number anyway...

[anonymous-user]

The garmin or any other gps tracking calorie burn is just an algorithm based on your weight and distance travelled. It could be out by quite a large margin. It's like a gym treadmill, you enter your age and weight and it gives you calories burned. It doesn't really know how hard your body has been working.

For more accurate measurement you need a heart rate monitor.

[Reardy Mister]

el stovey said:

The garmin or any other gps tracking calorie burn is just an algorithm based on your weight and distance travelled. It could be out by quite a large margin. It's like a gym treadmill, you enter your age and weight and it gives you calories burned. It doesn't really know how hard your body has been working.

For more accurate measurement you need a heart rate monitor.

Thats what I thought. Its a pretty arbitrary figure anyway but I wanted to confirm the deny the validity (or lack thereof) the figures it shows.

Cheers chaps.

[offendi]

Watchman said:

The only accurate way is to measure the amount of force applied to the pedals - for that you need a crank-based strain gauge.

Incorrect , the only way i know of thats accurate is measuring oxygen use

My HRM over estimates my KCals used and thats a very good thing. It gives you enaough KCals spare to stop for a brew and cake

[matt-ITR]

The only realistic way of measuring it while outside on a bike (not in a lab) is with a power meter.
That will measure work done in kJ.

But since the body is roughly 20-25% efficient on a bike at best, then as 4.2kJ = 1 kcal, the kJ is good rough estimate of amount of calories burnt.

Even in a lab with gas analysis it is still guess work (but more accurate).
HRM alone will not give a reliable estimate of calories used.

[crisisjez]

Reardy Mister said:

The Garmin Edge 200 this morning claimed that for our 25mile ride, averaging 15.3mph (it was windy!) with an elevation difference of 1325ft, for a rider at 78kg, that we burnt about 1400 calories.

That seems optimistic and further, how does the computer know how much resistance we encountered to achieve those figures? Wind? Tyre pressure? Rolling resistance of the surfaces etc?

Should we disregard the calorie count function or does that seem about right?

Even if its out by 20% thats enough to get straight down the nearest greasy spoon for a big breakfast special so well done

[anonymous-user]

surely its relative to the source of the calories too? os is that the point about measuring kilojoules?

[XitUp]

okgo said:

I think you can do it fairly accurately without having to buy a powermeter. And the point of a power meter is nothing to do with calories.

Does it have to be that accurate? I think it's fairly pointless number anyway...

This.

Are you getting fatter? You're not burning enough calories.

Are you passing out or going wobbly on your bike? You're burning too many.