MeckMeck GRE
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Today I did a small experiment on my home-trainer. The information I got from the display was :

Time : 34 minutes
Distance : 15 km
Energy : 344 Kcal

Now 34 minutes are 2040 seconds.
344 Kcal are 344.000 Cal are 1.376.000 J

1.376.000 J / 2040 s = 674,5 W

Now 674,5 Watt is quite too much for a untrained human. (It would almost equal 3A @ 230V)

Whats wrong ? Where is my mistake ?

krammer
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Erm - what was this? Running? 15km in 34 minutes is about 26km/hr which is about 17mph! If you can keep that up for over half an hour, I suggest you turn professional...

It seems most likely your equipment is broken/set wrongly....

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MeckMeck GRE
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krammer wrote:
Erm - what was this? Running? 15km in 34 minutes is about 26km/hr which is about 17mph! If you can keep that up for over half an hour, I suggest you turn professional...

It seems most likely your equipment is broken/set wrongly....

Cycling.... and its quite slow (or exactly : as slow as you are still able to enjoy a Simpsons episode while cycling).

Im happy that my equipment and not my physics skills are bad.

Doom
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Well, 344KCal equals ~1.440.000J (1 cal = 4,1868J). However, that only moves the final result to the wrong direction, up to 706W.

I'm with the data accuracy as well.

Znirk
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MeckMeck GRE wrote:
1.376.000 J / 2040 s = 674,5 W

Now 674,5 Watt is quite too much for a untrained human. (It would almost equal 3A @ 230V)

The calories indicator very probably isn't a measure of "force x distance" but an estimate of "chemical energy invested". I don't have a reliable source for figures, but from googling "energy expenditure cycling" the figure seems about right for half an hour's cycling at 26 km/h.

For reference: conventional wisdom has it that a person sitting quietly in a chair generates over 100W heat, and even with light activity like typing into a computer you already go over 150W. Recommendations for daily food intake for adults vary between 1600-2800 kCal -- that's in the general area of 6 to 12 MJ. Your home trainer's opinion is probably inaccurate, but not totally untrustworthy.

Oneiromancer
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I think Znirk is right on the money...think of it in terms of heat energy and not electrical energy and it might not be so concerning.

Although my first thought was that I seemed to recall calories being defined differently (in terms of orders of magnitude) between actual thermodynamical calories and the ones in food/exercise but I am not totally sure.

Game on,

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Znirk
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Oneiromancer wrote:
Although my first thought was that I seemed to recall calories being defined differently (in terms of orders of magnitude) between actual thermodynamical calories and the ones in food/exercise but I am not totally sure.

You may be thinking of how people refer to the kilocalories in food/exercise as "calories" for short.