Calories/Hour == Watts?

I'm trying to convert the calories/hour that a Precor elliptical
machine says I'm putting out into watts so I can compare it with
commonly-quoted power figures for cyclists.

When I use the Precor device for an hour, it says I've burned a
little over 1,000 calories.

But when I convert 1,000 calories/hour to watts using several
different sources (among them ConvertIt.com, which gives a factor
of .001163) I keep coming up with a little over one watt.

OTOH, my impression is that a cyclist in any kind of condition
can put out over 100 watts.

But if 100 watts is plausible, 1,000 calories/hour=1 watt doesn't
jell because then the 100-watt cyclist would be burning 100,000
calories per hour.....

I can think of a three possibilities right away:
--------------------------------------
- Precor's calorie count is way wrong.

- My conversion factor is wrong

- I'm doing something dumb.
--------------------------------------


My money's on #3.... but what?
--
PeteCresswell

On 2008-02-03, (PeteCresswell) wrote:
I'm trying to convert the calories/hour that a Precor elliptical
machine says I'm putting out into watts so I can compare it with
commonly-quoted power figures for cyclists.

When I use the Precor device for an hour, it says I've burned a
little over 1,000 calories.

It means Calories, with a capital C. One Calorie is 1000 calories.

But when I convert 1,000 calories/hour to watts using several
different sources (among them ConvertIt.com, which gives a factor
of .001163) I keep coming up with a little over one watt.

1000 Calories/hour is 1163W. Yes you would get 1.163W if it were
calories.

OTOH, my impression is that a cyclist in any kind of condition
can put out over 100 watts.

I think that's about right.

But 1163W is far too much. If the machine is telling you many Calories
it thinks you've expended, rather than output, you could divide that by
4 (since the human body is about 25% efficient).

290W for an hour is still impressive though. That would correspond to
about 37kph.

1163W on the other hand would be about 60kph, around about the current
hour record which stands at 56.375kph.

[...]
But if 100 watts is plausible, 1,000 calories/hour=1 watt doesn't
jell because then the 100-watt cyclist would be burning 100,000
calories per hour.....

I can think of a three possibilities right away:
--------------------------------------
- Precor's calorie count is way wrong.

- My conversion factor is wrong

- I'm doing something dumb.
--------------------------------------
My money's on #3.... but what?

The main thing is 1 Calorie = 1000 calories.

"Ben C" wrote: (clip) The main thing is 1 Calorie = 1000 calories.
^^^^^^^^^^^^^^^^^^
A slightly fuller explanation: In nutrition, a calorie is too small a unit,
so they capitalize it, and make it a kilocalorie.

But, that can't be the whole story, because this would result in a kilowatt
average for an hour. Maybe in the Tour de France.

Leo Lichtman wrote:
"Ben C" wrote: (clip) The main thing is 1 Calorie = 1000 calories.
^^^^^^^^^^^^^^^^^^
A slightly fuller explanation: In nutrition, a calorie is too small a unit,
so they capitalize it, and make it a kilocalorie.

But, that can't be the whole story, because this would result in a kilowatt
average for an hour. Maybe in the Tour de France.

I doubt that there are many riders in the TdF that could put out much
over 400 watts for a period of an hour.

--
Tom Sherman - Holstein-Friesland Bovinia
"And never forget, life ultimately makes failures of all people."
- A. Derleth

On Feb 3, 10:04*pm, Tom Sherman
wrote:
Leo Lichtman wrote:
"Ben C" wrote: *(clip) The main thing is 1 Calorie = 1000 calories.
^^^^^^^^^^^^^^^^^^
A slightly fuller explanation: *In nutrition, a calorie is too small a unit,
so they capitalize it, and make it a kilocalorie.

But, that can't be the whole story, because this would result in a kilowatt
average for an hour. *Maybe in the Tour de France.

I doubt that there are many riders in the TdF that could put out much
over 400 watts for a period of an hour.


Maybe somebody big like Magnus Bäcksted, but then since he has to lug
himself around, he doesn't go any faster. He just has to eat more at
dinner time.

But the OP's 290W is entirely plausible. But I think the machine
slightly overestimates, and the 25% should maybe be more like 24% so
maybe 260W or so.

Joseph

Per :
But the OP's 290W is entirely plausible. But I think the machine
slightly overestimates, and the 25% should maybe be more like 24% so
maybe 260W or so.

This from the OP: No way...

90 watts maybe. 100? Maybe... much over 100? doesn't jell
for somebody as old and decrepit as Yours Truly - who probably
has socks that are older than a lot of people in the NG.
--
PeteCresswell

On Feb 4, 3:09*am, "(PeteCresswell)" wrote:
Per :

But the OP's 290W is entirely plausible. But I think the machine
slightly overestimates, and the 25% should maybe be more like 24% so
maybe 260W or so.

This from the OP: *No way...

90 watts maybe. * 100? *Maybe... * much over 100? *doesn't jell
for somebody as old and decrepit as Yours Truly - who probably
has socks that are older than a lot of people in the NG.
--
PeteCresswell

100W is about 17mph on a road bike for an average sized person on a
flat road. 260W is about 25mph.

Joseph

Per :
100W is about 17mph on a road bike for an average sized person on a
flat road. 260W is about 25mph.

That works then: on a good day with no headwind, I can
aerobically hold about 16 mph on my FS with 55/55 tires at 35
psi.

So.... one way or another, 1,000+ "Precor calories" is coming out
to something in the vicinity of 100 watts... maybe a few more...
maybe a few less.... but in the ballpark.

Now I have to figure out how I'm messing up the conversion factor
and or the interpretation of "calorie".
--
PeteCresswell

On Feb 5, 1:17*am, "(PeteCresswell)" wrote:
Per :

100W is about 17mph on a road bike for an average sized person on a
flat road. 260W is about 25mph.

That works then: on a good day with no headwind, I can
aerobically hold about 16 mph on my FS with 55/55 tires at 35
psi.

So.... one way or another, 1,000+ "Precor calories" is coming out
to something in the vicinity of 100 watts... maybe a few more...
maybe a few less.... but in the ballpark.

Now I have to figure out how I'm messing up the conversion factor
and or the interpretation of "calorie".
--
PeteCresswell

Does the machine allow you to input your weight?

Joseph

"(PeteCresswell)" wrote in message
news
I'm trying to convert the calories/hour that a Precor elliptical
machine says I'm putting out into watts so I can compare it with
commonly-quoted power figures for cyclists.

When I use the Precor device for an hour, it says I've burned a
little over 1,000 calories.

[Snip]

1000 calories/hour is not an unreasonable figure for a regular cyclist on an
hours ride. I make it equivalent to about 20 mph riding with your hands on
the hoods. For me it would be at a heart rate of about 150 just below my
threshold i.e. a tempo ride.

What you need to consider working back from calories indicated on your
Precore are that these use the term Calories which are in fact kilocalories.
The conversion from Calories/hour to watts is 1.163. So your 1000
Calories/hour becomes 1163 watts. This however is the total energy your body
is using in propelling your bike but like all other machines its not all
that efficient at converting chemical energy into mechanical energy. Typical
estimates are in the 20 - 24% range. So your 1163 watts come down to
something like 240 watts at the pedals and allowing for transmission losses
about 230 watts at the rear wheel.

One further complication when working back from gym machines is whether or
not they include the Calories your body is also using in powering itself.
These are typically 60-70 Calories/hour. If your machine does then these
need to be netted off to get the "rear wheel" equivalent watts. That would
give you around about 215 watts at the rear wheel.

Graham.