Calories/Hour == Watts?

On Feb 3, 3:06*pm, "(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.

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

After factoring efficiency, etc., a rate of 1,000 calories per hour
yields avg. power for that hour of approx. 278 watts.
Best,
Bill Black

Per :
Does the machine allow you to input your weight?

Yes, and I do.

I suspect I'm gaming the system to a certain extent though.

I find consistently higher "calories/min" readings for the same
perceived effort level when I set "resistance" to max (i.e. 20)

I'm always sneaking glances at the people to my left and right
and for the ones that input their weight, their numbers never
seem tb over 14-15 calories/min and are often down around 10-12 -
while I'm doing 17.5-20.
--
PeteCresswell

Per graham:
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.

Thanks for the detailed analysis. I think some of the
considerations are starting to dawn on me now....

--
PeteCresswell

These machines vary a lot in how they estimate power and thus total energy.
Your mileage may vary.

The 25% efficiency factor needs some explanation. Sometimes it's 20%.

25% or a factor of 4 is for incremental energy generated. When you add in
the basal rate (what you'd burn sitting on the couch) it becomes 20%. That
is you divide by 5 not 4 to get your power output if the energy the machine
says you used includes the basal burn rate too.

This would get you down to around 200W, still pretty amazing for most of us.
Eddy Merxx was measured at 375W for the hour record (if I remember
correctly).

Most TdF winners are in this range and some of the pros can do 400W for
short periods of time.


"(PeteCresswell)" wrote in message
...
Per :
Does the machine allow you to input your weight?

Yes, and I do.

I suspect I'm gaming the system to a certain extent though.

I find consistently higher "calories/min" readings for the same
perceived effort level when I set "resistance" to max (i.e. 20)

I'm always sneaking glances at the people to my left and right
and for the ones that input their weight, their numbers never
seem tb over 14-15 calories/min and are often down around 10-12 -
while I'm doing 17.5-20.
--
PeteCresswell

On Mar 6, 8:48 pm, "Rocky" wrote:
These machines vary a lot in how they estimate power and thus total energy.

This would get you down to around 200W, still pretty amazing for most of us.
Eddy Merxx was measured at 375W for the hour record (if I remember
correctly).


375W - estimated not measured and that was at altitude. A sea-level
adjusted power output
would put him at around 435W

On 2008-03-06, Rocky wrote:
These machines vary a lot in how they estimate power and thus total energy.
Your mileage may vary.

The 25% efficiency factor needs some explanation. Sometimes it's 20%.

25% or a factor of 4 is for incremental energy generated. When you add in
the basal rate (what you'd burn sitting on the couch) it becomes 20%. That
is you divide by 5 not 4 to get your power output if the energy the machine
says you used includes the basal burn rate too.

This would get you down to around 200W, still pretty amazing for most of us.
Eddy Merxx was measured at 375W for the hour record (if I remember
correctly).

Most TdF winners are in this range and some of the pros can do 400W for
short periods of time.

A TdF sprinter can put out almost 2kW for a short period of time.

Per Rocky:
This would get you down to around 200W, still pretty amazing for most of us.

Further spport for my suspicion that the machine's algorithm is
seriously flawed.

I'm older than dirt and "real" road riders consistently blow past
me at a speed diffs of 3-5 mph. Yes, I'm riding 1.25" slicks on
a hardtail MTB... but that can't be good for more than 1 or 1.5
mph.

I'd be pleasantly surprised if it turned out that I could sustain
100 actual watts.
--
PeteCresswell

In article ,
"Rocky" wrote:

Eddy Merxx was measured at 375W for the hour record (if I remember
correctly).

Most TdF winners are in this range and some of the pros can do 400W
for short periods of time.

1200-1300W in the sprints for the very top sprinters. Of course that's
for about 10 seconds...

After factoring efficiency, etc., a rate of 1,000 calories per hour
yields avg. power for that hour of approx. 278 watts.
Best,
Bill Black

What is interesting is that a human needs an energy equivalent of ~10
power bars to produce these ~200 watts. These 10 powerbars weigh what,
a pound? Now, a kilowatt electric battery in a 1kW electric scooter
weighs what, 50 pounds? Pretty amazing how the human body can extract
energy from "biodiesel".

On Thu, 6 Mar 2008 20:26:58 -0800 (PST),
wrote:

After factoring efficiency, etc., a rate of 1,000 calories per hour
yields avg. power for that hour of approx. 278 watts.
Best,
Bill Black

What is interesting is that a human needs an energy equivalent of ~10
power bars to produce these ~200 watts. These 10 powerbars weigh what,
a pound? Now, a kilowatt electric battery in a 1kW electric scooter
weighs what, 50 pounds? Pretty amazing how the human body can extract
energy from "biodiesel".

"We don't know who struck first. Us or them. But we do know it was
us that scorched the sky. At the time, they were dependent on solar
power. It was believed they would be unable to survive without an
energy source as abundant as the sun. Throughout human history, we
have been dependent on machines to survive. Fate, it seems, is not
without a sense of irony."