On 2 Sep 2004 07:11:51 -0700, (Doug Evans) wrote
(more or less):

"chris christanis" wrote in message ...
I had a cheap Bell computer that did it for me but it fell off (cheap). So I
bought a cateye but it does not tell you calories burned. Anyway to figure
this out?

This is a very tricky question.

Having investigated this in the past, I know there is no agreed,
accurate method of determining the calories used.

A few observations, though.

1) Any method that does not take account of the speed at which you are
cycling is pure rubbish.

Why is that? The rolling resistance increases linearly with speed,and
the wind resistance only starts becoming significant at 15mph, and
only increases with a power law for a cyclist/bike of /constant/ shape
and frontal area. Most cyclists I know start to crouch and tuck more
as the speeds get up to aero-sensitive speeds.


2) Unless you are cycling on the flat at a steady speed, any method
that does not take account of the total moved mass is pure rubbish.

And even if you are on the flat.


3) Conversly, any method which ties the calories burned to the moved
mass without taking account of the altitude gained/lost and the amount
of acceleration/decelerations is pretty much rubbish.

Particularly true of the latter point. But as for altitude gains, for
most routes, and certainly for all circular routes, altitude gains
will be balanced by altitude drops. i.e. the distances you put in more
effort because you are climbing should be balanced by the distances
you can use less effort thanks to the downslope.

(And yes, I admit that this assumes that you're a constant-speed
rider...)


4) Any method that does not take account of the wind speed is likely
to be wildly inaccurate if the w/s is over about 5 mph (consider that
if you are cycling with a groundspeed of 15mph, your airspeed will
vary from 10 to 20 mph tail/head wind at this w/s. At 12 mph, the
difference would be 3 to 27 mph)


5) Within a fairly wide range, you can probably find a figure or
algrorithm that will give you any result you want, if you research
enough sites/books/articles.

The method I used to *ESTIMATE* the calorie burn was as follows.

a) Find a step aerobics machine which has a calories burned* readout.
b) Use an HRM and set the machine to various resistances. For each
resistance setting, wait until your heart rate stablises, and note the
Hr/Calories readings.
c) Plot a graph of these figures
d) Use an HRM that will give you a mean Hr for your ride, and use that
against your graph to determine your approximate calorie burn.

* Try and determine if the calorie readout is the number of calories
calculated from the kg/m raised on the machine, or whether the machine
introduces a "fudge factor" to account for the inefficiency of human
power generation/delivery. If it is the former, it will be a
considerable underestimate of the calories burned. All the heat you
produce is on top of the energy used to effectively raise your body
mass the distance used in the calculation.

If you can do the maths, you can use the Hr/Cal figures to produce an
equation, but as the relationship is non linear, it's not that easy

Apart from the above, I would say that the algorithm given based on
mean Hr and weight has the best chance of being accurate, although
both this, and the moethod I outline above will not be too good if
there is a large variation in Hr during your ride.

Plus if you're training for aerobic fitness, your HR for given effort
is going to vary over time.


--
Cheers,
Euan
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