Calories and calories

Hi all,

This question arises from me trying to calculate the average power
(wattage) of my cycling; just for information's sake and the fact that
I was bored at work... However, there is some confusion!

One calorie is the amount of energy required to raise the temperature
of 1ml of water by 1°C. One Calorie (capital C) is 1000 calories; also
referred to as kcal (kilocalorie) -- this is what is quoted in the
nutritional information of foods.
My cycling computer gives an accurate reading of the energy I have
expended during my trip. However, it isn't specific as to whether the
units are in calories or Calories... The display says "Cal", but the
manual says "calories".

On a typical cycle, it says I have expended about 2,300 [c|C]alories in
just under two hours. If I take this as kcal; then my power output is
something like 1370W -- that's more than an electric kettle. However,
if I take my units to be vanilla calories, my output is just
1.37W...Googling, I see that typical wattage values for cycling are
between 100 to 300W. Both my values are way out of this range; hence my
scepticism.
There's also the fact that, if this is calories, then that's about the
same amount of energy you would get from eating a slice of cucumber.
Whereas kcal would be equivalent to about two litres of ice-cream
(slightly more believable)... There's also that old chestnut of [pounds
of fat] = ([energy expended] - [energy consumed]) / 3,500. If the
energy in this formula is measured in calories; then it would take
about three years of intense, daily cycling to lose just 1lb of fat! So
what would be the point?

Mass confusion ensues!

Which genius thought it would be a good idea to give these units the
same name, just with different capitalisation, in the first place!?...
Actually, looking at an online unit convertor, the water is even more
muddied. I have the choice of International Table; thermochemical;
mean; 15°C; 20°C and food calories (and kilo~ versions of the first
two). Whilst they're all pretty similar, on conversion to Joules
(except the kilo~ and food, of course, which are an order of magnitude
different), it would be nice to know what is what.

In summary, basically there is a massive inconsistency that I cannot
resolve; and can't seem to find out anywhere... I really don't think
I'm pushing out 1.4kW when I'm cycling. However, I find it equally hard
to believe that one can cycle the best part of 20mph for two hours on
nothing more than a lettuce leaf!

What's going on!?

Christopher Harrison

P.S. I realise that the conversion of energy from food to the energy
available to ones muscles can never be 100% efficient and neither is
that of the energy put into cycling and the kinetic energy of actually
moving (although, I believe, it's about 90%; which is pretty good)...
However, I'm not questioning the laws of thermodynamics

P.P.S. Apologies that this has nothing to do with cycling and is only,
if anything, tenuously related. Please don't flame me!

I've used GPS measurements of speed and slope to calculate my
instantaneous power output (watts) - and then integrated this to
calculate the energy used (in kCal).

As a leisure cyclist my power output averages around 100 watts and for
a 1 hour ride this comes out at about 80-90 kCal of energy.

My understanding is that the human body is about 25% efficient at
converting food calories into actual energy output - so this means that
I use (as input) 320-360 kCals/hour.

I wonder if your computer is taking this factor of four into account?

How fast were you cycling?

Kirby

"Christopher Harrison" writes:

My cycling computer gives an accurate reading of the energy I have
expended during my trip. However, it isn't specific as to whether the
units are in calories or Calories... The display says "Cal", but the
manual says "calories".

On a typical cycle, it says I have expended about 2,300 [c|C]alories in
just under two hours. If I take this as kcal; then my power output is
something like 1370W -- that's more than an electric kettle. However,
if I take my units to be vanilla calories, my output is just
1=2E37W...Googling, I see that typical wattage values for cycling are
between 100 to 300W. Both my values are way out of this range; hence my
scepticism.

What's going on!?

My first thought is that your computer is whacky.
As a comparison, for running estimates for someone my size are 100 kcal
per mile. Near walking pace that's 300 kcal/hour, maybe going up to
600-700 kcal/hour working harder. These numbers seem to match how much
more I ate when I was running regularly.
When I compare that to the effort of cycling I would estimate my commuting
and touring intensity somewhere in the middle/lower end of that range.
On a rowing machine with a Watt display this is consistent: 100W
corresponds to 360 kcal/hour, anything over 200W is pretty hard to keep up
for an hour or more, and over 300W is pretty hard work even for a short
while...


If you're a strong man your numbers will be a bit different but not an
order of magnitude I'd think.

Roos

Christopher Harrison wrote:
This question arises from me trying to calculate the average power
(wattage) of my cycling; just for information's sake and the fact that
I was bored at work... However, there is some confusion!
[snip]
My cycling computer gives an accurate reading of the energy I have
expended during my trip. However, it isn't specific as to whether the
units are in calories or Calories... The display says "Cal", but the
manual says "calories".

Others might be able to pick me us on this, but IMHO unless your cycle
computer incorporates a fully-fleged power meter (unlikely if it's the
common or garden cycle computer!) you just don't stand a chance of
getting an accurate calorie reading from it (small or big 'C'!).

Your cycle computer probably bases all of it's energy calculations on a
single thing - the rate at which your wheel turns - and this just isn't
enough information to calculate cyclist power output. It doesn't take
into account drag, inertia, rolling resistance - which is to say, it
doesn't know if you're going up or down hill, being pushed by the wind
or pushing against it, or even if you're using knobbly tyres or
skinnies. These factors all have a massive affect on how hard it is it
push your bike, so the figure that the cycle computer comes up with is
totally disconnected from reality.

This doesn't stop manufacturers of cycle computers from putting calorie
counters read-outs on their products - to be honest I wish they
wouldn't, it causes an awful lot of confusion... I have a splendid GPS
cycle computer (Garmin Edge 305) which costs a couple of hundred pounds
- however, even with an incorporated heart-rate monitor, it's calorie
read-out is a complete work of fiction!

If you're *really* interested in measuring power output (and it *is*
supposed to be the holy grail in terms of cycle training analysis), you
might want to consider getting a bona-fide power meter (eg the Polar
Power system - about £180) - check out this review:

http://www.biketechreview.com/archive/pm_review.htm

These power meter products measure things like chain tension&speed, or
torque at the hub, to get an accurate figure reflecting your power
output...

best regards,
Roberto

Nutritionists always use the kilocalorie.

It is rather optimistic (erroneous?) to calculate more than 600kcal
expenditure per hour unless you're an Olympic rower.

--
Helen D. Vecht:
Edgware.

Christopher Harrison wrote:
My cycling computer gives an accurate reading of the energy I have
expended during my trip. However, it isn't specific as to whether the
units are in calories or Calories... The display says "Cal", but the
manual says "calories".

All cycle and hrm's I've seen display in kCals. I'm not sure, but I
think they work against empirical tables or similar: take body weight
against heart-rate at the sample rate, and figure the kCals expended
over the exercise period.

There's also that old chestnut of [pounds
of fat] = ([energy expended] - [energy consumed]) / 3,500.

Seems to be a pretty accurate approximation : I try and match my food
intake to my base metabolic rate (some 2000 kcals per day), and
averaged over the week, weight lost = exercise done (looked at over
many months, to remove the daily effects of dehyrdation or water
retention due to salty chips consumed)

Helen Deborah Vecht writes:

Nutritionists always use the kilocalorie.

It is rather optimistic (erroneous?) to calculate more than 600kcal
expenditure per hour unless you're an Olympic rower.

Or only doing a very short burst of work!
But as the original poster was talking about his 2-hour ride he should be
looking at numbers (Watts, Kcals) for endurance activities rather than
sprints.

Roos

Christopher Harrison wrote:

However, if I take my units to be vanilla calories,

WTF

Roos Eisma typed


My first thought is that your computer is whacky.
As a comparison, for running estimates for someone my size are 100 kcal
per mile. Near walking pace that's 300 kcal/hour, maybe going up to
600-700 kcal/hour working harder. These numbers seem to match how much
more I ate when I was running regularly.
When I compare that to the effort of cycling I would estimate my commuting
and touring intensity somewhere in the middle/lower end of that range.
On a rowing machine with a Watt display this is consistent: 100W
corresponds to 360 kcal/hour, anything over 200W is pretty hard to keep up
for an hour or more, and over 300W is pretty hard work even for a short
while...


If you're a strong man your numbers will be a bit different but not an
order of magnitude I'd think.

Your figures are of the size with which I would concur and accord with
my experience of long-distance cycling.

The OP's seem out by a factor of 2 or so.

Then there's joules, kilojoules and megajoules...

--
Helen D. Vecht:
Edgware.

Christopher Harrison wrote:

On a typical cycle, it says I have expended about 2,300 [c|C]alories in
just under two hours. If I take this as kcal; then my power output is
something like 1370W -- that's more than an electric kettle. However,

Factor of 10 error? 137W average for two hours would be reasonable.

Arthur

--
Arthur Clune