# Bicycle Mechanics - I wonder how it works

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View Full Version : I wonder how it works

Catalium'
04-30-08, 11:49 AM
i've got a Sigma PC-15 heartrate monitor,it has the function of calculating the amount of calories that you've burnt.
my question is,how does it work,is the statistic data reliable?
and what's the unit,KCAL as it presents?

CACycling
04-30-08, 12:12 PM
Using the age, sex & weight you entered, it measures your heart rate and calculates the kilocalories you are burning. It doesn't measure the calories burned, it computes them based on the variables entered and what an average person would burn under those circumstances so it will be close for most people.

datlas
04-30-08, 03:06 PM
I doubt this is really reliable....I could get my HR up to 150 by drinking 10 cups of coffee, which certainly does not burn as many calories as a HR of 150 on the bike!

On the other hand, who gives a flying f@ck how many calories are burnt?!!?? Just ride.

I have the same monitor, btw....and have not really explored its functions....just use the basic HR function, which works well....they are on sale for 39 bucks at performance....i see the OP is from china it is likely even cheaper there since that is where they are made.

Doug

neilG
04-30-08, 03:23 PM
Using the age, sex & weight you entered, it measures your heart rate and calculates the kilocalories you are burning. It doesn't measure the calories burned, it computes them based on the variables entered and what an average person would burn under those circumstances so it will be close for most people.

Close enough, for sure. I used an HRM to lose 50 lbs by counting calories. I looked into many methods of calculating calorie expenditure and found that the HRM was close to most of them.

Catalium'
04-30-08, 09:12 PM
so,the unit it uses to measure is KCAL?

if it's true,my power can reach up to 800W!

a bit ridiculous..~~

frankstoneline
04-30-08, 09:24 PM
so,the unit it uses to measure is KCAL?

if it's true,my power can reach up to 800W!

a bit ridiculous..~~

the "calorie" you see on the back of cereal boxes etc. is usually the KCAL I believe. A calorie is how much fuel is necessary to raise one gram of water one degree celsius, a KCAL is 1000 times that much.

SweetLou
04-30-08, 09:27 PM
Yes, kcal is a kilocalorie. This is what we use when we measure food energy. Say a pretzel is 30 calories, it is actually 30,000 calories, or 30 kcal or 30 C (capital "c" means kilocalorie).

SweetLou
04-30-08, 09:41 PM
the "calorie" you see on the back of cereal boxes etc. is usually the KCAL I believe. A calorie is how much fuel is necessary to raise one gram of water one degree celsius, a KCAL is 1000 times that much.Well, if you want to get more precise it is the amount of energy to raise 1 g of water from 14.5 degrees Celsius to 15.5 degrees Celsius at 1 atmosphere pressure. Or another choice is 1 thermochemical calorie is exactly 4.184 joules. Or the international steam table calorie is 4.1866 joules.
:eek: Too many choices. It's 1000 calories.

Catalium'
05-01-08, 02:41 AM
Oh,i see.

frankstoneline
05-03-08, 04:15 AM
Well, if you want to get more precise it is the amount of energy to raise 1 g of water from 14.5 degrees Celsius to 15.5 degrees Celsius at 1 atmosphere pressure. Or another choice is 1 thermochemical calorie is exactly 4.184 joules. Or the international steam table calorie is 4.1866 joules.
:eek: Too many choices. It's 1000 calories.

oof.
I just remember it from highschool chemistry.

TurboTurtle
05-03-08, 06:29 AM
i've got a Sigma PC-15 heartrate monitor,it has the function of calculating the amount of calories that you've burnt.
my question is,how does it work,is the statistic data reliable?
and what's the unit,KCAL as it presents?

HRMs measure heart rate extremely well. All the other things they claim to do are just 'random number generators'. - TF

CrankyFranky
05-03-08, 07:14 AM
Oh,i see.
Um, I don't, not by what has already been said. Thermodynamic calories are a purely physical measurement - the amount of heat required to raise a cubic centimeter etc. would be equal to a certain amount of fuel burnt. Others above have given you this definition.
The body doesn't burn food fuel by combustion, but by the exquisitely indirect process of metabolism to give us life energy. Because metabolism produces work (when you pedal) indirectly, nutritional or metabolic calories do not equate with thermodynamic (purely physical) calories. Normally, the physical mesurement is always expressed in kcal and the metabolic unit is expressed as calorie. Look up the nutritional/metabolic definition, not the definition in physics.
Therefore, if the HR monitor calculated that you had burned 800kcal, you would have to eat food that had 800 calories of food (energy) value.
As other posters have written, the caloric value given by the HR monitor is a calculation, and is mainly useful if (say) you wanted to lose weight by burning calories of fat that you have accumulated on your body by eating too many calories worth of food. For normal health maintenance in bike riding, the heart rate is a more important measurement than calories, because for proper physical training, you are supposed to get your heart rate up to a rate which approaches your maximum heart rate, (max. hr isdetermined by your age - as you age, your max hr decreases). The usual prescription is to attain a hr of (say) 85% of max. for a period of 30-40 minutes, and to do this three or four times a week for ordinary health. For competitive training, this is not enough.
The poster says, don't worry about it - ride the bike and enjoy the feedom and health benefits it gives you!:D

CdCf
05-03-08, 07:38 AM
so,the unit it uses to measure is KCAL?

if it's true,my power can reach up to 800W!

a bit ridiculous..~~

There are two kinds of power involved. One is the total power your body puts out while you ride (for example). The other is the power actually used for pushing yourself and the bike forward. The body has an efficiency of about 20 % for cycling, so if your energy expenditure would suggest that you put out 800 W, you probably did, but the power going into the pedals was about a fifth of that, or 160 W. Entirely reasonable.