Convert Kilojoule into calorie burn?

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Convert Kilojoule into calorie burn?

Postby cindylou » Wed Dec 21, 2005 9:22 pm

I have a Kettler Cross Trainer (Condor) which displays the kilojoule (energy?) reading. I want to know how many calories I am burning. Is this a conversion issue? I don't understand the concept. Anyone?
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Postby Guest » Thu Dec 22, 2005 5:39 am

Probably a longer answer than you want, but here goes.

A "real" calorie is the amount of energy that heats 1 g of water 1 degree C. This is a very small amount of heat. There is also a kilocalorie or Calorie (with a capital "C") which heats 1 kg of water 1 degree C. The "calorie" used in nutrition is really a kilocalorie or Calorie. In any case, the calorie is a lousy unit because the heat capacity of water is not constant, and there are at least six definitions of the calorie in common use, based on the initial and final temperatures of the water heated.

A nutritional calorie (kcal) = 4.1868 kJ based on the calorie defined in the International Steam Table, 1956. You may encounter other values that vary 1-2%. Since you aren't a steam engine, the thermochemical calorie might be better suited, and the value would be 1 kcal = 4.184 kJ. These are the two most common definitions. Note the joule or kilojoule is precisely defined, it is the calorie that has a variable definition.

The joule is a well defined unit of energy, whether it is heat, mechanical, electrical, or other form of energy. The calorie is a deprecated unit in the International System of units, and the kJ should be used to measure nutritional energy. It commonly is in some countries, but not the US.
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tried, and got a strange number

Postby cdaisy » Wed Dec 17, 2008 10:08 am

the ellipticals at the gym show calories burned, but my home elliptical shows kJoules.

I know that I burn about 10-12 cal per minute, so in a 30 minutes work out, I burn 300 - 360 cal.

On my elliptical, i got 5298kJ in 15 minutes. if I divide by 4.184, I get 1266 kCal... so to put that into calories, I multiply by 1000, but that number is way too high...

over a million cal burned in 15 minutes?

Other websites gave me the same calculation, so I'm not sure what I am doing wrong...
cdaisy
 

Re: tried, and got a strange number

Postby Guest » Wed Dec 17, 2008 7:26 pm

cdaisy wrote:the ellipticals at the gym show calories burned, but my home elliptical shows kJoules.

I know that I burn about 10-12 cal per minute, so in a 30 minutes work out, I burn 300 - 360 cal.

On my elliptical, i got 5298kJ in 15 minutes. if I divide by 4.184, I get 1266 kCal... so to put that into calories, I multiply by 1000, but that number is way too high...

over a million cal burned in 15 minutes?

Other websites gave me the same calculation, so I'm not sure what I am doing wrong...


Food calories are kilocalories not calories, so don't multiply by 1000.

Second, I thnik the elliptical is being VERY optimistic about your burn. That works out to a power of 5.9 kW. It would represent an exercise level of 59 METS, and imply you have the strength of 8 horses (well, only 7.9). The data it is providing is ABSURD.
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Re: Convert Kilojoule into calorie burn?

Postby parkerlindsey » Thu Aug 27, 2009 12:05 pm

'Kilocalorie' is a unit of heat equal to the amount of heat needed to raise the temperature of 1,000 grams of water by one degree Celsius.
As mentioned in the International Steam Table, I kcal = 4.184 kJ . So, get your kilojoule and divide it by 4.184 then multiply by 1000 , you will get calorie.
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