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converting Kilojoules to calories???(9 posts)

converting Kilojoules to calories???ozone
Oct 4, 2002 12:41 PM
The power tap computer measures Kilojoules but how do you convert it to calories.
re: converting Kilojoules to calories???DougSloan
Oct 4, 2002 12:51 PM
not what I am looking forozone
Oct 4, 2002 1:08 PM
That is fine but I know there are 4 kilojoules in a kilocalorie. What I want to know is how is there a conversion number that is practical for the power tap. The 4 to 1 conversion does not work with the power tap because the body is not 100% efficent.

What I am trying to say is that for example a typical 1 hour ride I may have used 500 kilojoules. I know I have burned more then 125 calories. I am just wondering if there is a conversion that would work for the power tap.
Oct 4, 2002 1:27 PM
Are you saying you want a conversion that accounts for the mechanical efficiency of you and your bike? Wouldn't that be variable? Sorry, can't help.

yeah, most of those measurements are quite crude.nmC-mond
Oct 4, 2002 1:31 PM
It won't do you any good, anywayLactate Junkie
Oct 4, 2002 2:19 PM
It isn't worth bothering with because it still won't correlate to your caloric consumption in any way shape or form.. The best you can do with the kilojoules number is use it as a representation of the total workload for your ride. Thus a 1000kj ride is half as hard as a 2000kj ride.
It won't do you any good- I agreepeloton
Oct 4, 2002 3:13 PM
Any figure you get for calories burned for your body from a mathematical equation for kilojoules taken from your bike probably won't mean too much. Your basal metabolism, and your body's efficiency when exercising in relation to caloric needs will be individual. The number you get for caloric expenditure won't be any more accurate than the readings you get on the lifecycle at the gym.
Why will it not do......ozone
Oct 5, 2002 1:11 PM
any good if a kilojoul is a direct measurement of energy expended in relation to power output. It is should be much more acurate then any measurement based on HR. I did a little research on the web since I was not getting the answer I was looking for and found an article by Jonathan Vaughters.

From Vaughters article:
The next set of numbers is that of kilojoules. This is quite simply the amount of work done mecahnically on the bike. Also, this can be converted to kilocalories burned, by simply multiplying the number of kilojoules by 1.2. Actually it is a bit more complicated , but end up being 1.2 as there are 4 kilojoules in a Kcal, but the human body is only about 25% efficient on a bike (the other 75% of the energy being used as heat). So, in the end the number of kilojoules you produced equals roughly the number of Kcal you burned. Anyhow, here's the breakdown for riders in the TdF. On a flat stage most guys will be putting out about 700 kjoules per hour, although if you are riding in a breakaway or chasing one back this number can rise to over 1000 per hour. So, in a five hour flat stage , most riders will burn around 3500 kilocalories, in addtion to the 2000 they burn just to stay alive every day. These numbers change quite a bit when the peloton hits the mountains. Now, the riders will be well over the 1000 kjoules per hour while climbing. Of course it's a lot less descending, but that doesn't take long, so most of the time is spent climbing. So at the end of a long mountain stage it's not unusual to see oer 5000 kjoules having been used, or about 5500 Kcal. Now, it becomes absolutely impossible to replenish glycogen stores as 7500 Kcal will have been burned for the day .Good thing this doesn't go on too long.
One book/article said the human body is about 25%...PdxMark
Oct 4, 2002 3:47 PM
efficient when it comes to cycling, on average. So, as a crude number you could divide by 4 and multiple by 4. Of course, everyone is different...