converter KJ - KCal

[dirtcrazy]

hi all - im on a diet that restrict me to 3500KJ intake (for the first 3 weeks,,, detox) - i cycle and gym daily and always have my polar at hand. I found a website translatorcafe.com - which indicates that 1KCAL=4.18KJ - would this be true??? If so, then if i loose approx 1000KCAL per day (500kcal in the morning and 500KCAL at night - i gym twice a day).. This means i will loose about 4800KJ per day and my intake is 3500-3800 per day... Please guys, am i on the right track regarding the KCAL-KJ ??? all help appreciated!! thx

[Underachiever]

1 Cal = 1 kCal = 4.18 kJ = 4180 J

[Minion]

There's a bit of confusion about the units used for food calories.

 

The unit most often used is the food Calorie (Cal / kcal). One food Calorie (with a capital C) is the same as 1000 'normal' calories (cal) and the same as 4.18 kilojoules (kJ).

 

1 Cal = 1 kcal = 1000 cal = 4.18 kJ = 4180 J.

 

It's really sloppy nomenclature to refer to Cal when talking about kilocalories and leads to confusion.

 

You've left off your BMR (Basal Metabolic Rate). This is the amount of energy you need to burn just to stay alive. It varies based on age, gender, weight etc. but is on the order of 1800kcal/day.

 

Your total consumption for the day, if you have a sedentary job and did that exercise would then be around 2800kcal or 11704 kJ.

[Underachiever]

Sounds logical. But loosing 500 Cal in the gym?

 

I rode 2 hrs yesterday at 150 bpm avg. Total energy was 1800 Cal, so you might overestimate the gym sessions?

[Underachiever]

Edman, nice summary, I was too lazy to mention the BMR. Cal is sloppy, but the Americans love it...surprise!

 

Ah...I see I made a mistake

 

1 Cal = 1 kcal......

[word]

Wow. 3500 Kj per day is about 800 calories!! Too little.

 

Regarding Underachiever, your burn is also overestimated. On Saturday I rode 76km at about 148 bpm. Ride time was 2:35 and Kcal burn was 1600 as per power meter

[amoryns]

what's the measure on one's polar...KJ or calories?

[Minion]

what's the measure on one's polar...KJ or calories?

Mine says kcal.

[Underachiever]

Wow. 3500 Kj per day is about 800 calories!! Too little.

 

Regarding Underachiever, your burn is also overestimated. On Saturday I rode 76km at about 148 bpm. Ride time was 2:35 and Kcal burn was 1600 as per power meter

 

Yep, only an indication - the Polar is not that accurate. bpm as percentage of HRR should also come into play?

[Underachiever]

Mine says kcal.

 

Ditto, you can change it to kJ on the watch, but the software (older version) kicks it back to kcal if I remember correctly.

[dirtcrazy]

Mine says kcal.

mine to, im still very much unfit and in a spinning class of about 50min i loose about 500kcal (as per my polar) -- so you say this is impossible eventhough im unfit??

[Willehond]

dirtcrazy, your figures sound good to me. Remember it is all weight related! If like me you are not a stick insect, then the figures make sense.

 

To calculate BMR and estimate energy output have a look at this great site that estimates it all for you:

 

http://www.caloriesperhour.com/index_burn.php

[Underachiever]

The way I understand the Polar algorithm is that is uses you activity level, weight and heart rate (height perhaps too??) - this you program into the unit at first. This is then used to calculate/estimate energy usage. Never as accurate as a power meter

[Willehond]

mine to, im still very much unfit and in a spinning class of about 50min i loose about 500kcal (as per my polar) -- so you say this is impossible eventhough im unfit??

The calorie calculator says that if you do "Bicycling - stationary, moderate" activity for 50minutes and you weigh 86kg, then you burn 502 calories (sic).

[Cheese]

mine to, im still very much unfit and in a spinning class of about 50min i loose about 500kcal (as per my polar) -- so you say this is impossible eventhough im unfit??

500-600 Calories per hour is a good guideline if you do not absulutely hammer it.

 

I use arounr 600-700 on endurance rides and just a bit over 1000 Calories an hour while racing.

Used 3200 Calories saturday morning .

[Minion]

The way I understand the Polar algorithm is that is uses you activity level, weight and heart rate (height perhaps too??) - this you program into the unit at first. This is then used to calculate/estimate energy usage. Never as accurate as a power meter

The more advanced ones also use an estimate of VO2max and Max HR. From what I've read, the algorithm is pretty accurate so long as the inputs are accurate at intensities below 85% max (I think that was the number). With bad inputs and high intensities, it doesn't work so well.