kJ vs cals for daily intake & cals burned

Good day all,

I’m a little confused and looking for some clarification on which is most accurate when it comes to calories burned on a ride & for proper refueling , even went back and listened to the June’19 podcast on Summer Nutrition where the topic was covered. So we’ve got kJ and cals (Kcal) - why on the head unit are the values different if they’re the same ?

This past weekend I had a 3.5hr Z2 with four Zone 6, 1min efforts, which was 2095 kJ of work and 1650 cals - that’s a difference 450 which is a fair bit but also 78.7% of the kJ which falls inline with stated efficiency of the human body to produce energy which is about 23-25% but at the same time that 450 is towards the upper end of recommended calorie deficit if looking to lose some weight…

Should I be using the kJ figure for cals burned for daily intake & refueling instead of actual stated figure in cals?


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Use the kJ’s measured by your power meter:


@Gavin Your numbers 2095 vs 1650 are what is weird. Typically for me TPeaks calculates my calories burned at around 94% of kJ which from what I read is reasonable math. The numbers you have are not reasonable math - the 75/25 efficiency number you mentioned occur elsewhere in the conversion from KJ to kcal. Is it possible your head unit is using HR or time/distance to calculate calories?

EDIT: did a little more math. If you are more efficient and are at the top of the range (25%) you burn .94 Calories per kJ. If you are less efficient (23%) then you burn 1.04 Calories per kJ. Thus the 1:1 kJ to Calories is a pretty reasonable estimate for fit people (for a specific sport). If you are a beginner or otherwise less efficient, like 20%, then the differences might start to be relevant for calorie counting.

All very interesting and kinda confusing at same time.

I switched my Wahoo over to display kJ (work) but it’s still off/lower (almost like it’s still showing cals) than Strava or TP, however Strava & TP are the same when it comes to total work kJ. My Wahoo is updated and I’m using Favero Assioma Duo’s for my power.

When I sync my head unit to my phone after my ride the Wahoo app says that cals burned and work kj are the same but when uploaded to Strave or TP that’s when I get the true value for kJ work.

I am quite new to cycling having just started last June and started my first workout program end of Feb with 18 weeks SS.


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Strange that that true data is in your Wahoo file somewhere but it doesn’t display it. But you can get it, so that’s what matters. :+1:

Its as simple as 1kJ from your powermeter = 1 calorie of food. 1,000kJ’s = roughly a chicken burrito

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