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Calories and Kilojouls always equal in my cycling sessions, why?

eilonshalev
over 4 years ago

Hello !

I have been using a hub power meter on my roadbike, with a heart rate monitor, and either Garmin 920XT or edge 530. in both garmin devices, when I finish the ride, I cannot help but notice that consistently, my Cal count and KJ count are remarkably similar. the other day 764 C vs 767 KJ. This level of (small) difference has been consistent also in longer rides when I go for 2.5 hours.

I thought that each Cal equals roughly 4 KJ. 

Why do I always see the same numbers for both Cal and KJ counts?

Thx!

  • 0 over 4 years ago

    1 Calorie equals about 4.2kJ

    People are about 20-25% efficient in turning energy into useful work.

    Factoring in this efficiency you will see that the number of calories used about equals the number of kJ output.  1 is 23.8% of 4.2.  It is just a useful coincidence that human efficiency about equals the scale factor between Calories and kJ.

  • 0 over 4 years ago in reply to Wongataa

    Wow - this answer makes a lot of sense to me. I guess my issue was my lack of knowledge about the human efficiency factor; naively I didn't consider at all that it could exist. Would love to read more about it, gonna search on my own, but if you have specific resources I should go to, pls feel free to add them to the thread, thx again so much!