Kilojoules vs kilocalories (or calories): which to monitor?


#1

Kind of confused here about which I should track when trying to top off energy stores during a long ride. I know that its nearly impossible to take enough on board over 5 hrs to maintain levels, but it seems simplest to have my Garmin monitor calories rather than KJ, and just try to keep up with calorie depletion. Any arguments for KJ that I should be aware of? What am I missing?

Thanks!


#2

The math just happens to work out 1:1. So every kilojoule of work you do you burn 1 dietary kilocalorie. There is noise that is hard/impossible to account for in your body spending energy to regulate its temperature. But for the most part you just take on your 60g (240 calories worth) of carbs/hour because any reasonable effort is going to put you over that burn rate anyways.


#3

Neither!

They are both made up and do not correlate to Food In and Energy Out


#4

This is not relevant to the discussion. A 5 hour effort from a trained cyclist is going to dominate the calorie expenditure for that day. OP is asking how to stay fueled, not how to lose weight.


#5

Too bad team Sky team didn’t know that calories were made up when they were driving Froome’s weight loss to a few grams precision during this year’s Giro!

But coming back to the OP’s question - really not much difference between Calorie/kJ, as long as the source of data is an actual power meter.


#6

we’re simplifying the calculation to say it is 1:1. That is assuming you have the near perfect 25% pedaling efficiency, otherwise your energy expenditure is greater than kj.


#7

Ok super helpful. Thanks. I won’t worry too much about it and will just estimate 1:1. I’m not on Team Sky at this time so this should be close enough for me. :slight_smile:
Much appreciated.


#8

For anyone looking for a bit more reading on this, we actually have an article on this exact topic within our Help Center :slight_smile: