This has probably been mentioned, but I’ve done 2 rides now with the new HUD, and the HUD displays a higher calorie count than what is displayed at the end of the ride(when you click Save and post-ride). On Sept 7, I did a 2hr ride and the HUD showed a bit over 1,800 calories burned, but when I ended my ride, Zwift showed 1,711. Today, I wanted to ride to 1,100 calories and I stopped the ride when the HUD hit that number, then when I saved it was 1,051. Is this a bug, or something else?
Are both these figures on zwift or is it another service like strava that’s showing the difference?
Typically the calorie figures are some function based on the kj figure ,either 1:1 or a close formula.
The premise that humans are around 4:1 efficient, i.e we supposedly burn about 4 calories for every 1 we can put into the pedals. The conversion from kilojoules to kilocalories is about 1:4 ish. So you can usually just take the kj figure directly as the calories figure it’s in the ballpark because the efficiency and conversion ratio cancel out.
If they’re using 4.01 or 4.1 or something else to get a different number a few calories different it’s immaterial - it’s just a ballpark figure and it’s based on an assumption of how efficient we are without us sitting in a lab being measured.
The same is true of cooking and eating food too - all the calorie figures are ballpark. You can’t really measure or count calories or burn calories to within 50 or 90 calories, get off the bike and think “I’ve burned 500 calories so I need to eat this sized piece of cake” - it doesn’t work like that. Especially with cycling because most of the calories you burn are after you stop when your body is recovering.
It’s not like a car where you put fuel in it, it uses the fuel while you’re driving and then when you stop and its on the drive it doesn’t use any fuel. People burn calories all the time 24/7 while they’re alive, whether they’re awake or asleep, riding a bike or sitting down. The only way to measure them is to sit in a lab breathing into a mask.
But, insofar as you want an idea of how many calories you used riding in zwift, the kj figure is close enough - and on strava or in another app the same data is likely to show a slightly different number.
The new HUD settings allow you to choose either “calories” or kj on the display. I wonder if you were comparing two different (but very similar) metrics…?
I got a different final kJ on Zwift Companion vs on my laptop Zwift final report.