WattBike vs Zwift vs Garmin Connect


Has anyone experienced these issues. My WattBike nucleus links to Zwift no problem and HR / Cadence / Watt Output all remain equal on each. However calories burned on Wattbike is signficantly more than what Zwift tells me at end of ride. When I then upload and save the zwift session to my Garmin Fenix via Garmin Connect it details the ride but Calorie useage is obviously signficantly different? 900 Calories eg on WattBike vs 600 or so on Zwift App. Is there a way to link so all data between Wattbike - Zwift and Garmin are all the same?

I guess somewhere along the way the different systems will be using different estimations of your effort and therefore giving different results.

To note if i run a 10k at one pace one day then the next day faster and therefore my HR is higher then the calories burnt doesn’t really change. That can’t be right?

tl;dr On fitness platforms “calories” (which are usually actually kilocalories) are often an estimate of input (food) energy required to produce the actual measured output energy, which are usually joules or average wattage which is just joules over time. Different apps or devices might estimate them differently.

For example, a “real” calorie unit is the same thing as 4.2 joules. And human biochemical/mechanical efficiency at converting food energy into power is estimated to be roughly 25%, depending on which study you read. So, 1 food (kilo)calorie is good for producing about 1000 joules of workout expended energy. 1kCal x 4200J x 0.25. Probably good enough as an rough estimate. There are a ton of other variables.

I’ll pretend i understand the science. :rofl:


Back in my university days I found a - at the time - old running book which stated that calories spend to run the same distance does not vary very much with speed. An estimate that worked remarkably well was to multiply bodyweight (in kgs) with distance (in kms) and the result was the energy (in kcal) needed for that distance. That is from a book from the 70‘s.

Could be something in that i suppose although I’d like to think that better research is available since the 70’s.

Luckily i don’t count the calories and for me exercise is more about having a bit of me time.

A few years ago some universities academics tested a range of wearable devices and found they all varied wildly with their estimates of calories burned.

I get the impression that every company has their own formula for calculating calories burned and that it’s not an exact science.

Is there a particular reason why you need them all to match? I know on Zwift you can’t edit ride stats, on Garmin you can, but I have no experience with Wattbike.

Hey that’s what I do!