One for the Xert team - does the current calculation of fat & carbs burned include basal metabolic rate or not? Thanks.
Not directly. If you stop pedaling, no fat/carbs are burned. But the 23% GE could be considered as having BMR baked in.
Great- thanks Armando 
It looks as though the calorie burn is based solely off cycling (not that I can blame Xert at this point), but it would be nice to have more accurate calorie burn info for running.
For example, my 10.5mi easy run this morning burned 1,018 calories per Garmin & Strava, while according to Xert it was 1,464 calories. At such a low HR/effort level there’s just no way that calorie count is accurate.
It’s based off of work performed and is independent of the type of exercise. We use a Gross Efficiency of 22% which is less efficient that what Garmin or Strava uses but is more in-line with published research.
I understand using power vs HR for calculations, but 1,464 calories for that run is at the very top-end of any and every calorie burn calculator I can find for running - typically about in line for what I’d see when factoring in active calories and BMR.
That could certainly help justify my recent “fueling” behavior, which would be a plus.
Did you record with a Stryd power meter or were the metrics derived using our new HR derived metrics?
I use Stryd for all of my runs and so I haven’t looked into the HR-derived metrics at all. Calorie burn from Garmin/Strava would have been based on HR, while Xert’s should have been based on power.
kCalories = Kilojoules / 4.184. Kilojoules = Sum of all power (assuming 1 sec recording) / 1000 / Gross Efficiency. The Gross Efficiency you use determines the overall calorie count. We use ~22% overall. Some literature reports higher for running and some reports lower for cycling. Without conducting research using direct calorimetry, these numbers remain WAGs in many ways.
Understood - thanks!
The feature hasn’t officially been announced since we’re still looking to iron out any new issues that come up but you can enable it under Account Settings / Profile. Activities without power but with hr (preferably hr and cadence), will be analyzed for XSS, Focus, Fat, Carb, etc.
Doesn’t running have gross (including elastic return from lower leg) and net power? Is the energy being calculated off gross?
The issue here isn’t the calculation, it’s the power numbers reported. For cycling, power is a simpler thing to understand and is measured pretty accurately but for running, the numbers are a much less solid estimate and validity of the absolute numbers has not yet been established. Garbage in, garbage out
Nailed it on the head, Billy.
For general training, running power is great because it is relatively consistent and repeatable. However, using that data for calculating caloric burn will be less than ideal, since all running “power meters” (minus the use of a running force plate) are calculated, not actually measured. I’ve seen large discrepancies in absolute power from Stryd, Garmin Running Power, and Polar Running Power from the same individual on the same run.
I don’t have a question about run calories burned. On 4 apps (Xert, Polar Flow, TrainingPeaks and Final Surge) calorie burn is within a 60 calorie range for a 45 min run.
However regarding the amount of fat burned there is a discrepancy of Polar Flow reporting 27% fat burned and Xert reporting 85% (75 g fat, 21 g cho 75x9=675/797=84.6%). This might be explained by Polar using a heart rate based calculation and Xert using a power based calculator. I am using a Stryd power meter.
I also wonder is the Xert number reported high from using a cycling based metabolic calculation using data from a running power meter?!?! If the Xert fuel breakdown is correct (75g/45min=1.67g/min) would have me as a world class fat burner based on information that I’ve read. My race results do not correlate to being world class in any physiological metrics.
The carb/fat won’t be as accurate for running, as we calculate Fat/CHO based on the gross efficiency of cycling
Is there a way to understand the amount of carbs/Fat that will be burned based on the low intensity/high intensity XSS in the workout builder? Thank you in advance.
Hi Alan,
Good question. We don’t have Fat/Carb utilization displayed in the workout player at this time, unfortunately.