Hi all,
I’d like to understand how Xert estimates carbs and fat burned. The numbers on one of my rides don’t seem to add up. For reference, i’m talking about the beta charts.
Ride: Difficult Mixed Puncheur Ride, 57 min
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Work: 714 kJ, avg 207 W, max 816 W
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HR: 156 avg, 191 max
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XSS: 90 (79 Low / 9.4 High / 1.3 Peak)
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Xert’s estimate: 221 g carbs, 3 g fat, 742 kcal (glycogen 198 g, glucose 29 g)
What I don’t follow:
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Carbs vs. calories: 221 g of carbs at ~4 kcal/g is about 900 kcal, which is more than the 742 kcal total Xert shows. What energy value per gram of carbs does Xert use?
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Fat close to zero: 3 g of fat means almost 100% carbs. Most of the strain (79 of 90 XSS) was low-intensity, so I’d have expected at least 15–25% of the energy to come from fat.
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Carb burn rate: 221 g in 57 min is about 3.9 g/min on average. That’s close to the maximum carb burn rate usually reported, which seems high for this ride.
Context: I had a breakthrough during this ride and my threshold power went up by 7 W.
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Was the activity analysed with my pre-breakthrough fitness profile?
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Would re-analysing it with the new profile change the carb/fat split noticeably?
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Which inputs drive the carb/fat split most: threshold power, HIE, peak power, or HR?
I’m mainly trying to work out how much to refuel, so I want to know whether 221 g is a realistic target.
Thanks!
