Fat calculation - dependant on maxHR value?

Couldn’t see any option for HR values and wondering if the fat usage numbers depend on those, ie. average ride HR as a percentage of maxHR or so? My fat usage on endurance rides is massive, so wondering if something might be off. In the example below 241g of fat converts to 2169 calories. Am I reading this right?


Work (kJ)

Equiv Power (W)

Strain Score (XSS)

Calories (kCal)

Fat (grams)

Carbs (grams)

Hey there,

Xert reports calories based only upon mechanical work performed, it does not include basal metabolism. We also use a gross efficiency of 23% compared to most companies that use 25% (which is higher than reported in the literature). What was your LTP for this ride?

Where do you see LTP for a specific ride?

You can follow LTP by viewing the fitness signatures aspect of your progression. You can get here by going to Progression, then change XPMC to Fitness Signatures.

Found it thanks… LTP is 264 for that ride/day

That’s really good! Our LTP is analogous to LT1/aerobic threshold, or essentially where the body maximizes fat utilization. Seeing as you had an XEP below LTP, this is not surprising that most of your energy came from fats. HTH

How did Xert come up with my LTP number I’m wondering now, does it just look at FTP and take a % of it, or is it looking at other stuff I’ve been doing like long rides or so?

Checkout our glossary entry on LTP and the original posts on Fitness Signature and MPA to see how LTP is determined. It is a modelling artifact based on your fitness signature whose derivation was obtained through modeling slow-recovery fatigue that occurs over long rides.

Thanks Armando but I’m still not clear how it’s worked out specifically. Is it looking at my long rides and working it out from those, or from a combination of difference points in the fitness signature? How can we use the LTP figure for training, how useful is it?

Our determination of LTP is based purely on power output, no HR. As Armando mentioned, it’s an artifact of your fitness signature. There’s an inverse relationship between HIE and LTP, so that two athletes (given the same PP and TP), the athlete with the higher HIE will have a lower LTP and vice versa. It becomes important when we start to consider your “endurance energy” aspect of your fitness signature. Essentially, after a very long ride, LTP will represent your TP. If you’re familiar with zone training, LTP tends to correlate well with LT1, or the aerobic threshold. If you’re following a polarized training approach, you should use LTP as the upper limit for your endurance/base rides. Personally, I use it to design base training/aerobic workouts - I generally use 90-100% LTP as the power target for those workouts.

It’s very high it seems, and I thought, perhaps wrongly now, that with polarised training the easy rides had to be much much easier than this. But it looks like tempo rides, or lower end tempo rides are actually fine then for polarised training? You’d be fresh enough to hit the hard stuff hard?

LTP should be the upper limit of those rides, you can always certainly ride below it. We put out a blog on this topic last year, you may find it interesting: http://baronbiosys.com/sweet-spot-threshold-and-polarized-training-by-the-numbers/

Perfect thanks, wish I’d spotted that blog post before!

Cheers, hope it helps! Let us know if there’s anything else we can help with