30s - 30m power prediction excellent. Bit of a gap on 60m+

Have been using Xert for a number of years now. Have found it an excellent tool for pacing KOMs / TTTs (TTE feature). I find the power curve is uncannily accurate for efforts between 30 seconds and 30 minutes. One thing that doesn’t quite work for me is the prediction of 60m+ power. At the pointy end of each season (about now) I can hold about 6W/kg for 5min and 5.5W/kg for 8min max efforts (age 51, weight 57kg). At this time, Xert tends to predict around 5W/kg for 60min max. I like to think I can suffer well in a 40km ITT or extended climb (and have a good feel for pacing correctly without a power meter), but there is no way I can hold 5W/kg for much more than 30m. And the 3hr prediction is actually just under what I can hold for 60m. Wondering what might lead to this?

Beyond one hour, and even potentially in the 30m to 60m area, Xert team are working on Xert 2.0 (some references in the forum) which is meant to better capture fatigue beyond what is already modeled (depleting HIE by riding above TP). The power curve today does have some approximations of that (hence hour power is not equal to TP, and 2 hour power is below hour power) but they acknowledge it’s rough. Plenty of challenges in getting it right though as eg fueling and hydration will have a big impact for longer efforts

In your case, sounds like you are in great shape and very experienced, so just a couple of additional considerations:

  • are your breakthroughs from long efforts, or rather shorter ones? In my experience, having longer, steadier BT efforts helps longer power prediction… if your BT always comes from 13x30-15s and that’s most of your hard riding, it can be hard to hold hour power (even though I know you can pace well)… I don’t mean super long but even 12 to 15m all out…
  • when you say you couldn’t TT for an hour at the Xert predicted 1 hour power (I assume from the power curve, rather than just your TP), could that also be because you are on a TT bike (different position)?
  • is your assumption you couldn’t do it also assuming a proper taper in the lead up, as opposed to just spontaneously attempting it in the middle of a training block? Just asking because Xert is predicting the max when fresh
  • are you appropriately fueling those efforts? You burn loads of carbs around threshold (or even above LTP) and for longer efforts you need to (at least partly) replace them

Thanks for the prompt, detailed and considered response.

  1. Thanks for the pointer on Xert 2.0, will read up on that. Was aware 60m+ was tricky to model, hadn’t realised that might extend to sub-60m. I think that’s answered the core of my question right there.
  2. My power numbers are consistent across road/TT bikes.
  3. Great question on the taper. Going into either a longer steady effort (whether race or assessment), I do aim to be properly rested.
  4. Great challenge on the fueling. The nutrition approach I’ve historically followed (for what it’s worth) is that for efforts up to an hour, on-board glycogen stores aren’t the rate limiting factor. So apart from a decent carb meal prior and a few gels leading up to the effort, I haven’t looked to consume carbs at the rate I would for say a 5 hour stage.

Thanks again for the pointers/questions.