A related but I think distinct issue with these modeled fitness parameters is the tendency to over-apply them outside of the applications where they’re most predictive.
Like if you take any of the aggregate “fitness” metrics (like CTL, intervals icu or Strava progress bar) and narrowly define them as proxying your progress in building specific adaptations that support generating power aerobically (like mitochondrial and capillary density), they actually work pretty well. They go up with volume increase, they go down w volume decrease, as they should. It works bc this doesn’t really depend on what the inputs are. Muscle contractions = pgc1A, and a contraction is a contraction and the more you do, the more pgc1A you get.
But if you want them to predict your performance, or the other fitness parameters that combine to create performance, they simply don’t work, because this does depend on the inputs and a high intensity input is not the same as a low intensity one, and converting them to same metric (eg TSS) it becomes kinda useless for many purposes.
The fitness scores therefor I think are still useful but for much narrower questions, like, what should I expect my endurance to be like? If you want to predict performance though, you gotta look at it alongside other things
Green is Productive (gaining fitness)
Yellow is maintaining
Blue is recovery
Purple is peaking (i had an event end of that week)
Pink is strained
Red is over reaching
Orange is unproductive
This is also 4 months with the coach and the 2-3 months prior without the coach. Basically he steps me up in blocks then maintains for a block. I had an early event so he just leveraged what I had in the bank and got me recovered from the over training and back on track just in time for a taper for it.
What I’m finding fascinating is the progression in load. I’m older which he knows and manages but he’s found that I recover very quickly so he’s pushed me onto longer blocks rather than a massive uplift in weekly load. This is because I’m targeting multi day big mileage next year. On a 5 week block now and so far so good. The recovery is hardcore tho. Like I get SO bored 3 days in but it is enough to keep me on maintaining rather than getting into “recovery” according to Garmin. Is also more like a recovery 9 days rather than 7.