I know what MPA means and also kind of what difficulty represents. I know that a breakthrough does not require a high difficulty rating and vice versa.
However, I’m struggling to understand how Xert analysed the ZRL TTT I just did. It has a difficulty rating of 238, which is very high, right? Still, no breakthrough (even though my power hit the MPA briefly). I am wondering whether this makes sense: Even though breakthroughs and difficulty do not need to go hand in hand, shouldn’t breakthroughs happen (almost every time?) when difficulty is extremely high (difficulty = 238)?
Not very important for the planning of my training, it’s more about understanding Xert’s modelling better.
My last BT was 5 days ago. Maybe it’s relevant that I had to pause cycling for 2 weeks in November/December. My Xert TP was 330-ish before. Now it’s at around 315. Yesterday’s effort was 315 avg for 45 minutes, and it was full gas; I got dropped.
If I set the TP to 320, the difficulty is still 188. At 330 (which is definitely above my current FTP), it would be 133.
Often times, but not necessarily. You’re correct that in most cases a high difficulty score also results in a breakthrough, but there are certainly exceptions.
It’s possible to get breakthroughs without having a high difficulty score. It might be physically difficult to do a high-power sprint and you might really have to try your hardest to hit your best numbers, but often times there is too much easy riding before/after max effort sprints to generate a high difficulty score.
The opposite is also true. It’s possible for you to pull MPA down for a long time (like your TT example), or repeatedly (such as in micro-intervals) without generating a breakthrough. If you stop each effort just before your limit (or right at your limit), you won’t achieve a Breakthrough (maybe you’ll see a Watt or two BT or Near BT, but that’s the error margin of most power meters)
With an accurate signature, I usually expect the effective upper limit of difficulty around 165. Since MPA decline (and therefore XSS accrual and difficulty score) is exponentially weighted, adding just a few watts to Threshold and refreshing will often bring the difficulty score down significantly, as @ridgerider2 pointed out. That is the case especially for very long, sustained efforts near threshold power, like a TTT
Well done! What was your team’s finish time? We were a rider short, but still managed a respectable 49:27 in the open B division. I wrapped up my training yesterday with a few “High” XSS intervals courtesy of Magic Buckets
