here’s a screenshot of an ai generated workout that i modified by extending the number of steps in the first set from 5 to 15 in order to better understand MPA.
the working intervals are 3min at 128%TP and for the first 6 reps MPA is logically getting pulled down. For reps 7-n the MPA pattern gets repeated despite the difficulty measure increasing. Intuitively i know that if i were to try this workout i would fail at some point and i’m surprised that MPA doesn’t reflect a level of accumulating fatigue beyond the first 6 steps.
As a test I changed the number of reps to 150 and the MPA pattern remained consistent for all 150.
If MPA declines in the first 6 sets @128%TP shouldn’t some level of decline persist in subsequent sets? Why would it flatline despite difficulty increasing?
I believe this is because rate at which you fill back your HIE depends on how much it is depleted. Say you have drained your MPA down to TP so that what is left of your HIE is 0 kJ. Even if you stop pedaling, your heart rate and breathing will
be elevated because you are working hard to reestablish your MPA/HIE. As the MPA/HIE increases, the heart rate and breathing will also go down. So your body will not work at full speed until MPA if full, but gradually decrease the speed.
The result of this is that you might end up in a equilibrium as you see in your graph because the lower you go the harder your body will work or refilling your MPA/HIE.
You can also use difficulty score to monitor central fatigue. Looking at this, I feel like I’d probably mentally quit first. Difficulty looks to be over 160 by ~30 min into the session. Another important factor that can’t really be modelled directly is that you’d be burning through your available glycogen stores pretty quick during these efforts, even if some is able to be restored via gluconeogenesis.
MPA is based on how much HIE is depleted/replenished. As @hpbieker mentioned, after the first couple of sets, you’ve essentially reached an equilibrium between how much HIE can be depleted & replenished during the ON/OFF intervals - if they were to be performed exactly as they’re described here in the workout designer.
Interesting.
I expected that accumulating fatigue resulting from high intensity intervals would cause the rate at which HIE recovers to degrade over time, resulting in a similar sort of decay in MPA’s ability to recover or an acceleration in MPA drawdown that couldn’t achieve equilibrium while difficulty was increasing. I expected HIE to work more like W’ but in reading the description in the help file I understand it is not the same.
I think i understand - So if i were to create a workout that is designed to facilitate a breakthrough should i look for the point where MPA crosses the interval power and expect that if it flatlines or repeats that it essentially expects me to fail at that point?
eg - I should be able to complete all of these
Yes, you have it right. If your signature is dialed in, you’d barely be able to complete the third interval and fail to complete the last two.
Since MPA by definition cannot exceed itself (without triggering a BT), the graph flatlines when power rises above MPA during an activity. Upon XO analysis the signature adjustment would recast the chart so MPA only touches the highest max effort peak recorded during the activity. That will be somewhere within the flatline portion of the activity. The shaded difficulty portion of the chart would also normalize and look reasonable.
Take a look at any of the workouts designed to drive you close to a failure point.
Example – Xert - A Pain That I’m Used To Workout Details
When Xert recommends tough/hard workouts like this (or you select one on purpose) you can preview how your current signature will apply.
While the goal of recommended tough/hard workouts is to drive you close to your limit without failing intervals, you may fail some depending on freshness, motivation, fueling, fan cooling, etc.
OTOH any workout that drives you close to a failure point is an opportunity to test your mettle and try for a BT if you want. Switch to Slope mode on EBC and keep going, ignoring target watts and/or duration. Or in the case of Ronnestad-style intervals extend the interval count if able.
I think it is important to be aware that only some physological responses are accounted for in the Xert model. The physiological response can be that your MPA will be slower at recovering during the workout. This can be due to various things such as muscle fatigue or running of glycogene. But this is not a part of the Xert model.
Especially longer effors might not be properly covered. As an example I have included a chart below showing what will happend to your MPA if you ride for 4 hours at TP – MPA is still at max and the difficulty maxes out at 100 (looks like the equilibrium value is the same for all fitness signatures). But I bet you will stuggle drain your MPA after 4 hours @ TP. Or even if you had one or two hours of rest after that effort.
