MPA Or Fitness Signature Is Off

TP = 257
PP = 1619
HIE = 39.3
LTP = 159 (this is every low)

I have a question about this chart. I felt like I was pushing pretty hard, yet my MPA barely dropped. I am not sure if my fitness signature is off or maybe I didn’t work hard enough? My heart rate was zone 4 and 5 for most of the ride.


Based on my experience, Xert is really good at predicting „point of failure” (intersection of MPA and actual power line), if your fitness signature is correct.

Therefore I would take one of „the breakthrough test” workouts and ride it until all-is-out. If your fitness signature is overestimated, you shall fail much earlier than pre-workout estimation of Xert.

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Thanks; this is what’s confusing me. I did a breakthrough workout last week and the numbers are based on that workout, and frankly, I had more in the tank. I’ll try to do another next week and see. I have an easier time with interval workouts than holding a steady pace around threshold probably because of the fast-twitch muscle fibres.

The workout above was harder than my breakthrough workout yet the MPA barely moved, this is why I am confused.

Many people find it easier to BT via repeated intervals vs one continuous effort - whether that’s a matter of practice or individual variability in MPA recovery between intervals is hard to say.

Riding at or slightly above TP is very hard in general though (especially if you are not used to it - practice improves it) and it doesn’t draw down MPA much unless you are quite a bit above TP… you can play with signature via advanced MPA to see the difference eg drop TP by 10w.

I am usually at max HR (unless it’s a short sprint) when I have a BT so suspect there is an element of you being able to go harder, as you suggest.

I also think your signature is likely higher than you think based on the very high difficulty score (with a higher signature it would be lower difficulty), and also your comment about the last BT

Could also have been a bad day, not recovered after the recent BT efforts

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Thanks, Wesley; I’ll keep riding and collecting data and see what happens over time. You might be right about not being recovered.

I appreciate your feedback, as always.

Your MPA will only drop when you are above threshold. That graph suggest you did not spend much time above threshold until the very end.
With such a high PP you will have to put a lot of effort above TP to get the MPA to drop down towards power, unless you can summon a massive sprint up and hold it for more than 5 seconds.

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I’m still learning and understanding Xert but it appears (to me) you have a very high PP and a high HIE which may result in you needing to ride quite a bit above TP or a long time above TP to bring your MPA down.
The same might apply to your low LTP as well.
So maybe your PP needs to be looked at more closely?
Others who know or understand more than I do may say something different.

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I don’t monitor HR much indoors, but it looks like you rose to a tempo pace for most of the workout and added a short Zone 5 effort at the end.

MPA drawdown only occurs when you spend enough time above TP. That can either be hovering above TP (not at TP) or spend longer intervals in yellow/orange or shorter spikes in red with minimal recovery in between (green/blue) to keep MPA down.
You lowered MPA to a point as difficulty and fatigue rose (shaded portion of the graph) but there was lots of time in green (below TP). IE, sweet spot/tempo territory. Challenging for sure, but not enough to continually drawdown MPA and trigger a BT. Had you done that (more orange/red) the graph may have looked more like this –
Let's See Some Recent BT's - #289 by Erph
Page through that thread and you’ll find various examples of MPA drawdown including some similar to yours but with enough efforts while fatigued to trigger a BT.

As @johnnybike and @Cyclingdoughboy mention your high PP/HIE is a factor. How often can you hit that maxP number outdoors when fresh?

You could experiment with your numbers by selecting the Advanced MPA tab for that activity, change any of the signature values and click Refresh. That will recast the chart. You don’t want to save the new signature, but you can use this method to play what-if scenarios. For example, what if TP was 10 pts higher.

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I see what you mean; I kept pushing above than resting below and repeating this. I am sure if I had stayed above the TP the entire ride, the signature would have changed. This makes sense.

My PP is accurate if they go on max sprint effort and if the trainer counts. It was closer to 1640, but it has been dropping. I will do some of the workouts selected by xert and see what happens. I have a hard time increasing the duration over 2 hours…its dreadful indoors, especially at my low LTP, I feel like I am doing nothing.

Yes - one other thing that I’ll point out… fatigue isn’t symmetric above & below TP. In other words, MPA does not recover at the same rate at a fixed distance below TP as it drains that same distance above TP.

You can see this by playing around with the Workout Designer… Here I’ve created two scenarios that consist of the same total work performed (and thus, same average power):

The first effort (on the left) is alternating 30s efforts @ 110% TP/95% TP (20 min average power: 102.5% TP)
The second effort (on the right) is a constant 20min effort @ 102.5% TP

Notice the difference in MPA between the two :slight_smile:


This makes a lot of sense, thanks so much. I will look through the thread. The PP I only hit indoors on Zwift using a wahoo kickr. I only have data as of last November.

I am pretty sure I can hit over 1600 watts anytime on a trainer, especially fresh. Its my endurance that’s lacking and trying to build with the help of Xert.

OH WOW, thanks for this!