I did an AI generated workout that was predicted to achieve 103 XSS. I did the workout on the trainer and the intervals achieved or exceeded by 1 or 2W the required interval powers. The Xert report tells me that the activity achieved 72XSS. Any ideas on why the discrepancy?
Hi. Did you use the Xert app or did you import the workout to Zwift or similar?
That is a substantial difference. 
View activity details, enable Target Power on the chart, and post a screenshot of that. (desktop view)
I assume it was a HIT workout of some type. What was the XSS ratio target? (low, high, peak)
@ridgerider2 On the chart I can’t get Target power to show when I enable the icon. Strangely, enabling all of the other icons work for their respective details. It wasn’t HIT, it was a pure endurance, the XSS was totally in the low range.
I don’t think it should make any difference but there is an adjustment I made to the workout. My trainer tends to be about 5W below interval targets so I set each interval 5W higher than the workout initially plans. This tends to get the interval power correct for what was initially intended. The predicted XSS I quoted is for what the workout would be at the lower power targets, and which is what was achieved on the workout.
Make sure the FTP in Indievelo matches the TP in Xert… The power targets in the workout files are typically scaled by the FTP.
I hadn’t done that. They are different and I can try that. Should that make a difference? When Xert says do a particular power for a particular duration, and then it looks at the completed workout and sees that power completed for that duration, should it not be doing an independent calculation of XSS which should match the prediction?
Xert will analyze the training you did, that is not the problem. The problem is/can be the targets you got in Indievelo were slightly lower than the targets set by Xert.
What is the percentage difference between Xert TP and Indievelo FTP?
When I import Xert workouts I normally change the FTP line in the .erg file to match whatever I have set in Zwift or TrainerRoad. Then I get the same watt targets as in Xert.
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The difference is quite substantial now that I look at it. The Indievelo FTP is 24% lower that the Xert TP. I must adjust that and see what happens. Just so we are talking about the same thing, the absolute value, in Watts, that Indievelo records me as doing for each interval, matches the absolute value in Watts that Xert said I should do for each interval, but an error could arise because of the ratio of those powers to the Indievelo FTP vs. the ratio of those powers to Xert TP?
Not exactly. Let’s say you create a workout in Xert where you will hold 300 W for some duration, which also happens to be your TP (100 %). The .erg file will have two lines, one for starting and one for stopping the interval at 300 W. Furthermore, it will contain a line that sets your FTP to 300 W.
When Indievelo loads the file, it will most likely scale all the power targets to reflect that your FTP is 225 W and not 300 W. This means that the 300 W target is replaced by 225 W.
But if you did the workout at the same targets as you saw in Xert, then something different happened.
If you open the .erg file you will see something like this:
[COURSE HEADER]
VERSION=2
UNITS=ENGLISH
DESCRIPTION=XXX
FTP=300
MINUTES WATTS
[END COURSE HEADER]
[COURSE DATA]
0.00 171.0
10.00 284.3
I will have a look at that. I’ll update the Indievelo FTP anyway and give it a go, doing the same workout again. Thanks.
Well, I learned a bit from doing that workout again. I realise now where I was going wrong in my description of the problem. I was saying about the intervals being supposed to be at a particular power for a particular time, and that those targets were being achieved. I was forgetting that when I was looking at the plan of the workout, I was looking at it after Indievelo had assigned powers (in terms of specific values of Watts) to the intervals. Your explanation should have helped me realise that, but it was only after a bit of experimentation that the sun broke through the fog.
I assigned XERT TP to the Indievelo FTP value but stopped after a while as I was exceeding XSS by quite a bit. I think I should have used LTP. It was the warmest warm-up I ever did.
Thanks for your help.
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I don’t have much experience with virtual riding apps, but does IndieVelo support using EBC on your phone to control the trainer and workout while you ride around in 3D world?
It should work, but you need a power meter that supports multiple Bluetooth connection or use a ANT+ dongle.
It doesn’t allow that facility. I checked out that possibility.