Extracting lower threshold?

How does Xert determine lower threshold at a point in time, and changes in lower threshold over time? Are changes estimated based on accumulated strain from workouts? Or are they extracted directly from performance data? How does this work?

Lower Threshold is derived from your Fitness Signature. It’s kind of like calculating your 5 minute power. This all comes from your three fitness signature variables.

Thanks – so it’s extracted from performance data. Makes sense. So does that mean if I just do base training (and don’t do a 3+ hour effort to “break through” the long end of the power-duration curve), xert won’t really pick up changes to lower threshold? And if I want to “prove” that I have had lower threshold gains, then I need to do some maximal efforts under fatigue to break through. Does that sound right?

LTP works quite a bit differently and I’d need a few more words and pictures to explain how it works mathematically. One of the things we’re finding is that if you spend too much time doing high-intensity training, this can lower your LTP but raise your FTP and HIE. For triathletes and other longer endurance race athletes, this is not likely a desirable outcome. Notably, tracking your FTP alone may miss this.

Your last point there is exactly why I am thinking about this. My sense is that in the past I unintentionally put more focus on “cheaper gains”, but have lots of opportunity to improve base fitness … so that’s what I am focused on for a few couple months. Thus trying to get a bit more sense of how the measurements work. Anyhow, not sure the right forum, but if you have the chance at some point to summarize, it would be quite educational.

That’s kinda where I’m at. My focus will be on long endurance/ultracycling stuff (24hr race in November). As such, I’m doing nearly everything at maximum aerobic function (MAF) which seems to be just a bit below LTP (will know again in a bit, haven’t had power meter on the trainer for awhile now). Many months coming up to build my (previously small) aerobic capacity. I also don’t plan to regularly do much of the high intensity stuff, though I feel I might need it once in a while to keep the Xert calculations more accurate.

Armando – any further insights into how lower threshold is extracted from the data? I am keenly interested in understanding this in order to see what level of credence to put into is as a measurement of longer term gains.

Feedback from a number of customers and sport scientists have suggested that LTP tracks your LT1 very closely. One thing you can do is to conduct a lactate test and confirm that LTP and LT1 do in fact coincide for you. Then as you train, continue to track LTP and use it to help you better understand your current fitness in between lactate tests.