In anticipation of using the smart workouts (cheap android device on its way!), I’ve spent the better part of the day trying to make sure my fitness signature is representative of my current fitness. I’ve always felt that Xert overestimates my TP, so I started to do some fiddling with my signature, finding some of my best efforts and lowering TP/raising HIE (from around 18 to 25) in tandem until I reached what I thought was a good estimation. I ended up recalculating my entire history (2 years) with a revised seed value of 900/23.5/305, and let Xert do its thing. I’m now at 1044/18/326, so it seems that Xert models me as a high TP / low HIE type of rider, regardless of the seed value I start with. I might be able to hold 315 watts for an hour right now, but 326 is a stretch. Ok, so here’s my question: LTP is very sensitive to changes in the TP/HIE relationship - as I would lower my TP and increase my HIE to a level I thought was more representative, my LTP would drop. During the recalculation, my LTP increased from 265 to 280, the result of Xert dropping my HIE from the seed value. How do I know what is right for me? I’m a big believer in your LTP ideas/workouts and sweet spot work in general, and want to make sure my LTP is as accurate as possible.
Sorry for the long winded question - Xert is an amazing piece of work, and it’s really changed how I look at my training. Thanks!
What we are seeing is the HIE and LTP are negatively correlated and LTP and TP are positively correlated.
To get LTP as accurate as possible, you’ll need an accurate signature as it is derived from it. I would not pay attention to what you believe you can hold for an hour as being what should be you TP. If the data is seeing that you don’t fatigue above 326, then that’s what you should be training to. If you feel it truly is off, then do the Xert test workout and see if you can generate two or more separated points of failure. This will help better identify HIE and TP, which will then determine LTP. Also, another thing you can do to see if a test is warranted to pedal at LTP. If you feel like you’re not getting tired at this intensity but going any harder starts to make you tire, then LTP is probably pretty close. If instead, you’re breathing is starting to labour and you feel like it’s a bit hard, either your HIE is too low, your FTP is too high or both - likely a bit of both. Similarly, if LTP feels a bit too easy, this could mean that HIE is too high, TP is too low or likely a bit of both.
Thank you very much for the quick reply, Armando. I’m planning on doing the test workout later this week, which I hope will add some clarity to my signature. Based on your perceived effort guide for LTP, I think my current signature is closer than before - 265w felt just a bit too easy for a sweet spot type of workout.
Is there any specific point on the power-duration curve that represents HIE? Is 5 minute power an approximation? The reason I ask is that in the Training Peaks power profile, my 5 minute power was always my strongest characteristic, 20 minute power was a close second, and 1 min and 5 sec power pretty average, at best (I’m no sprinter!).
HIE applies from 1s to 60s to 20 minutes and more. Xert uses a mathematically continuous relationship of how much HIE is usable for a given intensity. So there isn’t really an duration that represents HIE. To get a feel for how much HIE affects a particular intensity, experiment with the signature calculator. Enter 3 pairs from your current PD curve and then adjust a value to see what effect it will have on your signature and PD curve. You’ll notice that 5 minute power is still very much tied to TP. 1 minute power however will cause HIE to change more.