More like anything from about 5 minutes onward.
Think of it this way: if it didn’t ICU wouldn’t be able to do the reverse, i.e., accurately estimate your FTP based on your power at whatever duration.
Except I have yet see name-calling or the questioning of one’s sincerity, etc.
In my years of cycling I’ve noticed a few things as my Strava fit score rises my usual rides have less effect on that fit score. Also, as my fit score rises so too my average speeds and increasing achievements.
I would put zero value in it to compare two cyclists and I suspect comparisons between the same cyclist separated by a couple of years would be less useful than one may think.
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yes, and context is everything. Its primarily used by coaches to plan out the base and initial build, leading up to races. During base, one clear value of using CTL is as a proxy for “the size of your aerobic engine” or “increasing aerobic fitness.” Your aerobic fitness (aerobic capacity) scales with increasing number of hours, but if you don’t have 15-25 hours/week to train then you can reduce hours and in exchange for doing more ‘advanced aerobic’ work (tempo and low threshold aka sweet spot).
For example here is the 26 week full base (base1-base4) + build1 & build2 from VelociousCycling / Tim Cusick:
That is the 8-12 hours/week plan (weekly TSS in 350-750 range).
and a similar “base is about building aerobic fitness / CTL” chart for 8-12 hours/week from FasCat:
and same for TrainerRoad Mid Volume (Sweet Spot Base 1 > Sweet Spot Base 2 > General Build > Climbing Road Race)
IMHO the biggest value of tracking CTL is during the base and initial build phases. In classic periodization this is when you are NOT doing race specific interval work, it is when you are doing a lot of zone2 plus ‘advanced aerobic’ work in zone3 and zone4. This is when you are building the aerobic engine. This is when you are training to train. This is when CTL is a good proxy for the amount of aerobic development you’ve done, and in addition allows for easy comparison between the current base season and previous seasons.
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Can’t disagree with that!
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and it shows why TSS/CTL is better than simply using hours… because TSS factors in both hours and intensity.
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Well, to be fair, Strava did not invent the fitness/fatigue model. This was proposed in 1982 and Strava is simply using those terms. I believe the newer terms are more accurate, but the person with the “original intent” for these modeling ideas did specifically use these terms.
- He wasn’t referring to Strava (cough TrainingPeaks cough).
Really? I thought TP used CTL/ATL/TSB?
and he wasn’t referring to TrainingPeaks either…
Believe that reference is to Bannister and TRIMP, although I thought it was the early 1990s but really not sure about it.
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Ohh, did I my cross memory with WKO for that?
Earliest study cited by Coggan is 1975
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Proposed in 1982 by Bannister the fitness-fatigue model argues that different training stresses result in different physiological responses.
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Thanks old and cali, looks like Bannister was modeling dose-response and correlating those to fitness/fatigue all the way back in the 1970s.
- Chronic training load, or CTL, provides a measure of how much an athlete has been training (taking into consideration both volume and intensity) historically, or chronically. It is calculated as an exponentially-weighted moving average of daily TSS (or TRIMP, etc.) values, with the default time constant set to 42 d. CTL can therefore be viewed as analogous to the positive effect of training on performance in the impulse-response model, i.e., the first integral term in Eq. 1, with the caveat that CTL is a relative indicator of changes in performance ability due to changes in fitness, not an absolute predictor (since the gain factor, ka (or k1 ), has been eliminated).
Perhaps this is why Strava and others use CTL as a relative indicator of changes in performance ability due to fitness but opted to just shorten that and go with “fitness” for the sake of brevity?
Where did all the references go??
TSS is one metric for sure, but it erroneous to call it the “best” as @mcneese.chad has done. It’s on in the toolbox for sure, but it’s weakness is it’s quadratic in nature. A combination of RPE, Kj burned, HR/TRIMP and TSS really are needed to inform training load. I can’t remember the example exactly , but something like an hour at 1.00 IF gives you the same TSS as hours and hours at a slow pace where you expend exponentially more energy, muscle fatigue, etc… which is obviously absurd. The recent Scientific Triathlon podcast with the ex-Sunweb guy actually touched on this which is becoming the more common thought.
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LOL, plucking one word (that I deliberately listed in quotes to de-emphasize it in the first place) and then ignoring the entire context I added around it is a bit funny. 
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According to this slide, TSS parallels RPE pretty closely, but gives less weight to intensity than TRIMP during exercise at <50% of VO2max. (At >100% of VO2max, HR-based methods such TRIMP and EPOC don’t really apply, because HR reaches a plateau.)
I mean I’m not disregarding all that you are saying, which is very good advice, but I absolutely picked out that word specifically because it’s 180 degrees from accurate and I think it’s important to note that for people who are asking the question about it.
- So what is a better, single metric to use in the context I commented on then?
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