I think I understand CTL to basically be your average TSS per day for the last 42 days. If I understand that correctly then to reach CTL (or Strava fitness) of 100 you would need to average a weekly TSS of 700, or a daily TSS of 100, in other words average 60 min at threshold per day (or 120min at 50% threshold) for 42 days.
Is this the right understanding?
Thanks and Merry Christmas/Happy holidays!
For TR, yes, they use rolling 42 day average of your TSS as their version of CTL.
Other platforms exponentially time-weight CTL, placing more emphasis on TSS of recent workouts, so itâs not always an apples-to-apples comparison. CTL itself is a TrainingPeaks term.
TSS calculation is not correct, however. Youâd have to ride for 2hrs at 71% to get 100TSS.
TSS = [(time in s * IF * NP)/(3600 * FTP)] * 100
So TSS for that 50% two-hour ride =
[7200 * .5 *.5 / 3600] * 100 = 50TSS
Youâd have to ride four hours at 50% to get 100TSS because in a perfect steady state scenario, IF * NP/FTP just squares IF.
I found this example helpful. So, for example, if you want a CTL of 100, youâd need to be doing approximately 15 hours per week. Itâs a guesstimate, but in looking around, itâs pretty accurate.
Thanks for this, looks like I was tracking how CTL was calculated correctly but I had a misunderstanding of TSS. I think 60 min at ftp would do it.
Yeah, he has talked about using an average IF of .7 in thinking about things like this, and thatâs pretty good when I look at historical averages for my athletes. On lower volume it might be a bit higher, like .74 or .75, but typically when you get up around 15hrs, a .7 or maybe slightly less average is decent, and that would get you a CTL in that 100 neighborhood.
FWIW, when I plug in long group or unstructured rides for people I typically use .7 as an IF to estimate their TSS going into the week to balance things and itâs usually pretty good (unless that person really thrashes themselves).
Yeah I believe the TSS calculation was designed for 1 hour at FTP being 100TSS as the baseline. Dr. Coggan would have to confirm that, but pretty sure thatâs right.
Also pg 128 of Training and Racing with a Power Meter, so thatâs either Dr. Coggan or at least Hunter Allen with Coggan signed onto it. 
Yep, though notice that doesnât mean FTP is max 1 hr power. Some riders may never be able to generate 100 TSS in one hour.
Yes I was just trying to use that as an easy example for TSS, but Iâm glad I used both examples because it highlighted that I thought TSS was a little different than it is. I really appreciate everyoneâs input
This also made me remember that my Strava FTP was set higher than it actually is. I wish it would sync to TR
Maybe not in a steady effort, but I feel most can get there in a Zwift Race or Crit for instance, with some âNP bustersâ.
No need to ask him, just plug in the numbers and youâll get 100 TSS.
Well, you never know whether he actually agrees with Allen on that 
You can simplify it to TSS = (time in hours) * IF^2 * 100. I wonder why IF^2 was chosen over another power of IF.
Yeah I know the numbers work out that way, my point was he specifically designed TSS to be defined that way (such that 1hr at FTP = 100TSS) as the reference point, and as you know thatâs what they said in TRWAPM.
The year record attempts were sustaining around 1,000 TSS per day for 365 days. Which puts those records in perspective.
I think the industry has moved on from season PLANNING with TSS/CTL because itâs a foolâs errand. The industry hasnât moved on from FTP*** except for people for whom its in their interest to do so because theyâre selling something else. **
TSS has its uses. Primarily I use it as a check sum, and itâs also a really good tool for long term REVIEW.
*** I would include FTP and critical power concepts in this same discussion.
** These are just my opinions.
Iâd agree. Iâm still looking at TR plans with an eye on the hours and TSS Iâve done in previous years to get a sense of confidence.
But only because Garmin make it difficult to analyse/manipulate EPOC load data. Which I suspect is much better. I also look at active kcal.
I outperform Friel/Couzens predictions on hours and bike TSS for a mid pack Ironman triathlete, by about 30%. I put that down to indoor structured training.
Thatâs kind of a funny story. When Andy first came up with TSS, he was trying to mimic the formulation of TRIMPS. He had a long series of steps which he posted to the old Wattage List. Then maybe a day later he decided to revise the definition with a slightly different weighting scheme, and revised the long series of steps. A couple of hours after he posted, someone posted with âUm, donât all those new steps reduce down to 100 * duration in hours * IF^2 ?â
Hahaha. If thatâs true, then thatâs too funny. Iâm a math and physics guy, so these manipulations are completely intuitive and immediate.
Recently, someone posted a review by researcher of Loughborough University that compared the Cricital Power model to a power law. I was surprised by the state-of-the-art. One or two of the authors were from their math department and they included (mathematical) propositions and had proofs in the Supplementary Material. (These were things you could ask math undergraduates and they should know the answer.) When I interviewed for a position there, I was told that the sport sciences department was quite good.
Yeah, I have never gotten into thinking of my training in terms of CTL ramp rates and the like, so this sounds quite alien (and indeed, archaic) to me.
Do you have any alternative that is better? Iâm seriously asking.
I am not aware of another metric that is as universal as FTP (feel free to lump in CP). For most athletes, i. e. those that are not on the shallow part on the top-right of the S-curve, FTP (however you want to define/measure it) does strongly correlate with all other performance metrics. Whenever I hear replacements, refinements or some such bandied about, I almost always think âThe juice is not worth the squeeze.â â except in certain select circumstances.
