# Is a month of WKO+ data sufficient for CTL calculation?



## soulfly_nyc (Feb 16, 2007)

Is 1 month of WKO+ data sufficient to calculate my CTL reliably?

I checked my WKO+ and my CTL is 33. My ATL has recently been as high as 79 but now on my rest week it has dropped to 49. These numbers are result of about 1 month of powertap training and does not account for about 10-15% of my training week since it doesn't count races...

How much data is needed for a robust and reliable CTL calculation?


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## Guest (Aug 22, 2009)

Depends.

What are your training constants set at? And did you use seed values initially?

Confusing? Don't feel bad, I think it is. The training constants determine how many days back the calculation goes for your CTL (same applies for ATL but ATL and CTL use separate time constants). If yours is set at 42 for CTL (probably 7 for ATL) then you probably need to train longer than 42 days to get reasonable idea where you are at.

Seed values are where you initially set your CTL. If you got up off the couch after years of channel changing and set it at 0 then maybe thats accurate, if however you have been training for a while but without using a powermeter then a higher estimate might be in order. There are some guides for making this estimate on the training peaks site. But its important to realize I (you) could reach a CTL or 100 just by seeding the chart with 100 as a start value so what you input initially in the chart is a factor right now, until you have ridden enough days to get beyond the time constant from earlier.

This is no exact science either, even very experienced riders will often maintain more than one PMC chart with different time constants to try and evaluate which one most applies to them. Yours might even change over time. A 25 year old rider is likely to be effected by training over time much different than a 45 year old rider right?

Maybe Argentius or iliveonnitro can chime in, they are both better at using less words than I to explain something.


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## asgelle (Apr 21, 2003)

kytyree said:


> The training constants determine how many days back the calculation goes for your CTL


The performance manager as developed by Coggan and implemented in WKO+ always uses all available data going back to the earliest workout.


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## Guest (Aug 22, 2009)

True but I believe the time constant weights the impact of the more recent workouts reducing the impact of prior workouts.


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## STARNUT (Jun 19, 2005)

The amount of data needed is no different than in your stat class from college; the more the better. The CTL curve uses an algorithm that weights the last 42 days worth or effort or lack of effort. It is in effect a "rollin" calculation. So the really short answer is 42 days. The ATL is similar deal but a much shorter time frame, like 14 days. You can manipulate the ATL and CTL constants for various factors but most people fall into the 42/14 windows.

I'd say you current amount of data is not sufficient for CTL to be reliable enough for what you want. Additionally, the underlying assumption is that you have your FTP correctly set. all of the curves on the PMC chart are predicated on your FTP. If FTP ain't right, the lines ain't right.

Secondly, racing is training. I always tell my guys that if you're on the bike and the wheels are moving, I get a file. They are after all paying for a result and I need to know if it was my coaching or their race tactics that hosed them....... thus I get a file for everything. You should always race with a PM if you have one. The info gathered is extremely important and can be used to help nail down FTP and show changes in fitness at long and short durations. 

Why are you not using your PM in races.

Starnut


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## Alex_Simmons/RST (Jan 12, 2008)

1 month of data without a reasonable seed value for starting ATL & CTL is insufficient. 4 months is about right.

As for the proportion of data needed, any more than 10% of ride days missing is not good but you should be able to reasonably guesstimate TSS for days sans power meter. Guesstimation ability comes from experience and examining similar rides.


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## asgelle (Apr 21, 2003)

STARNUT said:


> The CTL curve uses an algorithm that weights the last 42 days worth or effort or lack of effort. It is in effect a "rollin" calculation.


Why do people continue to propagate this misinformation? Even a cursory reading of Coggan's derivation of the performance manager or Banister's original work shows it is simply not true.


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## Alex_Simmons/RST (Jan 12, 2008)

asgelle said:


> Why do people continue to propagate this misinformation? Even a cursory reading of Coggan's derivation of the performance manager or Banister's original work shows it is simply not true.


CTL is an exponentially weighted moving average of the daily TSS, with a half life set to (typically) 42 days.

ATL is the same thing but with a shorter half life, typically around 4-10 days, with the default setting at 7 days.


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## asgelle (Apr 21, 2003)

Alex_Simmons/RST said:


> CTL is an exponentially weighted moving average of the daily TSS, with a half life set to (typically) 42 days.


How is the starting point for the moving average set?


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## iliveonnitro (Feb 19, 2006)

asgelle said:


> How is the starting point for the moving average set?


I may be misunderstanding your question. Are you asking how you change the starting value for CTL and ATL? Those are what the moving average are based off.

Under your PMC chart, click: Options > Customize Chart > and change your CTL and ATL starting values.


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## asgelle (Apr 21, 2003)

iliveonnitro said:


> I may be misunderstanding your question. Are you asking how you change the starting value for CTL and ATL? Those are what the moving average are based off.


What I'm saying is that moving average is a bit of a misnomer. All workouts are considered in the calculation of ATL and CTL. An early value does not drop off as a new one is added. It's easy enough to see this in WKO+ by adding workouts with high TSS values at earlier and earlier dates. The effect gets smaller (exponentially) as the date gets earlier, but if the added values are large enough, there will always be a detectable effect.


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