Trying to understand how CTL, ATL and TSB are calculated in Suunto App

isazi

@MarioPedraza if it isn’t, it may be a bug. CTL is the 42 days TSS average, ATL the 7 days average. TSB is yesterday’s CTL - ATL.

Mads Hintz-Madsen

Hmmm, I think that the statement “ATL is the average TSS over the last seven days” may not be entirely correct. According to Training Peaks:

"…
TrainingPeaks calculates ATL, by default, as the exponentially weighted average of daily TSS for the past 7 days. Note that, in effect, ATL represents the training an athlete has done in the past two weeks given the nature of exponentially weighted averages.

Formula
ATLtoday = ATLyesterday + (TSStoday - ATLyesterday) (1/ATL time constant)
…"

I guess that the time constant in the above formula (which is not limited to 7 days) is set so that the weighted average is roughly equivalent to a 7 day moving average. By doing it this way, you will have a more smooth rolloff in the ATL instead of a somewhat abrupt transition to zero when you haven’t done any training for 7 days.

Source:
https://help.trainingpeaks.com/hc/en-us/articles/204071894-Fatigue-ATL-

isazi

@Mads-Hintz-Madsen good to know! Suunto is licensing these metrics from TrainingPeaks so they should work as defined by TrainingPeaks.

MarioPedraza

Thanks @Mads-Hintz-Madsen.

So we cannot calculate fatigue because we do not know how to calculate the ATL time constant. Well, we have it in Suunto App, it was out of curiosity.

MarioPedraza

More info if interested.

https://forum.slowtwitch.com/forum/Slowtwitch_Forums_C1/Triathlon_Forum_F1/Help_me_understand_the_pmc_calculations_of_ctl_and_atl_P5530452/

MarioPedraza

Now that I have a 30-day trial on Training Peaks, I see that the TSS values calculated by Suunto App is different from the TSS value of TP. So CTL, ATL and TSB do not match. In my case, I use Stryd so the TSS calculation takes power, and I have all the values correctly configured in both places. Shouldn’t they be the same?

Brad_Olwin

@MarioPedraza You need to have zones set up the same in both. My TSS values match.

herlas

@Brad_Olwin this has been discussed many times before, Stryd zones are defined with upper zone 3 limit as the FTP value, Suunto on the other hand uses upper zone 4 as the FTP and this is fixed there’s no setting.

This makes all power-based workouts on Suunto to have TSS under-estimated.

Training Peaks allows to set FTP value on its own, meaning not tied to a zone.

I’ve been using TP TSS scores and updating my Suunto workout TSS for almost the last 3 years that I’ve using Stryd to have same realistic values. Tendencies will be similar when not doing so but numbers will not be close to what they are.

Hope this helps @MarioPedraza

FYI https://forum.suunto.com/topic/6945/running-tss-power-based-need-option-to-set-ftp?_=1706106190848

MarioPedraza

@Brad_Olwin That’s how I set it, but the values are different in my case. Who knows…

MarioPedraza

@herlas Thanks.

Brad_Olwin

@herlas OP did not say power. I don’t use power, mostly HR.

herlas

@Brad_Olwin it’s there but no worries

Brad_Olwin

@herlas OP quote in first post
ATL is the average of your TSS over the last seven days. So, if I haven’t trained in a week or 10 days, my ATL should be zero, but it isn’t. Why? How CTL and ATL are calculated? Thanks.

MarioPedraza

@Brad_Olwin Ok