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Is there any sort of equivalent for those that train by HR?


Is WKO useful if I've not any PowerMeter but only a GPS ? (Forerunner 305 with cadence/speed option)

Joe Friel

Clement--useful for running, yes.

Joe Friel

Krystyna--Yes, TrainingPeaks.com offers a HR version of what I described here.


I use the WKO and understand how TSS fits in to TSB, CTL ATL, and the Performance Manager chart, but the unit analysis of the equation on which it is based has never made sense.

[(sec) x (watts) x (watts / watts)]
(watts) x (seconds/hour)

= hours

So it is a really geeky, unathlete question, but shouldn't TSS be unitless? Like Intensity Factor?

Joe Friel

Madeleine--I try not to worry about such things. :)

Michael Schaefer

Since IF = NP/FTP and since s/3600 = hours, the TSS formula simplifies as:

TSS = hours * (NP/FTP)^2* 100 = hours * IF^2 * 100


I also started using WKO+ and TSS but my problem is that this formular is based on pace. I am orienteer, meaning I run a lot offtrail somewhere in the woods. there is also a lot of climb. The surface and the climb both reduce running pace which will reduce TSS. Is there a possibility or ways to get a TSS but based on duration and heart rate?

Joe Friel

Wolfgang--TSS in WKO is based on 'normalized' pace, which takes course gradients into account. It does not, however, account for trail conditions or wind. That said, if you use TrainingPeaks.com instead of WKO for your data download and analysis you can then use HR to determine TSS.


ok, thx for the hint. I will give it a try!


It is vital to be recording HR when you have a powermeter or a GPS watch for running? Will it give you better data for TSS/ CTL?

Joe Friel

Chris--No, HR is not necessary for TSS in WKO+.


Just one for Madeline:

Technically/mathematically hours is the correct units but really its hours x [how hard you tried]. Essentially its a measure of the energy you burnt, or the effort you put in, in physics its called "work done".

The reason the units are confusing is we're dividing one power figure by another, implying that the units cancel out to a ratio, but the FTP figure can be regarded as a constant for a given athlete in a given period, so in that case the true units are hours x power which gives the correct units for work done in physics.

Its a very sensible (great) way of scoring a session although recently I decided it would be even more useful to track my TSS separately in each training or HR zone. So if my goals are building up base in the winter then seeing TSS for just my upper L1 to upper L2 figures seems more relevant to the adaptations I am trying to force at the time, rather than total TSS.

Joe I'd be interested in whether you agree with splitting up TSS into HR/power zones like this.


Joe Friel

Paul--That's an interesting idea. I've never done that. Will need to think my way through it.

Bill Osler

I know this is an old thread but I'm not sure that thinking of TSS as work in the physics sense is meaningful. As an alternative I would suggest that TSS/100 is the number of hours one would have to ride at a power = FTP to achieve similar training effects. Of course it generally is not possible to ride over an hour at FTP but looking at TSS that way sheds some light on the intensity of the effort.

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