Is TSS score linear?

triguy44

If you are riding absolutely perfect, will TSS increase at the same rate? IE:, if you rode for an hour and racked up 50 tss points, would 2 hours yield 100 tss points?

Scott Alexander

One hour @ FTP is 100 TSS even, if I recall. But all TSS are not created equal! I'm not a WSM (I didn't even stay in a Holiday Inn last night), so someone else will have to explain why.

Coach Rich

Yes, if you maintained the same Intensity Factor (IF) across both rides. 

tgarson

Yes as Rich said, if you ride at the exact same intensity (wattage) then TSS will be linear with time.

But as Scott said, all TSS are not created equal, meaning it is a mathematical model that is meant to approximate training stress. With practice, you will see that there are a whole lot of ways to accumulate say 200 TSS points in a ride through variations of intensity and duration.

At the end, they all 'cost' you the same TSS, but some of those rides will leave you significantly more fatigued than others, i.e. the model is not perfect.

William Jenks

TG makes a REALLY important point. The TSS model is flawed. It works best when you are in a relatively narrow range of differentiation of workouts (time and intensity). But it is, nonetheless, very valuable.



The basic calculation that's done is that you do some averaging on the power to give you a "rolling" IF for any given moment. The IF is raised to a higher power to regulate how much that "second of work" costs you in TSS points, where higher intensity stuff costs a lot more points than lower intensity ones. Then you simply add up the points earned each second. So, as a result, as long as you hold IF constant, it is linear with time. A scaling factor is applied so that 100 points = 1 hour at FTP



To give the formula in qualitative terms:  

• NP is the fourth root of the rolling average of the power raised to the fourth power.  This way of averaging makes the high power moments more important in the average.  It's the reason NP > AP.
• The IF is NP/FTP.  So that fraction is 1 when you are riding steadily at FTP, a little over 0.8 riding steadily at HIM power, and around 0.7 riding at IM power (for most people).
• The TSS points for any given second are IF^2 * (100/3600), where the latter fraction is what scales an hour to 100 points at FTP.

 

 

To give an example where the TSS model fails, consider the idea of doing a ~3 hour ride at around 0.8 IF (constant). This will simulate the number of TSS points that's pretty close to ideal for a HIM ride of about 180. Hard, but not crazy. Now consider the theoretical possiblity of riding at 100% FTP for 108 straight minutes, which would also give you 180 TSS points. By definition, this can't even be done, since FTP is supposed to be how hard you could ever possibly ride for 60 minutes before dropping out of the saddle in exhaustion. :-)

tgarson

That's a great example William. I always had to resort to trying to get people to examine their historical data and just think about how different rides at different TSS' made them 'feel', yours illustrates the point far better!