TSS - does heart rate make a difference?

I’m wondering if the TSS score for a workout or an outdoor ride affected by heart rate. I always wear my HRM on a TrainerRoad workout but don’t always wear it on an outdoor ride.

I find that some of my TSS scores for an outdoor ride are much lower than I would have expected. For example my climb up Stelvio last year from Bormio had a TSS of only 152.

TSS is a function of power and your FTP. Heart rate doesn’t come into it.

So you can spend a LOT of time learning about this if you read up on coach @chad 's suggested reading list, (there is a reference to this in the podcast from right before @Nate_Pearson did leadville as well, I will link it if i find it…) pretty much anything by Coggin or Friel. They all establish that you can determine an HrTSS using heart rate, and it will be SOMEWHAT accurate, but unlike power, its never an absolute. HR is affected by so many environmental concerns (Sleep, Fatigue, Hydration, etc) that its hard to treat as a hard metric. Not that it isn’t useful, just that it isn’t an absolute number like power. When you make 250 watts, its 250 watts. Like Henry Rollins says the Iron never lies, 200lbs is 200lbs.

From the TR Blog

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This is exactly right. If you’re interested in learning about the exact calculation, this is the general format:

TSS = (sec x NP® x IF®)/(FTP x 3600) x 100


  • “sec” is duration of the workout in seconds,
  • “NP” is Normalized Power®
  • “IF” is Intensity Factor® (a percentage of your FTP; in other words how intense the effort was),
  • “FTP” is Functional Threshold Power (your best average power for a one-hour race or test),
  • and “3600” is the number of seconds in an hour.


Thanks all that’s great information.

I was curious if HR had any affect on TSS because I notice that some of my rides outdoors don’t have a TSS score that I would have expected.

For example, last year I climbed Stelvio from Bormion & My TSS was only about 200.

There are a few reasons that your TSS might not match up with your expected TSS:

  1. Your Power Meter was not calibrated
  2. You experienced dropouts where your power meter was disconnected for a period of time.

Besides these possibilities, there is nothing else that should be able to throw your FTP off. Keep in mind that a very long ride at a relatively low intensity can have the same TSS as a much shorter ride at a higher intensity.

Hope this helps!