Running TSS (rTSS) is calculated using Normalized Graded Pace, so it is supposed to account for changes in pace when going up or down hill. For some people this is enough to give them accurate numbers while trail running. For others it doesn't account enough for the other factors that would change your pace a lot relative to effort, like the surface, wind, short steep pitches up and down that GPS can't detect well, and the rockiness/rootiness/general technical difficulty of trails. In this case we recommend changing the TSS calculation for trail runs to heart rate based TSS (hrTSS) instead of pace based TSS. You can do this for each workout
* Click on a trail run to open it
* Click running shoe icon in the upper left corner of the workout view
* Switch the run to "other"
* Click the "files" button, then click "recalculate"
* Where you saw rTSS (run TSS) before you should now see hrTSS
* Click the timer icon and switch the type back to running and don't recalculate
For this to work you do need accurate default heart rate threshold and zones set in your personal settings. Recalculating TSS based on heart rate should give TSS numbers that seem more reasonable when compared to road runs of similar duration and intensity.