Is XSS and TSS equivalent?

Uploaded a ride today. TP reports a TSS of 77. Xert reports 91. My FTP on TP is actually a few watts lower than my threshold on Xert, so I would expect TP to be slightly higher if anything. Ideas?

If you haven’t had a chance to read our blog post on this topic, please do: This blog too shows how strain can vary significantly despite TSS remaining unchanged:

The variance between TSS and XSS can increase a lot more when you go deep. TSS doesn’t account for fatigue directly. It only looks at a rolling 30s average.

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Thanks Armando. I didn’t go deep at any point during the ride, BUT…it did feel like a harder effort than a 77. I was surprised when I saw it in TP.