I’m having a hard time figuring out how TSS is calculated. The only thing that resembles a formula I can find on the Internet is this:

TSS = (t * NP * IF) / (FTP * 3600) * 100

where t is the ride duration in seconds.

That looks awfully complicated. For one thing, why measure t in seconds only to divide by 3600? Why not just measure it in hours (1 hour = 3600 seconds)? For another, isn’t IF just NP / FTP?

So the formula simplifies to this:

TSS = t * IF * IF * 100

where t is the ride duration in hours.

But why IF twice? A ride of the same length, but half as intense, yields a TSS only a quarter as much? What’s the reasoning behind this?