I think a big idea central to pacing your intervals is the convention that you can only spend 1 hour of time producing your max functional threshold power. LTHR is supposed to approximate FTP for interval purposes btw.

Most people can only stand around 40-50 min of true threshold efforts in one session (myself included) so things like 2x20, 3x15, 4x10; ect are all common (depending on your preference). Some hardcore people do 3x20's. I'm not one of them.

When people talk about their work intervals totalling >1hr (3x30's, ect), then by the conventional definition of FTP they are working at a slightly (to highly) lower intensity.


As to what works best for you, I suggest you just experiemnt and see what you like best!

Personally, I prefer 2x20's on a long rolling flat road, 90min of continuous tempo on a long loop or 3x15' (2 climbs, one flat on the way home) for my threshold building workouts.