Daniels suggests two kinds of intervals: interval pace (I) and threshold pace (T).
I intervals are roughly VO2 max pace, which is about the speed a person can go flat out for 11 minutes. Not sure why 11, but that's the way most of these things work.... if I remember my definitions correctly.
T intervals are supposed to be run at about the pace lactate starts to accumulate in the blood, or about the speed someone can hold for an hour, or so.
Anyway, yesterday was I intervals. Last week they had gone fairly poorly- about 20 seconds behind the pace I wanted. I thought with similar weather and traction conditions, it would be about the same.
It wasn't... it was better! Everything was at or a bit faster than my goal pace (7:02) and I had brief moments of thinking- "This is too easy- I must be going to slowly" when I was right on the money pace wise.
It was a good run- one of the best yet. And surprising, too! Though, interestingly, I'm starting a new phase of the program next week- and so far as I can tell, no more I intervals.
Which is all right, I guess... for all the wonderful things that can happen during them, they are a pretty bloody painful...