Slightly nerdy question here. Today I did Spencer + 2 which was… unpleasant, but I made an interesting observation. Over the course of the 3 minutes I noticed a relatively distinct pattern of finding the first 1:45 an increasing struggle, and then then I’d be able to nudge the cadence up and things got a touch easier again (obvs still suffering in the last minute). Was this down to crossing the treshold to the anaerobic system? In rowing (my other sport) it’s a well known phenomenon that the boat can have a bit of a wobble 90 s into a sprint race (of round about 4’ duration) and our coach told us that this is roughly when you hit the threshold, and afterwards you can settle in for further efforts. Is that how it works physiologically?
If anything you’re going to have a greater aerobic contribution the further you get into an effort. Rather than a distinct change in physiological systems (there is both aerobic and anaerobic contribution across a 3 min effort), I’d attribute the changed sensation almost entirely to psychology - which isn’t to say it isn’t “real”! The finish line is in sight, you start to realise you can last out the effort, etc. etc.
My general feelings through a VO2 interval: first third (not too bad, effort not hit yet), second third (this is horrific, there’s no way I can last), final third (end is in sight, "wait, I’ve actually got something left in my legs).
Psychology does a hell of a lot in training, esp. max aerobic intervals…