The standard American zone limits are nonsense, except for the 4/5 boundary. The new thinking is that there are really only 3 zones, below VT1, between VT1 and VT2, and above VT2. VT2 should be at the zone 4/5 boundary. See my new workout thread for a discussion of the ventilation thresholds. They are what I use on a ride, not arbitrary zone boundaries. I agree with the above, that work at all intensities is valuable. The issue with zone 3, whatever that is, is that it's too easy to do too much work in zone 3, leaving one too tired to effectively work in the upper zones, where the progress really is. That's sort of the essence of the 80/20 thing, though I also found it boring and don't do it. I much prefer group rides at a range of intensities. One need to find one's limits at all intensities and what mix of intensities work best to improve one's times. Thinking again about that 80/20 thing, on my very first group ride, my fellow riders forcibly pointed out to me that one produces a faster average speed by working very hard on the climbs and then recovering on the descents and flats.

.Be that as it may, more work like [MENTION=426467]rubiksoval[/MENTION] describes will produce the best results, that is if one has the training and talent to be able to do that.

Max HR is never a useful tool for figuring out effective working levels. VT1 and VT2 are far more effective.

So what is the name of the geometrical solid formed by rotating an oval on one of its axes?