Originally Posted by GeorgeBMac

There was a lot in that video -- which leads to a lot fine, possibly conflicting points, but, as I remember it:
I think the comparison (at least the one I paid attention to) was between 4x4 @ 95% vs 4x8 @ 90%. True, there were two other ranges in there, but I don't think either of them were intervals...

Right now I am doing 3x4 @ 95% and planning to go to 4x4 after the New Year. But, 4x8 at 90% sounds very interesting... I think mostly because of the duration factor: 12 or 16 minutes just doesn't "feel" long enough to do much good. Granted it is actually twice that long with the low intensity part of the interval -- and even longer if you add in warm up and cool down. But, still, it feels kinda short...

Edit:
I might add: it would be impossible (in my opinion) to do this without a heart monitor. I know in his studies, the perceived effort and the actual, measured effort was always very close. But I can't do it without a heart monitor -- especially if I'm shooting for a difference of only 90% - v 95%.

But, DigiFit on my IPhone (along with the Polar H7 monitor) does a great job: You set the blocks to show the target heart rate range and duration -- and then 'just' raise or lower your heart rate to stay in the appropriate block. Sweet!