Originally Posted by ZeCanon

ok, a couple more details about what I said before. One of my CSU teammates down here in Tucson with me is working on his PhD in exercise physiology (he's also a national level coach in Canada). He showed me a couple papers. I've only seen them in hard copy, I'll see if I can find them online for you guys. I still need to go back and ask some more questions, but here's the gist:

The goal is complete slow twitch fiber recruitment. I assume that results in the greatest gains. Simply put, the effort sustainable for 20 minutes straight (let alone 2x20) is below the level at which maximal slow fiber recruitment is achieved, while still adding extreme levels of fatigue. A more effective method is to use shorter intervals at slightly higher intensity, with shorter recovery between intervals. 105-110% FTP seems to be about right based on what I saw. Intervals should be in the 5 minute range. We did 8 of them, with 1 minute recovery between each. The number of intervals is what should increase, not the length of interval. The first two or three feel ok (as the first 10 minutes in a 2x20 would), the last ones get hard. You will work you over every bit as much as a 2x20 or 3x20 session, but apparently with bigger gains.

Now the numbers: I saw two studies, the first putting cyclists through 14 weeks of 2x20's. Total gains: 2.2% at threshold. The second had cyclists do only 7 weeks of the shorter intervals and saw a 7.9% increase in power at threshold. That's pretty huge. The fact that it was this particular guy showing me the studies and advocating the approach pretty much sealed the deal for me. He said there are others but he only had the two on hand.