Intensive and Extensive Interval Methods

Question:

In Nathaniel Mosher's article Training Endurance Athletes, he discusses the Intensive Method and talks about the 20 to 45 second timing of reps instead of doing a set number of reps. He doesn't discuss any sort of timing of reps for the Extensive Method, yet the table that outlines the resistance, reps, sets, rest intervals, etc. indicates that reps should be performed for 20 to 30 seconds and that the set should last about 60 seconds. I don't understand. He also mentions that the volume for the Intensive Method is slightly lower than that of the Extensive Method, but with sets lasting 20 to 30 seconds (or is it 60 seconds?) for the Extensive Method and 20 to 45 seconds for the Intensive Method, and with sets of three to six for both, the volume seems almost identical. Can my confusion be clarified? Thanks for any help you can provide.

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