Lactic acid is good? need more mitochondria?

Intense interval training to develop mitochondria?
I found somebody seriously advocating it:
http://www.biketechreview.com/perfor...tochondria.htm

In contradiction to lots of established coaching lore, that page doubts that
workouts longer than 60 minutes can give much stimulation for building up
mitochondria. (Why would I expect that working under my current aerobic
capacity would generate a stress to make my muscle fibers try to increase
that capacity?)

An interesting argument I found on that page is that older studies were
based on running -- and running short intense intervals on a flat track
requires very high-speed "explosive" contractions which the slow-twitch
muscle fibers are not suited for -- so they did not get stimulated, and
they're the fibers with lots of mitochondria. (Seems to me the same problem
could occur with flat Classic skiing)

But with non-explosive motions like bicycling, intense work intervals toward
100% of VO2max could be effective to stimulate buildiing mitochondria -- and
the page gives details about the biochemistry of this. Seems to me this
argument applies equally to Skating (? and perhaps also to Classic striding
up a steep hill ?)

Anybody heard more about this?

Ken