Without wanting to sound like WarrenG's lap dog, i gotta agree with him again. My uni professor (that is actually an professor of physiology, not just lecturer] loved high intensity training, and made us read a couple of one inch thick note books chock full of articles for and against interval training, and overwhelmingly it was in favour of interval training improving VO2max. As i stated in a previous post though, this is no guarantee of improved endurance performance. It must be done as part of a portfolio of training that will realise long term benefits for endurance performance, in the long term. There is no quick way, but this method will optimise your training. It should be noted though, that amateurs and those new to training derive the most benefit, most rapidly. Also, like Waren said, I would be doing more like 4-6 reps, 3 sets of high intensity bursts per session. You want to be able to maintain your target power level through all reps, there is no advantage to fatiguing early, especially within the first set. Thats why the session is so short. Lets face it, doing 30/30's it works out to only 4-6 minutes of actual work, and will give the same benefits as up to 4 hours of LT training. I would not recommend any interval shorter than this though. Some studies that i have read tested between varying intervals, and any intervals less than 30s of exertion showed no significant improvement in VO2max, it just doesnt stress the biochemical systems enough to elicit a cellular response, particularly in relation to gene expression [long term cellular changes].