http://well.blogs.nytimes.com/2009/06/2 ... a-week/?em
I've been inadvertently doing something very similar to this for over a year now. I workout at the Washington Sports Club basement gym in Gallery Place after work about* three times a week. The club's parking validation gives me free parking for an hour or less; after that, the larceny commences. So I began to do high intensity interval training 2-3 times a week simply to keep the wolf from parking garage door upon leaving. What I've found is that I get as much--and in some ways, more--results from this 30-45 minute "satisficing" regimen as from those years in twenties when I was working out 2 hours+, four times a week. In some areas, I am actually stronger than I was then, despite the fact that I'm not nearly as consistent now either. I also have about three times more endurance than I did when I headed back into the gym last year. The only down side has been psychological: I don't feel like I "earn" it like I used to. So when friend Matt, who has run several marathons over the past year alone and exercises with enviable discipline and vigor (read somebody who really IS in shape), said to me last week "Stephen, you're looking really fit," I felt a twinge of guilt--even a little pinch of embarrassment.

Yet according to this study, it looks like these shorter periods of interval training might indeed be not only quite a lot better than nothing, but perhaps even better than the much longer and more punishing periods/intervals of those traditional regimes of yore. That would certainly explain the baffling results I've been getting, and maybe relieve me of some of the guilt--this nagging sense that I'm getting away with something I have no right to enjoy, as if both ingesting and thoroughly metabolizing the proverbial free lunch. Apparently, it's quite possible that the body just works that way. And you don't even have to keep looking over your shoulder to see if karma and entropy are gaining on you. But the best part of all this is that the old "I just don't have time" rationalization might just be empty after all. Thirty minutes (counting rest) is time enough, in a pinch. (A stop watch is really useful for this approach, BTW, and helps maintain a sense of structure, as well as urgency.)
When it comes to distance running, apparently a similar logic applies. The above link dovetails nicely with another piece I read a few weeks ago on "run-walking," in which some marathoners were claiming they posted much better times using that technique than they ever could using the grueling purist's approach to distance running.
http://www.nytimes.com/2009/06/02/health/02well.html
Good news for the lazy and the busy alike. As I live solidly in both of those categories, I'm awfully happy right now.
Cheers,
Stephen