Looking to break out of an L.S.D. slump? Mihaly Igloi was a Hungarian distance coach who had great success using a large volume of short intervals usually ranging from 100 to 400 meters. He coached Americans Bob Schul (gold medalist in the 5,000 in 1964), Jim Grelle (former American record holder for the mile and 2 mile), and Jim Beatty (first to break 4 minute mile indoors) among others.
While he incorporated varied pace and stride length in his workouts, from what I’ve read easy days were few and far between. His athletes did 13 workouts a week, and just about every one included short intervals.
If you visit letsrun.com, you’ll find a facinating discussion of Igloi’s methods, including input from a few runners who actually trained under him. Another source worth reading is The Long Run by Bob Schul.
For the last 2-3 months I've added more short intervals- 8-10 x 400s twice a week, and there is no doubt they really are helping. I vary the recovery and intensity so I am not doing precisely the same workout each time. As soon as I feel ready I will move up to 800s, and now that I am comitted to entering a 3 race trail series, I will also add some uphill intervals.
If you are doing short intervals for the first time, take my advice and ease in with just 6. No sense risking injury.