In Norway, 4×4 intervals have almost become a dogma. Scientists from NTNU claim that running four-minute intervals four times, with “active rest” in-between is the best way to increase endurance. By active rest they mean you keep moving, but at a lower pace.
It’s definitely a good exercise to include, and easy to remember.
Another one I like is from the book Running With The Kenyans, and is just as simple: set your watch to beep every 1 minute, and switch between fast and slow pace everytime it beeps. The great thing about setting an alarm is that you don’t have to look at your GPS watch, just turn off your brain and run. Also, at least with my Garmin 305, intervals by time instead of distance means you don’t get any statistics on each single lap. Basically the watch does not control you or tell you how you did. I like that. It’s more exciting to do a benchmark test every once in a while, and not over-monitor the regular runs.
The beep method works just as well with 4 minutes of course, and that’s what I did today. It was fun, and I’m getting over she shyness of running fast. Just let people think what they want.
Legs were nice and rested after two days off. The higher pace was about 4:10/km – 4:30/km, which is fast for me, and It was surprisingly easy. I look forward to crushing my 1km record of 4 minutes, and am curious to see how my 5k time is coming along.