At the end of my base phase, I like to do workouts like;
-8x 400m Fast (faster than my mile pace) w/ 3 minutes recovery
-16x 200m w/ 2 min recovery (same pace as above)
I feel these workouts really help, and when I transition in 5k pace work (I am a 5k runner), it seems like a jog. I probably won't stop doing these because my body responds really well (I get use to a really fast pace, and ~2 miles of quality doesn't tire me too much), but what is the actually benefit? What am I working? Is this basically what Dr. Jack Daniels is calling for?