I struggled lots to get the fatigue out of my legs after the 8 mile tempo on Thursday followed by a 22 mile long run on Saturday. It took me a full four days to be in shape for another workout. I had planned to run it Wednesday but it had to wait until today, Thursday. That's cutting it close until my next workout on Sunday which will be a long run comprised of 8-10 miles easy running and Grete's Half Marathon in Central Park at a quicker pace. Six days later I will race the Rock 'n' Roll Brooklyn Half. I doubt I can do any kind of workout between the two. It's "scary" how few workouts I get done at all. After Brooklyn, my legs are likely smashed for a week which puts me at two weeks to go. Not much I can do from there anyway. At least I won't be overtrained for the marathon.
The workout I did today is my all time favorite: 3 by 1 min./2 min./3 min. with jogs in between for the same period. Paces are about mile/5k/10k. It's not really important to hit a certain pace. Key is to have three distinct paces. The workout can be done on any course or surface. If you don't have a great feeling for pace, it may take a couple of tries to get it right. As always in life, don't worry about making mistakes as long as you address them afterwards. The most common error is to go out too hard and then not being able to go the same pace for the third set. If in doubt, start out a little too easy. For those of you running with a GPS - I know, fucking everyone - DO NOT USE IT. This workout is also an exercise in judging pace by feel.
For runners who tend to get injured or who are 40 and older, it might be better to do 3x3'/2'/1' because you can ease into it. If you do it this way, you'll notice that the two hard blocks are 2'/1'/3' in the middle because the jog break after the fast 1' effort is rather short and you have to go back into the solid 3' still huffing and puffing.