After the week's plan was made, one question clearly remained: what pace should I run my intervals, in particular the 800s in the first week. This is a somewhat dreadful question, because interval training was what frustrated me last fall to the point that I quit training for a while. In retrospect, the reason may have been (at least in part) that I tried to do my intervals too fast. I could gut them out when they were just a bit over my VO2 max, but as they got longer and faster, I physically couldn't keep up.

It is very hard to know what shape I'm in. My easy running seems to be faster than it has ever been, and I can crank out the tempo intervals without too much trouble. But I haven't run longer tempos or fast intervals in many months.

Pfitzinger's plan makes you run at your current 5K pace for the first two weeks (for interval training), then it switches to 2-3 secs/lap slower than your goal pace, then it accelerates gradually to goal pace. My goal is to run sub-20, that is clear. But to achieve it safely, ideally I should shoot for a time about 19:35. In road races, you *always* run slightly more than 5 kilometers, there are hills, wind, other runners, so the 25 seconds buffer is very good to have. The following table shows lap paces on a 400 meter track and the corresponding 5K times:

1:34 -> 19:35
1:35 -> 19:47.5
1:36 -> 20:00
1:37 -> 20:12.5
1:38 -> 20:25
1:39 -> 20:37.5
1:40 -> 20:50

As for my current condition, my pessimistic guess is ~20:50, my optimistic is ~20:12.5. The plan ideally improves you by 3-4 seconds/lap, so if I start with an assumption of 20:50, it is a stretch if I even can do 20:00 pace by the end. So let's get more optimistic, and assume 20:25 for now. This means that my current pace should be 1:38 / lap = 3:16 / 800 m. If it feels too easy, I might go down to 3:15, but not faster than that, because I have to do 6 of these! Then we'll see how it goes today. Even more important will be the workout two weeks from today: 5 x 1000 meters at 2-3 sec/lap slower than goal pace. If I can do 1:36.5 laps then without having to "gut them out", I should be fine, otherwise I will have to adjust.