Unless you use software to generate your power distribution curve, same as you do in cycling, so that you know exactly what power you can generate and for how long. The simplest which will give you a ball park idea is to reverse "engineer" your power numbers. For the first 6-8 weeks, you should totally ignore the power numbers when you run as they mean nothing to you as you have no reference points yet. For these 6-8 weeks, just run and record the power data. Post run, look at the numbers and start writing down and recording the information. For a certain power you will run at a certain pace, and the opposite is true. So create 2 columns, one for pace and one for power. Your pace column will be from say 7min/km up to 4 mins/km (or whatever the fastest sprint you can do). Then go run, do 30s sprints, do 1 min sprints, 4-5min VO2max intervals, 20 min threshold runs, 30 min time trials, long runs, recovery runs. After you run, record your average pace and slot it in between your 7 and 4 min/km, see what your average power was for that run and write it down next to the pace. Zoom in on your VO2max intervals or sprints, write down the average pace and corresponding average power. In this way you start to build the 2 columns with Average Pace v Average power for many iterations of pace between your upper and lower extremes. Some runs you will have the same average power, you can then use this as a check to see if this runs power is similar to previous runs. If so then you know the data is becoming reliable. If it's a run with an average pace you have not done before, then you slot it in. i.e you had done runs at 5:15 and 5:25 mins/km and recorded the power, this run is at 5:21 mins/km, so you can slot the pace and power numbers between the 2. Eventually you will have a whole column of different paces between 4 and 7 mins/km and a corresponding column of different power numbers. Finally go do a lactate threshold test, will give you your lactate pace as well as your critical power. Now with all this data you will be able to set your zones for creating your workouts and plans https://www.velopress.com/jim-vances-running-power-zones/ You can also start testing your data. Do a race, go for a run, decide before what your goal pace will be. Look at your table of pace v power you have built up and see what the corresponding power will be for the pace you want to run at. Then go run at that power, ignoring pace and see how you do and whether the numbers work. They should do if you have been methodical. Same with races, you want to target a 1:50hr 21km, your pace will be 5:42min/km, look up in your table what the power for that pace is. Then run the 21km at that power, run on power and see how close to your target time is. Periodic do lactate test, recalculate your Critical Power (same as you do for cycling FTP), redo your zones. Rinse and repeat, to get faster, but running to power rather than to pace.
