If you're training for an intermediate distance event (10K to half-marathon), your target pace training should take the form of longer intervals that become progressively longer as you build fitness. Here's an example of a target pace interval workout progression for a 10K runner in a 16-week training plan:
|Weeks 1-4||4-5 x 1K @ target pace 3-min. jogging recoveries|
|Weeks 5-8||3-4 x 2K @ target pace 3-min. jogging recoveries|
|Weeks 9-12||3-4 x 3K @ target pace 3-min. jogging recoveries|
|Weeks 13-15||2 x 4K @ target pace 3-min. jogging recoveries|
If you're training for a marathon, it's best to integrate your target pace training into your long runs. In the early weeks of training, scatter a few marathon target pace segments lasting a few minutes apiece into one long run every other week. As your long runs become longer, make the marathon-pace segments longer, too (1-2 miles). During the final weeks of training, do marathon target pace segments that are as long as 5K apiece. Also, do one or two moderately long runs (10-15 miles) entirely at this pace.
What about the rest of your training? At the beginning of the training cycle, your training focus should be low-intensity "aerobic support" training (long, slow distance) and high-intensity "anaerobic" training (very short intervals done faster than race pace.) In other words, you should start by training the extremes. This will build a foundation for improvements in your target pace running ability.
As the training cycle unfolds, the average pace of your aerobic support training should move gradually upward toward your target pace. Your foundation and endurance workouts should get faster, tempo workouts should be introduced, and so forth.
Meanwhile, the average pace of your anaerobic training should move gradually downward toward your target pace. Your anaerobic intervals should become incrementally longer and slower. In the peak phase, your aerobic support and neuromuscular training should converge in a zone surrounding race intensity. Naturally, your long endurance workouts can be done only so fast, but the idea is to do them at a very challenging pace for the duration.
As your aerobic and anaerobic training paces move toward convergence, the amount of target pace training you do should increase as demonstrated in the tables above. And that's the recipe for achieving your goal time in your next race!race.