Running a faster 5K is possible once you identify the key elements that need attention. But, the 5K shouldn't be viewed as a race for beginners or for middle-distance aficionados. Half marathoners and marathoners should focus on their 5K PR a couple of times a year. To be a well-rounded runner, athletes shouldn't train to run at only half marathon or marathon pace, yet for so many runners this is the case.
If you want to improve your PRs at distances longer than 5K, you should take your 5K PR seriously, as virtually all runners who improve their 5Ks see improvements in the longer distances.
Your 5K PR Plan
Metabolically, the 5K is over 90 percent aerobic. While this isn't quite as high of a percentage as the marathon, with is 99 percent aerobic, you need to make sure that developing your aerobic metabolism is at the forefront of your 5K training. So don't skimp on the long run, don't stop doing your threshold runs, and don't stop doing your fartlek runs. All of those workouts will help you improve your aerobic fitness, which is the basis for a faster 5K time.
The next step: Take your most recent 5K time—a time from a certified course, preferably a course that is flat (rather than a challenging hilly course)—and use that as a baseline. You then want to make a very conservative goal of 10 to 15 seconds faster than that time.
Let's say you can run a 5K in 18:45. That's six minutes per mile, or 90 seconds per 400 meters. We'll call that your "date pace," a term that legendary coach Bill Bowerman used. Then we want to come up with a "goal pace." It's important to know what per-mile pace your goal pace is. We will shoot for one second per 400m faster than your date pace. So for the 18:45 runner who currently can run 90-second 400s, we will use 89 seconds per 400m as his goal pace. If you ran 89-second pace for 400m, that is 5:56 per-mile pace, and that would give you a 5K time of 18:33, which is a nice little PR.
More: How to Train for a PR
I know that's a lot of math, but it's important to know your date pace, and work with a new goal pace. Goal pace is what you're shooting for when you complete your race-pace workouts. These runs are simply workouts where you run at race pace. Some people love race-pace workouts, and some people hate them.
Race-pace workouts for 5K are different than race-pace workouts for the marathon. For a marathon, you might do a 20-mile run where you try to run at race pace for the second half of the run. But when you're training for a 5K, the workout is much shorter and faster, which makes sense as the 5K race distance is shorter and you hope to run it faster.