The length of a 5K, or 3.1 miles, is the shortest standard distance over which road races are held. This also makes them America's favorite, with 6.2 million finishers crossing U.S finish lines in 2012. Unlike the marathon and half-marathon, where raw endurance is enough to produce a successful athlete, the 5K requires you to build a significant degree of leg speed to complement your basic aerobic fitness if you want to race your best.
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Lay the Groundwork
Run a two-mile time trial to determine your basic fitness. A 400-meter track is ideal, but an accurately measured road course will do.
Determine your per-mile pace in the time trial and make this your goal pace for your next 5K. For example, if you run the two miles in 15 minutes, your per-mile pace is 7.5 minutes and multiplying by 3.1 gives you a 5K goal time of 23 minutes and 18 seconds.
Choose a race eight weeks from your time trial. Commit to running four or five times a week for at least 20 to 30 miles.
Up the Tempo
Do a tempo run of 30 or more minutes once a week. These are efforts at about your estimated 10K race pace.
Focus on effort rather than pace. This allows you to neglect the effects of hills, wind and other ambient factors on your speed.
Try talking during your presumed tempo-run effort. If you cannot quite speak in normal sentences but are not gasping for air, you are probably very close to the right intensity level.
Perform one interval track workout a week. According to Competitor Running, these are repeats of 200 to 1,600 meters and totaling 2 to 3 miles of fast running.
Run the repetitions slightly faster than goal 5K pace. Variables such as high or low temperature, humidity, hilly terrain and wind can slow your pace at a given intensity level by as much as 30 seconds per mile, so if you confront any of these in your workout, focus on maintaining what feels like 5K-race effort rather than your watch.
Walk or jog between reps for half the time it takes you to run your hard segments. For example, it your goal 5K pace is eight minutes per mile, you can run six times 800 meters in about three minutes and 55 seconds with about two minutes of walking or easy jogging in between.
Rest Up and Race
Take one or two days a week off from running and make sure that it you cross-train -- be it on a bicycle or elliptical machine or in the pool -- you reserve one day a week for resting altogether.
Reduce your mileage in the last two weeks before your 5K race, allowing your legs to regain any springiness your hard training has temporarily compromised. Don't run for a day or two before the race.
Pace yourself wisely. Start at a pace that feels too slow, as adrenalin may cause you to badly misjudge your speed while you're still fresh. Halfway or so into the event, you should be working very hard; at that point, focus on picking off runners ahead of you one at a time and maintaining a steady stride cadence.