Tempo RunsThis is hands-down the least complicated variety of speedwork. There are no distances to keep track of, no split times to remember, no hassles. All you have to do is run faster than your usual training pace, somewhere right around your 10K race pace. Unlike most speedwork which consists of relatively short bursts of high effort, tempo runs call for a single sustained effort. The result is that your body learns race economy: running at a fast pace for relatively long periods of time. Tempo runs will give your top speed a boost, too. By running nearly at race pace, your body becomes accustomed to running close to its upper limit (though not exceeding it). In doing so, you actually increase that upper limit, and you become gradually faster.
After your usual warmup routine, run at your easy training pace for at least ten minutes. Then pick up the pace. As mentioned above, this speed should be right around your 10K race pace (around 80 to 85 percent of maximum heart rate, if you use a heart rate monitor). The time, distance and pace of your tempo run, as with all phases of your running, depends on both your ability and your goals. For the distance you choose (3 and 5 miles are popular tempo distances), find a pace that is not so fast that you cannot sustain it for the distance, but not so slow that you do not feel challenged toward the end. Tempo runs should be tough, but not impossible. Depending on how you feel on any given day, how much spring is in your legs, and how far you are running, your tempo pace may vary from session to session. That's fine. The consistency that counts is the pace within each session. Try to keep your speed level for the full length of each tempo run.
Don't worry too much about figuring out the exact distance of your tempo run. It's really not terribly important. Three to six miles is probably a good range. The one value of knowing how far you are running, though, is that you are able to gauge your improvement over time. Still, this is easily done by doing most of your tempo runs on the same route. You may not know the specific distance, but you can still compare your times for that same fixed route.