Running is a simple process, you could, if you so wanted, do it with no equipment at all. No shoes or running gear at all, yet as runners we have to deal with complex ideas surrounding training. For the distance runner the method that probably causes the most confusion is Tempo running, a Lactate Threshold run, a LV run or a Threshold run. The fact that it does not have one simple name is a key to what makes it hard to get right. How fast is too fast? How slow is too slow? For the longer distance runner the Tempo run is deemed more important than the interval session by many running experts.
Now for the science, I shall make this brief! It is all based the body's efficient use of it's energy systems by teaching the body to use oxygen for metabolism more efficiently. One of the waste products of these energy systems is Lactate (Lactic acid), essentially the faster you run the more Lactate is produced and it works to protect the body ( if we could all run at 20 MPH for hours on end our bodies would not last very long). The figure that is generally accepted for Tempo Runs is 2 mmols/l (2 milli-mililitres of Lactate per litre of Blood). Lactate testing is fairly standard for Elite level athletes, blood is usually taken from the ear lobe and can even be tested out in the field. I was able to set my personal threshold levels using such a lactate test. Using the data I was able to determine what my heart rate was at 2 mmols, and that became my guide when training. For example whilst training at altitude I religiously kept my heart rate under this limit (153 bpm) for all steady runs.
So now we know roughly what is too slow (under 153 bpm for me) but how can we translate that for someone who does not use a heart rate monitor? You can use a perceived exertion test, an 8 on a 1-10 scale (comfortable would be 5 and racing close to 10). You should not be able to chat; a question like "pace okay?" would be possible but not more. It should feel "uncomfortably hard.
So what about distance, I would suggest you keep them short ( 20 mins) till you get the pace right and then increase. A 10 minute warm up and warm down is advisable. Pick a loop you can do regularly, as a middle distance runner I used a 3 mile loop, I knew where the mile points were on the course to check pace and over the years watched my times drop from 18.37 as a 13 year old to 13.25 in my mid-twenties. Once you have got this "uncomfortably hard" idea tamed you can increase. An excellent way of incorporating this into training is what we used to call the "turn and burn". It was something that Paul Evans(2.08 marathon runner) taught me, he would run 60 mins out (about 10 miles) then turn and tempo run back in 50 mins. It is a little extreme but the concept is simple and i would often do it by running 40 mins out ( about 6 miles ) then try to run back in 33/34 mins. But any time would work.
I have had good success with this style of training within my own running career and seen it improve my own clients race pace with regular use. Get the Pace right and it can really help you improve!
Photo credit: Unlisted Sightings