Bob Kennedy has been at the top of US distance running for over a decade, competing in the 1992 and 1996 Olympics in the 5,000 meter run, with a best finish of 6^th place in 1996. He is the American record holder on the track for 3,000 meters (7:30), and 5,000 meters (12:58). He is currently focusing on the 10,000 meter run and the 2004 Olympics. Bob is 33, he lives in Indianapolis, and he is co-owner of The Running Company (www.erunningcompany.com), a specialty running store. The following article, written by Bob, is from The Running Company's newsletter, Momentum.

One of the questions most frequently asked of me is some version of, “what is the one workout you would do if you couldn't do any other?”  Before I answer the question I first try to explain that there are many equally important pieces of the puzzle that make up a properly prepared distance runner.  When the body runs as fast as it can over a long distance it uses three or four different physiological systems (aerobic capacity, aerobic efficiency and aerobic/anaerobic power), which are all doing different things simultaneously yet relying on each other to accomplish the end goal of finishing the race in the shortest amount of time possible.  Each time we run or workout we are improving the efficiency of one or two of these physiological systems.  In general, easy running improves aerobic capacity, tempo running improves aerobic efficiency and fast interval running improves aerobic and/or anaerobic power.  Missing just one of those pieces will leave a hole in your performance.  But after going through all of that, my answer to the original question is definitely the tempo run!  For race distances at or above 10K the tempo run, if done properly, is by far the biggest bang for your buck.    

In order to understand how to do tempo runs properly, I think it is important to first understand what you are trying to accomplish by doing tempo runs.  Think of aerobic efficiency as using the fuel provided by your body in the most efficient way possible so that it lasts as long as possible at the pace you want to run.  I love the automobile analogy for this.  In the simplest form, it takes two things to make a car go:  An engine and fuel.  If you have a Ferrari engine under your hood and you put your foot on the gas pedal you are going to go pretty fast but it will be a relatively short ride because that engine, although fast, is not very efficient and will use the fuel up quickly.  On the other hand, if you have one of the diesel Volkswagen Rabbit's from the 80's and you put your foot on the gas you won't feel any sensation of speed but (once you finally get to speed) the ride will seem almost never ending.  The Volkswagen engine is built for efficiency, which is what you are trying to accomplish with your body's engine by doing tempo runs.

Tempo runs should be done at a pace that is the fastest you can go with your muscles using only aerobic energy for fuel.  The simplest way to determine this pace is to think of it as the fastest pace you can evenly sustain for one hour of running.  It should feel comfortably hard.  Running at a pace faster than this causes your muscles to utilize anaerobic energy for fuel, which is very limited in supply and lasts for a very short period of time (remember the Ferrari engine?).  Once you go anaerobic there is no going back.  The duration of tempo runs should be between 20 minutes and 50 minutes, which, of course, are preceded by a warm up and followed by a cool down.  If you have never done a tempo run, start with 10 minutes and work your way up from there.  The more running you do at this pace, the more efficient your body's engine will become at using fuel and the longer you will be able to sustain your goal race pace.