When I started running, I found that I increased in average speed (or more accurately, pace) as I increased my mileage and with it my fitness. But this kind of improvement can't continue to increase and as I ran more the effect was less dramatic.
I asked for advice on an internet forum I frequent (running mania) and was told, "in order to run faster, one must practice running faster".
But how fast and for how long?
The answer, "you run at speeds designed to challenge your physiology at your current fitness".
There is an injury risk to going out and running as hard as you can for as long as you can, or to say "I want to run that 5km race next month in 20 minutes, therefore I should go out and do my running at 4:00/km...". Depending just how far you are fitness-wise from running and maintaining 4:00/km will determine the risk of asking too much of your muscles, tendons, heart, lungs, ligaments, bones etc.
So how do we know how fast to train at to maximize gains and minimize injury?
Simple. Use Jack Daniels' Vdot system to figure out training paces from a recent race. A short race tends to provide more reliable paces. Here is an example of a Vdot calculator with training paces for my personal best 5km time of 22:35.
For that race performance (which was pretty recent) my Vdot is calculated as 43.19 and with it there is a whole series of training paces at different distances.
For example the calculator gives me an easy/long (E/L) pace of 5:57/km. So when doing easy (recovery, base building runs) or long runs, I should run at approximately 5:57/km to get the maximum physiological gains that the workout itself is striving to provide. This is an important pace, as it is this calculated pace that has helped me more than any other. In the past I ran my slow runs too fast, and thus at the fitness level I was at, I had nothing left for the faster-paced training runs. This is a double edged sword as you end up limiting any fitness gains from both the slow-paced and faster-paced workouts as you are unable to stimulate the correct physiological responses. Not surprisingly I became fatigued and eventually I became injured.
Once the penny had dropped about running the E/L runs at a slow enough pace, lo and behold, my fast-paced workouts became manageable, and better still, recovery time decreased and my speed increased.
So what are these faster-paced training runs I keep mentioning? They take the form of threshold runs (T) and interval training (I).
The diagram below (adapted from Daniels) illustrates the relative intensities of each workout type.
The T pace is designed to push your physiological systems to the edge (threshold) of lactate buffering (i.e. the process by which lactic acid formed in your muscles during anaerobic respiration is taken away in the blood stream and then broken down).
During light- and moderate-intensity exercise, blood concentration of lactate remains low. The body is able to absorb lactate faster than the muscle cells are producing it. However, as exercise intensity increases, there comes a point at which lactate removal fails to keep up with the rate of lactate production. This point is referred to as the lactate threshold and spells the beginning of the end of high-intensity exercise. Excessive blood lactate and the cellular acidity it produces combine to interfere with efficient and proper muscle contraction, and as a result, power output drops, suffering increases, and you are forced to slow down.
Lactate threshold training is designed to increase this threshold and thus allow a runner to run at faster speeds with less lactate buildup and thus less acidity in the muscles and a lower level of fatigue/suffering.
I (interval) paced runs are faster runs but over shorter distances, often with longer recovery periods.
They are run at a 98-100% effort and are by definition, hard. Typically a training run at this intensity is broken down into 400 meter, of 800 meter repeats at I pace (1:46/400m and 3:32/800m) with 400 meter rest periods in between that can be walked or run at E/L pace or slower. A typical number of repeats is 6 to 8 during any given session.
These types of training have improved my running no end, and I have gone from struggling to complete a workout with 5:30/km repeats to completing all my T workouts at a T pace of 4:47/km. I have also had a lot of success with I runs, which is achieved when you can run the final repeat of the workout at the same pace or faster than the first one (i.e. showing no slowdown from repeat to repeat).
The beauty of the Vdot system is that if you end up running a faster race time (as has happened to me several times this year) or when the workouts get easy, you calculate new more challenging paces and thus challenge your physiology all over again.
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