Complementing Distance Training
The runner who has plenty of quality mileage runs pretty hard for much of his training, includes hills in his runs, does tempo or steady state runs will have less need for intervals than the runner who runs easy mileage. For example, in the classic Lydiard training regime, a base of quality mileage is followed by hill repeats and then by a period of shorter intervals (200 meters to 400 meters). This works because the runner has the endurance and a high degree of aerobic fitness from his mileage. The shorter intervals add the final piece to the mix and further muscle development.
In contrast, under the old Oregon system, the endurance and anaerobic threshold were built on longer intervals (800 meters and up) and on shorter intervals with abbreviated rest periods or moderate speed recovery periods (similar to fartlek). The quality of the mileage was less important because so many other elements of fitness were obtained from the interval training.
The current world-class African runners tend to have a system more like the classic Lydiard programplenty of mileage (100 miles per week and up), much of it at a fast pace, plenty of hills and fartlek. This mileage is combined with a limited number of long and short interval sessions throughout much of their training.
Longer intervals can be done several ways. The most basic is to run a set of intervals of the same distance at a prescribed pace. For example, many runners like to do 4 x 1-mile at a set pace (usually about 10K race pace). This brings the heart rate up to the desired level and holds it there for several minutes during each interval.
The longest interval should rarely exceed 2 miles. Beyond that point little is to be gained from the workout that a simple tempo run a steady run at prescribed pace would not provide better. Also, the recovery time to effectively run really long intervals must be substantial in order to have quality hard efforts, and so the rest period itself becomes a problem. I can recall doing 3 x 1.7-mile cross-country loops where the rest period had to be 15 minutes to allow me to put in a good effort on the run. I would have been better served by simply doing a 5-mile tempo run.
The shortest "long" interval would be about 800 meters. It is safe to say that most runners seeking to maximize their 5K or 10K potential will need to regularly do intervals of 800 meters to 2 miles. Within that range, the runner is fairly free to choose the mix that works best for him.
To make these longer intervals more stimulating, varied pacing can be used. For example, do 400-meter laps of 80, 75, 70, 80, 75, 70 for a 6-lap interval at 5-minute mile pace. Two or three of these would be sufficient for a good workout for a 30-minute 10k runner. A variation of this that we had at Oregon was two laps at 80, two at 75 and then two at 70 (we actually ran faster than the schedule), and we did two or three of these. These speeds can be adjusted to reflect various performance levels (e.g., a 40-minute 10K runner might do laps of 105, 95, 85, 105, 95, 85 for an average pace of 6:40 per mile).
Some runners like to vary distances. Ladders are popular workouts like 200m, 400m, 800m, 1200m, 1600m, 1200m, 800m, 400m, 200m. Another strategy is to mix a longer interval with a shorter interval. Taking another example from Oregon of one of my favorite interval workouts, we would do an 800m hard effort followed by a 300m jog followed by a 300m hard effort followed by a 200m jog, which we would repeat three or four times. These would be done in a "cutdown" manner described below.
For runners who get tired of doing intervals on the track there are options. Trail or grass loops can be used. Many bike paths have mile markings that can be used. Alternatively, the interval distances can be done by time on relatively flat terrain, with the hard efforts lasting 3 to 5 minutes.
Shorter intervals are added to the mix to provide the final element of anaerobic threshold and muscle development. In sufficient quantities and at the right pace, shorter intervals can also provide some endurance building.
The interval distances can be as short as necessary to meet the athlete's needs. Lydiard would have his athletes do repeated 50-meter bursts to add the final sharpening for racing. It can be enjoyable and beneficial to do 100-meter repeats on a football field, or as "jog the turns, sprint the straights" on the track. However, these very short intervals should only be a small part of a 5K or 10K runner's regime.
The majority of short intervals will be of distances of 200m, 300m and 400m. They can be varied, like the longer intervals, or there can be a set amount at a specified pace. Like longer intervals, some runners prefer "cutdowns" gradually reducing the time of the hard efforts from relatively easy to very challenging.
Adding short intervals, such as 6 x 200m at a relaxed sprint, at the end of longer interval sessions or tempo runs can provide needed balance in developing overall race fitness.
Also as noted above, shorter intervals should not be the exclusive form of interval training unless the runner does a substantial amount of quality mileage. An athlete who does easy mileage and only shorter intervals will likely never develop the endurance to maintain his potential over a 5K or 10K.