A lot of runners reflexively associate interval workouts—repeats of 200 to usually 1,600 meters at 10K race pace or faster interspersed with rest jogs sufficient in duration to allow for two to five miles of total fast work—with any number of noisome physical and psychological stimuli: burning lungs and legs, seeing spots and a second look at one's lunch.
Although overzealous high-school hijinks are often responsible for this prejudiced view, the fact is that even very experienced runners often do their speed workouts too hard, with a tendency to lean toward excessive—and ever-lengthening—recovery times to compensate for too-fast repeats.
Understand that if you measure your recoveries in distance rather than time, you're almost certainly compromising your workout. If you're like the vast majority of runners, your "consistent" 200-meter recoveries between fast 400s are likely to swell from whatever number of seconds you begin with to about 50 percent more than that.
Having observed a slew of high school, college and open runners of all sorts over the years, including myself, I can assure you that this is true. It's of little use to be able to do 10x400 in 85 seconds if you have to extend your rest jogs from 1:00 to 2:00 as the workout progresses.
So get in the habit of using timed recoveries, which force you to stay under control and standardize your workouts from day to day, season to season and year to year. Shorter reps require recoveries of up to 100 percent of the duration of the work bout, while longer ones typically need no more than half as much recovery time relative to their duration.
Interval Workouts
You'll recall from the first two installments of this series (long runs and medium-long runs) that I've separated the most important kinds of running training into three general categories and within them have created three sub-categories.
Understand that this is more a matter of convenience than of physiology. Workouts and training benefits exist along a spectrum, not in the quantum form we assign for ease of scheduling. Your body knows nothing of training a single "system" at a time.
So in reality, a workout consisting of long intervals, for example, is usually classified as a VO2max-specific session, but if done right it offers a significant lactate-tolerance boost. By the same token, a hard tempo run serves to improve not only lactate tolerance but also VO2max.
It can be helpful to think of the entire range of paces you touch on in training as an octave, and while some notes (or chords) are especially important (depending on the event you're training for), you need to be sure to hit all of them at least occasionally to maximize your competitive effectiveness.
Short Intervals
Even a true endurance athlete needs some genuine speed work. Think of it as a "training vaccine:" You don't need it often, but skipping it is hazardous to your competitive health.
Short intervals should be done at about one- to two-mile race pace and consist of work periods of 2:00 or less (400 to 600 meters or so), and the recovery interval should amount to 75 percent to 100 percent of the repetition duration. In these workouts, the number of reps is on the high side, but the total mileage covered tends to be low, as running at or near one-mile race pace is deceptively (or not) taxing.
Strides, or 15- to 20-second pick-ups in which a runner builds from about 5K pace to a near-sprint, are a good way to help maintain turnover via neuromuscular facilitation without incurring the soreness and fatigue that can result from genuine speed work. These can be done during or at the end of an easy run about once a week, and runners should take all the recovery time they need between strides.
Medium Intervals
These are done at about two-mile to 5K race pace, include reps of two to four minutes in duration (400 to 600 meters at the low end, 800 to 1,200 at the high end) and include recovery periods of no more than 75 percent of the duration of the work bout.
Here, both the number of reps and the mileage covered at a fast clip are moderate. (Physiological aside: The speed corresponding to VO2max pace is that which you can hold for about 10 to 12 minutes going flat-out, so medium-length intervals fall within this range for most people.)