Keep Interval Intensity Steady
With cooler weather and cross-country racing at its peak, many runners take their workouts to new levels at this time of year. Part of any well-rounded training regimen, of course, is the interval workout. There can be confusion surrounding the ideal intensity at which to perform interval workouts, and the subject occasionally bears the need for fresh review.
One of the classic texts on the subject of intervals is the chapter on them in Jack Daniels' well-known book, Daniels' Running Formula. The statements in this esteemed work are carefully backed by experiments on athletes that Daniels conducted over many years. And one of the things that Daniels has found is that runners often perform intervals at too great a speed. He has a clear understanding what the goal of interval training is, and his recommendations serve solely that purpose: to spend as much time during the workout as possible at VO2max. The reason that this does not translate into all-out running on each lap is because to sustain training at maximal oxygen consumption, you must manipulate the duration of the intervals and the duration of the rest periods, rather than simply sprint until you are exhausted. Let's face it—that is a very good way to fatigue too quickly and wind up injured or cutting a workout well short of the mark.
As a rule of thumb, Daniels recommends that you aim for a running intensity that you could keep up for 10 to 15 minutes in a race setting. Most runners might cover a distance of 3 to 4K in this time, whereas professional athletes might cover a full 5K. The distance of a work bout in a session of interval training should not determine the intensity. For this reason, Daniels has suggested that you don't obsess over distance covered within certain lap times. This also means that you should always remember to run 400 meters at the same pace you would run a mile interval. This is counterintuitive for many of us, but it is the key to getting the most out of your training.
Since the main goal is to achieve VO2max for prolonged periods, the duration of each interval is the focus. If your pace is correct, and the rest periods appropriate, you should achieve VO2max after only about two minutes of running. Daniels says that you should never perform an interval work bout of a duration over 5 minutes. That's because too much blood lactate will develop at (otherwise proper) interval intensity. Therefore, if your interval pace is slower than a five-minute mile, avoid mile repeats.
That said, five-minute bouts are a very effective way to achieve prolonged VO2max running. Run these often in your sessions, regardless of how far you get. Rely on your own body-stress self-monitoring, not on covering x distance over y time.
The next factor you can manipulate to obtain high amounts of VO2max running is rest duration. When your interval bouts are shorter than five minutes, shorten your rest period accordingly. Though intervals of less than 30 seconds have little benefit, one-minute bouts with rest that fails to allow full recovery will accumulate until you are indeed spending a good portion of the entire session at maximal oxygen consumption. Never vary intensity; the stress of shorter intervals comes from pairing them with shorter recoveries. Keep the rest interval equal to or lesser than the time running (regardless of recovery distance). The following is a sample workout for a 6:00-mile interval runner, which breaks down to: 90 per every 400 meters:
six 2:00 runs with 1:00 recovery jogging in between;
eight 1:00 runs with :30 recovery jogging in between; and
eight :30 runs with :15 recovery jogging in between.
This adds up to 24 minutes of interval running with 12 minutes of recovery jogging for a total session of 36 minutes. A once weekly training session like this, or a comparable session of three- and five-minute runs with longer recoveries, will yield noticeable benefits to your fall racing. Remember to keep this type of training to no more than 8 percent of your total weekly mileage, but with a hard cap at 10K per week regardless of other mileage. If you are racing regularly, consider these races a substitute for intervals and keep this type of training to a minimum.