Understanding intervals.

The full throes of track season, if not exactly beckoning us, perhaps whisper in our ears that we runners explore interval training. You don't have to be a high school athlete to benefit from these weekly workouts. By pushing your oxygen consumption to its maximal threshold (VO2max) on a regular basis in a controlled setting, you'll run farther, race faster and feel better than you did when every run was an ordinary training run.

There is no end to the variations you can create on the track to keep these sessions fresh once you understand the basic principles of intervals.

Ideal intensity. You should aim for a running speed that you could keep up for 10 to 15 minutes in a race. Most runners might cover 3 or 4K in this time; it's a full 5K for a professional. If you're out of shape you may use a 5K pace as an intensity reference until you improve.

The distance of each work bout in a session of intervals should not determine the intensity. You should run 400 meters at the same pace you run a mile.

Ideal duration. The main goal of an interval workout is to achieve VO2max for prolonged periods. With this in mind, while interval workouts are most often referenced by distance ("I ran six half-mile repeats"), the real issue is time. Running at the ideal pace outlined in the above section, you would typically reach VO2max only after two minutes of running.

In this way, time dictates the workout. Going for over five minutes results in too much blood lactate accumulation, so avoid mile repeats if your interval pace is above a five-minute mile. You might find you can schedule at most three times around the track in a single bout; so be it.

Note, though, that five-minute bouts are excellent to achieve prolonged running at VO2max. You should run these often in your sessions regardless of how far you get. Rely on the feeling of stress you experience, and not on a pre-determined distance goal over a certain time.

Ideal recovery. If VO2max is reached only after two minutes of running at interval pace, and shorter work bouts like quarter miles may well be only 80 seconds long, how is maximal oxygen consumption reached without going faster for shorter distances? The answer is by varying the amount of rest between the work bouts. Generally, running intervals less than 30 seconds in length is of little benefit. But knocking back one-minute bouts on the track can work for you if your recovery periods are sufficiently short. As you fail to allow a full recovery in between bouts, you will reach VO2max more quickly in subsequent bouts, and there remain for large portions of the overall session.

Don't play with intensity. The stress of running shorter intervals comes from shortening the recoveries, not from running at faster speeds. Recover with easy jogging, which helps clear blood lactate and keeps muscles loose, in addition to further preventing a return to resting VO2. Keep the time of recovery less than or equal to the time running at interval pace--again, regardless of recovery distance.

Here's a sample workout for a runner at 6:00/mile interval pace (:90/400m):

six 2:00 runs with 1:00 recoveries;

eight 1:00 runs with: 30 recoveries;

eight: 30 runs with: 15 recoveries.

This totals 24:00 at interval pace and 12:00 easy, for a 36:00 session. The time spent at VO2max is comparable to a workout of three- and five-minute runs with longer recoveries.

Ideal mileage. Finally, cap your intervals at 8% of your weekly mileage, with a 10K maximum regardless of how much you're logging on the roads. And drop your interval training when serious race season begins.

(Adapted from Daniels' Running Formula by Jack Daniels, PhD, Human Kinetics, Champaign, IL, 1998, 287 pp. $18.95)

RELATED ARTICLE: The Clothing Thermometer 

As winter thaws but undoubtedly hangs on in unexpected ways, each year we find spring is the season with the most temperature variation. Bright sun one day, high winds and rain the next, frustrate runners as they head outdoors either sweating or underdressed. The following clothing thermometer will help you take the guesswork out of gearing up (though wind and humidity play significant roles as well). All temperatures are in Fahrenheit:

60+ * t-shirt/shorts

50 * long-sleeved t/shorts

40 * long-sleeved t/t-shirt/tights or wind pants

30 * windbreaker/long-sleeved t/t-shirt/shorts and tights or wind pants/gloves/hat

20 * windbreaker/thick long-sleeved polypro top/long-sleeved t/polypro pants/gloves/hat

(Adapted from Marathon! by Jeff Galloway, Phidippides Publication, Atlanta, GA, 2000, 234 pp. Available at www.americanrunning.org, $11.95 members, $14.95 non-members)