The basics of interval training are simple: instead of training at a steady pace, you break a session into alternating fast and slow intervals. The fast intervals (called work intervals) are performed at an intensity higher than you can sustain long-term. The slow intervals (called rest intervals) are performed at a low enough intensity to allow a quick recovery.

The details get more complicated, because there are so many variables concerning the length and intensity of the intervals, the number to do per session, and how to integrate intervals into your larger training plan.

There are likely different sets of advantages for workouts with long vs. short intervals. Which means it’s worthwhile to try both. Or to pick one and then switch to another if you hit a plateau. Here are some typical approaches.

Short intervals:

15-minute thorough warmup

4 to 6 sets of the following:

• 1-minute high-intensity interval
• 2-minute rest interval (brisk walk or slow jog)
• 5-minute cool down

Long intervals:

15-minute thorough warmup

4 to 6 sets of the following:

• 4-minute high-intensity interval
• 2-minute rest interval (brisk walk or slow jog)
• 5-minute cool down

30-20-10 intervals

(This workout is best done on a running track, away from traffic. The sudden speed changes make it impractical on a treadmill).

15-minute thorough warmup

4 sets of the following:

• 30 seconds easy jogging
• 20 seconds normal training pace run
• 10 seconds sprint
• 2-minute easy recovery jog
• Repeat the entire cycle (4 sets of 30-20-10 + recovery jog) 1 or 2 more times
• 5-minute cool down

The work interval should be intense. You should quickly cross your anaerobic threshold and should be breathing very hard. The precise intensity level will vary with the interval type. If you’re running 60-second intervals, you’ll need a much higher intensity than when running 4-minute intervals. You’ll know you’re doing it right when you feel you can barely finish the last scheduled interval.

Don’t try to get extra credit by working hard during the rest intervals. You’ll just be sabotaging the maximum intensity of the next work interval. A gentle warmup pace is adequate.

The workout plans above all have 2-minute rest periods. Feel free to adjust this if you need more recovery. You’ll be more likely to need a longer recovery after a shorter, very intense interval than after a longer interval.

It’s important to build a solid base, with several weeks of moderate, steady-state training, before incorporating intervals. When you first start interval training, expect that you’ll need a few sessions to get the intensity and the timing just right. It’s better to start conservatively and to ramp up the intensity slowly.

Start with an interval workout just once a week. Schedule it so that it follows a moderate day, and precedes a recovery day. As your season progresses, you may find it helpful to add a second interval workout. This usually makes sense mid-season, when you have a very strong base, but before you get into the period immediately preceding your biggest races of the year. Stop doing all intervals at least two weeks before a major event, like a marathon.

In general, high-level athletes spend around 80% of their training time at low intensities (like long slow distance endurance runs) and 20% of their training time at very high intensities (intervals, tempo training). They spend precious little time in the “mediocre middle” between those intensities.

Good luck! We hope you’ll what other athletes have found: that interval training is the most powerful tool in your fitness-building toolbox.