Dear Coach: When Should I Be Doing Interval Training?

Knowing when and how to incorporate intervals into your training is an important part in reaching your potential.

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This is a great question and one that, as a coach, I hear a lot at this time of year. Although we often think of these winter months (in the northern hemisphere) as base phase time, interval workouts should have a place on your training calendar pretty much year-round.

Aside from days/weeks post-race and certain recovery weeks, I typically recommend one bike interval workout and one run interval workout every week for my athletes. Swim intervals, being less fatiguing for your body, can be incorporated as two-thirds of your weekly swim volume. Experienced athletes with a solid base of fitness can often benefit from additional bike and/or run interval workouts as well as an increased proportion of interval training in the pool.

The trickier component of the interval training equation is which intervals to incorporate during which phases of your training season and on which days of your training week, so let’s dive into this equation piece by piece.

Over the entire course of your season, you should aim to incorporate a wide variety of the full range of interval types:

  • Sub-threshold intervals: just below your functional threshold power (FTP)/lactate threshold heart rate (LTHR)/threshold pace (fastest 30-minute run pace/fastest 1000 swim pace). Duration should typically be five to 20 minutes on the bike and run, and up to several hundred yards/meters in the pool;
  • Threshold intervals: right at your FTP/LTHR/threshold pace. Duration should typically three to five minutes for bike and run, and up to 200 yards/meters in the pool;
  • Supra-threshold intervals: above your FTP/LTHR/threshold pace. Duration should typically be 30 seconds up to three minutes for bike and run, and up to 100 yards/meters in the pool;
  • Hill repeats: sub-threshold, threshold, or supra-threshold intervals executed on a hill with a 3-6% grade;
  • Tempo intervals: sustained durations of 10-30 minutes or sometimes even longer at a designated pace, typically threshold, sub-threshold, or long-course race-pace.

Of course, the next obvious question is during which phases of your training season should you include these different interval types? Generally speaking, short-course triathletes will want to start with sub-threshold intervals and move toward supra-threshold intervals as their season progresses, while long-course triathletes will want to employ the opposite approach. All triathletes will benefit from incorporating race-pace tempo intervals as they approach each race of the season, particularly “A” races, and hill repeats can be used at almost any time to build power, strength, and add variety to training.Knowing which days to schedule this type of intensity is also important. You’ll want to schedule interval workouts on days where you can come in sufficiently rested while also allowing for sufficient recovery prior to your next key training session. And yes, that’s exactly as narrow a window as it sounds. Layer onto this already complicated equation the additional factors, such as your base fitness, training experience and history, and upcoming race distances and goals, and the solution becomes even more nuanced and personalized. For this reason, relying on a triathlon-specific training plan or working with an experienced triathlon coach is your best bet to successfully incorporate interval training in a way which maximizes benefit and minimizes your risk of injury or overtraining.

Alison Freeman is a co-founder of and triathlon coach with NYX Endurance in Boulder, Colorado. She works with a wide range of age-group athletes, but athletes new to triathlon are her favorites because there is no such thing as too many questions.

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