Triathlon Training: High Intensity for High Performance

By Chris Carmichael

For a group that is perceived to be one of the hardest-working groups of endurance athletes, it’s surprising to see how resistant some triathletes are to high-intensity training. Triathletes will ride, run or swim all day long; and pack more individual training sessions into a week or a month than any other endurance athlete. But ask you to go harder and give maximal efforts during your workout… well, that’s just crazy talk.

But it’s not. In fact, it’s one of the only ways that time-crunched triathletes can achieve the workload necessary to continue making progress. The disconnect between the science of performance and the culture of triathlon is that the sport’s most iconic races are contested at paces below lactate threshold. You win long triathlons with sub-threshold speed, but you gain the ability to be fast at a sub-threshold intensity by training with efforts at and well above threshold. This is especially true for those triathletes who are limited to training 8-10 hours a week because of competing priorities like a job and a family.

The reason you need to incorporate short (:30 to 5:00) intervals at very high intensities (120% of lactate threshold power on the bike, for instance) is that you need bigger and more abundant mitochondria in your muscles cells so they can break fat and carbohydrate down to usable energy more quickly. When they can’t keep up with your demand for energy, your body takes a metabolic shortcut that can produce energy more quickly but also produces lactate. With greater capacity in your mitochondria, you can go faster before you reach the point where accumulated lactate forces you to slow down (lactate threshold). And since mitochondria also re-integrate lactate into normal aerobic metabolism so it can be broken down to usable energy, more and bigger mitochondria also mean you can recover from hard, lactate-accumulating efforts more quickly.

Why can’t you grow more and bigger mitochondria from longer, lower-intensity training sessions? To a point, you can, but if you’ve progressed to being a moderately-fit or above-average triathlete, then you’ve most likely reached the point where volume alone won’t lead to continued increases in mitochondrial density. Moderately-fit triathletes frequently have VO2 max values in the high 50s and 60s (ml/kg/min), and age-group winners in the 35-50 year old range often have VO2 max values around or above 70ml/kg/min. Studies by Laursen and Jenkins (2002) and earlier work from Londerlee (1997) suggest that for athletes with VO2 max values above 60ml/kg/min, high-intensity interval training is necessary for achieving increased mitochondrial density – no matter how much time you have available for training.

High-intensity training works, but it can be tricky to manage. There are three commandments you have follow in order for high-intensity training to be beneficial and not lead to injury:

  1. Max means Max – If you can’t achieve the pace or power output necessary to call the interval a VO2 max interval, it’s not hard enough to create the necessary training stimulus. VO2 max interval training is cross-eyed, burning-lungs, I-think-I’m-going-to-puke intensity. That means 120% of LT power output on the bike (or greater), 92% of your 5k race pace (or faster), and 75-93% of your average 100-meter split from a 400-meter swimming time trial.
  2. Commit to Recovery – Your best option is a complete rest day the day after a VO2 max training session. If that’s not possible, then nothing harder than an endurance ride or swim the next day. High-intensity training sessions work great for time-crunched athletes because your busy schedule often means at least two days a week when training isn’t possible.
  3. Technique Above All – Increased intensity exacerbates weaknesses in your form and technique. At lower intensities your body may be able to compensate for poor form, but at high intensities those flaws can easily lead to injuries. On the bike make sure your fit is professionally dialed in. For running and swimming, I’d recommend coach-supervised track and swim sessions so your technique can be evaluated as you increase intensity. When fatigue causes your form to deteriorate, your VO2 max interval session is over.

VO2 workout examples
VO2 intervals on the bike are pretty straight forward: go as hard as you can for 1-3 minutes with recovery periods equal to the duration of the intervals. For running and swimming, try these options:

Track workout:
2 mile warm up
4x 15sec running strides
7x800meter, 3:00 rest between intervals


6x1000meter, 4:00 rest between

6×3:00minute Fartlek max efforts, 3:00 endurance jog between efforts.
1 mile cool down

Swimming workout:
800 meter mixed warm up
5x100m MAX with 2:00 rest between
5x50m MAX with 1:30 rest between
4x100m kick, descend (accelerate) each to max effort last 25m
100m cool down

Chris Carmichael is the author of “The Time-Crunched Triathlete” and founder and CEO of Carmichael Training Systems, the Official Coaching and Camps Partner of Ironman. For information on coaching options and official Ironman Camps and Coaching Packages, visit or call 866-355-0645.

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