Become a Member

Get access to more than 30 brands, premium video, exclusive content, events, mapping, and more.

Already have an account? Sign In

Become a Member

Get access to more than 30 brands, premium video, exclusive content, events, mapping, and more.

Already have an account? Sign In



High Intensity For High Performance

High-intensity training is one of the only ways that time-crunched triathletes can achieve the workload necessary to make progress.

Heading out the door? Read this article on the new Outside+ app available now on iOS devices for members! Download the app.

For a group perceived to be one of the hardest-working of all endurance athletes, it’s surprising 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 when asked to go harder and give maximal efforts during their 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 intervals (anywhere from 30 seconds to five minutes) at very high intensities (120 percent of lactate threshold power on the bike, for instance) is that you need bigger and more abundant mitochondria in your muscle cells so they can break down fat and carbohydrate into usable energy more quickly. 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 reintegrate lactate into normal aerobic metabolism so it can be broken down to usable energy, having more and bigger mitochondria also means you can recover from hard, lactate-accumulating efforts more quickly.

Why can’t you grow more and larger 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 VO₂max values in the high 50s and 60s (ml/kg/min), and age-group winners in the 35–50 range often have VO₂max values around or above 70ml/kg/min. Several studies suggest that for athletes with VO₂max 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 must follow for high-intensity training to be beneficial and not lead to injury:

Max means max. If you can’t achieve the pace or power output necessary to call the interval a VO2max interval, it’s not hard enough to create the necessary training stimulus. VO2max interval training is cross-eyed, burning-lungs, I-think-I’m-going-to-puke intensity. That means 120 percent of LT power output on the bike (or greater), 92 percent of your 5K race pace (or faster), and 75-93 percent of your average 100-meter split from a 400-meter swimming time trial.

Commit to recovery. Your best option is a complete rest day the day after a VO2max training session. If that’s not possible, do 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.

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 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 VO2max interval session is over.

RELATED – 55-Minute Workout: Core Work Bike Intervals

VO2 Workout Examples

VO2 intervals on the bike are straightforward: 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

4x15sec running strides

7x800m, 3:00 rest between intervals OR

6x1000m, 4:00 rest between intervals OR

6×3:00 fartlek max
efforts, 3:00 endurance jog between efforts

1-mile cool-down

Swimming workout:

800m 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.

RELATED: How To Maximize Your Weekend Training