short intervals

Why Short Intervals Work for Improving Performance


By Chris Carmichael,
Founder and Head Coach of CTS

In exercise science and coaching there are long and passionate debates about the structure of interval workouts, the intensities that should be used, the duration of efforts and recoveries, and the total amount of work performed during a training session or a block of training. The question of whether very short intervals (30 second max efforts with 15 second recoveries) are superior to longer five-minute intervals bubbles to the surface regularly, including this interesting Twitter thread. From the sports science side, short intervals work. What’s important for athletes and coaches to understand, however, is that the reasons they work go beyond physiological adaptation. Here’s the bigger picture of why my coaches and I incorporate very short intervals into our athletes’ programs.

Short intervals ranging from 10 to 40 seconds, with 1:1 or 2:1 work:recovery ratios, have been a staple of training programs since the 1990s, and were used less formally before that. In a study published in 1996, Dr. Izumi Tabata described a protocol of 20-second high intensity efforts separated by 10 seconds of recovery. The result was an increase in both maximum aerobic capacity (VO2 max) and anaerobic capacity.

By comparison, the group that performed steady efforts at 70% of VO2 max saw a smaller improvement in maximum aerobic capacity and no improvement in anaerobic capacity. Soon, “Tabata workouts” gained popularity, and the concept broadened out to “High Intensity Interval Training” or HIIT workouts. Over time, the duration and structure of intervals and recovery periods were manipulated as sports scientists and coaches sought to optimize the adaptations for specific sport demands and unique needs of individual athletes.

New Information

Fast forward to 2020 and an interesting article by Alex Hutchinson for Outside Magazine, which describes the results of a 2020 study that showed that 30:15 intervals (3 sets of 13 x 30 second max RPE efforts with 15 seconds recovery between efforts and 3 minutes between sets) yielded greater real-world performance improvements than 5-minute intervals (4 x 5-minutes at max RPE with 2.5 minutes of recovery between efforts). Both groups performed 3 workouts per week for three weeks, and the work times for each group were essentially equal (19.5 minutes for the short interval group and 20 minutes for the long interval group).

Neither group achieved an increase in VO2 max after 3 weeks. It is important to note, however, that this was a group of highly trained cyclists with mean VO2 max values of 73 ml/kg/min, so the total work may not have created enough stimulus to achieve positive adaptations for such a highly trained group. Previous research has also shown that longer intervals (3-5 minutes with 2:1 work:recovery ratios) are more effective than very short intervals for increasing VO2 max.

What did improve, by nearly 5%, was the short interval group’s mean power output during a self-paced 20-minute time trial. There was also an increase, from 5.7 to 7.5 mmol/liter, in the short interval group’s average lactate level during the 20-minute test. The long interval group experienced a small decrease in mean power output (-1.4%), and no increase in average lactate level during the 20-minute test.

Physical and Mental Benefits of Short Intervals

There are both physiological and psychological reasons that very short, very high-intensity intervals improve performance. When my coaches and I work with athletes, we have to recognize that we have to help athletes build greater physical capacity as well as the psychological tools to actually use it. Here’s how short intervals do both:

More time at higher intensity

Research from Bent R. Rønnestad (here’s a video of a good lecture, for those interested) indicates that during maximum perceived exertion efforts, 30 second intervals with 15 seconds rest allow athletes to accumulate more time above 90% of VO2 max than 5 minute intervals. Stephen Seiler, another well known researcher in the field, pointed out that a 13 x 30/15 interval set really ends up resembling one effort with variable power outputs. The recovery periods are so short that VO2 doesn’t have that much time to drop.

Improved lactate tolerance

Lactate is not the enemy of high performance, as it was once believed to be. It is a fuel, and increasing the rate at which you can process it for energy is a key part of training. So is increasing the blood lactate levels you can tolerate while still performing hard work. To do that, you have to perform workouts that produce a lot of lactate.

To pace longer intervals – even at maximum perceived exertion – riders produce lower power outputs. The higher power outputs achieved in repeated short efforts appear to increase lactate tolerance. We see that in the present study. The average blood lactate level increased during the 20-minute time trial, and mean power output increased at 4 mmol/liter for the short interval group.

Threat and Willingness

All intervals are intimidating in different ways. Some athletes experience anxiety around the intensity of shorter intervals. Other others get anxious about the duration of longer intervals even though the intensity will be lower. Thankfully, there are often multiple ways to create a similar training stimulus. Sometimes the key is to design the workout that the athlete is most likely to complete well.

A set of thirteen 30-second efforts with 15 seconds recovery is really hard, but short intervals and even shorter recovery times give athletes small markers to hit. Athletes look at it as “I can do anything for 30 seconds” because the end is always within site. For many athletes, the structure is an important component for keeping them engaged and willing to continue to the end of the effort.

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Attentional Control

There’s a concept in sports psychology called attentional control. Your attention can range from broad to narrow and external to internal. Broad external attention is useful for noticing cues and details about the environment around you. Broad internal attention can be big picture evaluations of how you feel today or at this point in an event. You use narrow external attention when you focus on hitting a power number on your computer, catching a rider ahead of you, or sprinting to a finish line.

An example of narrow internal attention is the very specific self-talk you use when the going gets tough. It’s the “You can do this” narrative in your head when “this” is something very specific, like digging deep to stay on the wheel during a group ride or negotiating a tricky rock garden on your mountain bike.

Source: CTS Coaching Continuing Education Webinar with Dr. Justin Ross

Hard efforts require you to narrow your attention, either to something external (the clock) or internal (you can do this). From a coaching perspective, short and hard efforts leverage an athlete’s ability to narrow their attention. This often results in more time at intensity and more time at greater intensities. We also use short efforts to train and develop this aspect of attentional control so athletes can use it to optimize performance at critical moments in competition.

Are Shorter Intervals Best?

No. Short intervals serve an important purpose, but they are a component of training that is as valuable as other components. Intervals of 3-5 minutes at high perceived exertion are shown to increase VO2 max, as described well in this article. Intervals of 10-20 minutes at the maximum sustainable pace for that duration have been shown to increase power at lactate threshold.

So why bother with 30/15 or 40/20 interval sets that are so hard? Because you can’t underestimate the importance of focus and engagement in workout effectiveness. Workouts must be interesting to keep people engaged. There’s also benefit to being uncomfortable in training – and training to be uncomfortable – so similar efforts are tolerable during competition. Even if you could achieve identical physiological adaptations with all lower intensity training, it might not yield a winning result. Athletes may not develop the fortitude and willingness to tolerate the discomfort required to maximize real world performance.


Rønnestad BR, Hansen J, Nygaard H, Lundby C. Superior performance improvements in elite cyclists following short-interval vs effort-matched long-interval training. Scand J Med Sci Sports. 2020 May;30(5):849-857. doi: 10.1111/sms.13627. Epub 2020 Feb 5. PMID: 31977120.

Tabata I, Nishimura K, Kouzaki M, Hirai Y, Ogita F, Miyachi M, Yamamoto K. Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max. Med Sci Sports Exerc. 1996 Oct;28(10):1327-30. doi: 10.1097/00005768-199610000-00018. PMID: 8897392.

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Comments 27

  1. Pingback: What Is The Most Effective Prostate Cancer Treatment? → Gcapmd

  2. Pingback: How to Incorporate HIIT Workouts into Your Fitness Routine? - CONQUERITO

  3. 50 years late. We were doing this kind of workout in swimming that long ago. Glad you all are finally catching up!

    Oh, and if you really want to understand interval workouts go watch a real swim team work out. That is all they do, every day.

  4. Is there any evidence (in either direction) about whether short intervals have a higher or lower probability of causing an injury? And does this change with age?

    I ask as I have personally tended to get injured when I have done more high-intensity work as a percentage, and am currently resting for several weeks with Achilles tendinitis. This followed a very intense ten weeks of Zwift races and workouts.

  5. I would re-title this article “Why Short Intervals Didn’t Work for Me for Improving Performance” 🙂 Last year I did six weeks (!) of 30-15’s at max sustainable effort during the 30 second “on” part, for two sets of 10-11 reps. They were so hard I never could complete 13 reps. My heart rate sometimes went up to within 3-4 beats of measured max. And my heart rate dropped some but stayed pretty high even during the 15 second “off” parts. I could barely pedal home after each workout. After all that, what I got was a ZERO watt increase in my FTP. Not.a.single.watt. I rested enough during those six weeks on other days and could consistently hit the same watts during the short intervals, so it wasn’t due to over-training.

    After that I did another five weeks of traditional time trial intervals — zone 4 with some dips into zone 5, 2×15 min or 2×20 min. That raised my FTP significantly. I don’t think I’ll be doing short intervals…ever again.

  6. Should intervals be a consistent part of a winter base training program or are these prescribed later in the training as the goal event gets closer?

  7. there is a small but important error in this report. The LI group had a decrease in the average power for the 20 minute test of -1.4% (+/- 2.2%) while the SI group had and increase of 4.7% (+/- 4.4%). Thus the difference is more dramatic than presented in your assessment and is different at a p<0.01). It might be good to reference the original paper not an article about the paper?

    1. Post
  8. 80% of weekly training is done in zone 2 (for resistance) and 20% in HIIT zone (30/15) ie polarized training. I do not need to take breaks in longer times. Weekly polarized training is the scientifically proven key to increased resistance and peak peak power

  9. Pingback: Short Intervals: Should Ultrarunners Jump on the 30-Second Interval Bandwagon? - Jason Koop

  10. I would be very careful with regards to this.

    Training is all about specificity. Workouts that increase lactate mmol may help some forms of performance but hinder others. Very broadly they help short sharp but reduce longer endurance.

    A further complication is that lab studies are biased. It is easy to test short intervals, much harder to test endurance. So typically they do not control for this effect.

    However for the vast majority of cyclists endurance is just as important as sprint. This is the case even for out and out sprinters if they take part in road races where getting to the finish with enough left to perform is more important than peak watts while fresh.

    This is covered by Sebastian Weber in Fast Talk episode 67. IMO he is one of the most authoritative sources out there having worked with some of the best cyclists in the world.

    One of these is Tony Martin. In the show he describes how changing away from efforts like the ones advocated here to others more relevant to his discipline resulted in a step change in his ranking and played a big part in his world wins.

  11. This article seems cycling focused or is it. How does this transfer to running or ultra training and would you suggest the same time frames?

    1. Check the Twitter link and the original article and you’ll see it includes running, with references to Prefontain (sp?) at Oregon

  12. As a former runner, and a High School coach, we use “SHIT” =Super High Intensity Training. 30 seconds flat out, like racing a 200m, then 90 seconds rest. Basically HR to the max, then rest to let it return to”steady state.” If you can do 8 of those, you are fit and you are tough.

    My understanding is that we can only go at 100% for 20 seconds, give or take (for running, anyway) so this trains you mentally to do that, and maybe a little more. I was told it helps you tolerate, and clear lactate – which, as you point out, is actually adapting to processing it more efficiently. The 90 second rest seems critical for running. Any less and you just cant approach 100% after a few of these.
    I find these work great for me on my indoor bike, too. I don’t think I could do 100% on only 15 sec recovery. I am curious who can!
    So I wonder, which is more important, the 100% or the quick turn around you describe.
    We always feel like doing the 100% added a mental edge, and I always built that up, talking with the kids about how tough that made them. most buy into it and start believing, which is HUGE with teenagers!

    1. Right Larry, I also was wondering who could possibly keep up such a short rest interval after max effort for any appreciable period of time. I call nonsense on those who tell me they can 🙂

    2. The 30s part of a 13×30-15 rep isn’t done at 30s max, this CTS article lacked specificity in this regard. If your plan is to do 3x(13×30-15) then the 30s “on” efforts are done not at 30s max, or even at the max you can achieve for a set of 13, they’re done at session max, the highest you can do the total of 39 30s reps at and still finish the workout. Takes some time to figure that out, a good place to start is to do the 30s “on” efforts at 4 min power, you can adjust up or down from there.

      Another important component of doing these not explored here is the power during the 15s “off” or rest period. The original research specified these were to be done at 50% of the 30s power. If you soft-pedal at 100 watts during the rest period this workout won’t do much for you.

      Through experimentation I’ve found keeping the 15s rest power even higher yields the biggest results (for me). On power is between 4 and 5 min power and the off power is about 80% of FTP, but still the effort level of both on and off segments is balanced to achieve session max.

  13. I’ve always been a fan of ramp intervals, they work like the running bleep test where the cadence increases every 30 seconds, then it drops again but the resistance increases on the next level. I got mine off ebay ‘vollebak bleep test’ I think it was called. I have never felt so strong leaving the winter period and feel like I have done half the normal mileage. Really worth checking out.

  14. What about so called Miracle Intervals? Those promise what seems too good to be true, improved fitness/performance without killing yourself, very short work intervals 15-30 seconds, followed by very long recovery intervals of 4-5 minutes. Is there any research on whether those work and how they compare to the types of intervals you wrote about above?

    1. Interesting–
      Selene Yeager mentions Miracle Intervals in most recent Bicycling Mag article, and touts them as helpful in improving fat metabolism. She, however does not cite specific research showing miracle intervals as being superior to typical HIIT regimen. I’m skeptical.

      1. I believe Gale Bernhardt is the coach that originated the term “Miracle Interval”. She has written about them and cites some research, but to me it conceptually falls right in line with this article. I’ve personally used them with good success.

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