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.
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.
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.